RhC catalysts for methanol hydrocarbonylation.: II.: Activity in the presence of MeI

The performance of the carbon supported rhodium catalysts with metal loadings of 3-8 wt% was investigated in the vapour phase hydrocarbonylation of methanol. The initial activity of the catalysts in terms of total conversion varied between 1% and 70%, and it was not directly related to the amount of metal or dispersion. The type of support appeared to influence the activity and selectivity of the catalysts. The peat based carbon supported catalysts, 5 wt% Rh/C(N), produced both homologation and carbonylation products; the coconut shell based catalysts, 8 wt% Rh/C(C), yielded predominantly homologation products and the wood based carbon supported catalysts, 7 wt% Rh/C(T), produced mainly carbonylation products. The selectivity was also related to the size of the rhodium particles on the surface, i.e., it was suggested that the carbonylation activity took place on very small particles present on both Rh/C(N) and Rh/C(T) catalysts, and the homologation activity on aggregated particles present on Rh/C(N) and Rh/C(C) catalysts. The homologation selectivity of 42% for Rh/C(C) was surprisingly good in the light of the used low synthesis gas H-2/CO ratio and mild reaction conditions. (C) 1999 Elsevier Science B.V. All rights reserved.