Selective hydrogen production from formic acid decomposition over Mo carbides supported on carbon materials

The decomposition of formic acid to obtain hydrogen has been studied using molybdenum carbides supported on activated carbon and two high surface area graphites, H 200 (200 m 2 g −1 ) and H 400 (400 m 2 g −1 ). Particular attention is paid to the effect of Mo loading. The catalysts were prepared in situ using a mixture of CH 4 and H 2 at a temperature of up to 700 °C. Under these conditions, carburization was mostly complete. We observed that the support influenced the Mo x C phase obtained so that it seems that the ratio of defective carbon influences the phase. However, for these materials the C/Mo ratio did not influence the obtained crystal phase. Characterization by XRD showed that while the β-Mo 2 C phase was obtained over activated carbon and over H 200 , in contrast, MoO x C y was obtained over H 400 . These catalysts reached 100% conversion on formic acid decomposition at temperatures in the range of 190-250 °C and were also highly selective under these mild conditions, with values for CO 2 selectivity in the range of 85.0-96.5%. The best results were achieved over a 10 wt% Mo loading on activated carbon that reached 96.5% selectivity to H 2 . Also, changes in the molybdenum phases were observed on the spent catalyst. Some redox transformations during reaction were responsible for the transformation of β-Mo 2 C into oxycarbide MoO x C y . In summary, the results of the catalytic performance indicated that the β-Mo 2 C phase was more active, selective and stable than MoO x C y under the studied conditions. The support influenced the carbide phase obtained so that a higher ratio of defective carbon favoured the formation of β-Mo 2 C phase vs. MoO x C y . Redox transformations during the reaction might be responsible of the transformation of β-Mo 2 C into MoO x C y .