Methyl Pyruvate on Ni(111): Coverage-Dependent Thermal Chemistry

The dissociative interaction of methyl pyruvate (CH 3 COCOOCH 3 ) with Ni(111) was studied between 200 and 450 K. This temperature range includes the typical temperatures, 300−320 K, at which the heterogeneous enantioselective hydrogenation of methyl pyruvate to methyl lactate occurs on supported platinum particles. The observed decomposition of such a relatively complex adsorbate is surprisingly simple; the initial decomposition step involves scission of the CC bond between the two carbonyl functions to form surface acetyl and methoxycarbonyl species. These groups, in turn, undergo decarbonylation to co-deposit CO, hydrocarbon species, and atomic hydrogen. RAIRS measurements made during exposure to methyl pyruvate with the sample held at 250 and 300 K were used to probe the evolution of the composition of the adsorbed layer as a function of coverage. The stability of the different intermediates was highly coverage dependent. A brief comparison of data for methyl pyruvate on Pt(111) and Ni(111) reveals a very different decomposition chemistry on the two metals.