Investigation On The Selective Oxidation Performance Of Nano Au-Pd Alloys

The precious metals such as Au and Pd have gained increasingattention due to their excellent catalytic performance in a lot of reactionssuch as CO oxidation at low temperature, the selective oxidation ofalcohols, the synthesis of vinyl acetate, the hydrochlorination of alkyn, theepoxidation of alkene and the direct synthesis of H₂O₂from H2and O2.Bimetallic gold-palladium alloys have been found to significantly improvecatalytic efficiency compared to the monometallic Pd and Au counterparts.In this thesis we investigate the reaction mechanisms of H₂O₂synthesis on three low index and two stepped surfaces. The reaction andactivation energies are obtained by means of density functional theory（DFT） calculations. The results show that Pd₁/Au（111） is the most suitablesurface for the synthesis of H₂O₂. Especially, our studies finds that theactivation energies of five elementary steps for H₂O₂synthesis have anexcellent linear relation with their reaction energies on three flat surfacesand the step edge sites of two stepped surfaces, which are consistent withthe Br nsted-Evans-Polanyi relations. Our investigation provides a simplemethod to estimate the reaction barriers of elementary steps of H₂O₂ synthesis. The study on H₂O₂synthesis on a series of Au surfaces is alsohelpful for designing the Au nanoparticles with high activity and selectivityof H₂O₂in catalysis fields.The reaction mechanisms of the epoxidation of propylene using Oatom and OOH as oxidant are also investiagted on three surfaces includingAu（111）, Pd（111） and AuPd（111）. The results suggest that the activationenergy of the formation of allyl is much lower than that of the formation ofpropylene oxide （PO） on three surfaces. On AuPd（111） surface, the OOHis more beneficial for the formation of OMMP1, the O atom is morebeneficial for the formation of Allyl. On Au（111） and AuPd（111）, thepathway of direct formation of PO from propylene and O atom is morefavored. Whereas on Pd（111）, the pathway that propylene and O atomfirstly turn into OMMP （propylene oxametallacycle） and then the OMMPturns into PO through a transition state（TS）is more favored. The barriersof all the elementary reactions on Pd（111） are higher than that of Au（111）and AuPd（111）.