(634c) Catalytic Deoxygenation of Benzaldehyde Over Supported Gallium Catalysts

The deoxygenation of benzaldehyde was investigated over supported Ga catalysts as part of a program leading to the study of model reactions involving aldehydes, acids, furfurals, and oxygenated aromatics that may be present in pyrolysis oil (bio-oil). Ga/silica and Ga/ZSM-5 catalysts were prepared by impregnating precipitated silica and NH4ZSM-5 supports with Ga(NO3)3 solution. The reaction conditions, H2 concentration, Ga content, and Ga dispersion in the catalysts were varied to investigate the effect of these parameters on activity, selectivity, and stability. TPR gave evidence for a partial reduction of Ga/silica in the range 500-650 ˚C. Increasing H2 concentration (3-100%v/v) was found to enhance activity (~25-100%) and toluene selectivity (40-75%). Reaction at low temperature (< 500 oC) leads to the formation of high molecular weight oxygenates and consequently rapid catalyst deactivation (< 2 h). Interestingly, highly dispersed Ga in the restricted pore structure of ZSM-5 provides a relatively higher stability (>24 h) with a benzene/toluene product ratio ~ 1. In contrast, no benzaldehyde conversion can be observed over a physical mixture of Ga2O3 and silica.