Catalytic reforming of glycerol in hot compressed water: Role of metal and support

The objective of this study is to maximize the hydrogen yield from hydrothermal reforming of glycerol by screening different catalysts. Catalysts with different active metals (Platinum, Ruthenium, Palladium, Nickel and Rhodium) on alumina support and palladium with different supports (Alumina, Titania, Zirconia, Activated Carbon, Ceria modified Zirconia) were synthesized, characterized, and tested at hydrothermal conditions (450 °C and 250 bar) for glycerol reforming up to 6 h duration. With different metals, maximum carbon gasification efficiency of 70% and hydrogen yield of 2.023 mol/mol was achieved with platinum metal while the lowest carbon gasification efficiency of ~ 7.5 was obtained with nickel-based catalyst with a very low hydrogen yields of 0.021 mol/mol. Since, the amount of active metal loading (~ 1.5 wt%) was very low, in the case of nickel it led to inactive and stable phase of NiAl₂O₄ having poor catalytic performance. With different supports, maximum carbon gasification efficiency of ~ 65% and hydrogen yield of 2.475 mol/mol was obtained with ceria modified zirconia support. Lowest conversion and hydrogen yield of 17.3% and 0.155 respectively were achieved with titania support. The order of gasification efficiency with respect to different supports was in the order of CeZrO₂ ~ ZrO₂ > Al₂O₃ > AC > TiO₂. Analysis of the spent catalysts showed significant phase change of alumina support from γ-Al₂O₃ to α-Al₂O₃ with maximum coke deposition evident from the thermogravimetric analysis without any catalyst deactivation. These findings provide new opportunities for rational design of catalyst for the hydrothermal conversion of glycerol to hydrogen rich product gas.