Catalytic aerobic oxidation of carbohydrates to formic acid over H5PV2Mo10O40: Rate relationships among catalyst reduction, catalyst re-oxidation and acid-catalyzed reactions and evidence for the Mars-van Krevelen mechanism

Catalytic aerobic oxidation of biomass-derived carbohydrates is a promising way to sustainably produce formic acid. Understanding the rate relationships among catalyst reduction, catalyst re-oxidation and acid-catalyzed reactions occurring in catalytic systems is significant for the revelation of catalytic mechanism and the selec-tion of reaction conditions. Herein, the rate relationships among the multiple reactions over an excellent ho-mogeneous catalyst, H5PV2Mo10O40 (HPA-2) were investigated. A rate matching relationship between catalyst reduction and catalyst re-oxidation was unveiled by the separate redox kinetics of catalyst, indicating that higher O2 pressures are required to maintain the activity of HPA-2 at higher temperatures. The consistency between the separate redox kinetics and the catalytic oxidation provided the first kinetic evidence of the Mars-van Krevelen mechanism for catalytic oxidation of carbohydrates. Furthermore, rate relationships among the multiple re-actions at different conditions were discussed to clarify the correlation between product selectivity and reaction conditions.