In-situ FT-IRAS study of the hydrogenation of CO on Ru(001) : potassium-promoted synthesis of formate

Utilizing in-situ Fourier transform infrared reflection absorption spectroscopy, we have characterized potassium-promoted Ru(001) surfaces under CO hydrogenation conditions at elevated temperature and pressure (1-50 Torr). Interaction of the [radical]3 [times] [radical]3-R30[degrees]-K-Ru(001) surface with at 300 K resulted in the formation of carbonate, which was hydrogenated to formate via the reaction K[sub 2]CO[sub 3] + CO + H[sub 2] [l reversible] 2KHCO[sub 2]. The steady-state ratio of formate and carbonate coverage under reaction conditions was found to depend on the CO:H[sub 2] pressure ratio, with carbonate being present in excess hydrogen. Time-resolved FT-IRAS determined the initial rate of formate synthesis from carbonate to (1.7 [+-] 0.8) [times] 10[sup [minus]3] molecules site[sup [minus]1] s[sup [minus]1] at 500 K. Isotope transient measurements resulted in a comparable synthesis rate under equilibrium conditions and hence demonstrate the reactivity of the formate. The isotope transient data and the formate to carbonate conversion in excess hydrogen are consistent with two possible mechanisms: (i) Decomposition of the formate to carbonate, i.e., the reverse of the formate synthesis reaction, or (ii) further hydrogenation of the formate to methanol or methane. 38 refs., 11 figs., 1 tab.