Studies On Multi-component Mn Based Catalyst And Bimetallic RuPt Catalyst For CO Oxidation And Water-gas Shift Reaction

With the development of modern industry,the protection of environment also faces huge challenge about air pollution that mainly resulted from vehicle exhaust and industrial waste gas.Among these gases,flammable carbon monoxide(CO)is extremely harmful to human bodies that can cause death in long-time contacts.The CO that generated from the insufficient combustion of fuels is directly oxidized by oxygen in the exhaust purification system of vehicle.After the methanol and methane reforming in industry or fuel cell,the concentration of CO at the exit can be above 10%and should be firstly reduced to be lower than 1%by water-gas-shift(WGS)reaction,further below 10 ppm by preferential oxidation(PROX)in H₂-rich atmosphere to avoid the poison of catalysts,such as the Fe in ammonia synthesis and Pt in fuel cell.The CO can chemisorb on the transition metals due to the fac-ile combination of the lone pair electron of CO and the empty d-orbitals of metals,which is wildly used in the CO removal.Despite excellent activity in CO elimination,the applica-tion of noble metals,such as Pt and Au,is limited for their high cost and low reservation.On the other hand,the ternary Mn based oxide with better chemical stability(than binary one)due to the stable skeleton structure also show good activity and promise for applica-tion in CO oxidation and WGS reaction.While in the PROX reaction,the oxides suffer serve deactivation due to the formation of carbonates in the feed gas that containing CO₂and the research about highly active PROX catalysts is mainly focused on the use of the noble metals with lower price.In this paper,Sm Mn₂O₅(SMO)mullite based,Cu-Mn spinel(CMO)based and Pt/Ru composite catalysts are studied for CO oxidation,WGS and PROX reaction,respectively,with the strategy that aiming at reducing the usage of noble metals.The activity or selectivity is improved by loading active metal oxides,increasing the amount of oxygen vacancies and controlling the interfacial structure,respectively,where the interaction between the active component and the relationship between the surface property and activity are studied.Finally,the reaction mechanism over the catalyst surface is explored.The main contents and results of the research are listed as follows:1)First,the metal oxide(MO_x,M=Mn,Fe,Co,Ni and Cu)are loaded on the mulite SMO by deposition-precipitation method to construct the oxides interfaces for the better activity.Except for the Fe,all MO_x loaded composite catalysts exhibit better activity compared with the substrate mullite.The CuO_x/SMO process the best reaction rate among these catalysts with a CO conversion of 40%at 100?.The amount and activity of oxygen species are improved that aroused from the interaction between the MO_x and SMO facilitate the decomposition of carbonate(hydro-carbonate)and mitigate the corresponding block effect,which promoting the cyclic reaction of CO.Furthermore,the additional adsorption of CO on CuO_x also contributes to the enhanced activity by increasing the reaction sites.2)Then the Cu-Mn oxide that is consisted of Cu_1.5Mn_1.5O₄ spinel and Mn₂O₃ are prepared by combustion of ethylene glycol and methanol(EGM),fractional pre- cipitation(FP)and template growth(TG)method,respectively.The amount of surface oxygen defect is increased to promote the WGS reaction.Compared with the catalyst synthesized by co-precipitation(CP)method,the as-prepared CMO catalysts exhibit better distribution of Cu-Mn component and more ion transition between Cu and Mn.The higher reducibility and more abundant oxygen vacancies as demonstrated by the chemical analysis can facilitate the dissociation of water, resulting more generation of active hydroxy groups and improving the WGS ac- tivity.The CMO prepared by EGM method exhibits the best activity (122.72?mol _CO/(g _cat.·s)without pre-reduction treatment,which is better than the commercial Cu/ZnO/Al₂O₃ catalyst(73.62?mol _CO/(g _cat.·s)and less deactivated after exposed in air(6%loss for the CO conversion).3)In addition,Pt is deposited on partial crystal plane of Ru by atomic layer deposition to prepare bifunctional Pt/Ru composite catalyst,where the structure and the number of Pt atomic layers are controlled to enhance the PROX reactions.The existence of intergranular stress leads to the preferential deposition of Pt on Ru (001)due to the lower lattice mismatch with Ru(101)exposed.There exists the synergistic effect at the interface between Pt(111)and Ru(101).The co-adsorption of CO and O at the interface greatly reduces the oxidation barrier and the corresponding T₅₀ reduced for 61 and 94? compared with the pure Pt and pure Ru catalysts.Deposition of monolayer Pt can accelerate the electron transfer from Ru to Pt to the maximum extent,which reduces the d-band center(0.8eV)and adsorption energy(0.7eV)of CO.Besides this,the adsorption of H is also weakened(0.4eV),which suppresses the competitive reaction of H₂.These factors contribute to the better reaction activity and selectivity for PROX reaction.