(768d) Scaling Relationships at Bifunctional Metal/Oxide Interfaces: A Case Study of Doped Au/MgO

Choksi, T. S. - Presenter, Purdue University
Majumdar, P., Purdue University
Greeley, J. P., Purdue University
Transition metal nanoparticles dispersed on metal oxides possess interesting catalytic properties through bifunctional catalytic sites located at the interface between the metal and oxide. These sites enhance catalytic activity in comparison with individual metal or oxide sites, for several reactions such as the Water Gas Shift reaction (WGS) [1] and methanol synthesis [2]. Although experimental and theoretical investigations have observed bifunctionality at the metal/oxide interface, strategies enabling computational design of these catalysts have not been developed. Linear Scaling Relationships (LSRs), which relate adsorption energies of reaction intermediates to atomic species known as descriptors, are an important part of the descriptor-based catalyst design strategy. They have been reported for transition metals [3], metal oxides [4] and zeolites [5] in prior literature. In this talk, we show that LSRs can be developed at a metal/oxide interface using the Au/MgO (100) system as a representative model for a metal/oxide catalyst. This choice is motivated by the small strain between Au and MgO (100), thereby preventing additional complications arising from nanoparticle relaxation. Electronic properties of the interface are modified through cationic (Mg substituted with Na, Cu, Zn, Fe, Al, Ga, In, Sn, Zr, Ti, Mo, W, V, Cr) and anionic doping (O substituted with C, N, S, F and oxygen vacancies). Based on the dopants valence with respect to the host atom, electrons/holes are released to the interface, modifying adsorption strengths of reaction intermediates. Adsorption energies of a series of molecular fragments (COOH*, O2*, OH*, OOH*, CH3O, CH2O*, CHO*, CH2OH*, CHOH*, NH­2O*, NHO*, NHOH*), involved in catalytic reactions at metal-oxide interfaces, are shown to scale linearly with the adsorption strength of O*. Thus, the oxygen binding energy is proposed as a descriptor these chemistries. All dopants, irrespective of their location in the oxide matrix, and their formal oxidation state, fall on the same LSR for each adsorbate. Slopes of the LSRs are greater than that established via adsorbate bond counting arguments, which are valid for metals [3], metal oxides [4] and zeolites [5]. Moreover, the slope is dependent on the coordination of the bifunctional adsorbate fragments that are bound to both MgO and Au. Closed shell species (CH2O*, O2*) which do not follow LSRs on transition metals, are shown to do so at the interface. Finally, we discuss the physical origin of the LSRs in terms of electronic and electrostatic properties of these systems.

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