DECOMPOSITION OF METHYL FORMATE ON W(100), W(100)-(5 X 1)C, AND W(100)-CO(BETA) SURFACES
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The decomposition of methyl formate was examined using temperature-programmed reaction spectroscopy under ultrahigh vacuum conditions on single-crystal W(100), W(100)-CO(), and W(100)-(5 1)C surfaces. The W(100) surface was highly selective toward formation of CO() and hydrogen from methyl formate. Hydrocarbon species, including methane, were produced on this surface from a complex with a stoichiometric excess of hydrogen only after the CO() states were saturated by cracking methyl formate. Passivation of the surface by adsorption of CO to form the W(100)-CO() surface prior to exposure to HCOOCH3 shifted the selectivity in favor of H2CO and CH3OH. Methyl formate decomposition on this surface followed a reaction pathway different from that on the W(100) surface: no hydrogen-excess surface complex was formed, and no methane was produced on the W(100)-CO() surface. Passivation of the surface by formation of the carbide chemilayer also shifted the selectivity toward hydrocarbon formation. The reaction pathways observed on the W(100) and W(100)-CO() surfaces both took place on the W(100)-(5 1)C surface, and methane was again evolved as on the W(100) surface via a complex involving an excess of hydrogen. This unusual complex appears to involve multiple methoxy groups and surface tungsten atoms which stabilize the excess hydrogen. 1980.
