Speaker
Description
Gallium containing alloys and intermetallic compounds have recently received significant attention in catalysis, in particular for selective hydrogenation of alkynes (on Pd-Ga)$^{1}$ and CO$_{2}$ hydrogenation to methanol at low pressures (on Ni-Ga).$^{2}$ The discovery of the Ni-Ga catalysts triggered studies on other Ga-promoted 3d-metal catalysts, in particular Cu,$^{3}$ which is also a crucial component of the industrial Cu/ZnO/Al$_{2}$O$_{3}$ catalyst for methanol production. Here, we studied interaction of Ga with the single crystal Cu(001) and (111) surfaces and monitored environment-induced surface transformations. The results show that Ga readily intermixes with Cu upon deposition in vacuum forming kinetically–limited metastable alloy islands. Annealing in UHV results in atomically flat, well-ordered surfaces. Using near ambient pressure XPS and STM techniques, we found that the Ga-Cu surfaces in the CO$_{2}$ hydrogenation reaction at elevated temperatures results in Ga oxidation and the formation of a two-dimensional (“monolayer”) Ga oxide islands uniformly covering the Cu surface. For comparison, we also performed XPS and STM experiments in oxygen atmosphere. The results show that the Ga-doped Cu surface under reaction conditions exposes a variety of structures including GaOx/Cu interfacial sites, which must be taken into account for elucidating the reaction mechanism.
References
1. M. Armbrüster, et al., ChemCatChem 4, 1048 (2012).
2. F. Studt, et al., Nature Chemistry 6, 320 (2014).
3. J. Medina, et al., Catalysis Science & Technology 7, 3375 (2017).
