Carbon Monoxide and Carbon Dioxide Hydrogenation Catalyzed by Supported Ruthenium Carbonyl Clusters: A Novel Procedure for Encapsulating Ru3(CO)12 within the Pores of Na-Y Zeolite

摘要

Zeolite-supported ruthenium catalysts for the hydrogenation of carbon monoxide and carbon dioxide have been prepared by sorbing Ru(CO)5 (molecular diameter 6.3 A) onto Na-Y zeolite and Linde 5A molecular sieve. Although the metal carbonyl is not absorbed into the pores of the molecular sieve (diameter 4.2 A), it is readily absorbed into the pores (diameter 7.4 A) and supercages (diameter 13 A) of the Na-Y zeolite. The Ru(CO)5 in Na-Y coverts in the absence of carbon monoxide to the much larger Ru3(CO)12 (diameter 9.2 A), which remains on the surface of the molecular sieve but is trapped within the supercages of the Na-Y zeolite because it cannot pass through the smaller pores. Slow, temperature-programmed heating of the Ru3(CO)12 in Na-Y to 350 C under a flow of hydrogen results in decarbonylation and formation of a CO hydrogenation catalyst that produces a very atypical (for ruthenium) hydrocarbon distribution truncated at about C10. The unusual product distribution presumably arises because the catalyst sites are situated within the zeolite supercages. Thus the metal is highly dispersed and or the growing hydrocarbon chains are subject to geometrical limitations on their growth. Consistent with this prothesis, ruthenium carbonyl clusters immobilized on the external surfaces of Na-Y zeolite, Linde 5A molecular sieve, and gamma alumina all exhibit typical, nonselective hydrocarbon product distributions. Reprints. (mgm)