Bio-oils produced by fast pyrolysis of biomass offer a potentially inexpensive and renewable source for liquid fuels. Raw bio-oils, however, are complex chemical mixtures with a high oxygen content, which leads to a number of undesirable characteristics such as a low heating value compared to conventional fuels, chemical instability, and high acidity. Consequently, catalytic upgrading of bio-oils is critical to reduce oxygen content and generate a “drop-in” ready fuel. Upgrading of bio-oil vapors directly after pyrolysis offers the additional advantage of yielding a stabilized product upon condensation, however, this process requires higher temperatures and lower H2 pressures than typical deoxygenation via hydrotreating. Therefore, effective deoxygenation under these conditions requires catalysts that can readily activate H2, are active in low hydrogen-to-carbon environments, and are stable under acidic conditions. Metal phosphides are a promising class of materials that have exhibited hydrotreating activities similar to, or better than metal sulfide-based materials and noble metals, and have the capability to activate hydrogen at low pressures. Significant advances in the solution phase synthesis of nanomaterials have enabled a high level of control over the size, shape, and composition of nanostructured catalysts, which can have a significant impact on the resulting catalytic performance. Here, we have designed a facile approach utilizing air-stable, inexpensive metal-phosphine precursors to form solid, phase-pure metal phosphide nanoparticles (NPs). Single-source molecular precursors provide an alternative route to access metal phosphide NPs with controlled phases and without the formation of a metal NP intermediate that can lead to hollow particles. The resulting catalytically relevant NPs (e.g., Ni2P, Rh2P, Pd3P) were dispersed on high surface support materials to assess their catalytic performance relative to standard bulk-scale metal phosphides. Vapor phase upgrading of model bio-oil compounds including acetic acid and guaiacol was performed to evaluate the metal phosphide catalysts for deoxygenation and hydrogen incorportation abilities. Additionally, the effects of pre-treatment conditions on the fate of the organic molecules required for stabilization of the metal phosphide NPs during synthesis was investigated with regards to the long-term stability and catalytic activity of these materials.

Nanostructured metal phosphide catalysts for conversion of biomass to liquid fuels

249th National Meeting (2015)

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