Studies of the synthesis of transition metal phosphides and their activity in the hydrodeoxygenation of a biofuel model compound

详细信息    查看全文

• 作者：Phuong Bui ; Juan Antonio Cecilia ; S. Ted. Oyama ; Atsushi Takagaki ; Antonia Infantes-Molina ; Haiyan Zhao ; Dan Li ; Enrique Rodr¨ªguez-Castell¨®n ; Antonio Jim¨¦nez L¨®pez
• 关键词：Hydrodeoxygenation ; Phosphides ; Transition metal ; 2-Methyltetrahydrofuran ; Phosphate ; Phosphite ; Mechanism
• 刊名：Journal of Catalysis
• 出版年：2012
• 出版时间：October, 2012
• 年：2012
• 卷：294
• 期：Complete
• 页码：184-198
• 全文大小：1107 K

文摘

A series of silica-supported metal phosphides was prepared by two methods involving the reduction of phosphite (I) or phosphate (A) precursors and was studied for the hydrodeoxygenation (HDO) of 2-methyltetrahydrofuran (2-MTHF). The I method required lower temperature than the A method and resulted in catalysts with higher surface area. The activity was evaluated in a packed-bed reactor on the basis of equal CO chemisorption sites (30 ¦Ìmol) loaded in the reactor with comparison made to a commercial Pd/Al₂O₃ catalyst. At 300 ¡ãC and 1 atm, the order of activity was Ni₂P > WP > MoP > CoP > FeP > Pd/Al₂O₃. The principal HDO products for the iron group phosphides (Ni₂P and CoP) were pentane and butane, whereas for the group 6 metal phosphides (MoP and WP), the products were mostly pentenes and pentadienes. For the Pd/Al₂O₃ and the low-activity FeP/SiO₂ catalyst the products were mostly pentenes and C4 mixtures. There were no significant differences in the turnover frequency between materials prepared by the two methods, except possibly for the case of WP. There were likewise no great changes in selectivity toward HDO products at 5 % total conversion, except for WP. The differences in the case of WP were attributed to the surface P/W ratio that X-ray photoelectron spectroscopy (XPS) showed to be twice as large for the I method than the A method. Contact-time studies were used to develop reaction networks for the most active catalysts, Ni₂P/SiO₂ and WP/SiO₂. For Ni₂P/SiO₂ by both methods, the selectivity profiles were similar and could be explained by a rake mechanism with pentenes as primary products, 2-pentanone as a secondary product, and pentane as a final product. In contrast, for WP/SiO₂, the selectivity depended greatly on the preparation method, but produced a preponderance of unsaturated compounds. The results could be explained from the surface composition.