(242b) Enhancement of H2 Production From Glucose Using La Promoted Ni/Al2O3 Catalysts in Supercritical Water

Biomass is being considered as one of the major sources for green energy given its carbon neutrality balanced by photosynthesis. Gasification of biomass produces syngas (H₂+CO) which allows using cleaner combustion technology as well as direct feeding to high efficiency internal combustion engines. However, high drying cost due to the large water content of the biomass feedstock makes the gasification process less competitive. On the other hand, gasification of biomass in supercritical water offers attractive alternatives to avoid the energy intensive drying process. In this approach biomass is hydrolyzed by water into smaller molecules in presence of a suitable catalyst. This study was aimed at developing an alumina supported nickel based catalysts suitable for biomass gasification in supercritical water. To this end a La promoted Ni/Al₂O₃ carrier material was synthesized and evaluated.

In catalyst preparation an incipient wetness impregnation method was adopted for metal loading on the alumina support. After impregnation, the resultant sample was dried slowly (0.5 °C/min) and then treated by NH₃-H₂O to convert metal salt anion to ammonium salt. The NH₃-H₂O vapor treated catalyst was dried from 60°C to 120°C in 2h and then at 250°C for 1.5 h. Finally, the catalyst was reduced at 700 °C using hydrogen.

The prepared catalysts were characterized by temperature programmed reduction and oxidation for metal support interaction and stability test. Pulse chemisorption was conducted to measure the dispersion and crystalline diameter of nickel particles. It appeared that the addition of La reduced the metal support interaction and increased the dispersion of Ni on the alumina support. In catalyst evaluation glucose was used as a model compound for biomass given that glucose is the building block of cellulose and is soluble in water in room temperature. It was observed that hydrogen production from biomass model compound (glucose) in supercritical water reduced after certain loading of Ni due to methanation reaction. Hydrogen production was enhanced by retardation of methanation reaction of carbon dioxide by promoting Ni/Al₂O₃ with La. Besides catalyzing the reaction, La also absorbs one of the reaction products CO₂ by forming a carbonate complex. The formation of this complex decreases the concentration of CO₂ in the product, thereby helping to shift the equilibrium to the right hand side. As a result, the selectivity of the hydrogen productivity significantly increased. Water gas shift reaction also enhanced by extra carbon monoxide formed during scavenging of deposited coke on the Ni surface by lanthanum oxycarbonate formed during reaction condition.