Structure And Electronic Properties And The Adsorption Of Oxygen Of Palladium-Gold Bimetallic Nanoparticles:A Theoretical Investigation

Using the density functional theory, we investigated systematically the effects of atomic composition and distribution on structural and surface electronic properties of a series Pd-Au bimetallic nanoparticles (NPs), and study the role of Pd and Au atoms in adsorption of O2. We employed the 55-atom icosahedral model in this work and the main studies and findings are listed as follows:1?For the Pd-Au bimetallic NPs, it is found that the structure with more Pd-Au bonds number presents more stability. The surface Pd and Au take positive and negative charge, respectively. The electrons redistribution of the surface atoms, especially for the Au atoms, is strongly influenced by the atomic distribution. The valance d-band vacancy number of the surface Pd and Au atoms decreases due to the mixing of the two metals. In contrast to the Au atoms, the d-band center of the surface Pd changes almost linearly with the Pd composition increasing. In addition, the d-band center of the vertex atoms is closer to the Fermi level compared with that of the edge atoms in PdnAu55-n bimetallic NPs. The investigations may be helpful in designing catalysis of Pd-Au bimetallic NPs since d-band center could be used as a general measure of local surface reactivity.2?The adsorption energy of O2 on "C-J" Pd-Au bimetallic NPs presents the same change trend, which is different from that on the Pd-Au bimetallic NP with Au trimer. Compared to Pd55 NP, both of the "C-J" and Au trimer Pd-Au bimetallic NPs present less energetic favorable for O2 adsorption. However, the Pd-Au bimetallic NPs with 12 Pd and with Pd trimer are more energetic favorable for O2 adsorption with respect to AU55 NP. The most favorable adsorption of O2 on these bimetallic NPs is chemisorptions. Interestingly, the lower the adsorption energy is, the larger the O-O stretching vibration frequency is. The O-O bond is elongated due to 02 obtaining electron from NP. Additionally, the 4d orbital of Pd and 5d orbital of Au arise overlap with 2p orbital of O. The limited overlap between 5d orbital of Au and 2p orbital of O indicates that the interaction between Au and O is week. Because of the alloying effect, Au makes the energy of 4d orbital of Pd move away from the Fermi level and the Pd-O unoccupied orbital near the Fermi level become narrow, which weakens the interaction between Pd and O. It indicates that Au atoms in the Pd-Au bimetallic NPs cannot enhance the 02 adsorption. By contrary, the Pd atoms are expected to promote the O2 adsorption. Interestingly, the stability of adsorbed O2 depends on the atoms composition and distribution and for Pd-Au bimetallic NPs the most favorable adsorption structure is Pd3Au52-? with site H2 (the hollow adsprption site with three Pd atoms).