Operando Raman Spectroscopic Studies on Propane Dehydrogenation Over Co-Based Catalysts

Abstract

The development of cost-effective and eco-compatible nonnoble metal oxide catalysts for large-scale propene production via nonoxidative propane dehydrogenation (PDH) is a key topic of current research in heterogeneous catalysis. Cobalt-based catalysts show remarkable catalytic performance and are promising alternatives to industrially established platinum- or chromium oxide-based catalyst systems. The formation of coke deposits under the reaction conditions has a significant influence on their performance. Time-resolved operando Raman spectroscopic experiments have been performed during the PDH reaction using a catalyst system containing 3-wt.% Co on silicalite-1 as a support (3Co/S-1) to elucidate the role of carbon-containing species. Three stages during the PDH process were identified. During the initial 5 min on propane stream, propane is preferentially oxidized to carbon oxides and water. This indicates the removal of lattice oxygen from Co₃O₄, whereby this species is reduced to metallic cobalt (Co⁰). With increasing time on propane stream, the formation of C₁–C₂ hydrocarbons was observed, pointing to the occurrence of cracking and deep dehydrogenation reactions of propane. Subsequently, intense G and D bands appeared in the Raman spectrum due to the formation of carbon deposits. Simultaneously, there was a substantial enhancement in propene formation, which indicates that carbon-containing species are necessary for the selective dehydrogenation of propane to propene. The catalyst showed high activity and durable operation in a series of seven dehydrogenation/reoxidation cycles under relevant conditions. The induction period observed for the fresh catalyst was shortened for the catalyst system in course of the PDH/reoxidation cycles.