CATALYTIC REACTIONS OF N-HEXANE ON K-FREE AND K-DOPED PT BLACK

A Pt black produced by reduction of H2PtCl6 by hydrazine hydrate conta ins no potassium impurity. Electron microscopy shows more regular poly hedral particles in this catalyst, as opposed to the rounded ones seen after reduction with HCHO in the presence of KOH [Z. Paal, H. Zimmer, J. R. Gunter, R. Schlogl, M. Muhler, J. Catal. 119, 146 (1989)]. The surface purity after reduction and deliberate addition of KOH was stud ied by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy and the respective catalytic propensities were tested in reactions of hexane isomers. Different compositions were obtained afte r line-fitting the O 1s and C 1s regions in these cases, ethylene trea tment producing more graphite and CxHy polymer. Carbon removal was eas ier in the presence of KOH either after catalytic runs or after an art ificial carbonizing with ethylene, The role of KOH can be (i) to facil itate aggregation of surface carbon and (ii) to promote its catalytic oxidation. Adding little KOH increased catalytic activity; much KOH, i n turn, caused deactivation, No maxima were observed in the product yi elds from n-hexane as a function of the hydrogen pressure with the pre sent Pt catalysts. The effects of the different morphology or higher s urface purity of the present samples can be more important reasons for this than the presence or absence of potassium. (C) 1995 Academic Pre ss, Inc.