**4. Conclusions**

In this work, the hydrothermal conversion of CO2 captured as sodium bicarbonate and ammonium carbamate was studied. Glucose was used as a reducing agent, and metal and metal oxides (Cu, Ni, Pd/C 5%, Ru/C 5%, Fe2O3 and Fe3O4), as well as activated carbon (C), were used as catalysts. The main products of the reaction with ammonium carbamate were formic acid, acetic acid and lactic acid.

The yields of formic acid, acetic acid and lactic acid obtained by the reduction of ammonium carbamate were much lower (less than 25%) than those observed when sodium bicarbonate was used as the carbon source (less than 53%).

For ammonium carbamate experiments, C and Fe3O4 promoted higher yields of FA over AA and LA in comparison to the rest of the catalysts and improved the yield of FA in comparison to the sample without catalyst.

In the experiments with sodium bicarbonate, C and Fe3O4 appeared to be the most promising catalysts for improving the yield of formic acid. The origin of the carbon forming formic acid was investigated by using NaH13CO3. It was found that although C and Fe3O4 achieved the highest total formic acid yield, they seem to favor the oxidation of glucose instead of the reduction of CO2. However, it should be noted that even though Pd/C 5%, Ni and Ru/C 5% yields of total formic acid were lower, they were shown to be more selective in producing formic acid from CO2 than the other catalysts. This aspect is important when considering the selection of a catalyst for making a process that primarily promotes a higher conversion of the carbon source.

**Author Contributions:** Conceptualization, M.D.B., F.A.M., Á.M. and M.I.C.; methodology, M.D.B. and M.I.C.; formal analysis, M.I.C.; investigation, M.D.B. and M.I.C.; resources, M.D.B., F.A.M., Á.M. and M.I.C.; writing—original draft preparation, M.D.B. and M.I.C.; supervision, M.D.B., F.A.M. and Á.M.; funding acquisition, M.D.B. and Á.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Ministerio de Ciencia y Universidades by project RTI2018- 097456-B-I00 and by the Regional Government of Castilla y León and the EU-FEDER program (CLU-2019-04).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** M.I.C. acknowledges Universidad de Valladolid and Banco de Santander for the predoctoral grant. The authors acknowledge Laboratorio de Técnicas Instrumentals UVa for their assistance in the NMR and SEM analysis.

**Conflicts of Interest:** The authors declare no conflict of interest.
