| The reactions of diazomethane and azomethane on a clean, H-covered, and an O-covered Pt(111) surface were studied by TPD. For diazomethane, the products on the clean H-covered surfaces were methane, ethylene, and hydrogen. The reactions of diazomethane were similar to those of ethylene and acetyene. The results can be explained by the presence of two types of sites on these surfaces: clean Pt atoms, and Pt atoms with preadsorbed hydrogen. Diazo- methane first decomposed into an adsorbed methylene species on adsorption. On the O-covered surface, CO, CO(,2) and H(,2)O were observed in addition to the products for the clean surface. On the O-covered surface, methylene was first partially oxidized to an intermediate of CH stoichiometry, similar to the oxidation of ethylene and acetylene. On all three surfaces diazomethane decomposed to methylene and nitrogen at 100(DEGREES)K; the nitrogen was desorbed at 100(DEGREES)K.; On the clean and H-covered surface, the products from azo- methane TPD were HCN, methane, methylamine, cyanogen, and hydrogen. On the O-covered surface, these products along with CO, CO(,2), H(,2)O and NO were observed. The TPD spectra did not resemble the TPD of ethylene, acetylene, or diazomethane except for the production of methane, which was similar to that from diazomethane. Oxidation to an intermediate of CH stoichiometry did not occur.; The structure sensitivity of the decomposition of 2-propanol over ZnO was studied at pressures of 0.2 to 4 mtorr, and temperatures of 60 to 435(DEGREES)C, on the (0001), (000(')1), and (50(')51) surfaces. On the non- polar surface the active site was the step site. Over the temperature range of 135-260(DEGREES)C, the turnover frequency for the Zn polar surface was approximately twice that for the nonpolar surface and 5 times that for the O-polar surface. Thus, the average reaction rate for the polar surfaces was close to the rate for the nonpolar surface. As a result, the reaction may be observed as structure insensitive in powder studies. On the stepped (50(')51) surface, the turnover frequency was three to four times higher if the reactant approached the surface in the direction up the steps rather than down the steps. Zn desorption, well in excess of typical amounts due to sublimation, was observed for all surfaces studied. |
