In situ hydrodeoxygenation of phenol with liquid hydrogen donor over three supported noble-metal catalysts

- Ru/MCM-41 performs best in the in situ hydrodeoxygenation of phenol with formic acid.
- The conversion of phenol has a maximum value when Ru/MCM-41 is reduced at 400 °C.
- Cyclohexane has a maximum yield at the 10 wt% of Ru loading amount in Ru/MCM-41.
- An increased ratio of formic acid to phenol can improve the conversion of phenol.
- COx derived from formic acid is harmful for the increase of phenol conversion.

In situ hydrodeoxygenation of phenol with liquid hydrogen donor over three supported Pd, Pt, and Ru catalysts was investigated. The method of incipient wetness impregnation was used to load the three noble metals on the support of MCM-41, which is a cylindrical mesoporous material with a hierarchical structure. The in situ hydrodeoxygenation of phenol was conducted at 280 °C, under pressures from saturated vapor of solvent and compressed initial N2 with gas products. Among the three catalysts, Ru/MCM-41 was found to be the best one, with highest phenol conversion of 73.9% and deoxygenation degree of 72.2%. The performance of Ru/MCM-41 increased with increasing theoretical loading amount of Ru and with reduction temperature. However, when the reduction temperature reached to 500 °C, or the Ru theoretical loading amount increased to 15 wt%, the activity of Ru/MCM-41 decreased reversely. Through the characterizations by small-angle XRD, wide-angle XRD, H2-TPR, and SEM analysis, the reason for the deteriorated performance of Ru/MCM-41 under high reduction temperature or high Ru loading amount was deduced as the collapse of MCM-41 structure and severe overlaps of Ru atoms. Hydrogen donors were also tested, and formic acid was found in best performance owing to its fast decomposition rate and high productivity of hydrogen. Though an increased feed ratio of formic acid to phenol could improve the hydrodeoxygenation potential of phenol, much simultaneously generated COx from decomposition of formic acid might occupy active sites of the catalyst and led to a decreased growth rate of phenol conversion.