Ni catalysts for steam gasification of biomass: Effect of La2O3 loading

Abstract

La2O3 promoted Ni/γ-Al2O3 fluidizable catalysts are studied for the steam gasification of a cellulose surrogate (glucose) and a lignin surrogate (2-methoxy-4-methylphenol) in a CREC Riser Simulator. Two γ-Al2O3 are considered as the support for an active and stable Ni catalyst. La2O3 modified supports and catalysts are characterized using BET specific surface area, XRD, TPR, TPO, and H2-pulse chemisorption. Pyridine FTIR, NH3-TPD and CO2-TPD are employed to establish the effect of La2O3 on the aciditiy-basicity of the alumina used. It is shown that increasing the La2O3 up to 5wt% improves the BET surface area and the CO2 adsorption capacity, as well as reduces support acidity. XRD results revealed the formation of undesirable LaAlO3 on the Ni catalyst containing 10wt% La2O3.The 10wt% La2O3 also favors the formation of larger Ni crystallites which are susceptible to coking. In agreement with this, the catalyst containing 10wt% La2O3 gives lower dry gas yields and carbon conversions, as well as yields higher coking than the catalyst supported on alumina with 5wt% La2O3. On the other hand, catalysts supported on Sasol γ-Al2O3 display higher surface area, Ni reducibility and dispersion, and CO2 adsorption capacity than the Alcan γ-Al2O3 supported catalysts. The addition of 5wt% La2O3 further enhances both the structural properties and the reactivity of Ni/Sasol γ-Al2O3 catalyst. In particular, catalytic gasification using 20% Ni on a 5% La2O3-Sasol γ-Al2O3 catalyst shows promising glucose and 2-methoxy-4-methylphenol conversions to a high-quality synthesis gas at only 650°C. This catalyst yields a 95% carbon conversion of glucose to permanent gases with no tar formation and negligible coke deposition; whereas a 81% carbon conversion with only 10.5wt% tars is achieved from 2-methoxy-4-methylphenol gasification.