Demonstration and Characterization of Ni/Mg/K/AD90 Used for Pilot-Scale Conditioning of Biomass-Derived Syngas

A fluidizable, Ni/Mg/K/AD90(90% α-Al₂O₃) catalyst was evaluated in a pilot-scale study with oak-derived syngas for tar and methane reforming at 900 °C. The catalyst was operated in a semi-batch mode for ten individual reaction cycles, each separated by a regeneration protocol consisting of steaming followed by H₂ reduction. During the experiment, subsequent reaction cycles showed a decrease in activity as indicated by decreased initial methane conversion. During each reaction cycle, H₂S poisoning was the dominant deactivation mechanism, while coking was deemed to be minor in comparison. Catalyst characterization by XRD and TPR suggest that the loss of activity for subsequent reaction cycles coincides with the formation of a NiAl₂O₄ species that is not fully reduced under process conditions, which in turn results in a decreased number of potential metallic nickel (Ni⁰) sites available for hydrocarbon steam reforming. An increase in nickel crystallite size with time-on-stream was also observed using XRD, indicating that sintering may also play a role in loss of catalyst activity, although this is not considered the primary deactivation mechanism because activity loss was observed even when nickel crystallite sizes remained nearly constant.