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

Abstract

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.