Effect of Zirconia Morphology on Hydrodeoxygenation of Phenol over Pd/ZrO2

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• 作者：Priscilla M. de Souza ; Raimundo C. Rabelo-Neto ; Luiz E. P. Borges ; Gary Jacobs ; Burtron H. Davis ; Uschi M. Graham ; Daniel E. Resasco ; Fabio B. Noronha
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：December 4, 2015
• 年：2015
• 卷：5
• 期：12
• 页码：7385-7398
• 全文大小：796K
• ISSN：2155-5435

文摘

This work studies the effect of zirconia structure on the performance of Pd/ZrO₂ catalysts for hydrodeoxygenation of phenol at 300 掳C and 1 atm using a fixed bed reactor. Benzene was the major product over Pd/t-ZrO₂, while significant formation of cyclohexanone was observed over Pd/m-ZrO₂. On the other hand, Pd/m,t-ZrO₂ exhibited intermediary behavior. DRIFTS of adsorbed pyridine, NH₃-TPD, and the dehydration of the cyclohexanol reaction revealed that the Pd/t-ZrO₂ catalyst exhibits a higher density of oxophilic sites than Pd/m-ZrO₂ and Pd/m,t-ZrO₂. This promoted the formation of deoxygenated products. However, a mechanism involving dehydration of cyclohexanol to cyclohexene, followed by dehydrogenation to benzene, may not be ruled out. Pd/ZrO₂ catalysts significantly deactivated as a function of time on stream. Results of dehydrogenation of cyclohexane and dehydration of cyclohexanol indicate that the Pd particle size increased and the density of oxophilic sites decreased during the hydrodeoxygenation of the phenol reaction. In addition, the DRIFTS spectra under reaction conditions demonstrated that the coverage of oxophilic sites by phenoxy and intermediate species increased during the reaction. The growth of Pd particles is likely responsible for the losses in the metal鈥搒upport interface that gradually inhibits the ability of the adsorbed species to turnover at the metal鈥搒upport boundary.