Sulfided heterogeneous, bimetallic Ru/Mo catalysts derived from mixtures of Ru 3 (CO) 12 (or RuCl 3 ) and a molybdenum heteropolyanion: The reactions of ethanol with tetrahydroquinoline

Abstract

Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ). In the course of these studies, it was discovered that in ethanol, under hydrogen and in the presence of carbon disulfide (CS 2 ), precatalyst solutions containing ruthenium [as Ru 3 (CO) 12 or RuCl 3 ] and molybdenum [as the H 3 PMo 12 O 40 heteropolyanion (HPA)] decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5Μm depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1 to 1Μm can be prepared reproducibly. BET-measured surface areas for these size particles ranged from 2 to 20m 2 g −1 . These sulfided particles were found to catalyze, at temperatures of 200–250°C and hydrogen pressures of 200–1000 psig (1.4–6.9 MPa) hydrogen, the N -ethylation of THQ to form N -ethyltetrahydroquinoline ( N -Et-THQ), rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N -ethylation by comparison with the bimetallic catalyst. In the absence of hydrogen, the reaction proceeds so that THQ is converted to quinoline, N -Et-THQ, N -C 4 H 9 -THQ and N -C 6 H 13 -THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N -Et-THQ, or self-condenses (aldol condensation) prior to reaction with THQ, thereby giving higher-homolog alkylation products.