Porous glass ceramics for the conversion of greenhouse gases in a cold plasma catalysis process

Abstract

The present invention relates to a porous glass ceramic comprising an amorphous phase and a crystalline phase, wherein the amorphous phase and / or the crystalline phase comprises at least one of the following substances: alkali oxide, alkaline earth oxide, boron oxide, phosphorus oxide, metal oxide, mixed metal oxide, metal borate, mixed metal borate. The present invention further relates to a process for the conversion of greenhouse gases, in particular for the conversion of CO2, wherein a greenhouse gas-containing gas is introduced into a porous glass ceramic according to the invention in the presence of a cold plasma. The object of the present invention is to propose a new catalytic system and process for the conversion of greenhouse gases, in particular CO2 and / or CO, which exhibits a higher CO2 conversion rate and can be better integrated into a cold plasma catalysis process.

Description

[0001] The present invention relates to a porous glass ceramic for the catalytic conversion of greenhouse gases, in particular CO2, in a cold plasma catalysis process.

[0002] In this context, greenhouse gases refer in particular to carbon dioxide, methane, tetrafluoromethane, nitrous oxide, fluorocarbons, sulfur hexafluoride and nitrogen trifluoride.

[0003] Among the long-lived greenhouse gases, anthropogenic CO2 currently makes the largest contribution to the greenhouse effect and the resulting warming of the Earth's climate.

[0004] The capture, processing, and subsequent conversion of CO2 into higher-value products, also known as carbon capture and utilization (CCU), is therefore considered an important technology in the fight against climate change. It represents an alternative to fossil fuels and thus avoids the emissions generated during their extraction and use. Furthermore, the captured CO2 remains bound, at least temporarily, through chemical conversion.

[0005] The challenge in converting CO2 into higher-value chemicals lies in supplying the amount of energy required to break the C=O double bonds. Temperatures between 2000 °C and 3000 °C are necessary to thermally split CO2.

[0006] Non-thermal plasma catalysis (also known as cold plasma catalysis) is a technology that allows the conversion of CO2 to be carried out at much lower temperatures and atmospheric pressures.

[0007] In recent years, various plasma-assisted CO2 conversion reactions have been investigated, including CO2 hydrogenation for the production of synthetic methane, dry reforming, and CO2 splitting. CO2 splitting involves the direct splitting of CO2 into CO and O2. The resulting carbon monoxide is an important chemical building block that can be further converted into valuable hydrocarbons, for example.

[0008] By introducing catalytically active packing materials into the plasma, CO2 conversion and the energy efficiency of CO2 splitting can be improved.

[0009] For example, FR 3115 711 A1 discloses a catalytic system with a support containing cerium and / or zirconium. The catalytic system further comprises nickel as an active component and a promoter selected, for example, from yttrium, strontium, copper, manganese, cobalt, and mixtures thereof. This catalytic system is used for the conversion of a gas containing CO2 and / or CO in the presence of a cold plasma.

[0010] This and similar catalyst systems known from the prior art have several disadvantages, especially with regard to efficient use in non-thermal plasma catalysis (cold plasma catalysis processes): The catalysts are usually only available as granules or pellets. These are only conditionally suitable for integration into a cold plasma reactor.

[0011] The microstructure of catalysts, such as their specific pore volume, specific surface area, or pore size distribution, is defined by the initial particle sizes of the catalyst and the binder systems used. As a rule, the support material contributes little or nothing to the catalytic activity. This is especially true for cold plasma catalysis processes.

[0012] The catalytic properties result from additionally introduced, catalytically active components, which are usually inhomogeneously distributed in or on the porous support material.

[0013] The generation and transport of charged particles (e.g., electrons, ions, defects, etc.) is essentially only possible via the catalytically active component and is limited, for example, by the surrounding binder material and the distance between the catalytically active catalyst crystallites. Furthermore, the catalytically active components must be sufficiently accessible to the molecules involved in the reaction.

[0014] Based on this, the object of the present invention is to propose a new catalytic system and process for the conversion of greenhouse gases, in particular CO2 and / or CO, in a cold plasma catalysis process, which has a higher CO2 conversion rate and can be better integrated into a cold plasma catalysis process.

[0015] The problem is solved by a porous glass ceramic with the features of claim 1.

[0016] Beneficial further training opportunities are listed in the dependent requirements.

[0017] According to the invention, a porous glass ceramic is provided with an amorphous phase and a crystalline phase, wherein the amorphous phase and / or the crystalline phase comprises at least one of the following substances: alkali oxide, alkaline earth oxide, boron oxide, phosphorus oxide, metal oxide, mixed metal oxide, metal borate and / or mixed metal borate.

[0018] The porous glass ceramic represents a binder-free catalyst that enables the conduction of charged particles and provides a high affinity for the adsorption of CO2 and CO.

[0019] In contrast to conventional supported catalysts, where a catalytic component, e.g., nickel, is deposited on a metal oxide, e.g., Al₂O₃, the glass ceramic according to the invention can be used directly as a catalyst in a cold plasma catalysis process. While it is easily possible to deposit further catalytically active components onto the porous glass ceramic, the glass ceramic itself can already be used as a catalyst in non-thermal catalysis.

[0020] In other words, with existing catalysts, a mostly inert support material with the desired microstructure is first produced, and then catalytically active components are applied, for example by impregnation followed by calcination and reduction. In contrast, the glass ceramic according to the invention has an outer and inner surface accessible to reactants, which already contains catalytically active centers.

[0021] A porous glass-ceramic differs from a porous glass in that, in addition to amorphous components, it also exhibits a partially crystalline structure. Thus, the glass-ceramic material contains both an amorphous and a crystalline phase. The crystalline phase forms through crystallization processes within the glass, also known as devitrification. Crystal nucleation can be achieved through targeted heat treatments or by adding nucleating agents such as TiO2. The growth of the crystal phases can be influenced by targeted heat treatment.

[0022] The tendency to crystallize, as well as the crystallization process itself, is significantly influenced by the components of the glass-forming system. Whether a glass melt crystallizes depends on the nucleation rate, the crystal growth rate, and the temperature ranges in which these processes occur. Furthermore, it is influenced by the cooling rate of the glass melt. A high cooling rate counteracts crystallization.

[0023] The porous glass ceramic is permeated with cavities and channels, these cavities and channels forming a three-dimensionally branched pore structure accessible from the outside.

[0024] The amorphous phase contains alkali oxides and / or alkaline earth oxides and / or boron oxide and / or phosphorus oxide and / or metal oxides and / or mixed metal oxides and / or metal borates and / or mixed metal borates.

[0025] For example, it is an amorphous phase that comprises less than 50% by weight of the porous glass ceramic. This amorphous phase contains, for example, oxides of cerium, zirconium, titanium, iron, aluminum, manganese, zinc, yttrium, and / or vanadium as catalytically active components. Thus, the amorphous phase not only acts as a support but also contributes to catalytically activated reaction processes itself, for example, through ion conduction, adsorption, and transport processes.

[0026] The composition of the amorphous and crystalline phases, their dimensions, and crosslinking are determined, for example, by the targeted melting of a starting glass composition that exhibits a miscibility gap within a specific temperature range. Phase separation and crystal formation occur through subsequent heat treatment. Following selective extraction, a porous glass-ceramic is obtained.

[0027] The crystalline phase can contain metal oxides, transition metal oxides, and / or aluminum, gallium, and germanium oxides. Both pure metal oxides in various oxidation states and mixed oxides can be present. The crystalline phase can contain one or more metal oxides. Examples include CeO₂, Ce₂O₃, CeZrO₂, Al₂O₃, TiO₂, TiFeO₂, and other oxides of Ce, Zr, Ti, Nb, V, Fe, Co, Ni, Mn, Zn, and Y.

[0028] The amorphous phase forms an oxide network that may contain transition metal oxides and / or aluminum, gallium and germanium oxides.

[0029] Example of the composition of the amorphous and / or crystalline phase: The proportion of B₂O₃ or phosphate is less than 90 mol%, preferably less than 50 mol%, further preferably less than 20 mol%, further preferably less than 10 mol%, further preferably less than 5 mol%, and further preferably less than 1 mol%. For example, the amorphous phase and / or the crystalline phase contains only traces of B₂O₃ or phosphate, or the amorphous phase and / or the crystalline phase contains no B₂O₃ or phosphate.

[0030] The proportion of alkali metal oxides and / or alkaline earth metal oxides is, for example, less than 50 mol%, preferably less than 15 mol%, and more preferably less than 5 mol%. For example, the proportion of alkali metal oxides and / or alkaline earth metal oxides is less than 1 mol%, or only traces or no alkali metal oxides and / or alkaline earth metal oxides are present in the amorphous phase and / or the crystalline phase.

[0031] In the amorphous phase and / or the crystalline phase, the proportion of transition metal oxides and / or Al2O3 and / or Ge2O3 is, for example, more than 50 mol%, preferably more than 70 mol%, particularly preferably more than 95 mol%.

[0032] For example, the amorphous phase and / or crystalline phase contains oxides of at least one of the following metals: Ce, Zr, Ti, Nb, V, Fe, Co, Ni, Mn, Zn, Y.

[0033] The crystalline phase and / or the amorphous phase may be doped with copper or lanthanum.

[0034] The glass ceramic may have an additional surface loading, the surface loading containing, for example, nickel, copper, cobalt, iron, iridium, rhodium, platinum and / or palladium.

[0035] The porous glass-ceramic according to the invention can be shaped as required. For example, plates, membranes, granules, powders, and monoliths can be formed from the glass-ceramic. Shaping can be carried out directly from a glass melt. Furthermore, shaping based on ceramic technology with a subsequent sintering process using ground glass is possible. Due to the many shaping possibilities, the porous glass-ceramic can be optimally adapted to different catalytic processes and integrated into any reactor. This applies in particular to the field of cold plasma catalysis and the reactor types used there.

[0036] The glass ceramic according to the invention also offers the possibility of subsequent functionalization. This can be used to modify the crystalline phase and / or the amorphous phase. For example, the crystalline phase can be completely or partially recrystallized to a solid solution phase. Dopants can be introduced into the amorphous phase, for example, or the conductivity of the amorphous phase can be increased by ion exchange.

[0037] Furthermore, other active components, such as organometallic compounds, Ni, Cu, Ba, Zr, Mg, etc., can be deposited on the surface of the porous glass ceramic.

[0038] In one embodiment of the invention, the amorphous phase contains boron oxide and / or cerium oxide and / or zirconium oxide and / or titanium oxide and / or iron oxide and / or their mixed metal oxides. For example, the amorphous phase consists of cerium oxide and / or zirconium oxide and / or titanium oxide and / or iron oxide and / or their mixed metal oxides.

[0039] In one embodiment of the invention, the crystalline phase contains cerium oxide and / or zirconium oxide and / or titanium oxide and / or iron oxide and / or their mixed oxides. For example, the crystalline phase contains cerium oxide and / or zirconium oxide and / or titanium oxide and / or iron oxide and / or their mixed metal oxides, or the crystalline phase consists of cerium oxide and / or zirconium oxide and / or titanium oxide and / or iron oxide and / or their mixed metal oxides.

[0040] The glass ceramic consists, for example, of at least 50 mol% of metal oxide, such as CeO2 and / or ZrO2, which ensures high chemical stability.

[0041] It is possible that CeO2 and / or ZrO2 is at least partially replaced by TiO2, Y2O3 or other metal oxides.

[0042] The porous glass ceramic preferably contains no SiO2.

[0043] The amorphous phase contains, for example, more than 5 mol%, preferably more than 20 mol%, further preferably more than 50 mol%, and even more preferably more than 90 mol% cerium oxide or mixed oxides of CeO2 and ZrO2 or TiO2 or mixed oxides of TiO2 and Fe2O3 or Al2O3.

[0044] The crystalline phase contains, for example, more than 5 mol%, preferably more than 20 mol%, further preferably more than 50 mol%, and even more preferably more than 90 mol% metal oxide, in particular cerium oxide or mixed oxides of CeO2 and ZrO2 or TiO2 or mixed oxides of TiO2 and Fe2O3 or Al2O3.

[0045] For example, the porous glass ceramic has a specific pore volume of at least 0.1 cm³. 3 / g, preferably of at least 0.2 cm 3 / g, further preferably of at least 0.5 cm 3 / g on.

[0046] In one embodiment of the invention, the glass ceramic has a specific surface area of ​​at least 10 m². 2 / g, preferably from at least 50 m 2 / g and especially preferably of at least 200 m 2 / g on.

[0047] In one embodiment of the invention, the porous glass ceramic is produced by extraction of a phase-separated starting glass.

[0048] The extraction of a phase-separated and partially crystallized starting glass is a preparative method that enables the reproducible production of porous glass ceramics with a flexibly adjustable pore structure.

[0049] The production of porous glass ceramics by extraction (subtraction preparation principle) begins with the production and shaping of a base glass (starting glass) with a suitable glass composition. Subsequent heat treatment induces phase separation and growth. The phases resulting from phase separation exhibit a mutually interpenetrating structure. Due to their differing chemical compositions, the phases have varying resistances to solvents. This differing solubility of the resulting phases is exploited to selectively extract (subtract) one of the phases. What remains is a porous skeletal structure. The properties of the pore system are determined by the composition of the starting glass, the temperature and duration of the heat treatment, and the extraction conditions. By systematically adjusting these parameters, texture data of the pore system, e.g.,control a specific surface area, a specific pore volume and / or a pore size distribution.

[0050] The starting glass preferably contains no SiO2.

[0051] For example, a starting glass containing the components CeO2, B2O3, and Na2O undergoes separation into two phases: a sodium borate-rich phase and a CeO2-rich phase. The sodium borate-rich phase can be extracted, resulting, for example, in a porous glass ceramic with more than 80 mol% CeO2.

[0052] The prerequisite for glass demixing is the presence of a miscibility gap. Phase separation occurs at a temperature within this miscibility gap, between the glass formation temperature and an upper critical demixing temperature.

[0053] In principle, segregation occurs during the manufacturing process when the melt of the starting glass cools. Rapid cooling can reduce this premature segregation.

[0054] Controlled phase separation of the base glass is achieved through heat treatment at a defined temperature and duration. In glass-ceramics, this step involves not only phase separation but also nucleation and crystal growth. The longer the heat treatment duration and the higher the temperature, the larger the pores that can form and the more crystalline regions develop. Furthermore, the cooling rate after phase separation can also influence the shape of the pore system.

[0055] Selective extraction of a phase is made possible by the different solubilities of the separated phases in various media. Depending on the glass composition, suitable extraction solvents include, for example, water, acids, alkalis, or alcohols.

[0056] In the case of a starting glass containing CeO₂, B₂O₃, and Na₂O, the readily soluble sodium borate-rich phase can be extracted with hot water. The progress of the extraction can be monitored, for example, by measuring the pH value, as a basic extraction solution is formed when the alkali borate phase dissolves. After extraction, a stable, insoluble CeO₂-rich network with open pores remains, containing very little to no B₂O₃ and Na₂O. The resulting porous glass possesses high chemical and thermal stability as well as an increased specific surface area compared to the starting glass.

[0057] In an embodiment of the invention, in which the porous glass ceramic is produced by extraction of a phase-separated starting glass, the starting glass was heat-treated prior to extraction at a temperature of 300 °C to 1200 °C, preferably from 400 °C to 800 °C, particularly preferably from 450 °C to 700 °C.

[0058] In an embodiment of the invention, wherein the porous glass ceramic is produced by extraction of a phase-separated starting glass, the porous glass ceramic is produced by extraction of a phase-separated alkali borate starting glass, preferably a sodium borate starting glass.

[0059] Alkali borate glasses, especially sodium borate glass (Na2O-B2O3 glass), are characterized by a high tendency to form glass, deformability and optical transparency.

[0060] Sodium borate glasses are excellent host systems for various rare-earth metal oxide ions. By incorporating variable concentrations of these ions into the glass-forming system, the physical and chemical properties of the glasses can be modified.

[0061] In an embodiment of the invention, wherein the porous glass ceramic is produced by extraction of a phase-separated alkali borate starting glass, preferably a sodium borate starting glass, the respective starting glass contains CeO2 and / or ZrO2.

[0062] The incorporation of CeO2 into a Na2O-B2O3 starting glass system results in a more compact and robust glass structure. Furthermore, the band gap decreases and the dielectric constant increases with increasing CeO2 content.

[0063] The porous glass ceramics based on CeO2 and / or ZrO2-containing starting glasses are characterized by an increased specific surface area, a well-controlled pore structure, and improved temperature resistance.

[0064] Instead of CeO2 and / or ZrO2, the amorphous and crystalline phases of the porous glass ceramics according to the invention, which are produced by the extraction of a phase-separated starting glass, can also consist largely of oxides and mixed oxides of at least one element selected from: titanium, iron, manganese, vanadium, yttrium, zinc, aluminum, nickel, cobalt, germanium and / or other transition metal oxides. "Largely" in this context means that the amorphous and crystalline phases consist of more than 50 mol%, for example, more than 75 mol%, more than 90 mol%, more than 95 mol%, or more than 99 mol% of the aforementioned oxides.

[0065] The problem is further solved by a method for converting greenhouse gases, wherein a greenhouse gas-containing gas is brought into contact with a porous glass ceramic according to the invention in the presence of a cold plasma.

[0066] In this context, "cold plasma" refers to non-thermal plasma.

[0067] The use of non-thermal plasmas makes it possible to initiate thermodynamically unfavorable chemical reactions, such as the dry reforming of methane, CO2 hydrogenation and the splitting of CO2 into CO and O2, even at lower pressures and temperatures.

[0068] In this context, the term plasma refers to a gas that is at least partially ionized, that is, a gas with freely moving electrons as well as freely moving positively or negatively charged ions. Due to the presence of free charge carriers in the gas phase, the physical properties of a plasma differ significantly from those of a neutral gas. For example, plasmas are characterized by high electrical conductivity.

[0069] The high-energy particles of a plasma can easily interact with other atoms and molecules, thus making it possible to initiate a variety of chemical reactions.

[0070] Thermal plasmas are characterized by the fact that all constituent species are in local thermal equilibrium. Electrons, ions, and neutral particles have, on average, the same temperature. In contrast, non-thermal plasmas (cold plasmas) are characterized by a non-uniform temperature distribution. The electrons in non-thermal plasmas have a significantly higher temperature than the other particles. The temperature of the electrons is typically on the order of 1 to 10 eV, while the plasma as a whole has a considerably lower temperature, between approximately 300 and 700 K.

[0071] For example, the following plasma reactors are suitable for generating cold plasma: Microwave Discharge Reactor (MWD), Radio Frequency Plasma (RF Plasma), Gliding Arc Discharge Reactor (GAD), Plasma Torch, Glow Discharge (GD), Capillary Discharge (CD), Atmospheric Pressure Plasma Jet (APPJ), Corona Discharge, and Dielectric Barrier Discharge Plasma Reactor (DBD).

[0072] In the process according to the invention, the porous glass ceramic according to the invention is integrated into a plasma reactor in order to enable the selective production of desired products and to improve the yields and energy efficiency of plasma-assisted reactions. The advantages of heterogeneous catalysis (high selectivity) are combined with those of non-thermal plasma (activation at low temperature).

[0073] The glass ceramic can be introduced directly into or directly behind a plasma zone of the plasma reactor. Direct introduction into the plasma zone offers the advantage that the glass ceramic can interact with all species generated in the plasma. This enables, for example, reactions with vibrationally excited particles and ionized species that have very short lifetimes in the nanosecond or microsecond range.

[0074] Positive effects in terms of selectivity, yield and energy efficiency resulting from the use of porous glass ceramics in conjunction with cold plasma in the conversion of CO2 are due to an interplay of various plasma-catalyst interactions.

[0075] The process according to the invention can be used for plasma-assisted CO2 splitting. This typically produces CO and O2.

[0076] Due to the two double bonds between carbon and oxygen, CO2 is a highly stable molecule, which is why thermocatalytic CO2 splitting proves extremely difficult. Even at temperatures above 1000 °C, the conversion rate of CO2 is less than one percent.

[0077] By using non-thermal plasma, the unreactive CO2 molecule can be activated even at low temperatures. The conversion of carbon dioxide can be initiated via two pathways. High-energy electrons cause electronic excitation and ionization, ultimately leading to dissociation. This pathway is known as plasma-assisted CO2 conversion. Alternatively, collisions with lower-energy electrons can lead to vibrational excitation. This pathway is known as plasma-induced CO2 conversion.

[0078] Assisted and induced electrons are distinguished by their average electron energy (3 / 2 k). B T e), which is described by the electron energy distribution function. If the average electron energy is greater than the bond energy of the C=O double bond, using CO2 as an example (5.5 eV), a plasma-assisted CO2 reaction occurs, in which CO2 dissociates immediately with each electron-molecule collision (electron-molecule collision reaction).

[0079] The process according to the invention can be used, for example, for plasma-assisted CO2 conversion by methanization and dry reforming of methane, in addition to plasma-induced CO2 conversion.

[0080] In CO2 methanization, CO2 is converted with hydrogen to synthetic natural gas (CH4).

[0081] When green hydrogen is used, the methane produced can be employed as a sustainable energy carrier in transportation, industry, and power generation. This technology not only makes it possible to utilize CO2 but also to simultaneously use sustainably produced hydrogen.

[0082] Dry reforming describes the production of synthesis gas by reacting CO2 with methane. The synthesis gas can then be converted into higher hydrocarbons and various fuels. Conventional thermal-catalytic processes require temperatures exceeding 800 °C to carry out dry reforming. Similar to CO2 splitting, the use of a non-thermal plasma allows the endothermic reaction to proceed under milder conditions. Dry reforming enables the simultaneous conversion of two significant greenhouse gases into valuable products.

[0083] In this process, the porous glass ceramic acts as a catalyst, which is exposed to the greenhouse gas to be converted, in particular CO2 and / or CO. Exposure can mean that a bed is formed containing or consisting of the porous glass ceramic, and that this bed is forcibly permeated by a greenhouse gas-containing gas.

[0084] The porous glass ceramic not only serves as a substrate for optionally applied catalytically active substances, but also supports CO2 conversion through its amorphous and crystalline phases.

[0085] For example, a glass ceramic according to the invention with a high CeO2 content exhibits a very high oxygen storage and release capacity. The formation of oxygen defects (CeO2) is crucial here. 2-x) on a surface of the cerium oxide. Since nascent oxygen is stabilized by binding to the CeO2-containing glass ceramic, a back reaction to CO2 is prevented, and the CO molecule can desorb. The remaining oxygen atom recombines with O radicals from the cold plasma and is desorbed as O2. In this process, the oxygen vacancies are regenerated, and the catalytic cycle repeats.

[0086] In one embodiment of the method, the cold plasma is generated in a Dielectric Barrier Discharge (DBD) plasma reactor.

[0087] DBD plasma reactors have a robust and relatively simple design. They are comparatively inexpensive and allow for easy reaction control.

[0088] DBD plasma reactors are based on an electrically driven gas discharge between two electrodes (volume DBD) or on the electrodes themselves (surface DBD), with at least one of these electrodes being insulated by a dielectric. Typical dielectric materials include glass, ceramics, or polymers. The dielectric prevents current flow and thus the occurrence of spark discharges and arcs, which would heat the plasma and damage the electrodes. The electrodes can be arranged concentrically or as two parallel plate electrodes.

[0089] When a high-frequency alternating voltage is applied, an electric field spreads between the electrodes despite the electrical insulation. At a sufficiently high field strength, a discharge occurs, meaning that some of the gas in the plasma reactor is ionized, creating a plasma.

[0090] The space between or on top of the dielectric and the second electrode (or, if both electrodes are insulated, between the two dielectrics) is called the discharge gap. The breakdown voltage, which must be applied to ignite the plasma, depends on the pressure, the width of the discharge gap, and the gas composition. DBD plasma reactors, for example, are operated at atmospheric pressure. Depending on the gas properties and generator selection, either a homogeneous or a filamentary, inhomogeneous plasma can form. In most cases, as with CO2, a filamentary plasma is formed. Here, the discharge occurs in the form of many micro-discharges, which lead to the formation of thin, short-lived discharge filaments. These filaments make up approximately 1–10% of the total gas volume.The remaining non-ionized part of the gas serves to absorb the energy released during the micro-discharges and to transport newly formed, long-lived species.

[0091] In one embodiment of the process, the conversion of CO2 and / or CO takes place in the presence of H2, H2O and / or CH4.

[0092] In one embodiment of the process, the conversion is carried out at a reaction temperature of 0 to 250 °C. For example, the reaction temperature is 15 to 200 °C or 50 to 150 °C.

[0093] The invention will now be explained in more detail using exemplary embodiments, with reference to the Fig. 1 and Fig. 2. Reference is made to this. Fig. Figure 1 schematically shows an embodiment of a device for carrying out an embodiment of a cold plasma catalysis process. Fig. Figure 2 schematically shows a cross-section through the reactor. Fig. 1.

[0094] The embodiments of the porous glass ceramic according to the invention are porous glass ceramics produced by extraction of a CeO2-B2O3-Na2O starting glass.

[0095] Cerium(IV) oxide (CeO2, Acros Organics, 99.9%), boron(III) oxide (B2O3, Thermo Fisher Scientific, 98%) and sodium carbonate (Na2CO3, anhydrous, VWR Chemicals, 99.9%) were used to produce the CeO2-B2O3-Na2O starting glass.

[0096] In the exemplary embodiment, the glass composition of the CeO2-B2O3-Na2O starting glass is 16.1 mol-% CeO2, 72.1 mol-% B2O3 and 11.8 mol-% Na2O.

[0097] The mixture of boron(III) oxide and sodium carbonate was transferred to a Pt / Rh crucible (80 wt% Pt / 20 wt% Rh). The crucible was sealed with a lid and placed in a high-temperature chamber furnace preheated to 1400 °C. After 10 minutes at 1450 °C, the cerium(IV) oxide was added portionwise to the melt over 70–85 minutes. For this, the crucible was removed from the furnace at two-minute intervals, and approximately 500–600 mg of CeO₂ was added each time. After all the cerium(IV) oxide had been added, the temperature was increased to 1500 °C and held for two hours. The crucible was then removed from the furnace, and the hot, red-hot melt was immediately poured onto a brass plate at room temperature and weighted down with another brass plate.

[0098] Three batches of the manufactured starting glass were further processed by subjecting them to different heat treatments and then extracting them.

[0099] Parameters of the heat treatments performed are listed in Table 1. Fractions of the manufactured starting glass were each transferred to a corundum tray and heated in a chamber furnace. After the heat treatment, the starting glasses were left in the furnace for at least 10 hours to cool and then removed. Table 1: Heating rate [K / min] Temperature [°C] Holding time [h] CBN1 10 580 4 CBN2 10 620 8 CBN3 10 660 32

[0100] The heat-treated starting glasses CBN1, CBN2, CBN3 were each crushed into granules with a particle size of approximately 1 to 3 mm in diameter.

[0101] The heat-treated glassware was then extracted. The procedure was as follows: The granules were divided into Teflon mesh bags, which were then placed in PET (polyethylene terephthalate) containers. Each container held approximately 10 to 15 g of one of the granules. The containers were filled with approximately 150 ml of deionized water as solvent, sealed with a lid, and placed in a shaking water bath. Extraction was carried out at a water bath temperature of 80 °C and a shaking rate of 90 min⁻¹. -1 The pH in the containers was tested daily, and the solvent was changed as soon as a basic shift (7 < pH ≤ 10) was observed. Extraction was stopped after 13 to 42 days, once a neutral pH was measured and remained unchanged for at least 24 hours.

[0102] For solvent exchange, the extracted starting materials were stored in ethanol for one day and then filtered through filter paper. The granules were dried overnight in air at room temperature and subsequently at 70–80 °C in a drying oven until a constant mass was achieved.

[0103] Texture data (specific pore volume V) P , specific surface area A P and mean pore size d P The values ​​determined by both mercury intrusion (Hg intrusion) and nitrogen sorption (N2 sorption) are listed in Table 2 below. Table 2: Hg intrusion N2 sorption, 77 K calculated d P / [nm] V P [cm 3 / g] d P / [nm] V P [cm 3 / g] A P [m 2 / g] V P [cm 3 / g] CBN1 9 0,304 6 0,397 269 0,383 CBN2 7 0,260 6 0,253 161 0,304 CBN3 87 0,620 16 0,150 94 0,645

[0104] The specific surface areas were determined according to BET from the isotherms, as were the pore diameters and volumes according to BJH. Furthermore, the last column of Table 2 shows a calculated specific pore volume, which is the sum of the specific pore volume determined by N2 sorption up to a pore size of 3.7 nm and the specific pore volume from the Hg intrusion.

[0105] The extracted starting glasses described in more detail here represent only embodiments of the porous glass-ceramic according to the invention. The porous glass-ceramics according to the invention are not limited to the starting glasses and their heat treatments and subsequent extraction conditions described in the embodiments. The glass-ceramic according to the invention can be produced in different ways, whereby in particular the starting glass composition, the heat treatment conditions, and the extraction conditions can be varied.

[0106] The inventive process is explained below using plasma-assisted CO2 splitting in a DBD reactor, wherein the porous CeO2-containing glass ceramics produced as described above are used as packing material.

[0107] A schematic representation of an embodiment of a device for carrying out an embodiment of the method according to the invention is shown in Fig. 1 shown.

[0108] The processes used two different tubular reactors, referred to below as tubular reactor R1 and tubular reactor R2.

[0109] The tubular reactor R1, R2 is in Fig.Figure 2 shows a schematic cross-sectional view. The tubular reactor R1, R2 has a base electrode 10, a dielectric 11, a packing material 12, and a high-voltage electrode 13. The base electrode 10 and the high-voltage electrode 13 are connected to a high-voltage generator 2. The device has an inlet 4 for a greenhouse gas-containing gas into the tubular reactor R1, R2. In this case, the inlet 4 is a pressurized gas cylinder containing CO2. The gas flow from the inlet 4 into the tubular reactor R1, R2 is regulated by a first mass flow controller 6.

[0110] At the outlet of the pipe reactor R1, R2 there is a cold trap 7.

[0111] At the outlet of the cold trap 7, the reaction gas / gas mixture exiting the tubular reactor R1, R2 is mixed with an inert carrier gas from a carrier gas inlet 3. In this case, the carrier gas inlet 3 is a pressurized gas cylinder containing nitrogen.

[0112] The gas mixture of carrier gas and reaction gas is fed to a processing device 8. The processing device has an analysis device 9 with which the gas composition of the gas mixture can be determined. In the Fig. In the embodiment shown in Figure 1, the analysis device 9 is a gas chromatograph.

[0113] The tubular reactor R2 features a stainless steel inner electrode, allowing for temperature control of the reactor during the process. Specifications for tubular reactors R1 and R2 are listed in Table 3. Table 3: Tubular reactor R1 Tubular reactor R2 Inner electrode material molybdenum stainless steel Diameter of inner electrode 28 mm 28 mm Outer electrode material Stainless steel (mesh) Stainless steel (mesh) Dielectric / housing material Quartz glass Quartz glass Dielectric layer thickness 1.7 mm 2.1 mm Discharge Gap 2.5 mm 1.9 mm Reactor volume (discharge zone) 14.5 cm 3 10.7 cm 3 Contact time 12.79 s 9.42 s

[0114] The packing material consisted of a mixture of 33 vol% of the CeO2-containing glass ceramics and 66 vol% of an Al2O3 support material (Thermo Fisher Scientific, 0.80 cm3 g). -1 ≤ V p,spez ≤ 120 cm 3 G -1 , 220 m 2 G -1 ≤ A spez ≤ 280 m 2 G-1 , calcined at 450 °C). The samples were used as granules with particle sizes in the range of 0.5 mm ≤ d ≤ 1.6 mm. The discharge zone of the reactor was completely filled with the packing material.

[0115] The porous glass ceramics CBN1, CBN2, and CBN3 were initially investigated sequentially in the tubular reactor R1. Before plasma ignition, a baseline measurement was performed to determine the initial concentrations of CO2 and N2. The gas flow rate per unit time was set using mass flow controllers. The gas composition of the exiting gas stream was determined using an Inficon Micro GC Fusion gas analyzer. A CO2 volume flow rate of 40 mL / min was used. Nitrogen was employed as a reference gas to detect changes in volume flow rate. After the baseline measurement, the plasma was ignited. The CO2 conversion was investigated under various plasma conditions. For this purpose, the power of the high-voltage (HV) generator was varied between 60 and 230 W by adjusting the voltage and frequency.Temperature changes in the plasma reactor were recorded using an IR sensor (Optris CT LT22) aimed at the outer electrode. All measurements were performed at atmospheric pressure (1 atm).

[0116] The measurements were then repeated with samples CBN1, CBN2, and CBN3 in the tubular reactor R2. It was possible to cool or heat the inner electrode, thus maintaining the reactor and the glass-ceramic packing at an approximately constant temperature. The experiments were conducted at 150 °C (referenced to the IR sensor). For sample CBN1, an additional test was performed with maximum reactor cooling, achieving temperatures between 105 °C and 147 °C, depending on the plasma power.

[0117] The highest CO2 conversion of 18.7% ± 0.9% in tubular reactor 1 was achieved with the glass ceramic CBN3 with a specific energy input of 48.8 kJ L -1 ± 5.3 kJ L -1 achieved.

[0118] The highest conversion of 34.7% ± 4.0% using tubular reactor 2 at a temperature of 150°C was achieved with the glass ceramic CBN3 at a specific energy input of 95 kJ L -1 ± 11 kJ L -1 achieved. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] FR 3115 711 A1

[0009]

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