Novel chemical looping oxidation of biomass-derived carbohydrates to super-high-yield formic acid using heteropolyacids as oxygen carrier

In recent years, formic acid (FA) shows great potential in fuel cells and hydrogen storage. For FA production from renewable resources, catalytic aerobic oxidation of biomass to FA has been reported. However, the yield of byproduct CO2 is fairly high, limiting the FA selectivity and causing greenhouse gas emission. Herein, a novel chemical looping oxidation of biomass-derived carbohydrates to FA was first proposed. A heteropolyacid H8PV5Mo7O40 (HPA-5) was selected as an excellent oxygen carrier. Oxidation of carbohydrates to FA and reoxidation of reduced HPA-5 (HPA-5red) by O2 were separately performed, by which the FA yield from glucose achieved 95.4%. The extremely high yield of FA is attributed to two reasons. On one hand, the chemical looping process avoids over-oxidation caused by the hydroxyl radicals formed in the re-oxidation of HPA-5red. On the other hand, abundant HPA-5 promotes the glucose oxidation to FA, suppressing the acid-catalyzed decomposition and the oxidation toward saccharic acids. Besides, HPA-5red can be completely re-oxidized by O2 and the chemical looping oxidation has stably performed well in five chemical cycles. This oxidation strategy also shows outstanding FA yields from xylan, cellulose and raw biomass.

Automated summary

In this study, a novel chemical looping oxidation strategy using a heteropolyacid H8PV5Mo7O40 as an oxygen carrier was proposed for the production of formic acid from biomass-derived carbohydrates. The strategy achieved a high formic acid yield of 95.4% from glucose and also showed excellent yields from xylan, cellulose, and raw biomass.