(138h) Upgrading of Biomass Pryolysis Vapors of Modified ZSM-5: Effects of Metal(s) Loading and Pretreatment
Ga/ZSM-5 and Ni/ZSM-5catalysts with varied nickel loadings were evaluated for their ability to produce aromatic hydrocarbons by upgrading of pine pyrolysis vapors. The effect of catalyst pretreatment by hydrogen reduction was also investigated. Results indicate that the addition of gallium or nickel increases the yield of aromatic hydrocarbons while simultaneously increasing the conversion of oxygenates, relative to ZSM-5, and these effects are more pronounced with increasing nickel loading. Additionally, while initial activity differences were observed between the oxidized and reduced forms of nickel on ZSM-5 (i.e., NiO/ZSM-5 vs. Ni/ZSM-5), the activity of both catalysts converge with increasing time on stream. These reaction results, coupled with characterization of pristine and spent catalysts, suggest that the catalysts reach similar active states during catalytic pyrolysis, regardless of pretreatment, as NiO under goes in situ reduction to Ni by biomass pyrolysis vapors. This reduction of NiO to Ni was confirmed by reaction results and characterization by NH3 TPD, TPR, and XRD. This finding is significant in that the ability to reduce or eliminate the need for a pre-reaction H2 reduction of Ni-modified zeolite catalysts could reduce process complexity and operating costs in a biorefinery-based vapor phase upgrading process to produce biomass-derived fuels and chemicals. The ability to monitor catalyst activity in real-time with a molecular beam mass spectrometer used to measure uncondensed, hot pyrolysis vapors, allows for improved understanding of the mechanism for improved activity with Ni-addition to ZSM-5, which is attributed to the ability to prevent deactivation by deposition of coke and capping of zeolite micropores.