Mechanochemical method for reduction of carbon dioxide to carbonaceous material

Abstract

A method of producing carbonaceous material from gaseous CO2 is disclosed. A gas containing CO2 is introduced into a suspension of metal-containing particles, preferably a mixture with a unique and specialized core-shell morphology containing different metals. Mechanical and / or acoustic energy is added to the system, preferably by stirring, under conditions that produce turbulent or chaotic flow. The CO2 is reduced to carbonaceous material, primarily crystalline carbon, which can then be separated from the system.

Description

MECHANOCHEMICAL METHOD FOR REDUCTION OF CARBON DIOXIDE TO CARBONACEOUS MATERIALFIELD OF THE INVENTION

[0001] This invention relates in general to methods for reduction of carbon dioxide. It relates specifically to mechanochemical methods of reduction of carbon dioxide to solid carbonaceous material that are catalyzed by metal particles under mild reaction conditions.BACKGROUND OF THE INVENTION

[0002] Anthropogenic climate change is largely driven by Greenhouse gas (GHG) emissions into the atmosphere. Carbon dioxide (CO2) plays a predominant role in this process. Current levels of CO2 in the atmosphere have been measured to be at 426 ppm (https: / / climate.nasa.gov / carbon-dioxide), and it is widely believed by the scientific community that the margin of surplus CO2 between this continuously rising concentration of carbon dioxide and the pre-industrial revolution baseline level of 280 ppm is a driving force behind climate change. Moreover, once added to the atmosphere, CO2 remains for long periods of time, between 300 to 1,000 years (https: / / www.climate.nasa.gov / the-atmosphere-getting-a- handle-on-carbon-dioxide.amp). Climate system modeling performed by the IPCC in its latest report (www.ipcc.ch / 2024 / ) warns that even a drastic reduction in GHG emissions would at best serve to mitigate some of the most devastating consequences of climate change, but that it will not suffice to reverse changes in weather pattern trends that are beginning to occur. More needs to be done urgently, and the only way to stabilize the climate systems is to reduce the already existing levels of GHG in the atmosphere through CO2 removal which lowers the existing inventory found in the atmosphere, redressing the damage already done, as well as through mitigation of CO2 emissions into the atmosphere, therefore, avoiding further stockpiling the atmosphere with CO2.

[0003] Carbon dioxide is the greenhouse gas most responsible for altering global temperatures (https: / / earthobservatory.nasa.gov / images / 82142 / global-pattems-of-carbon). Greenhouse gases absorb and radiate heat. In contrast to oxygen and nitrogen which make up most of our atmosphere, greenhouse gases absorb heat generated from earth’s land and ocean surfaces radiation of thermal infrared energy and release it gradually over time, instead of letting it dissipate into space. Hence, they act as a heat capsule around the planet. The amount of greenhouse gases in our atmosphere plays a delicate balance in maintaining the temperature, climate and weather patterns that have been so crucial in creating a goldilocks environment forthe flourishing of human life. Carbon Capture and Storage technology (CCS) allows for the storage of gaseous CO2 drawn-in from the atmosphere through methods such as Direct Air Capture (DAC), Bioenergy Capture (BECCS), and Marine and Ocean Capture (mCDR), and mitigation of emissions through Point Source Capture. While the storage component of CCS is currently mostly geared towards geological sequestration because of its scalability and relatively straightforward implementation through the pumping of gas into bedrock, there are potential risks arising from the creation of pressure points in fissures found in the bedrock and the resulting stress that could produce geological instability. Furthermore, there is a real risk of leakage of gaseous CO2 back into the atmosphere through fissures in the bedrock or of seepage through porous areas of the bedrock before it mineralizes over a long period of time.

[0004] Therefore, for CCS’s potential to be fully appreciated, utilized and applied at scale, it is imperative to discover methods of using the captured CO2 in ways that will create a demand for it as a raw material or precursor for further re-use. Stored CO2 has now been proposed as a chemical precursor, a complementary component or as an additive for a variety of potential uses in different industries. Currently, there are projects at a demonstration or partially commercialized stage whereby CO2 captured mainly at point sources throughout different industries is used in the production of biofuels, chemicals, injected into concrete for storage, and for the production of basic substances such as Syngas / Methanol, Hydrogen, etc. The pathways for CO2 reduction span gas-phase high-temperature catalysis, electrochemical reduction in liquids, and emerging liquid metal and nanoparticle-based approaches. Products range from gaseous fuels (CO, syngas, CH4, C2H4) to liquid chemicals (HCOOH, CH3OH, C2- organics) and solid carbons (CNTs, graphene, diamond-like carbon).

[0005] However, a method for CO2 reduction that is reproducible, environmentally sustainable, energy-efficient, cost-effective, and capable of delivering high yields with quantifiable efficiency remains a long-felt but unmet need.SUMMARY OF THE INVENTION

[0006] The invention disclosed herein is designed to fulfill this unmet need. Disclosed herein is a mechanochemical method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) preparing a suspension comprising a catalytic system composed of two distinct components: a core-shell particle, the shell of which at least partially coats the core, and a complementary particle that may also be a core-shell; (b) either placing the suspension into a reaction vessel or carrying out suspension preparation in the reaction vessel; (c) introducing a gas comprising carbon dioxide into the suspension; and (d) providingmechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reduced catalytically by the catalyst system to a solid carbonaceous; wherein the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension.

[0007] In some embodiments, the first solvent is a polar aprotic solvent having a dielectric constant of between 7 and 80, at 25 °C.

[0008] It is therefore an object of the present invention to disclose a method and system for mechanochemical reduction of CO2 to a solid carbonaceous material in which a CO2- containing gas is introduced into a suspension of a core-shell catalyst in aprotic polar solvent having a dielectric constant of between 7 and 80, at 25°C, and energy is applied to the suspension in the form of mechanical energy (e.g., by stirring) or acoustic energy (e.g., by sonication) in a way that causes a chaotic environment stemming from turbulent flow within the suspension. In some embodiments, the core-shell catalyst is in a form selected from the group consisting of nanotube, rod, nanowire, platelets, fibers, discs, nanosheets, polyhedral nanoparticles, nano or micro particles, including any combination thereof.

[0009] In some embodiments, the carbonaceous material is crystalline or poly-crystalline.

[0010] It is therefore an object of the present invention to disclose a method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) preparing a suspension comprising at least one catalyst encompassing a core-shell structure in a first solvent; (b) placing the suspension into a reaction vessel; (c) introducing a gas comprising carbon dioxide into the suspension; and, (d) providing mechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reduced catalytically by the catalyst to a solid carbonaceous material. It is within the essence of the invention wherein the first solvent is a polar aprotic solvent characterized by a dielectric constant of between 7 and 80, at 25 °C and the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension.

[0011] In some preferred embodiments of the invention, the reduction of CO2 to a solid carbonaceous material comprises reduction of at least part of the CO2 to solid carbon and molecular oxygen (O2).

[0012] In some embodiments of the invention, the catalyst comprises particles of a metal that is liquid at a temperature at which the reduction is performed. In some embodiments of theinvention, the reduction is performed at a temperature below the melting point of material from which the catalyst is made.

[0013] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the catalyst comprises particles comprising a core at least partially coated by a shell, wherein the shell comprises a metal or metal alloy. In some preferred embodiments of the invention, the core comprises a material selected from the group consisting of include Pt, Au, Ag, Ce, Fe, Cu, Ni, Pb, brass and any combination or alloy thereof. In some preferred embodiments of the invention, the core comprises a material selected from the group consisting of Pt, Au, Ag, Ce, Fe, Cu, Ni, brass and Pb doped with at least one material selected from the group consisting of Ga, In, and Sn. In some preferred embodiments of the invention, the core comprises a material selected from the group consisting of oxides of a metal or semi-metal selected from the group consisting of Ga, Ce, In, Tl, Al, B, Fe, Cu, Ni, Pb, Zn, brass and any combination thereof. In some preferred embodiments of the invention, the shell comprises a metal or metal alloy selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, Al, Cu, Zn, and mixtures, compounds, and alloys thereof. In some preferred embodiments of the invention, the shell comprises a liquid metal selected from the group liquid metal selected from the group consisting of Ga, In, Sn, and any combination or alloy thereof. In some preferred embodiments of the invention, the reduction is performed at a temperature above the melting point of the metal or metal alloy from which the shell is made. In some preferred embodiments of the invention, the reduction is performed at a temperature below the melting point of the metal or metal alloy from which the shell is made. In some preferred embodiments of the invention, the shell has a median thickness of 1 -90nm. In some preferred embodiments of the invention, the shell comprises of islets of 1 -90nm thickness that cover 10 -100% of a surface of the core. In some preferred embodiments of the invention, the shell comprises a metal that is different from the core component. In some preferred embodiments of the invention, the core comprises Ag, the shell comprises Gay.

[0014] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the catalyst comprises at least one substance selected from the group consisting of Ga; Cu; Ag; In; Sn; Ce; and brass mixtures of at least two substances selected from the group consisting of Ga, Cu, Ag, In, Sn, brass and Ce; alloys of at least two substances selected from the group consisting of Ga, Cu, Ag, In, Sn, brass, and Ce; and, compounds of at least two substances selected from the group consisting of Ga, Cu, Ag, In, Sn, brass and Ce. In some preferred embodiments of the invention, the at least one substance comprisesGalinstan. In some preferred embodiments of the invention, the suspension comprises nanoparticles of Ga and nanorods of AgxGai-x. In some more preferred embodiments of the invention, the suspension comprises nanoparticles of Ga and nanorods of AgxGai-x.

[0015] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the catalyst comprises a material selected from the group consisting of CeCh and Ce2O3.

[0016] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the first solvent is a polar aprotic organic solvent.

[0017] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the first solvent is characterized by a dielectric constant of between 7 and 80 at 25 °C.

[0018] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein said first solvent is dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or tetrahydrofuran (THF), including any combination thereof.

[0019] It is a further object of this invention to disclose the method as defined in any of the preceding, further comprising adding to the suspension a second polar aprotic solvent in which carbon dioxide is more soluble than it is in the first solvent, the second solvent characterized by a dielectric constant at 25 °C of at least 30. In some preferred embodiments of the invention, the second solvent is a polar aprotic organic solvent. In some preferred embodiments of the invention, the second solvent is characterized by a dielectric constant of between 7 and 80, at 25 °C.

[0020] In some preferred embodiments of the invention, the second solvent is ethanolamine (ETA).

[0021] In some especially preferred embodiments of the invention, the first solvent is DMF and the second solvent is ETA. In some particularly preferred embodiments of the invention, the first solvent and the second solvent are present in a volume ratio of between 70:30 and 98:2.

[0022] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the reduction is performed at a temperature of 10 -100°C.

[0023] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the suspension comprises particles of Ga and the method is performed at a temperature above the melting point of Ga.

[0024] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the suspension comprises particles of Ga and the method is performed at a temperature below the melting point of Ga.

[0025] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the gas containing CO2 is selected from the group consisting of air, air enriched in CO2, CO2 obtained from Direct Air Capture system, CO2 obtained from a body of water by a marine Carbon Dioxide Removal system (mCDR), exhaust gases, flue gas, CO2 emissions from industrial processes, industrial tailpipe emissions, waste emissions, and emissions generated at a point source.

[0026] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the step of introducing a gas containing CO2 into the suspension is preceded by a step selected from the group consisting of filtering the gas, scrubbing the gas, separating the CO2 from the gas, and increasing a concentration of CO2 within the gas.

[0027] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the step of introducing a gas containing CO2 into the suspension comprises introducing the gas containing CO2 into the suspension by a method selected from the group consisting of bubbling, misting, aerating, injecting, and introducing a flow of the gas into the suspension.

[0028] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension without formation of a vortex.

[0029] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the step of providing mechanical energy to the suspension comprises mechanically stirring the suspension. In some preferred embodiments of the invention, the step of mechanically stirring the suspension comprises mechanically stirring the suspension so as to create turbulent flow conditions within the suspension. In some preferred embodiments of the invention, the step of mechanically stirring the suspension comprises mechanically stirring the suspension so as to create chaotic flow conditions within the suspension. In some especially preferred embodiments of the invention, the step of mechanically stirring the suspension comprises mechanically stirring the suspension with an impeller selected from the group consisting of anchor impellers and pitched blade impellers.

[0030] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the method further comprises placing at least one baffle within the reaction vessel.

[0031] It is a further object of this invention to disclose the method as defined in any of the preceding, wherein the method is a method for producing substantially crystalline carbon.

[0032] It is further object of this invention to disclose of a solid carbonaceous material is characterized by a density higher than Ig / ml.

[0033] It is a further object of this invention to disclose the method as defined in any of the preceding, further comprising separating the carbonaceous material from the suspension. In some preferred embodiments of the invention, the step of separating the carbonaceous material from the suspension comprises centrifuging the suspension. In some particularly preferred embodiments of the invention, the step of centrifuging is followed by a step of gravimetric filtration. In some preferred embodiments of the invention, the step of separating the carbonaceous material from the suspension is followed by a step of determining the quantity of carbonaceous material produced by the method.

[0034] It is a further object of this invention to disclose a system for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) a reaction vessel; (b) means for imparting mechanical and / or acoustic energy to a liquid, solution, or suspension within the reaction vessel; and, (c) means for introducing a gas comprising CO2 into the reaction vessel. It is within the essence of the invention wherein the means for imparting mechanical and / or acoustic energy comprise means for inducing chaotic or turbulent flow in the liquid, solution, or suspension.

[0035] It is a further object of this invention to disclose a mechanochemical method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) preparing a suspension in a first solvent, the suspension comprising particles of at least one carbon dioxide reduction catalyst selected from the group consisting of metal nanoparticles, metal nanorods, metal microparticles, metal microrods, metal oxide nanoparticles, metal oxide nanorods, metal oxide microparticles, metal oxide microrods, and core-shell particles characterized by a core at least partially coated by at least one metal and / or at least one metal alloy differing from material comprising the core; (b) placing the suspension into a reaction vessel; (c) introducing a gas comprising carbon dioxide into the suspension; and, (d) providing mechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reducedcatalytically by the catalyst to a solid carbonaceous material, wherein: (a) the first solvent is a polar aprotic solvent; and (b) the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension.

[0036] In some embodiments, the method is a method for reducing carbon dioxide to crystalline or polycrystalline solid carbonaceous material.

[0037] In some embodiments, the method is a method for reducing carbon dioxide to solid carbonaceous material characterized by a density higher than 1.1 g / ml.

[0038] In some embodiments, the method of reducing gaseous carbon dioxide to a solid carbonaceous material comprises reducing gaseous at least part of the carbon dioxide to solid carbon and molecular oxygen.

[0039] In some embodiments, the catalyst comprises particles of a metal that is liquid at a temperature at which the reduction is performed.

[0040] In some embodiments, the reduction is performed at a temperature below a melting point of material from which the catalyst is made.

[0041] In some embodiments, the catalyst comprises at least one substance selected from the group consisting of Ga, Cu, Ag, In, Sn, Ce, and mixtures, alloys, and compounds thereof.

[0042] In some embodiments, the at least one substance comprises Galinstan.

[0043] In some embodiments, the suspension comprises nanoparticles of Ga and nanorods of AgxGai-x.

[0044] In some embodiments, the catalyst comprises a material selected from the group consisting of CeCh and Ce2O3.

[0045] In some embodiments, the at least one catalyst comprises core-shell particles, and the core comprises at least one substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al, and mixtures, alloys, and compounds thereof.

[0046] In some embodiments, the at least one catalyst comprises core-shell particles, and the core comprises a material selected from the group consisting of a substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, and Al doped with at least one material selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, and Al.

[0047] In some embodiments, the at least one catalyst comprises core-shell particles, and the core comprises a material selected from the group consisting of oxides of a metal selected from the group consisting of Pt, Pd, Au, Ag, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al and any combination thereof.

[0048] In some embodiments, the at least one catalyst comprises core-shell particles, and the shell comprises at least one substance selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, and Al, and mixtures, alloys, and compounds thereof.

[0049] In some embodiments, the at least one catalyst comprises core-shell particles, the core comprises Ag, the shell comprises Ga, and the particles are characterized by an overall composition of AgxGai-x.

[0050] In some embodiments, the suspension comprises at least two different carbon dioxide reduction catalysts, at least one of which comprises at least one substance selected from the group consisting of Ag, Ga, Sn, In, Bi, Pb, Tl, Al, and mixtures, alloys, and compounds thereof, and at least one of which is characterized by a core-shell structure.

[0051] In some embodiments, the at least two different carbon dioxide reduction catalysts comprise core-shell particles that differ in their composition, shell structure, or both.

[0052] In some embodiments, the at least one catalyst comprises core-shell particles, and the shell comprises a plurality of layers.

[0053] In some embodiments, each layer of the shell comprises a material that differs from the material of the layer below it.

[0054] In some embodiments, the core comprises at least one substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al, and mixtures, alloys, and compounds thereof.

[0055] In some embodiments, each layer of multi-layered shell comprises at least one substance selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, Al, and mixtures, alloys, and compounds thereof.

[0056] In some embodiments, the catalyst comprises particles having a core-shell structure characterized by a median shell thickness of 1 - 90 nm.

[0057] In some embodiments, the catalyst comprises particles having a core-shell structure, and the shell comprises islets characterized by a thickness of 1 - 90 nm that cover collectively 10 - 100% of a surface of the core.

[0058] In some embodiments, the first solvent is characterized by a dielectric constant between 7 and 80 at 25 °C.

[0059] In some embodiments, the step of providing mechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reduced catalytically by the catalyst to a solid carbonaceous material is performed at a temperature of between 10 °C and 100 °C.

[0060] In some embodiments, the first solvent is selected from the group consisting of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and any combination thereof.

[0061] In some embodiments, the first solvent is tetrahydrofuran (THF).

[0062] In some embodiments, the method further comprising adding to the suspension a second polar aprotic solvent in which carbon dioxide is more soluble than it is in the first solvent.

[0063] In some embodiments, the second solvent is a polar aprotic organic solvent.

[0064] In some embodiments, the second solvent is characterized by a dielectric constant of between 7 and 80 at 25 °C.

[0065] In some embodiments, the second solvent is ethanolamine (ETA).

[0066] In some embodiments, the first solvent is DMF and the second solvent is ETA.

[0067] In some embodiments, the first solvent and the second solvent are present in a volume ratio of between 70:30 and 98:2 by mixture volume.

[0068] In some embodiments, the gas containing CO2 is selected from the group consisting of air, air enriched in CO2, CO2 obtained from Direct Air Capture system, CO2 obtained from a body of water by a marine Carbon Dioxide Removal system (mCDR), exhaust gases, flue gas, CO2 emissions from industrial processes, industrial tailpipe emissions, waste emissions, and emissions generated at a point source.

[0069] In some embodiments, the step of introducing a gas containing CO2 into the suspension is preceded by a step selected from the group consisting of filtering the gas, scrubbing the gas, separating the CO2 from the gas, and increasing a concentration of CO2 within the gas.

[0070] In some embodiments, the step of introducing a gas containing CO2 into the suspension comprises introducing the gas containing CO2 into the suspension by a method selected fromthe group consisting of bubbling, misting, aerating, injecting, and introducing a flow of the gas into the suspension.

[0071] In some embodiments, the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension without formation of a vortex.

[0072] In some embodiments, the step of providing mechanical and / or acoustic energy to the suspension comprises mechanically stirring the suspension.

[0073] In some embodiments, the step of mechanically stirring the suspension comprises mechanically stirring the suspension so as to create turbulent flow conditions within the suspension.

[0074] In some embodiments, the step of mechanically stirring the suspension comprises mechanically stirring the suspension so as to create chaotic flow conditions within the suspension.

[0075] In some embodiments, the step of mechanically stirring the suspension comprises mechanically stirring the suspension with an impeller selected from the group consisting of anchor impellers and pitched blade impellers.

[0076] In some embodiments, the method further comprising placing at least one baffle within the reaction vessel.

[0077] In some embodiments, the method is a method for producing crystalline carbon characterized by a particle size above 1pm [Dv(50)].

[0078] In some embodiments, the method further comprising separating the solid carbonaceous material from the suspension.

[0079] In some embodiments, the step of separating the crystalline carbonaceous material from the suspension comprises separating by a method selected from the group consisting of centrifuging the suspension, filtering the suspension, and any combination thereof.

[0080] In some embodiments, the step of separating the solid carbonaceous material from the suspension is followed by a step of determining the quantity of crystalline carbonaceous material produced by the method.

[0081] In some embodiments, the reaction vessel further comprises at least one baffle.

[0082] In some embodiments, the means for imparting mechanical and / or acoustic energy comprise means for imparting mechanical and / or acoustic energy without creating a vortex in the liquid, solution, or suspension.

[0083] In some embodiments, the means for imparting mechanical energy are selected from the group consisting of anchor impellers and pitched blade impellers.BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The invention will now be described with reference to the drawings, wherein:

[0085] FIGs. 1A and IB present schematic illustrations of a number of non-limiting morphologies of core-shell catalyst particles used in the method disclosed herein, and TEM photographs of non-limiting examples of catalyst particles comprising a metal core and a liquid metal coating, respectively;

[0086] FIGs. 2A and 2B present cross-sectional views of non-limiting embodiments of impeller designs for use in the invention disclosed herein and of flow patterns of liquid in a vessel in which the impeller is rotating, respectively;

[0087] FIG. 3 presents an electron micrograph of solid carbonaceous material produced by the method disclosed herein;

[0088] FIG. 4 presents a graph showing theoretical calculations of the energy for formation of Ga2CE on various faces of gallium as a function of the number of layers of gallium atoms; and

[0089] FIGs. 5A-5B present an electron micrograph of core-shell catalyst encompassing (5A) nanoparticles morphology, and (5B) microrods morphology, according to some embodiments of the present invention; and

[0090] FIG 6. presenting images of high resolution transmission electron microscopy (HR- TEM) and X-ray diffraction of crystalline covalent structure of carbon.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0091] In the following description, various aspects of the invention will be described. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent to one skilled in the art that there are other embodiments of the invention that differ in details without affecting the essential nature thereof. Therefore, the invention is not limited by that which is illustrated in the figures and described in the specification, but only as indicated in the accompanying claims, with theproper scope determined only by the broadest reasonable interpretation of the claims. In some cases, for clarity or conciseness, individual elements of the invention are discussed separately. Nonetheless, any combination of individual elements of the invention disclosed herein that is not self-contradictory is considered by the inventors to be within the scope of the invention.

[0092] All prior art documents cited in this application are incorporated in their entirety by reference.

[0093] In all cases in which an embodiment is described as "comprising" a set of components or method steps, i.e. the invention may include components or method steps in addition to those explicitly listed, the scope of invention is to be understood to include embodiments in which the invention "consists of' the listed components or method steps, i.e. embodiments that include the listed components or method steps and no others, and to include as well embodiments in which the invention "consists essentially of the listed components or method steps, i.e. embodiments that do not include any components or method steps not listed that would materially affect the basic and novel characteristics of the invention.

[0094] Unless specifically stated otherwise, any range disclosed herein is understood to include within its scope any subrange. As non-limiting examples, if a range is stated to be "1 - 10%, " ranges of 1 - 5%, 2 - 9%, etc., are considered by the inventors to be within the scope of the invention; similarly, if a range is stated to be "less than 50%, " ranges of less than 40%, less than 25%, less than 10%, etc., are considered to be within the scope of the invention.

[0095] As used herein, unless defined otherwise, with reference to numerical quantities, the term "about" refers to a range of ±25% about the nominal value.

[0096] As used herein, the terms "mechanochemistry" and "mechanochemical" refer to chemical reactions that are initiated or promoted by input of mechanical energy into the system.

[0097] As used herein, the term "nanoparticles" refers to a particles having a largest dimension of between 1 nm and 1 pm.

[0098] As used herein, the term "nanorods" refers to nanoparticles characterized by a substantially elongated shape.

[0099] As used herein, the term "microparticles" refers to particles having a largest dimension of between 1 pm and 100 pm.

[0100] As used herein, the term "microrods" refers to microparticles having a substantially elongated shape.

[0101] Disclosed herein is a method and system for reducing CO2 to carbonaceous material, in preferred embodiments to elemental carbon, under mild conditions. The method disclosed herein uses highly active catalysts for CO2 reduction that comprise particles of weakly reducing metals or semi-metals or alloys thereof. Non-limiting examples of metals and semi-metals that can be used in the inventive method include indium (In) thallium (Tl), cerium (Ce), silver (Ag), aluminum (Al), zinc (Zn), gallium (Ga), tin (Sn), and alloys, compounds, or mixtures thereof. Non-limiting examples of alloys and compounds that are suitable for use in the inventive method include Ga-CeCh, Ga-CeCh-Ce, Ga-Al, Ga-Ag, Ga-Ag-Al, and Ga-In-Sn (Galinstan). In preferred embodiments of the method, the metal, semi-metal, compound, or alloy is liquid at the temperature at which the CO2 reduction is performed. Embodiments of the method in which the reduction is performed at a temperature below the melting point of the catalyst material are, however, within the scope of the invention.

[0102] In some embodiments, the core-shell catalyst is in a form selected from the group consisting of nanotube, rod, nanowire, platelets, fibers, discs, nanosheets, polyhedral nanoparticles, nano or micro particles, including any combination agglomeration, aggregation and organization thereof.

[0103] In some embodiments, the core-shell catalyst is preferably in a form of a particle and / or rod most preferably in the form of a nanoparticle, nanorod, microparticle, or microrod including any combination, agglomeration, aggregation and organization thereof. These forms have the advantage of a higher surface-to-volume ratio than the bulk material. A person skilled in the art would appreciate that the catalyst is morphology may assume irregular or non- uniform geometries. Accordingly, reference to “catalyst form” herein encompasses both conventionally shaped and irregularly shaped bodies. For example, the catalyst particle can be of a form of a sphere, ellipsodial, cylinderical. disc-like cubic, platelet, flake-like, irregular or aggregated or engineered shapes (e.g., lobed, ring), including any combination thereof.

[0104] Reference is now made to FIGs. 5A-5B present an electron micrograph of core-shell catalyst according to some embodiments of the present invention; 5A represents core-shell metal catalyst aggregate nanoparticles and 5B represents core-shell catalyst microrods.

[0105] In some preferred embodiments of the invention, the catalyst particles are partially or entirely coated by a metal shell that encapsulates a core. In some non-limiting preferred embodiments, the core has a maximum dimension of 0.1 -90pm. Non-limiting examples of core materials include Platinum (Pt), Gold (Au), Silver (Ag), Cerium (Ce), Iron (Fe), Copper(Cu), Nickel (Ni), Lead (Pb), Cobalt (Co), Iridium (Ir), Rhodium (Rh), Aluminum Al, Bismuth (Bi) , brass or any combination or alloy thereof. Additional non-limiting examples of core materials include Pt, Au, Ag, Ce, Fe, Cu, Ni, brass or Pb doped with at least one of Ga, In, and Sn. In some other non-limiting embodiments, the core comprises an oxide of a metal or semimetal selected from the group consisting of Ga, Ce, In, Tl, Ag, Al, B, Fe, Cu, Ni, Pb, Zn, brass and any combination thereof. As used herein the term "brass" refers to a copper-zinc alloy.

[0106] In some preferred embodiments of the invention, and the metal shell has a median thickness of between 1 nm and 90 nm. In some other preferred embodiments of the invention, the shell layer comprises of islets of between 1 nm and 90 nm thickness that covers between 10 % and 100 % of the surface of the core. In preferred embodiments of the invention, the coating shell is a metal that is different from the metal of the core component. Non-limiting examples of materials from which the shell can be made include In, Tl, Ce, , Al, B, and Zn. In some other non-limiting preferred embodiments of the invention, the shell component is a metal comprising at least one metal selected from the group consisting of Ga, In, Sn, and any combination or alloy thereof. In some preferred embodiments of the invention, the shell retains the properties of the phase at the temperature at which the conversion of CO2 takes place.

[0107] In some embodiments the shell component can be a metal that is an alloy comprising any combination of Gallium (Ga) with Indium (In) and / or with Tin (Sn) and / or with zinc (Zn) and / or with Silver (Ag) and / or with aluminum (Al).

[0108] In some preferred embodiments of the invention, the catalyst comprises an oxide of cerium (preferably either or both of CeCh or Ce2C>3) either as its sole component or as the core material of a core-shell catalyst particle. As discussed in more detail below, without being bound by theory, it appears that the use of the oxide rather than the pure metal provides a surface that is suitable for generation of charge for piezoelectric or triboelectric charge transfer to dissolved CO2 molecules. It is also plausible that micromechanical stresses at the oxide surface during collisions enables the piezoelectric effect to occur more efficiently.

[0109] Reference is now made to FIG. 1A, which illustrates schematically a number of nonlimiting morphologies of a core-shell catalyst according to some embodiments of the present invnetnion, comprising core 100 and shell 110. Reference is now made to FIG. IB, which presents TEM photographs of a number of non-limiting examples of catalyst particles comprising a metal core and a metal coating. In some embodiments, the core is or comprises a metal, a metal oxide, or an alloy, including any combination, or agglomerate thereof. In someembodiments, the shell is or comprises a metal, a metal oxide, or an alloy, including any combination, or agglomerate thereof. In some embodiments, the shell is or comprises a plurality of layers.

[0110] In some non-limiting embodiments of the invention, the core-shell system is prepared separately by applying sonication to the mixture of a solid metal and a metal or oxide. In some embodiments, a weight ratio of the metal: solid metal is between 2: 1000 and 9: 2000. In some preferred embodiments, the metal: solid metal weight ratio is 1 :3000. In preferred embodiments of the invention, the core-shell system is prepared by sonication, chemical bath deposition (CBD) high shear, or vapor deposition, including any combination thereof. The sonication is typically applied at a power of 40 - 1000 W with the use of tip sonicator or by using a bath sonicator. In typical embodiments, a total energy of 10,000 - 200,000 W s is applied.[OHl] In some non-limiting embodiments of the invention, the preparation of the metal catalyst particles is performed in steps by sonication or high shear. In some preferred nonlimiting embodiments of the invention, the metal particles are prepared separately by using a tip sonicator or bath sonicator. The preparation is typically performed by applying a power between 40 - 1000 W. In typical embodiments, a total energy of 10,000 - 200,000 W s is applied.

[0112] In the inventive method, a suspension of catalyst particles is prepared in a polar aprotic solvent, preferably an organic polar aprotic solvent, that comprises molecules containing a lone pair of electrons and is characterized by a dielectric constant between 7 and 80 at 25 °C. The suspension may also be prepared in a mixture of such solvents. In preferred embodiments of the invention, the solvent is a polar aprotic organic solvent characterized by a dielectric constant of between 7 and 80 at 25 °C. In preferred embodiments of the invention, the solvent is one in which CO2 is highly soluble; in especially preferred embodiments of the invention, the solubility of CO2 in the solvent at 25 °C is 0.005 - 2.0 mol L’1.

[0113] Non-limiting the second solvent includes but are not limiting to amides (e.g., dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone), dimethyl sulfoxide, tetrahydrothiophene 1,1-dioxide, or nitriles (e.g., acetonitrile, propionitrile, butyronitrile).

[0114] Non-limiting examples of solvents suitable for use in the instant invention include dimethylformamide (DMF), ethanolamine (ETA), and mixtures thereof. In some preferred embodiments of the method, the suspension is prepared in (v / v) mixture of DMF and ETA. Insome embodiments, the molar ratio between DMF and ETA is between 70:30 and 98:2, including any value or range in between. Any means known in the art for preparing the suspension may be used. Solvents characterized by low viscosity are preferably used.

[0115] Non-limiting examples of polar aprotic solvents include but are not limited to: dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile, acetone, propylene carbone, sulfolane, hexamethylphosphoramide (HMPA), tetramethylurea, tetrahydrofuran (THF), 2- methyltetrahydrofuran, 1,2-dimethoxy ethane (DME), di ethylene glycol dimethyl ether, or 1,4- dioxane, including any combination thereof. In some embodiments, the first solvent is DMF, THF or DMSO, including any combination thereof.

[0116] In some non-limiting preferred embodiments of the invention, the suspension comprises nanoparticles selected from the group consisting of Ga nanoparticles characterized by a size of 0.01- 1 pm; Ag particles of diameter 0.3 - 90 pm coated with a 2 - 90 nm thick layer of Ga; Ag2Ga rods coated with a 2 - 90 nm thick layer of Ga; particles comprising a core made from Ag, and a shell made of Ga; or mixtures and combinations thereof.

[0117] The suspension is introduced into a reaction vessel containing means for creating chaotic motion within the reaction vessel. Any means known in the art may be used; nonlimiting examples include stirrers, agitators, and impellers. Embodiments in which the suspension is prepared in a separate container and transferred to the reaction vessel and in which the suspension is prepared in situ in the reaction vessel are both considered by the inventors to be within the scope of the invention.

[0118] Reference is now made to FIG. 2A, which presents schematic cross-sectional views of a number of non-limiting embodiments of stirrer / impeller geometries. Reference is now made to FIG. 2B, which illustrates non-limiting embodiments of reaction vessels into which the impellers illustrated in FIG. 2A are illustrated, and flow patterns of liquid within the reaction vessel upon activation of the impeller. In FIG. 2B, embodiments the invention are shown in which the interior surface of the reaction vessel comprises baffles, but embodiments in which the reaction vessel does not include such baffles are within the scope of the invention as well. Upon activation of the stirrer or agitator, chaotic motion (which may be, but is not limited to, turbulent flow) is induced, as illustrated schematically by the arrows in FIG. 2B.

[0119] CO2 is introduced into the suspension. In some non-limiting preferred embodiments of the invention, CO2 is bubbled or flowed continuously through the suspension from an externalsource such as a tank, but any means known in the art for introducing CO2 into the system may be used. Non-limiting examples include bubbling, misting, aerating, injecting. In preferred embodiments of the invention, the CO2 is introduced into the suspension, and the reduction performed, at atmospheric pressure. Embodiments in which the system (including the CO2 introduced into the reaction vessel) is maintained at a pressure higher than atmospheric are considered by the inventors to be within the scope of the invention. In preferred embodiments of the invention, the molar CO2 concentration is 0.03% - 100%, where 100% represents a saturated solution. The gas supplied in the method need not be pure CO2; any gas comprising CO2 may be used. Non-limiting examples include commercially available high-purity CO2, air, air enriched in CO2, CO2 obtained from Direct Air Capture (DAC) systems, CO2 present in bodies of water such as oceans and lakes in which the CO2 is obtained from a Marine Carbon Dioxide Removal (mCDR) system, exhaust gases, flue gas, CO2 emissions from industrial processes, industrial tailpipe emissions, waste emissions, and emissions generated at a point source. In typical non-limiting embodiments of the invention, CO2 is injected into the system at a rated of 1 - 1000 standard cubic centimeters per minute (seem).

[0120] The CO2 reduction may be performed at any temperature within the liquid range of the solvent. In preferred embodiments of the invention, the CO2 reduction is performed at a temperature of 10 -100°C. In especially preferred embodiments of the invention, the CO2 reduction is performed at room temperature. In some preferred embodiments of the invention, the CO2 reduction is performed at a temperature below the melting point of the material from which the catalyst particles are made, or, in the case of catalyst particles comprising a core and a shell, below the melting point of the material comprising the shell.

[0121] Mechanical or acoustic energy is applied to the suspension, preferably by mechanical stirring, under conditions in which the application of mechanical or acoustic energy leads to chaotic (generally turbulent) flow. In order to maintain a reasonable throughput and high product yield while keeping the external energy requirements low, it is crucial that conditions of chaotic or turbulent flow (high Reynolds number) be maintained. In fact, the inventors have found that the reaction is most efficient when the reaction vessel includes baffles on the interior surface of its walls, which will increase the turbulence of the motion of the liquid when mechanical and / or acoustic energy is applied. The inventors have also discovered that the efficiency of the CO2 reduction is improved when the reaction medium is stirred in a manner in which a vortex is not produced, indicating that the reaction is most efficient when laminar flow is avoided. Without being bound by theory, it appears that the mechanical agitation insidethe reaction vessel generates a chaotic and highly turbulent flow motion with a high Reynolds number. The chaotic movement, in contrast to laminar movement, increases the probability for collisions to occur, in particular, between the catalyst particles of the catalysts and the molecules of dissolved CO2.

[0122] In one non-limiting embodiment of a system for mechanochemical reduction of CO2 to solid carbonaceous material, the system contains a double or triple jacketed reaction vessel. The system contains an injection system for gaseous CO2. The injection can be performed through one or more tubes or bubblers into the reactor. The injection can be performed to any spatial position in the reaction vessel. As shown in FIG. 2B, in preferred embodiments of the invention, the system comprises at least one mechanical stirrer / mixer / agitator that is connected to a rod for the CO2 conversion.

[0123] Each of the mechanical stirrers is connected to an electric motor. In a non-limiting example, for a vessel volume of 250 ml, the power supply of the electric motor is 75 - 450 W. In typical embodiments of the invention, the stirring is performed at a rate of 50 - 3000 rpm. Additionally, or alternatively, the system may contain a sonication system for the CO2 conversion. For an 80 ml reaction vessel, the power of the sonication device is 75 - 1500 W. In some embodiments, the sonication is applied via a probe sonotrode. The CO2 conversion method of the system can contain both the mechanical stirrers and the sonication system applied to the reaction vessel simultaneously or separately. Additionally, or alternatively, the combination of stirring and sonication for the conversion of CO2 can be performed in different vessels that interconnect via tubes and pumps (e.g., a peristaltic pump). The stirring can be performed in a chemical reactor and the sonication in a flow cell.

[0124] Solid carbonaceous material can then be removed from the reaction system. As a nonlimiting example, solid carbonaceous material can be removed by centrifugation followed by filtration.

[0125] In some preferred embodiments the solid carbonaceous material is generated on the surface of the catalysts. In some embodiments, the solid carbonaceous material is characterized by a density higher than 1.1 g / ml between 10-100°C A person skilled in the art would appreciate that density higher than 1.1 gr / ml corresponds with the density of crystalline carbonaceous materials, for example density of diamond is -3.51 g / ml, graphite - 2.20 g / ml, or carbon nanotubes -1.3-1.4 g / ml. Furthermore, since most common polar aprotic solvents like THF, DMSO or DMF density range between 0.9 and 1.1 the solid carbonaceous materialgenerated on the core-shell catalyst detaches from the core-shell catalyst surface it sinks to the bottom of the reaction vessel.

[0126] In some embodiments, the solid carbonaceous material is characterized or comprises a sp2 orbital carbon configuration.

[0127] Reference is now made to FIG 6 presenting a high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction of crystalline covalent structure of carbon. The HR-TEM analysis shows the presence of crystalline structures in the examined carbonaceous material samples. As seen in the X- ray diffraction we see “dots” / ’’specs” which indicate the polycrystalline structure with the carbonaceous material.

[0128] It is therefore an object of the present invention to disclose a mechanochemical method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) preparing a suspension comprising (i) a core-shell catalyst particle in a first solvent, each particle having a core comprising at least one metal or oxides and a shell comprising at least one different metal, and the shell at least partially coats the core; and (ii) another particle comprising one or more metals or oxides with or without a shell comprising one or more different metals or oxides; and (iii) the first solvent is a polar aprotic solvent having a dielectric constant of between 7 and 80, at 25 °C; (b) either placing the suspension into a reaction vessel or carrying out suspension preparation in the reaction vessel; (c) introducing a gas comprising carbon dioxide into the suspension; and (d) providing mechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reduced catalytically by the catalyst to a solid carbonaceous; wherein the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension.

[0129] It is therefore an object of the present invention to disclose a method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: (a) preparing a suspension comprising at least one catalyst encompassing a core-shell structure in a first solvent; and another catalytic unit comprising a different core-shell or a metal or oxide particle (b) placing the suspension into a reaction vessel; (c) introducing a gas comprising carbon dioxide into the suspension; and, (d) providing mechanical and / or acoustic energy to the suspension until at least part of the carbon dioxide in the gas is reduced catalytically by the catalyst to a solid carbonaceous material. It is within the essence of the invention wherein the first solvent is a polar aprotic solvent characterized by a dielectric constant of between 7 and80, at 25 °C and the step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within the suspension. As used herein, the tern “unit” refers to an additional catalytic element.

[0130] In some preferred embodiments of the invention, the reduction of CO2 to a solid carbonaceous material comprises reduction of at least part of the CO2 to solid carbon and molecular oxygen (O2).

[0131] Upon application of mechanical energy, the catalyst particles react with the dissolved CO2, reducing at least part of it to solid carbonaceous material. In preferred embodiments of the invention, mechanical energy is applied until the CO2 is reduced to solid material comprising substantially solid carbonaceous material. In especially preferred embodiments of the invention, the method yields molecular oxygen in addition to solid material comprising substantially pure elemental carbon, i.e., the net reaction is given according to eq (6):CO2-> C + O2(6)

[0132] Reference is now made to FIG. 3, which presents an electron micrograph of solid carbon produced by the method disclosed herein.

[0133] Without being bound by theory, the inventors have proposed the following mechanism for the reduction of CO2 by the method disclosed herein. It is emphasized that the following discussion is presented in order to demonstrate to a person of ordinary skill in the art of the utility of the invention disclosed herein, and is not to be considered limiting in any way.

[0134] The inventors have discovered that the efficiency and yield of the method disclosed herein strongly depend on the solvent being polar and aprotic, and having a dielectric coefficient of between 7 and 80, at 25 °C. Again, without being bound by theory, it appears that the polarity of the solvent and the presence of a lone pair are necessary for the initial interaction with the CO2 molecule. The lone pair can interact with the partial positive charge on the carbon atom of the CO2 molecule, causing it to bend away from the linear structure of CO2 towards the bent structure adopted by the CO2 radical anion in aprotic solvents [9], The higher energy of the bent structure of the CO2 molecule relative to the ground-state linear structure may reduce the energetic requirements for CO2 conversion. The high dielectric constant of the solvent may stabilize formation of a transient electric charge on the surface of the catalyst particle and limit charge dissipation in the solvent.

[0135] As was mentioned previously, the chaotic movement is crucial to increase the probability of successful collisions between participants of the CO2 conversion. The collisions between the metal droplets and the core / shell system involves friction between the two particles and cause a local electrification in the contact area. The local electrification creates a suitable environment for charge transfer from the metal particle (M) to CO2, generating the energetically unstable radical anion radical of carbon dioxide, CCb'T In the inventive system disclosed herein, the activation energy required for this reaction can be provided by the piezoelectric effect or the triboelectric effect or by a combination of the two.

[0136] As is well-known in the art, the piezoelectric effect is the ability of certain materials to generate electric charge as a result of mechanical stress applied on them. In the present case, local charge generation can occur after a collision between the M particles and the core / shell system leads to local oxidation on the surface of the metal particle and to generation of a metal oxide, eq (7):M + O2U MxOy(7)

[0137] In the case of M = Ga, reaction (7) produces Ga2Ch on the surface of the catalyst particle. The contact between the particles and the core / shell system may lead to a phase transition from the energetically favorable P-GazOs (high crystallographic symmetry) phase to a piezoelectric s-Ga2O3 (low crystallographic symmetry, lack of inversion center) phase. This transition facilitates electron transfer towards CO2 and generation of the radical anion CCb'T

[0138] The triboelectric effect occurs when two uncharged particles are charged as a result of a mutual contact. The contact can occur as a result of frictional contact between two bodies or when approaching and distancing between two bodies occurs. In the system disclosed herein, an initial collision between the droplets and the core / shell system may initiate a triboelectric effect because its occurrence in a highly dielectric environment prevents the dissipation of the locally evolving charge. Charge generation as a result of the triboelectric effect can occur on the surface of the a-Ga surface of the Ga metallic lattice of the gallium droplet. This charge generation can facilitate the generation of the radical anion CCb'C

[0139] In both of these mechanisms, the charge transition occurs from the Fermi level (Ef) of the catalyst particle to the lowest unoccupied level of CO2. Theoretical calculations performed by Prof. Dan Thomas Major of the Chemistry Department of Bar-Ilan University, Ramat-Gan, Israel that were made available to the inventors [unpublished results] show a favorable generation on the (100) face of Ga. Since -Ga2Ch generation is favorable on that surface andsince in most cases this oxide phase undergoes transition to the piezo-electric s-Ga2O3 phase, any further collisions will lead to charge generation on the oxide surface and will facilitate the generation of the radical anion CCh’-. Reference is now made to FIG. 4, which presents a graph comparing energy for production of oxide on different faces of gallium as a function of the number of layers of gallium atoms.EXAMPLES

[0140] The following examples are provided to assist a person of ordinary skill in the art to make and use the invention disclosed herein, and are not intended to be limiting in any way.

[0141] All materials used in the experiments are commercially available materials are can be found in Sigma- Aldrich, Across, Merck, Thermo scientific, Acros and Fluka.Example 1Preparation of a Ga-Ag catalytic suspension and reduction of CO2

[0142] Between 1.8 g and 2.2 g of Cu and Ag particles were placed in a 40 ml glass cylinder to which 20 ml of solvent, either DMF, THF or DMSO were added. The cylinder was then sonicated 15 min and 45 min according to a program of on-off cycles of 0.9 s - 0.1 s.

[0143] After the conclusion of the sonication, up to 0.5 g of molten Ga (prepared by placing Ga in a hot water bath for 10 - 15 min) was added to the sonicated Ag / Cu / solvent. The amount of molten Ga added for shell, was depended on the core weight comprises Ag / Cu, to generate a shell of a thickness of 2 to 50 nm. The glass cylinder was then returned to the sonicator and sonicated. The sonicated Ag / Cu / Ga / solvent was transferred to a 250 ml reaction vessel, and the glass cylinder rinsed with an additional 20 ml of solvent which was then added to the reaction vessel.

[0144] A second sample of Ga (up to 20 g) was placed in a 40 ml glass cylinder along with 20 ml of solvent. This sample was then sonicated. Upon completion of the sonication, the sonicated Ga / solvent was added to the reactor, and the cylinder rinsed with an additional 20 ml of solvent which was then added to the reaction vessel. Additional solvent was added to provide a total volume of 200 ml. The reaction mixture was then mixed with an agitator stirrer.

[0145] The reaction vessel was placed in a constant-temperature bath set to 50 °C. The reaction mixture was stirred by a mechanical stirrer for 3 h with continuous bubbling of CO2 at a rate of 21.86 ml min'1. After 3 h of reaction, the CO2 tank was closed (for a total delivery of ~0.16 mol CO2), the stirring stopped, and solids allowed to settle. The supernatant solvent was removed.

[0146] The product was isolated by vacuum filtration on 0.45-micron PTFE paper, followed by rinsing three times with doubly distilled H2O followed by rinsing with acetone, and drying in a vacuum oven for 3 h at 60 °C. 1.65 g C obtained of crystalline carbon was. As used herein, the term “crystalline” refers to a material state in which the atoms, ions, or molecules are arranged in a highly ordered, repeating, three-dimensional pattern that extends over long distances. This ordered structure produces distinct diffraction patterns (e.g., sharp peaks in XRD or electron diffraction) and often gives the material a well-defined melting point and characteristic physical properties. In some embodiments, the solid carbonaceous material is crystalline, or semi-crystalline. A person skilled in the art would appreciate that a solid carbonaceous material can comprise a mixture of crystalline, semi- crystalline, and / or amorphous material.Example 2 Preparation of a Ga / CeCb catalytic suspension

[0147] 3.0 g of CeCh particles were weighed and placed in a 40 ml glass cylinder to which 20 ml of solvent, either THF, DMSO, orDMF were added. The cylinder was placed in a sonicator and sonicated as in the previous example. Up to 0.75 g of molten Ga (prepared by placing Ga in a hot water bath for 10 - 15 min) was added to the sonicated CeCh solvent. The amount of molten Ga added for shell, depended on the core weight of the CeCh, to generate a shell of a thickness of 2 to 30 nm. After completion of the sonication, the sonicated Ga / CeCb / solvent was transferred to a reaction vessel, and the cylinder rinsed with an additional 20 ml of solvent, which was then added to the reaction vessel.

[0148] An additional 15 g of Ga was placed in a glass cylinder along with 20 ml of solvent. The cylinder was then placed in a sonicator and sonicated as in the previous example. Upon completion of the sonication, the sonicated Ga / solvent was added to the reaction vessel, and the glass cylinder rinsed with an additional 20 ml solvent, which was then added to the reaction vessel. The reaction mixture was stirred with an agitator stirrer to ensure complete mixing.

[0149] The product was isolated by vacuum filtration on 0.45-micron PTFE paper, followed by rinsing three times with doubly distilled H2O followed by rinsing with acetone, and drying in a vacuum oven for 3 h at 60 °C. 1 g C was obtained.Example 3 Reduction of CO2

[0150] Several independent runs were performed of the method disclosed herein. A catalyst suspension was prepared and connected to a CO2 cylinder. CO2 was bubbled through the system at a rate of 10 seem under stirring at a rate of 60 - 2500 rpm. After 2 - 72 hours of reaction, the carbonaceous product was separated from the suspension by either centrifugation gravimetric filtration, or both.Example 4Production of Ga-coated Ag catalyst particles and reduction of CO2

[0151] Between 0. 5 g and 3 g of Ag particles and between 0.1 g and 1 g of brass particles composed of two-thirds copper and one-third zinc were weighed in a weighing dish. 20 ml of solvent, either THF, DMSO, or DMF was added to a 50 ml glass cylinder, and the Ag was added to the solvent in the cylinder.

[0152] The glass cylinder containing the solvent and Ag / brass were sonicated as previously mentioned above.

[0153] About 0.6 to 1 g of Ga was added to the glass cylinder containing the solvent / Ag / brass, the amount used depended on the core weight comprises Ag / brass, to generate a shell of a thickness of 2 to 90 nm. The cylinder was returned to the sonicator and sonicated

[0154] A 100 ml reaction vessel was prepared by placing a stirrer at the lowest point possible without hitting the bottom or sides of the vessel. A bubbler was inserted from the top of the reaction vessel with its end placed as deep as possible without hindering the stirrer. The output of a CO2 tank was attached to the bubbler and the CO2 flow adjusted to be as low as possible.

[0155] The Ag / brass / Ga / solvent suspension was removed from the sonicator and added to the reaction vessel. The glass cylinder was rinsed with an additional aliquot of 20 ml of solvent to remove residual Ag and Ga, which was then added to the reaction vessel.

[0156] A second suspension of Ga in solvent was prepared by adding between 5 g and 20 g of Ga to 20 ml of solvent in a 50 ml glass cylinder and sonicated, d. The sonicated Ga particles were then added to the reaction vessel. The cylinder was rinsed with 20 ml of solvent to remove residual Ga, which was then added to the reaction vessel.

[0157] The stirrer was activated at a speed of -450 rpm for 3 h with continuous bubbling of CO2 at a rate of 21.86 ml min'1. After 3 h of reaction, the CO2 tank was closed (for a total delivery of -0.16 mol CO2), the stirring stopped, and the mixed catalyst and product removed from the reactor and placed in a 200 ml glass beaker. The supernatant solvent was removed.

[0158] The product was isolated by vacuum filtration using a polyvinylidene fluoride filter paper, followed by drying in a vacuum oven for 3 h at about 60 °C. 0.18 g C was obtained.Example 5Reduction of CO2 with Ga-coated Ag particles and Ga spheres

[0159] Ga-coated Ag particles were prepared and added to a reaction vessel as in the previous example.

[0160] Solvent, either THF, DMSO, or DMF (20 ml) was added to a 50 ml graduated cylinder. 10 g of Ga was added, and the sample was sonicated as above. The Ga spheres were then added to the reaction vessel.

[0161] The volume in the reaction vessel was corrected to 80-90 ml by addition of solvent. The suspension was stirred at 300 - 500 rpm with a flow of CO2 as in the previous example for 3 h 50 min (total delivery of -0.21 mol CO2).

[0162] The solids in the reactor were allowed to settle and a clear supernatant is poured off, leaving a black powder which was filtered and collected. 0.55 g C was obtained.Example 6Reduction of CO2 with Ag Ga mixture

[0163] The process of CO2 reduction was examined according to some embodiments of the present invention. In general, the mechanochemical reduction was carried out under the turbulent and chaotic flow conditions for high Reynolds numbers, with continuous mixing and in some cases, sequential cycling.

[0164] The morphology effected by the two different metal catalyst encompassed was evaluated by comparing the yields and solid carbonaceous material obtained using (i) a mixture of Ag and Ga were used, (ii) The ratio between Ag and Ga in the mixture correlates to the ratio between in a AgxGai-xcore-shell catalyst so as to be comparable. Surprisingly, the Ag Ga mixture showed no reaction (0 mg) and no reduction capabilities.Example 7Reduction of CO2 with AgxGai-xcore-shell catalyst compared to AgF Ga (non core-shell) mixture.

[0165] The process of CO2 reduction was examined according to some embodiments of the present invention. In general, the mechanochemical reduction was carried out under the same turbulent and chaotic flow conditions for high Reynolds numbers, with continuous mixing and in some cases, sequential cycling.

[0166] The morphology effect by the two different metal catalysts encompasses was evaluated by comparing the yields and solid carbonaceous material obtained using (i) a core-shell catalyst according to some embodiments of the present invention, and (ii) a mixture of AgF and Ga were used. The core-shell catalyst is AgxGax-i and the ratio between AgF and Ga in the mixture correlates to the ratio between the AgxGai-xcore-shell catalyst. Surprisingly, it was found that the yield obtained using the core-shell catalyst of the present invention, was at least 10 to 50 times higher than when mixture of AgF and Ga were used (11 mg compared to between about 100 mg and 500 mg, respectively).

[0167] Furthermore, it was found that solid carbonaceous material obtained in the presence of AgF and Ga mixture (i) the solid carbonaceous material floats, meaning it has a density lower than 1.1 g / ml, (ii) it is amorphous based HR-TEM.

[0168] Whereas, the solid carbonaceous material formed in the presence of the core-shell catalyst (i) sinks, meaning it is characterized by a density higher than 1.1 g / ml, and (ii) is crystalline as demonstrated by FIG.6.

Claims

CLAIMSWhat is claimed is:

1. A mechanochemical method for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: preparing a suspension in a first solvent, said suspension comprising particles of at least one carbon dioxide reduction catalyst selected from the group consisting of metal nanoparticles, metal nanorods, metal microparticles, metal microrods, metal oxide nanoparticles, metal oxide nanorods, metal oxide microparticles, metal oxide microrods, and core-shell particles characterized by a core at least partially coated by at least one metal and / or at least one metal alloy differing from material comprising said core; placing said suspension into a reaction vessel; introducing a gas comprising carbon dioxide into said suspension; and, providing mechanical and / or acoustic energy to said suspension until at least part of said carbon dioxide in said gas is reduced catalytically by said catalyst to a solid carbonaceous material; wherein: said first solvent is a polar aprotic solvent; and, said step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within said suspension.

2. The method according to claim 1, wherein said method is a method for reducing carbon dioxide to crystalline or poly crystalline solid carbonaceous material.

3. The method according to claim 1, wherein said method is a method for reducing carbon dioxide to solid carbonaceous material characterized by a density higher than 1.1 g / ml.

4. The method according to claim 1, wherein said method of reducing gaseous carbon dioxide to a solid carbonaceous material comprises reducing gaseous at least part of said carbon dioxide to solid carbon and molecular oxygen.

5. The method according to claim 1, wherein said catalyst comprises particles of a metal that is liquid at a temperature at which said reduction is performed.

6. The method according to claim 1, wherein said reduction is performed at a temperature below a melting point of material from which said catalyst is made.

7. The method according to claim 1, wherein said catalyst comprises at least one substance selected from the group consisting of Ga, Cu, Ag, In, Sn, Ce, and mixtures, alloys, and compounds thereof.

8. The method according to claim 7, wherein said at least one substance comprises Galinstan.

9. The method according to claim 7, wherein said suspension comprises nanoparticles of Ga and nanorods of AgxGai-x.

10. The method according to claim 1, wherein said catalyst comprises a material selected from the group consisting of CeCh and Ce2O3.

11. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, and said core comprises at least one substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al, and mixtures, alloys, and compounds thereof.

12. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, and said core comprises a material selected from the group consisting of a substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, and Al doped with at least one material selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, and Al.

13. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, and said core comprises a material selected from the group consisting of oxides of a metal selected from the group consisting of Pt, Pd, Au, Ag, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al and any combination thereof.

14. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, and said shell comprises at least one substance selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, and Al, and mixtures, alloys, and compounds thereof.

15. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, said core comprises Ag, said shell comprises Ga, and said particles are characterized by an overall composition of AgxGai-x.

16. The method according to claim 1, wherein said suspension comprises at least two different carbon dioxide reduction catalysts, at least one of which comprises at least one substance selected from the group consisting of Ag, Ga, Sn, In, Bi, Pb, Tl, Al, and mixtures, alloys, and compounds thereof, and at least one of which is characterized by a core-shell structure.

17. The method according to claim 16, wherein said at least two different carbon dioxide reduction catalysts comprise core-shell particles that differ in their composition, shell structure, or both.

18. The method according to claim 1, wherein said at least one catalyst comprises core-shell particles, and said shell comprises a plurality of layers.

19. The method according to claim 18, wherein each layer of said shell comprises a material that differs from the material of the layer below it.

20. The method according to claim 18, wherein said core comprises at least one substance selected from the group consisting of Pt, Pd, Au, Ag, CeCh, Fe, Cu, brass, Rh, Ru, Ni, Co, Ir, Al, and mixtures, alloys, and compounds thereof.

21. The method according to claim 18, wherein each layer of multi-layered shell comprises at least one substance selected from the group consisting of Ga, Sn, In, Bi, Pb, Tl, Al, and mixtures, alloys, and compounds thereof.

22. The method according to claim 1, wherein said catalyst comprises particles having a core-shell structure characterized by a median shell thickness of 1 - 90 nm.

23. The method according to claim 1, wherein said catalyst comprises particles having a core-shell structure, and said shell comprises islets characterized by a thickness of 1 - 90 nm that cover collectively 10 - 100% of a surface of said core.

24. The method according to claim 1, wherein said first solvent is characterized by a dielectric constant between 7 and 80 at 25 °C.

25. The method according to claim 1, wherein said step of providing mechanical and / or acoustic energy to said suspension until at least part of said carbon dioxide in said gas is reduced catalytically by said catalyst to a solid carbonaceous material is performed at a temperature of between 10 °C and 100 °C.

26. The method according to claim 1, wherein said first solvent is selected from the group consisting of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and any combination thereof.

27. The method according to claim 1, wherein said first solvent is tetrahydrofuran (THF).

28. The method according to claim 1, further comprising adding to said suspension a second polar aprotic solvent in which carbon dioxide is more soluble than it is in said first solvent.

29. The method according to claim 28, wherein said second solvent is a polar aprotic organic solvent.

30. The method according to claim 29, wherein said second solvent is characterized by a dielectric constant of between 7 and 80 at 25 °C.

31. The method according to claim 30, wherein said second solvent is ethanolamine (ETA).

32. The method according to claim 30, wherein said first solvent is DMF and said second solvent is ETA.

33. The method according to claim 30, wherein said first solvent and said second solvent are present in a volume ratio of between 70:30 and 98:2 by mixture volume.

34. The method according to claim 1, wherein said gas containing CO2 is selected from the group consisting of air, air enriched in CO2, CO2 obtained from Direct Air Capture system, CO2 obtained from a body of water by a marine Carbon Dioxide Removal system (mCDR), exhaust gases, flue gas, CO2 emissions from industrial processes, industrial tailpipe emissions, waste emissions, and emissions generated at a point source.

35. The method according to claim 1, wherein said step of introducing a gas containing CO2 into said suspension is preceded by a step selected from the group consisting of filtering said gas, scrubbing said gas, separating said CO2 from said gas, and increasing a concentration of CO2 within said gas.

36. The method according to claim 1, wherein said step of introducing a gas containing CO2 into said suspension comprises introducing said gas containing CO2 into said suspension by a method selected from the group consisting of bubbling, misting, aerating, injecting, and introducing a flow of said gas into said suspension.

37. The method according to claim 1, wherein said step of providing mechanical and / or acoustic energy comprises providing mechanical and / or acoustic energy so as to cause chaotic and / or turbulent motion within said suspension without formation of a vortex.

38. The method according to claim 1, wherein said step of providing mechanical and / or acoustic energy to said suspension comprises mechanically stirring said suspension.

39. The method according to claim 37-38, wherein said step of mechanically stirring said suspension comprises mechanically stirring said suspension so as to create turbulent flow conditions within said suspension.

40. The method according to claim 37-39, wherein said step of mechanically stirring said suspension comprises mechanically stirring said suspension so as to create chaotic flow conditions within said suspension.

41. The method according to any one of claims 37-40, wherein said step of mechanically stirring said suspension comprises mechanically stirring said suspension with an impeller selected from the group consisting of anchor impellers and pitched blade impellers.

42. The method according to any one of claims 37-41, further comprising placing at least one baffle within said reaction vessel.

43. The method according to claim 2, wherein said method is a method for producing crystalline carbon characterized by a particle size above 1pm [Dv(50)].

44. The method according to claim 1, further comprising separating said solid carbonaceous material from said suspension.

45. The method according to claim 44, wherein said step of separating said crystalline carbonaceous material from said suspension comprises separating by a method selected from the group consisting of centrifuging said suspension, filtering said suspension, and any combination thereof.

46. The method according to claims 44-45, wherein said step of separating said solid carbonaceous material from said suspension is followed by a step of determining the quantity of crystalline carbonaceous material produced by said method.

47. A system for reducing gaseous carbon dioxide to a solid carbonaceous material, comprising: a reaction vessel; means for imparting mechanical and / or acoustic and / or thermal energy to a liquid, solution, or suspension within said reaction vessel; and, means for introducing a gas comprising CO2 into said reaction vessel; wherein said means for imparting mechanical and / or acoustic energy comprise means for inducing chaotic or turbulent flow in said liquid, solution, or suspension.

48. The system according to claim 47, wherein said reaction vessel further comprises at least one baffle.

49. The system according to either one of claims 47 or 48, wherein said means for imparting mechanical and / or acoustic energy comprise means for imparting mechanical and / or acoustic energy without creating a vortex in said liquid, solution, or suspension.

50. The method according to claims 47 - 49, wherein said means for imparting mechanical energy are selected from the group consisting of anchor impellers and pitched blade impellers.

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