Background: The hydrothermal reduction of CO2 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 CO2 and by degradation of glucose degradation in alkaline hydrothermal media.
Methods: This article analyzes the origin of formic acid using NaH13CO3 as CO2 source, assisted by HPLC and 13C-NMR to study the origin of FA.
Significant findings: 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-13C, whereas longer reaction times lead to a higher yield to FA-13C. 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 NaHCO3 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-13C/ total FA.
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