Studies Of Carbon Dioxide Hydrogenation Over Indium Oxide And Ceria Supported Catalysts

In recent years,atmospheric carbon dioxide is accumulating due to human activities.This results in a series of environmental problems such as the greenhouse effect and sea level rising problem.Therefore,the utilization of CO₂,especially CO₂ hydrogenation to fuel,is attracting attention worldwide.In this work,experimental and theoretical studies on CO₂ hydrogenation over catalysts supported on indium oxide and ceria were carried out.Ni/CeO₂ catalysts were prepared by cold plasma technique using argon as the discharge gas.The plasma treated catalyst shows outstanding methanation activity at low temperature and large space velocity compared to the conventional calcined sample.We identified the active sites during the reaction and found that metallic nickel is the active phase,while the supported cerium oxide was partially reduced.In addition,the Ni nanoparticles in the plasma treated sample is better dispersed and show stronger interaction with the support.The support ceria also exhibits a higher oxygen vacancy density during the reduction and reaction process.These factors improved the activation of H₂ and CO₂ at low temperatures,and also the hydrogenation of surface intermediates.In addition to CO₂ methanation,this simple preparation strategy can also be applied to catalysts for methane reforming,syngas methanation and other reactions.We prepared Pd-P/In₂O₃ catalysts using peptide-assisted room temperature electron reduction technique.The obtained catalyst showed higher activity than the catalyst prepared by the conventional method in the CO₂ hydrogenation to methanol reaction.The characterization results show that the Pd particles in Pd-P/In₂O₃ catalyst are better dispersed,and forming more Pd-In₂O₃ interface.They can also inhibit the formation of Pd In alloy,showing excellent hydrogen dissociation ability.In addition,In₂O₃ exhibits high oxygen vacancy density,which can activate more CO₂.The N-doping caused by the peptide reduces the energy barrier of the CO₂ hydrogenation reaction,making the reaction easier.We prepared Au/In₂O₃ catalyst and found that it shows improved CO₂ hydrogenation activity towards methanol.By using in-situ characterization,we found that the active sites are Au^δ+-In₂O_3-x interface under the reaction condition.The positively charged Au^δ+is capable to dissociate hydrogen,while the Au^δ+-In₂O_3-xinterface can activate CO₂.These two steps take place synergistically to produce methanol.In addition,we also studied the high temperature deactivation mechanism under the reducing atmosphere.The indium oxide on the surface was completely reduced to amorphous metallic In,covering the surface of the In₂O₃ and the Au^δ+-In₂O_3-x interface,resulting in the catalyst deactivation.Based on density functional theory,we constructed the Au₄/In₂O₃（110）model system.The positively charged Au^δ+cluster provides the possibility of activation of the H₂ molecule,while the Au₄-In₂O₃ interface provides the active sites for CO₂ activation.In this way,the interface and the Au cluster play a synergistic role in the reaction.H₂ is continuously activated by the Au₄ cluster,and then is transferred to the adsorbed CO₂ to produce methanol at the interface.The calculated reaction pathway showed that the CO₂ hydrogenation to methanol on the Au₄/In₂O₃ model catalyst was mainly achieved by the HCOO pathway,in which the H₃CO pathway was easier to carry out than the H₂COH pathway;HCOO was important intermediate.