Formate stability and carbonate hydrogenation on strained Cu overlayers on Pt(1 1 1)

Abstract

Formate (HCOO) synthesis, decomposition and the hydrogenation of carbonate (CO 3) on Cu overlayers deposited on a Pt(1 1 1) 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(1 1 1) (∼460 K), as well as for thicker Cu layers where we assign an observed decomposition peak at 440 ± 5 K to relaxed, but defect-rich Cu(1 1 1). However, the thermal stability of formate on strained and defect-rich Cu is similar to previous results obtained for supported, and lattice-strained, Cu nanoparticles. 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.