PREPARATION OF SUPPORTED HETEROGENEOUS CATALYSTS BY PULSE IMPREGNATION - APPLICATION TO RU3(CO)12/2,2'-BIPYRIDINE/SIO(2) CATALYST

In this paper we introduce pulse impregnation, a method tor preparing supported heterogeneous catalysts by successive impregnation cycles. Pulse impregnation is a method for preparing supported heterogeneous catalysts from the liquid phase. In the pulse-impregnation technique the catalyst surface is grown gradually in consecutive cycles, with each cycle consisting of separate deposition and activation steps. During the deposition step, the catalyst precursor or precursors are deposited onto the support from a suitable solvent. The actual chemically bonded catalyst phase is formed during the activation step (e.g., thermal activation). Pulse impregnation was tested in the separate deposition of 2,2'-bipyridine and Ru3(CO)12 onto a silica support, and in the preparation of RU3(CO)12/2,2'-bipyridine/SiO2 catalyst, in a column-type reactor system. Macroscopically uniform deposition was achieved with both 2,2'-bipyridine and Ru3(CO)12. Various solvent systems were used to control the amount of solute adsorbed during deposition. In the preparation of the Ru3(CO)12/2,2'-bipyridine/SiO2 catalyst, the ruthenium content increased nearly linearly with the number of preparation cycles. The effect of the preparation method on the catalyst activity was also tested in 1-hexene hydroformylation. (C) 1994 Academic Press, Inc.