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

The performance of the carbon supported rhodium catalysts with metal loadin gs of 3-8 wt% was investigated in the vapour phase hydrocarbonylation of me thanol. 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 activit y and selectivity of the catalysts. The peat based carbon supported catalys ts, 5 wt% Rh/C(N), produced both homologation and carbonylation products; t he coconut shell based catalysts, 8 wt% Rh/C(C), yielded predominantly homo logation products and the wood based carbon supported catalysts, 7 wt% Rh/C (T), produced mainly carbonylation products. The selectivity was also relat ed to the size of the rhodium particles on the surface, i.e., it was sugges ted that the carbonylation activity took place on very small particles pres ent 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 homolog ation 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) 1 999 Elsevier Science B.V. All rights reserved.