Formate stability and carbonate hydrogenation on strained Cu overlayers on Pt(111)

摘要

Formate (HCOO) synthesis, decomposition and the hydrogenation of carbonate (CO_3) on Cu overlayers deposited on a Pt( 111) single crystal are investigated to examine the reactivity of a Cu surface under tensile strain with defects present. Formate is synthesized from a 0.5 bar mixture of 70% CO_2 and 30% H_2 at varying temperatures, and the evolution is followed with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Subsequent TPD reveals decomposition of the formate species into CO_2 and H_2 at 420 ± 5 K for strained Cu at sub-monolayer to monolayer coverages. This is a significantly lower decomposition temperature than obtained earlier on pristine Cu(111) (～460K), as well as for thicker Cu layers where we assign an observed decomposition peak at 440 ± 5 K to relaxed, but defect-rich Cu(111). However, the thermal stability of formate on strained and defect-rich Cu is similar to previous results obtained for supported, and lattice-strained, Cu nanopartides.The hydrogenation of carbonate produced by 0.3 bar CO_2 exposure at room temperature was monitored with XPS and TPD showing a significant loss of carbonate when subjected to 0.2 bar H_2 at room temperature. However, the presence of formate on the surface, or any other hydrogenation product, could not be established during or after H_2 exposure by PM-IRRAS, EELS or TPD. Even so, the results suggest that carbonate and its hydrogenation may constitute a relevant pathway to methanol production.