CATALYSIS BY THE RH/B SYSTEM .1. VAPOR-PHASE HYDROFORMYLATION OF ETHYLENE AT ATMOSPHERIC-PRESSURE ON RH/B ON SILICA

A Rh/B system with rhodium crystallites of small dimensions was formed by reducing rhodium trichloride supported on silica with NaBH4 at low temperature. Thermal treatments in Ar and/or in CO/H-2 strongly modify the surface composition but induce only a small modification in the crystallite diameter. After treatment in Ar at 543 K and in CO/H-2 the Rh/B system catalyzes the vapour-phase hydroformylation of ethylene at atmospheric pressure in a flow reactor. The reaction proceeds with very good chemoselectivity toward the hydroformylation products (at 398 K, R is greater-than-or-equal 0.7). The formation of the catalytic species and the surface modifications were studied by X-ray diffraction, FF-IR and XP spectroscopy. The presence of boron seems to play an important role both in preventing sintering of rhodium particles and in favouring good chemoselectivity toward the hydroformylation reaction.