Study Of Carbonate/CO₂ Hydrogenation To High Value-added Products

Excessive emission of CO₂is the main cause of global warming.The core reaction of the cement industry is the thermal decomposition of calcium carbonate.As an industry with high energy consumption and high carbon emission,the cement industry has a serious impact on the global ecological environment.Direct CO₂emissions from the decomposition process can be reduced at the source through coupled reactions.Indirect CO₂emissions generated from fuel consumption and electricity supply processes can be converted into high value-added chemicals by adopting carbon capture,utilization and storage（CCUS）approach.Transforming CO₂into CO,followed by CO transformation into high value-added chemicals through reactions like F-T synthesis can reduce the greenhouse effect and alleviate the energy crisis.The main results are as follows:（1）We developed a concept of co-thermal in-situ reduction of inorganic carbonates by using the energy released by carbonate decomposition under pure hydrogen atmosphere,which reduces the decarboxylation temperature and significantly inhibits the CO₂emissions.Under pure hydrogen atmosphere,CO selectivity is up to 93.7%at 750°C and the CO generation rate is 0.756mmol min^-1.Compared with the complete decomposition of calcium carbonate above 900°C in air,the complete decomposition temperature of calcium carbonate in pure hydrogen atmosphere is reduced by about 150°C,and high purity and porous solid product Ca O is obtained.A combination of hydrogen-deuterium exchange,isotope experiment,and density functional theory calculations demonstrates that the CO results from the selective cleavage of Ca-O bonds at the surface of Ca CO₃via the direct hydrogenation mechanism at relatively low temperature.However,it undergoes the reverse water-gas shift reaction path at high temperature,i.e.,CO being produced by the reduction of CO₂released by the decomposition of carbonates.（2）Pt single-atom catalysts has been successfully prepared for CO₂reduction,achieving high selectivity and stability in RWGS reaction.Zn Al-LDH were prepared by co-precipitation method,further calcined in air to obtain Zn Al-MMO,and then loaded with metal Pt using a stepwise incipient wetness method.Finally,high-temperature calcination was uesd to form Pt single-atom.The catalysts are easily prepared and it show good high temperature stability for RWGS with the conversion of CO₂at 600°C can reach 60%,which is close to the equilibrium conversion.At the same time,the selectivity for CO is close to 100%.There is no significant decrease in the conversion of CO₂after a long reaction time of 48 h under the condition of GHSV=480000 m L g^-1h^-1.Pt single-atom can be stabilized through a strong metal support interaction and the formation of Pt-O-Zn promotes the RWGS reaction activity of the catalyst,which has good prospects for application.Combined with the reaction performance evaluation results and characterization results of XRD、XPS、HR-TEM and In situ DRIFTS,the morphology,structure,active center and reaction mechanism of Pt-Zn Al-MMO catalysts were analyzed.