Gas phase catalysis by metal nanoparticles in nanoporous alumina membranes

Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1,3-butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 10(9) - 10(11) pores per cm(2), all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 mum thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane.