Hydrogen generation from glycerol steam gasification over cobalt loaded MgO–Al₂O₃ hydrotalcite supports

The objective of this research was to determine the effect of the composition of MgO–Al₂O₃ in hydrotalcite (HT) on the performance of cobalt catalysts in glycerol steam reforming (GSR) for hydrogen. The co-precipitation method was used to prepare five hydrotalcite supports with varying MgO:Al₂O₃ compositions (1:1, 1:3, 3:1, 1:5, and 5:1), which were then loaded with a 20 wt% Co using the incipient wetness impregnation method. All the catalysts were systematically characterized by X-ray diffraction and temperature-programmed studies (H₂ reduction, both CO₂ and NH₃ desorption). The impregnation of cobalt oxide on hydrotalcite produced different types of cobalt oxides depending on the hydrotalcite composition. HT with high MgO to Al₂O₃ (3:1, 5:1) ratios favored the formation of a Co-(Mg)–O solid solution, while HT with low MgO to Al₂O₃ (1:3 and 1:5) ratios favored the formation of Co₂AlO₄ and CoAl₂O₄. On the other hand, HT with a 1:1 mol ratio of MgO to Al₂O₃ minimized the formation of Co-(Mg)–O solid solution and cobalt aluminates while encouraging the formation of mixed phases (Co₃O₄, Co₂AlO₄, and CoAl₂O₄). Interlinked mesopores (N₂-physisorption) were observed in the 20 wt% Co/(1:1) MgO:Al₂O₃ catalyst, and its surface was discovered to be amphoteric (from NH₃ and CO₂ TPD). Each catalyst was investigated for hydrogen production from glycerol in the range of 400–700 °C. The best hydrogen yield and glycerol conversion to vapor-phase achieved at 600 °C on the 20 wt% Co/(1:1) MgO–Al₂O₃ catalyst are due to high reducibility and an adequate amount of cobalt available on the surface. The amphoteric behavior of the catalyst prevented hydrogen consumption in the methanation reaction. It is also speeding up the WGS reaction and enhancing the hydrogen yield.