LOW-TEMPERATURE C-C BOND SCISSION DURING ETHANOL DECOMPOSITION ON PT(331)

The adsorption and decomposition of ethanol was studied on clean, and oxygen pre-covered Pt(331) surface by using mainly TPD, LEED and AES. II was found that ethanol adsorbed molecularly on the Pt(331) surface al low temperature. Upon heating, part of the ethanol desorbed molecul arly from surface at 220 K, and part of the ethanol underwent C-C bond scission to form methane and a variety of other products. There are t wo distinct methane peaks at 240 K and 310 K in the desorption spectru m suggesting that there are two different pathways for ethanol decompo sition on this surface; both pathways-involve C-C bond scission since methane is a major desorption product. CO adsorption experiments as we ll as experiments with H-(ad) and O-(ad) suggest that the lower temper ature pathway involves C-C bond scission at temperatures below that wh ere the ethanol appreciably dehydrogenates, while the high temperature pathway involves dehydrogenation of the ethanol followed by C-C bond scission. O-(ad) additions suppress the low temperature pathway and en hances the high temperature pathway presumably by speeding the dehydro genation of the ethanol. H-(ad) additions slightly enhance the low tem perature pathway. We also observe hydrogenolysis of the ethanol to yie ld methanol at 180 K and methane at 240 K in the presence of excess hy drogen. These results show that the step sites on the Pt(331) surface have unusual activity for C-C bond scission in ethanol. (C) 1997 Elsev ier Science B.V.