DFT Studies On The Catalytic Activities Of Transition Metals And PdNi Alloys For The Key Steps Of Ethanol Oxidation Reactions

The promising application of ethanol fuel cells is hindered by the lack of ideal catalysts for complete ethanol oxidation reaction?EOR?.Nowdays,the most studied catalysts for EOR are the Pd-based catalysts.However,these kinds of catalysts have poor activities for C-C bond cleavage with CH₃COOH as the dominant by-products of EOR.In this work,a series of transition metals and Pd-based alloys were investigated on their catalytic abilities toward EOR using density functional theory?DFT?.Firstly,8 transition metals M?M=Pd,Ni,Pt,Ir,Rh,Ru,Au,and Ag?were studied on their activities for two key steps of EOR.The DFT results indicated that Ni,Pt,Ir,Rh,and Ru were good catalysts for EOR among all studied metals.Furthermore,it was found that there is a correlation between the catalytic activities of transition metals and their position in the periodic table.Ni was considered to be the most promising metal to promote the Pd-based catalysts toward EOR.In addition,six key elementary steps of EOR were calculated on the Pd?111?.It was found that the reaction barrier of CH₃COOH formation on Pd?111?was only 0.19eV,which was much lower than that of C-C bond scission,implying the high selectivity for CH₃COOH formation.Thus,pure Pd could not be an ideal catalyst for EOR,and it was necessary to add other transition metals into Pd.Finally,three different PdNi?111?alloy models were constructed through adding Ni as the second component into Pd.For PdNi alloy that is Pd-only on surface,the addition of Ni changed insignificantly for the adsorption of intermediates and the key reaction pathways.However,the presence of Ni in PdNi alloys could result in both“electronic effect”and“bimetallic effect”.The“bimetallic effect”in PdNi alloys might contribute to inhibit the generation of CH₃COOH to some extent,and thus facilitates the formation of CO₂.Moreover,the“bimetallic effect”was much more pronounced by the extent of Ni exposure on the surface of PdNi alloy catalysts,where the relationship between these two elements were found to be rather linear.