Hydroformylation of butene-1 and butene-2 over rhodium-slp catalysts, as compared with the hydroformylation of ethene and propene: Part III. The influence of the degree of pore-filling on the performance

Abstract

The catalytic hydroformylation of butene-1 and butene-2 ( cis and trans) is compared with the hydroformylation of ethene and propene, using supported liquid phase rhodium catalysts (Rh-SLP catalysts). Attention is paid to the reaction rates, the linear-to-branched alkanal ratios (1/b), and the catalyst stabilities found with the various alkenes. It is shown that the degree of pore-filling of SLP catalysts not only determines the catalytic activity per unit weight of rhodium, but the linear-to-branched alkanal ratio as well. This is due to the fact that the alkene conversion must be attributed to two classes of rhodium complexes, viz rhodium complexes at the gas-liquid interface and those dissolved in the liquid phase. The relative contribution of these two classes of complexes to the catalytic performance changes as a function of the degree of pore-filling. In studying SLP catalysts with the macroreticular resin XAD-2 as a support, it appeared that on decreasing the degree of pore-fuling, the linear-to-branched alkanal ratio decreased with a simultaneous increase in catalytic activity per unit weight of rhodium. Catalysts with a very low degree of pore-filling are attractive with respect to their high activity per rhodium complex. It is shown that the rhodium complexes at the gas-liquid interface exhibit a higher activity and a lower 1/b ratio than the complexes in solution. Butene-2, which exhibits an extremely low hydroformylation activity due to steric hindrance, could only be hydroformylated over Rh-SLP catalysts having a very low degree of pore-filling (monolayer catalysts).