Probing the reduction state of Mo oxide catalysts by the deoxygenation of carboxylic acid

XPS Characterization of CeO2 Catalyst for Hydrogenation of Benzoic Acid to Benzaldehyde

“…However, ZrO 2 -based catalysts in the hydrogenation of benzoic acid are not stable and produce significant amounts of by-products. Subsequently, other metal oxide catalysts, such as ZnO [5][6][7], Mo oxides [8][9][10], were also studied. Based on these reports, a typical Mars and van Krevelen mechanism is proposed in the hydrogenation of benzoic acid to benzaldehyde on metal oxides catalysts [11], as shown in Scheme 1.…”

Deactivation of CeO2 catalyst in the hydrogenation of benzoic acid to benzaldehyde

“…Catalytic stability measurement Figure 1 shows the evolution of hydrogenation performance of CeO 2 catalyst as a function of reaction time in a fixed-bed reactor. Initially, conversion of benzoic acid and selectivity to benzaldehyde are 97.4% and 94.6%, respectively, which are a little higher than those on Zn and Mo oxide catalysts as reported previously [8,12]. However, it is apparent that the catalytic activity declined gradually with increasing time on stream.…”

“…At present, there are still many controversial issues regarding the application of metal oxides in hydrogenation of benzoic acid. One of previous studies has shown that hydrogenation of benzoic acid in presence of molecular hydrogen on Mo oxides and suboxides leads to the deep reduction of the catalysts [12]. This phenomenon results in a low catalytic performance of Mo oxides.…”

“…Recently, other metal oxide catalysts, such as ZnO [8][9][10][11], Mo oxides [12,13], and CeO 2 [9,14], were also studied. Based on these studies, a type of Mars and van Krevelen mechanism is proposed in the hydrogenation of benzoic acid to benzaldehyde on metal oxides catalysts [10,15], which consists of two steps: 1) hydrogen activates the oxide by the reduction to form oxygen vacancies; and 2) benzoic acid re-oxidizes these vacancy sites and yields benzaldehyde subsequently.…”

The influence of the hydrogen origin at the surface of Mo suboxide during the deoxygenation of carboxylic acid

“…Benzene is likely formed by a radical-like mechanism at the surface of the catalyst without needing oxygen vacancies [1][2][3][4]. Recently, we used this reaction with success to demonstrate the reduction pathway of Mo 8 O 23 [5]. This was possible because the large excess of hydrogen and the nature of the solid (Mo suboxide) induced a deep reduction of our catalyst toward MoO 2 .…”