1690results about "Carbon monoxide" patented technology

An article for joule heating is described, including a three-dimensional substrate on and / or in which a pyrolyzate of a phenolic resin or polymer forms an electrically conductive carbon network. Such articles may be incorporated in structured materials applications, which may include support, sorbent, and or catalyst components. Also described are methods of fabricating such articles and structured materials, and apparatus comprising same, and methods of use of such articles and structured materials and apparatus for conducting material transformation processes requiring input of heat for their performance, such as CO2 adsorption, methane pyrolysis for hydrogen and carbon production, hydrogen-assisted conversion of CO2 to hydrocarbons, including catalytic conversion of CO2 to olefins, catalytic conversion of CO2 to propane (liquefied petroleum gas), and catalytic conversion of CO2 to renewable natural gas, reverse water gas shift reaction, steam ethane cracking, propane cracking, steam methane reforming, and dry methane reforming.

The invention relates to the technical field of reverse water-gas shift, in particular to a reverse water-gas shift catalyst, a preparation method thereof and a reverse water-gas shift method.The method comprises the steps that 1, precious metal is loaded on a carrier through an impregnation method, first calcination is conducted, and the carrier is selected from one or more of titanium dioxide, aluminum oxide, zirconium oxide and silicon dioxide; (2) mixing the product obtained in the step (1) with cerium dioxide, grinding, then carrying out secondary calcination, and reducing; the content of the noble metal element is 0.2-1wt% of the mass of the carrier; the mass ratio of the product obtained in the step (1) to cerium dioxide is 1: (0.5-2); and the noble metal is selected from one or more of rhodium, ruthenium and palladium. The reverse water gas shift catalyst prepared by the preparation method has the advantages of high carbon dioxide conversion rate, good carbon monoxide selectivity and stable catalytic performance when being used for reverse water gas shift reaction.

The invention discloses a preparation method of lead-free double perovskite nanofibers capable of efficiently photocatalytic reduction of CO2 at room temperature. The method comprises the following steps: fully dissolving cesium bromide, silver bromide and bismuth bromide in an organic solvent to obtain a precursor solution, adding a ligand and a polymer into the precursor solution, fully magnetically stirring to obtain a spinning solution, and preparing a nanofiber product by utilizing an airflow spinning technology. The airflow spinning technology is creatively adopted to enable the lead-free double perovskite quantum to grow on the nanofiber, a large number of catalytic reaction sites are provided, and the catalytic activity is remarkably improved. According to the method, large-scale preparation of the lead-free double perovskite nanofibers is achieved at the room temperature, controllability and high stability are achieved, operation is easy, the method is suitable for the field of photocatalytic CO2 conversion and the like, and a new thought is provided for sustainable energy development.

The invention discloses a capacity configuration optimization method for preparing methanol by coupling wind-solar hydrogen production with biomass gasification, belongs to the field of methanol preparation, and develops a comprehensive optimization framework to evaluate the technical economic feasibility of renewable methanol production. According to the framework, renewable energy power generation, an energy storage technology, hydrogen production through water electrolysis and methanol synthesis are integrated together, so that a production system with cost effectiveness is constructed. And establishing an optimization model to determine the optimal investment and operation strategy of green methanol production. According to the model, investment and operation decisions of a plurality of system components are considered, and a series of decision variables are set. Through the solution of the optimization model, the problem of insufficient economic evaluation and comparison technology of synthesizing methanol from renewable energy sources is solved, a scientific basis is provided for a project in planning, design and decision-making stages, and the development of the field of synthesizing methanol from renewable energy sources is promoted.

An article for joule heating is described, including a three-dimensional substrate on and / or in which a pyrolyzate of a phenolic resin or polymer forms an electrically conductive carbon network. Such articles may be incorporated in structured materials applications, which may include support, sorbent, and or catalyst components. Also described are methods of fabricating such articles and structured materials, and apparatus comprising same, and methods of use of such articles and structured materials and apparatus for conducting material transformation processes requiring input of heat for their performance, such as CO2 adsorption, methane pyrolysis for hydrogen and carbon production, hydrogen-assisted conversion of CO2 to hydrocarbons, including catalytic conversion of CO2 to olefins, catalytic conversion of CO2 to propane (liquefied petroleum gas), and catalytic conversion of CO2 to renewable natural gas, reverse water gas shift reaction, steam ethane cracking, propane cracking, steam methane reforming, and dry methane reforming.

A method for Carbon Dioxide (CO2) production comprising producing super-heated steam, utilizing a small modular nuclear reactor power plant system, receiving Sodium Formate (HCOONa) into a first reaction chamber, the first reaction chamber receiving a first portion of the super-heated steam at a first temperature, decomposing the Sodium Formate (HCOONa) into Sodium Oxalate ((COO)2Na2) and Hydrogen (H2), receiving the Sodium Oxalate ((COO)2Na2) into a second reaction chamber, the second reaction chamber receiving a second portion of the super-heated steam at a second temperature, decomposing the Sodium Oxalate ((COO)2Na2) into Sodium Oxide (Na2O), Carbon Monoxide (CO), and Carbon Dioxide (CO2).

A method for the generation of a gas mixture including carbon monoxide, carbon dioxide and hydrogen for use in hydroformylation plants, including the steps of evaporating water to steam; feeding the steam to a solid oxide electrolysis cell (SOEC) or an SOEC stack at a sufficient temperature for the cell or cell stack to operate while effecting a partial conversion of steam to hydrogen; utilizing the effluent SOEC gas including H2 together with CO2 from an external source as feed for a RWGS reactor in which the RWGS reaction takes place, converting some of the CO2 and H2 to CO and H2O; removing some of or all the remaining steam from the raw product gas stream; using said gas mixture comprising CO, CO2 and H2 for liquid phase hydroformylation utilizing carbon monoxide and hydrogen as reactants, while recycling CO2 to the RWGS reactor.

The invention discloses preparation of a high-performance carbon matrix embedded iron-based catalyst based on a metal organic framework precursor and application of the high-performance carbon matrix embedded iron-based catalyst in reverse water-gas shift reaction. In the preparation process, commercially available 1, 3, 5-trimesic acid iron (the chemical formula is C9H3FeO6, abbreviated as Fe-BTC) is selected as a raw material, pyrolysis treatment is carried out in an argon atmosphere, then air passivation is carried out, and finally the high-performance carbon matrix embedded iron-based catalyst based on the metal organic framework precursor is successfully prepared. The MOF-600 has excellent performance in many catalysts, the carbon dioxide production rate reaches 24.0 mmol CO.gcat <-1 >. S <-1 > at the temperature of 400 DEG C in a reverse water gas shift reaction, the performance is remarkably superior to that of an existing non-noble metal catalyst, and extremely high catalytic efficiency and application potential are shown.

The invention discloses a monatomic catalyst capable of retaining surface defects of a catalyst as well as a preparation method and application of the monatomic catalyst, and belongs to the field of catalysis. The monatomic catalyst comprises an active metal component, a doping element and a carrier, the carrier is a semiconductor material rich in surface defects. The preparation method adopts a light-induced migration-conversion strategy. The monatomic catalyst which is obtained by the preparation method and retains the surface defects of the semiconductor material is applied to the fields of photocatalysis, thermocatalysis and electrocatalysis, and shows excellent performance.

The invention discloses a lanthanum-doped CuMgAl catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The preparation method of the lanthanum-doped CuMgAl catalyst comprises the following steps: adding a copper salt, a magnesium salt, an aluminum salt and a lanthanum salt into water to obtain a first solution; adding a precipitator into water to obtain a second solution; adding the second solution into the first solution to adjust the pH value to 10.5 to obtain a mixed solution, stirring the mixed solution to generate a co-precipitation reaction, after the reaction is completed, carrying out aging treatment to promote growth and structure ordering of layered double hydroxide crystals, and then carrying out calcination treatment to convert a layered double hydroxide precursor into an oxide, thereby obtaining the layered double hydroxide. And the lanthanum-doped CuMgAl catalyst is obtained. The lanthanum-doped CuMgAl catalyst prepared by the preparation method disclosed by the invention has excellent activity and stability.

The invention relates to the technical field of catalysts, in particular to a plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: 1, synthesizing mesoporous molecular sieve TS-1 powder; and 2, mixing the mesoporous molecular sieve TS-1 and CH3OH to prepare a suspension, injecting an AgNO3 aqueous solution into the suspension, and carrying out ultraviolet irradiation, filtration, washing and freeze drying to obtain the plasma silver nanocluster coated mesoporous molecular sieve TS-1 photocatalyst. The obtained electron-rich Ag cluster / mTS-1 shows an Ag-Ag coordination number (CN = 2.0 + / -0.1) lower than that of a mesoporous molecular sieve TS-1 (CN = 2.9 + / -0.2) loaded with Ag nanoparticles, so that the electron-rich Ag cluster / mTS-1 has higher CO2 adsorption and activation performance. In addition, the silver nanoclusters are firmly anchored on the surface of the mesoporous molecular sieve TS-1, so that the mesoporous molecular sieve TS-1 has high stability, and therefore, the mesoporous molecular sieve TS-1 shows high-stability CO2-to-CO photocatalytic conversion activity under simulated sunlight irradiation, and the yield of CO within 4 hours is 350 [mu] mol g <-1 >.

The invention provides a method for preparing H2-CO energy gas from steel slag, and belongs to the field of metallurgy and solid waste treatment. The preparation method comprises the following specific preparation steps: step 1, blowing weak oxidizing gas to the liquid level of the steel slag in a molten state to oxidize FeO in the steel slag, so that hydrogen and carbon monoxide gas are generated while ferric oxide is converted into a magnetic phase which is easy to separate; and 2, separating and collecting the reacted gas. After the steps, the energy gas containing H2 and CO is finally generated for recycling. Through the treatment steps provided by the invention, (1) CO2 is absorbed and converted into CO energy gas, and carbon emission is reduced; (2) waste heat of the steel slag is utilized, water vapor is converted into clean energy H2, and the hydrogen production cost is remarkably reduced; and (3) the injection proportion of H2O-CO2 gas is regulated and controlled, and the generation rate of H2-CO is remarkably increased.

The invention provides a system and a method for co-production of synthesis gas with adjustable and controllable hydrogen-carbon ratio through carbonate reduction refining. The system comprises a hydrogen supply unit, a carbonate feeding unit and a carbonate fluidization hydrogenation reactor, the carbonate fluidization hydrogenation reactor comprises a first reaction chamber, a second reaction chamber and a cyclone separation unit; according to the system and the method for co-producing the synthesis gas with the adjustable hydrogen-carbon ratio through carbonate reduction refining, the reaction intensity of the first reaction cavity and the second reaction cavity of the carbonate fluidization hydrogenation reactor is adjusted and controlled, so that the hydrogen-carbon ratio in the product synthesis gas at the synthesis gas discharge hole can be accurately controlled; and proper reaction raw materials are directly provided for chemical synthesis of a series of subsequent high-added-value carbon derivatives.

The invention relates to a method for preparing carbon monoxide by reverse water gas shift, which comprises the following steps: under the catalytic action of a supported catalyst, carrying out reverse water gas shift reaction, carrying out pressure swing adsorption treatment on mixed gas generated in the reaction process, and desorbing to obtain carbon monoxide. By coupling the reverse water gas shift reaction and the pressure swing adsorption process and exerting the synergistic effect of the reverse water gas shift reaction and the pressure swing adsorption process, efficient and rapid separation of carbon monoxide is realized, the reverse water gas shift reaction is promoted to be carried out in the forward direction, the reaction requirement of reverse water gas shift is reduced, the reverse water gas shift reaction is carried out under relatively mild conditions, and the reaction efficiency is improved. The long-period efficient conversion of carbon dioxide is realized, and the conversion rate of carbon dioxide and the selectivity of carbon monoxide are further improved.

The invention provides a Ce-doped Cu and Zn-Al layered bimetallic oxide catalyst for reverse water gas shift and a preparation method thereof, the catalyst is composed of ZnO, Al2O3, CuO and CeO2, and the mass ratio of ZnO to Al2O3 to CuO to CeO2 is (71-78): (12-15): (5-6): (2-11). According to the preparation method, CeO2 is selected to be doped in layered bimetallic oxide (LDO) formed by calcining Cu-LDH, and compared with TiO2 doping, it is found that CeO2 has a more remarkable catalytic effect compared with TiO2, and the prepared catalyst has excellent stability and can maintain high activity under long-time testing; and the catalyst has CO yield close to equilibrium yield under the condition of relatively low catalytic temperature (450 DEG C), has excellent industrial implementation conversion prospect, and is simple in process steps and suitable for continuous production.

The application provides a reverse water gas shift catalyst, a preparation method and application thereof, and the reverse water gas shift catalyst prepared by the preparation method has excellent catalytic activity and high CO selectivity in a reverse water gas shift reaction. The preparation method comprises the following steps: contacting a precipitating salt solution with a precipitant aqueous solution and performing co-precipitation, and simultaneously controlling the reaction temperature to be 40-80 DEG C and the pH to be 6-8; optionally performing aging after the co-precipitation is completed; filtering the obtained precipitate to obtain a filter cake, washing the filter cake, then drying the filter cake, and calcining the filter cake at 300-500 DEG C to obtain the reverse water gas shift catalyst; wherein the precipitating salt solution is a mixed aqueous solution of a soluble salt of divalent metal ions and a soluble salt of trivalent metal ions, the divalent metal ions are selected from divalent ions of Mg and / or Zn, and the trivalent metal ions are selected from trivalent ions of Al, In and / or Ga.

The invention discloses a preparation method of a reverse water gas shift catalyst and an application thereof, comprising the following steps: S1: weighing a metal oxide precursor, a molybdenum oxide precursor and citric acid respectively and dissolving them in a beaker to obtain a mixed solution A; S2. adjusting the pH value of the mixed solution A with an acidic solution; S3. heating and stirring the mixed solution A in a water bath until it is in a gel state and drying, and then calcining it in a muffle furnace to obtain a carrier material; S4-S6. preparing a reverse water gas shift catalyst; the catalyst of the invention loads copper on the carrier material by a co-precipitation method, and the carrier material is reported for the first time, and has the advantages of simple preparation steps, easy availability of raw materials, safe operation, etc. At the same time, the catalyst obtained by the invention has an excellent CO conversion rate and a CO selectivity close to 100%.

The invention discloses a calcium-based carbon capture-conversion integrated method based on NaAlO2 stable catalysis, and relates to the technical field of carbon dioxide capture and conversion, the specific method comprises the following steps: CaO and NaAlO2 are introduced into a carbonation reactor, CO2-containing flue gas is absorbed to generate CaCO3, NaAlO2 plays a role in inhibiting CaO sintering, so that the carbonation reaction is more stable; then the generated CaCO3 and NaAlO2 are transferred into a conversion reactor, charcoal is added for an in-situ conversion reaction, high-concentration CO gas and CaO are obtained, NaAlO2 serves as a catalyst, and charcoal serves as a reducing agent; and the generated CaO material enters the carbonation reactor again for cyclic utilization. According to the method, CO2 in the flue gas is converted into CO in situ, and emission reduction and utilization of CO2 are promoted.

The invention concerns a reaction system and a method for carbon dioxide hydrogenation comprising: (a) providing a carbon dioxide feed stream (106) at a temperature of at least 600°C; (b) providing a first hydrogen feed stream (112) at a temperature of at least 600°C; (c) mixing the carbon dioxide feed stream and the first hydrogen feed stream obtaining a first mixed feed stream (114); (d) optionally, heating the first mixed feed stream in a first heat exchanger (136) to a temperature of at least 800°C obtaining a heated first mixed feed stream (138); (e) feeding the first mixed feed stream and / or the heated first mixed feed stream at a temperature of from 800°C to 1000°C to a first reactor (116) where it is contacted with a catalyst to obtain a first product stream (118) containing at least carbon monoxide, water and unreacted carbon dioxide.

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a manganese ferrite / bismuth tungstate heterojunction photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) dissolving sodium tungstate dihydrate, bismuth nitrate pentahydrate and hexadecyl trimethyl ammonium bromide in deionized water, and obtaining bismuth tungstate by using a hydrothermal method; 2) dissolving ferric chloride hexahydrate and manganese chloride tetrahydrate in water, then adding a sodium hydroxide solution, and obtaining manganese ferrite by using a hydrothermal method; and 3) dissolving bismuth tungstate and manganese ferrite into a sodium hydroxide solution, stirring, and drying to obtain the manganese ferrite / bismuth tungstate heterojunction photocatalyst. The formation of the heterojunction can greatly improve the activity of the manganese ferrite / bismuth tungstate in photocatalytic reduction of carbon dioxide.

An integrated energy system comprising a power plant including at least one nuclear reactor and an electrical power generation system a syngas generation system operably coupled to the power plant, the syngas generation system comprising a first reaction chamber configured to receive Sodium Formate (HCOONa), and a second reaction chamber configured to receive Sodium Oxalate ((COO)2Na2), and a methanol generation system operably coupled to the syngas generation system.

The invention discloses a COFs (Covalent Organic Frameworks)-based photocatalytic material with an improved structure as well as a preparation method and application of the COFs-based photocatalytic material. The covalent organic framework-based photocatalytic material with the anti-protein structure is obtained by taking silicon dioxide photonic crystal microbeads as a template and 4, 4 '-biphenyl dinitrile as a template, carrying out in-situ polymerization on the 4, 4'-biphenyl dinitrile in confinement pores in the silicon dioxide photonic crystal microbeads and then etching silicon dioxide. The preparation method comprises the following steps: (1) adding a catalyst into a 4, 4 '-biphenyl dinitrile monomer, then adding silicon dioxide photonic crystal microbeads, and carrying out a polymerization reaction; and (2) etching the silicon dioxide to obtain the covalent organic framework-based photocatalytic material with the inverse opal structure. The COFs material and the inverse opal structure are combined, so that the photocatalytic activity of the material is remarkably enhanced, and efficient and selective conversion of CO2 is promoted.

A system (11) is provided, comprising: a furnace (102); a heat exchanger (104), a gas separator (106) and a first thermochemical reactor (112). The heat exchanger (104) is arranged to receive and cool a flue gas (121 ) comprising carbon dioxide and nitrogen from the furnace (102) thereby producing a cooled flue gas (122). The gas separator (106) is arranged to receive the cooled flue gas (122), and to separate the cooled flue gas (122) into a nitrogen rich gas (124) and a carbon dioxide rich gas (125). The heat exchanger (104) is arranged to heat the nitrogen rich gas (124) and the carbon dioxide rich gas (125). The first thermochemical reactor (112) comprises a thermochemical compound. The first thermochemical reactor (112) is configured to, in a first mode of the system (11), receive the heated carbon dioxide rich gas (126), and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas (126) by oxidation of the thermochemical compound to form a carbon monoxide rich gas (125).

The invention provides a biomass gasification coupling iron ore powder reduction device and method with CO2 circulation, and relates to the technical field of direct reduction of iron from biomass gasification products. The biomass gasification coupling iron ore powder reduction device with CO2 circulation comprises a biomass gasification reaction device and a circulating fluidized bed reduction reaction device. The method comprises a method of a biomass gasification reaction device and a method of a circulating fluidized bed reduction reaction device. Through structural arrangement and application of the biomass gasification reaction device and the circulating fluidized bed reduction reaction device, CO2 gas circulation, zero carbon emission and high-purity iron raw material efficient utilization preparation can be achieved; the preparation method is simple and easy to operate, green and environment-friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

A composite photocatalyst, comprising V2C@V2O5 / TiO2, is disclosed herein. Additionally, a process for producing this composite, particularly V2C@V2O5 / TiO2, involves the steps of preparing V2C@V2O5 / TiO2 composite; grinding the V2C@V2O5 / TiO2 composite; and calcining the ground product to obtain the composite photocatalyst V2C@V2O5 / TiO2. Furthermore, the disclosure encompasses utilizing the composite photocatalyst in a CO2 reduction process, wherein the photocatalyst is irradiated in a photoreactor system.

The invention discloses a carbon nitride loaded metal diatom photocatalytic material as well as a preparation method and application thereof. The invention belongs to the field of photocatalytic materials. The invention aims to solve the technical problems of complex preparation process and low photocatalytic efficiency of the existing metal diatom photocatalyst. The method comprises the following steps: dissolving a nitrogen source and a phosphorus source in deionized water, and carrying out hydrothermal reaction to obtain a precursor; dissolving the precursor in a mixed solvent of alcohol, and then refluxing at constant temperature for a certain time to obtain a pre-product; and adding a metal compound solution capable of forming a conjugated system into the pre-product, carrying out ultrasonic treatment, heating in a constant-temperature water bath kettle, and calcining to obtain the carbon nitride loaded metal diatom photocatalytic material. The obtained photocatalytic material has the advantages of high visible light utilization rate, low photo-induced electron-hole recombination rate and high electron transfer rate. The method is used in the fields of photocatalytic hydrogen production, carbon dioxide reduction and organic matter oxidation.

The invention discloses an iron oxide-iron cluster catalyst for a reverse water gas shift reaction and preparation of the iron oxide-iron cluster catalyst. The catalyst is a double-site material Fe2O3-Fe4 / C of carbon-loaded iron oxide particles and iron clusters. The preparation method comprises the following steps: firstly, synthesizing an NH2-MIL-88B (Fe) material through a solvothermal method, then grinding and uniformly mixing the NH2-MIL-88B (Fe) material with KCl, feeding the mixture into a tubular furnace for high-temperature calcination, and washing after cooling to obtain the MOFs-derived double-site catalyst, namely Fe2O3-Fe4 / C. The MOFs-derived Fe2O3-Fe4 / C double-site catalyst prepared by the invention is low in cost and simple and convenient in process, and when the MOFs-derived Fe2O3-Fe4 / C double-site catalyst is applied to a low-temperature catalytic reverse water-gas shift reaction, the CO2 conversion rate and the CO space-time yield are greatly improved, and the industrial application potential is huge.

The invention discloses a preparation method and application of a nickel-titanium composite catalyst, and the preparation method of the nickel-titanium composite catalyst comprises the following steps: (1) roasting TiO2 in the presence of a reducing gas to obtain an intermediate; and (2) mixing and heating the intermediate obtained in the step (1) and a Ni precursor solution, and roasting in the presence of reducing gas to prepare the nickel-titanium composite catalyst. The preparation method of the catalyst provided by the invention has the advantages of easily available raw materials, simple process and easiness in industrialization. By changing the particle size of the TiO2 carrier, the interaction between metal Ni / TiO2 can be effectively adjusted, then the Ni / TiO2 photo-generated charge separation efficiency is adjusted, and finally the selectivity of a carbon dioxide hydrogenation reaction product is adjusted. The catalyst provided by the invention can realize photothermal conversion without an external heating device, and the nickel-titanium composite catalyst can realize strong light absorption under a full spectrum.

The present application discloses a bimetallic element doped silicon dioxide composite nanomaterial and its preparation method and application. The composite nanomaterial comprises a metal element and silicon dioxide with a hollow shell structure; the metal element is selected from at least two of zinc, cobalt, nickel, manganese, copper or iron; the internal cavity size is 50 to 500 nm; the specific surface area is 500 to 1000 m 2 / g, pore volume is 1.2~2.0cm 3 / g. The process of this application is simple, and the removal of the template and the construction of a complex hollow mesoporous structure are achieved at the same time. The rich and ordered metal composition and unique coordination instability of the coordination polymer are used as a metal source and a structure-guided template to form an internal cavity and dope metal elements at the same time. The material has a regular morphology, uniform size, good dispersion, single / double shell and hollow structure, high specific surface area and large pore volume, and has good application prospects in catalysis, energy utilization and conversion.

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a graphite-phase carbon nitride / iron-doped bismuth oxychloride heterojunction photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, putting urea into a crucible with a cover, and calcining in air by utilizing a thermal polymerization method to obtain graphite-phase carbon nitride; then uniformly dispersing the graphite phase carbon nitride into a mannitol solution in which bismuth nitrate pentahydrate is dissolved, then adding ferric nitrate nonahydrate and potassium chloride into the solution, and obtaining the graphite phase carbon nitride / iron-doped bismuth oxychloride heterojunction photocatalyst by utilizing a hydrothermal method. The formation of the heterojunction can greatly improve the activity of the graphite-phase carbon nitride in photocatalytic reduction of carbon dioxide.