Density Functional Theory Study On Oxidation Of CO Catalyzed By Doped Palladium And Copper Clusters

Within the metal catalysts, doped transition metal materialshave been one of the important catalysts. And an increasingnumber of studies have shown the advantage of the use ofbimetallic clusters in catalysis. Previous studies on dopedpalladium clusters leave no doubt that the doping of the otherelements not only influences geometric, but also strongly inducesthe physical and chemical properties of host clusters. Particularly,Prior investigations found that Pd exhibits strong interaction withAl atoms resulting in the formation of noble metal-like electronicstructure of Pd/Al alloys. Based on the research of structures ofAlPdn(n=1-3) clusters, we have elucidated the mechanism of COoxidation catalyzed by AlPdnclusters through first-principledensity-functional theory (DFT) calculation. It is found that thesesubnanometer species transfers into reaction complexes withcatalyze CO oxidation through two different mechanisms,occurring via Langmuir-Hinshelwood (LH) paths. It is shown thatmixing two different metals (Al and Pd) can have more beneficialeffects than pure palladium on the catalytic activity and the alloyed AlPd2cluster is proposed as the best effectivenanocatalysts.Preferential oxidation of CO (CO-PROX) is an important practicalprocess to purify H2for use in polymer electrolyte fuel cells.Aiming at illustrating the mechanism of CO-PROX, have beenstudied on CunPd(n=3-12) clusters by density function theory (DFT)calculations. The mechanism of CO-PROX reaction is proposed,which is different from ordinary oxidation of CO with O2. And thereaction via the carboxyl (COOH) and hydroxyl (OH) intermediates(IM) is demonstrated to be the most likely mechanism for CO-PROXin our paper. Cu6Pd cluster is predicted to have the lower barriercompared with other CunPd clusters and proposed as the besteffective nanocatalyst. To gain insights into the high catalyticactivity of the CunPd nanoparticles, the nature of the interactionbetween adsorbate and substrate is also analyzed by the detailedelectronic local density of states. The results should be helpful indeveloping and tailoring the efficient catalyst toward CO-PROXreaction.The water gas shift reaction (WGSR), is an important industrialreaction in providing high-purity hydrogen for fuel cells andnumerous industrial applications. The importance of WGSR is thatit removes the poisonous CO, which is a side product in theproduction of hydrogen fuel, and produces extra H2fuel. A densityfunctional theory (DFT) calculation has been carried out toinvestigate WGSR on Cu6TM(TM=Co, Rh, Ir, Ni, Pd, Pt, Ag, Au).The results indicate that WGSR mechanism involves the redox,carboxyl, and formate pathways, which correspond to CO*+O*→ CO2(g), CO*+OH*→COOH*→CO2(g)+H*, and CO*+H*+O*→CHO*+O*→HCOO**→CO2(g)+H*, respectively. It is found that WGSR issensitive to the properties of different transition metals. Anddopant Co, Rh, Ni, and Pd on copper cluster can have morebeneficial effects than pure copper on the catalytic activity andthe alloyed Cu6Co cluster is proposed as the best effectivenanocatalysts. The result shows that WGSR is mostly follows theredox pathway on Cu6TM(TM=Ni, Pd, Pt, Cu, Ag, Au) surface due tothe lower CO oxidation barriers; on the other hand, all the threepathways contribute similarly in WGSR on Cu6(TM=Co, Rh, Ir)surfaces.