Reactions of alkanes and cycloalkanes on platinum–gold alloy films

Abstract

The reactions of a series of cyclic and acyclic alkanes in excess hydrogen have been studied on evaporated films of Pt–Au. Film homogeneity was established by X-ray fluorescence spectroscopy and X-ray diffraction.

The reactions which occur fall into two groups. First, there are those whose rate is dramatically affected by Au incorporation in Pt, and these include the hydrogenolysis of ethane, neopentane, n-pentane, neohexane and n-hexane, the isomerization of neopentane and n-pentane and finally the ring opening and hydrocracking of the cyclopentane ring. Secondly, there are reactions whose rate is essentially unaffected by moderate Au incorporation in Pt, comprising the 1,5-cyclization of n-pentane, the 1,6-cyclization of n-hexane, the ring enlargement of methylcyclopentane and of 1,1-dimethylcyclopentane and finally dehydrogenation of saturated hydrocarbons to alkene and alkadiene.

These results may be rationalized on either an electronic factor or by postulating that gold atoms locate preferentially at rough regions of the surface.