Formic acid production by simultaneous hydrothermal CO2 reduction and conversion of glucose and its derivatives

• The mechanism of hydrothermal reduction of CO 2 to formate is tracked with NaH 13 CO 3 . • Formate is obtained by reduction of CO 2 at reaction times of 2 – 3 h. • Formate is also produced by degradation of organic reductants at short times. • Formaldehyde obtained from glycolaldehyde or glyceraldehyde is a key intermediate. The hydrothermal reduction of CO 2 using organic molecules such as alcohols can produce renewable fuels and platform chemicals, such as formic acid (FA). If the process is performed using glucose as reductant, the yield is especially high, because FA is selectively produced both by reduction of CO 2 and by degradation of glucose degradation in alkaline hydrothermal media. This article analyzes the origin of formic acid using NaH 13 CO 3 as CO 2 source, assisted by HPLC and 13 C-NMR to study the origin of FA. Results show that two reactions pathways take place: the first one, at short reaction times, consists on the decomposition of glucose into formic acid and other by-products, achieving low yield to FA- 13 C, whereas longer reaction times lead to a higher yield to FA- 13 C. Similarly, temperature plays an important role, being 300°C the optimal. Further reactions were performed using the main by-products of previous reactions (acetic acid, lactic acid, glycolaldehyde and glyceraldehyde) as reductants to understand the reaction mechanisms. Results indicate that the reduction pathway of NaHCO 3 take place by oxidation of the by-products rather than by the oxidation of glucose itself, needing long reaction times to achieve significant high ratios of FA- 13 C/ total FA.