Catalytic hydrodesulfurization by supported bimetallic sulfide cluster catalysts

Abstract

The synthesis, characterization, and thiophene hydrodesulfurization (HDS) activities of novel organometallic sulfide cluster catalysts are presented. The catalysts are composed of H 2SRu 3(CO) 9, HSRu 2Co(CO) 9, SRuCo 2(CO) 9, and [(CO 3S 2(CO) 7] 2 supported on carbon and -γAl 2O 3. Although the clusters decompose at industrial HDS temperatures, the catalytic properties of the cluster catalysts at lower temperatures depend on the ratio of ruthenium and cobalt. Temperature-programmed decomposition (TPD) of the supported clusters in flowing hydrogen was monitored using FT-IR and mass spectrometry (MS). Temperatures of decomposition (as determined by the maximum rate of CO evolution) follow the order H 2SRu 3(CO) 9⪢HSRu 2Co(CO) 9⪢SRuCo 2(CO) 9⪢[Co 3S 2(CO) 7] 2. Significant amounts of H 2O are detected as products of cluster decomposition on alumina. TPD/MS data of H 2SRu 3(CO) 9 labeled with C 18O indicate that the H 2O evolved is mostly formed from the alumina surface and not from cluster-bound carbonyls. Kinetics measurements at 150 °C show that the mixed-metal cluster catalysts are more active for thiophene desulfurization than catalysts containing only one metal component. This trend is reversed at higher temperatures and for catalysts sulfided at 400 °C; that is, the mixed-metal catalysts are less active for thiophene desulfurization than catalysts containing only one metal component. The carbon-supported cluster catalysts are more active for thiophene hydrodesulfurization and more selective for butane formation than catalysts supported on γ-Al 2O 3.