Effect of supercritical water gasification treatment on Ni/La ₂O₃-Al₂O₃-based catalysts

Demand for low cost and high activity catalysts for use in biomass gasification is gaining significant attention. This study investigated the effect of supercritical water gasification (SCWG) on Ni-based Al ₂O₃ catalysts doped with La₂O₃ in order to gain a better understanding of the catalyst's role. The investigated micron and nano sized catalysts were characterized both before and after SCWG treatment by temperature programmed reduction (TPR) and oxidation (TPO) for determining metal-support interactions and stability. Temperature programmed desorption (CO₂-TPD) was measured for CO₂ adsorption to the catalyst surface. Pulse chemisorption was conducted to measure the dispersion and crystalline size of the nickel particles while XRD, TGA and Raman analysis were carried out to examine the crystalline phase and coke deposition. The results showed that exposure to SCWG severely affected the physical and chemical structure of the Ni/Al₂O₃ catalysts leading to agglomeration of active metals, particularly for nanostructured catalysts. Adding La₂O₃ to the Ni/Al₂O₃ catalysts retarded coke formation, especially graphitic type coke by forming lanthanum oxycarbonate species.