Support effects in the ruthenium-catalyzed hydrogenation of carbon monoxide: Ethene and propene addition

Abstract CO hydrogenation catalyzed at about 500 K by 2.6% Ru/silica (I), 1.5% Ru/13X-zeolite (II), 17% Ru/titania (III), and 5% Ru/magnesia (IV) gave methane and 1-alkenes as primary products. 1-Alkene isomerization and hydrogenation gave internal alkenes and alkanes as secondary products. Specific activity varied in the sequence III ⪢ II > I > IV whereas selectivity for methane formation, as opposed to higher hydrocarbon formation, varied in the sequence I > II > III > IV. Comparison of one catalyst with another showed that when the methane yield was high the fraction of higher hydrocarbon appearing as alkane at moderate conversions was also high, and vice versa. Ethene addition to CO hydrogenation over (I) and (II) at low conversions (2 to 15%) markedly increased the rate of higher hydrocarbon formation without greatly influencing the methanation rate, whereas ethene addition over (III) and (IV) enhanced the rate of higher hydrocarbon formation by a factor of less than 2 and reduced the methanation rate. Propene addition to CO hydrogenation over (I) increased the rates both of higher hydrocarbon formation and of C 2 -hydrocarbon formation, again without markedly affecting the methanation rate. The single most important factor in the determination of the total product distribution is the availability of adsorbed hydrogen which varies from catalyst to catalyst in the sequence I > II > III > IV. The activity sequence is ascribed to various metal-support effects.