A theoretical study on the mechanism for thiophene hydrodesulfurization over zeolite L-supported sulfided Co-Mo catalysts: Insight into the hydrodesulfurization over zeolite-based catalysts

摘要

The mechanism for the hydrodesulfurization (HDS) of thiophene over zeolite L-supported sulfided Co-Mo catalysts was investigated using density functional theory (DFT) calculations. Both the direct desulfurization (DDS) pathway and hydrogenation (HYD) pathway for thiophene were studied in detail. In the DDS pathway, the C-S bond of thiophene is directly broken by hydrogenolysis. In the HYD pathway, hydrogenation of one or both C=C bonds occurs before C-S bond scission. On the basis of the energetic analysis of the elementary steps, the favored reaction pathway was proposed: (1) Firstly thiophene is hydrogenated to 2,5-dihydrothiophene (2,5-DHT) intermediate; (2) then the C-S bonds of 2,5-DHT are broken by the hydrogenolysis pathway or elimination pathway. The Mulliken charge results show that zeolite L loses electrons after the adsorption of thiophene and all the other hydrogenated intermediates, indicating that zeolite L acts as electron donor in the HDS reaction. The pore framework of zeolite L plays a key role in decreasing the energy barrier by the stabilization effect. Compared with other zeolites, the intrinsic superiority of zeolite L as a support for Co-Mo catalysts in thiophene HDS reaction can be attributed to its perfectly fitted pore structure and ideal stabilization effect for the reactant. This study provides an atomic-scale understanding of the HDS mechanism of thiophene over zeolite L-supported sulfided Co-Mo catalysts. (C) 2014 Elsevier B.V. All rights reserved.