Various transition metal oxo species, for example, perrhenate, methyltrioxorhenium and heptamolybdate, have been identified as active catalysts for the deoxydehydration of vicinal diols to olefins. This reaction, which combines dehydration and deoxygenation by a sacrificial reductant into a single step, is useful for the removal of OH groups in feedstocks derived from biomass processing via fermentation, acid hydrolysis, or pyrolysis. Soluble rhenium catalysts have been found to be particularly effective for deoxydehydration, but the rarity and high cost of rhenium and difficulty involved with catalyst recovery impede any large-scale adoption of this type of catalyst. Oxo-rhenium species supported on metal oxide supports have shown good catalytic activity; however, rhenium species have shown a propensity for leaching. Leaching is a common phenomenon when molecular catalysts are immobilized on supports, and a general solution for this issue is still lacking.<br/>With the goal to better understand and ultimately control leaching, we have investigated how the catalyst support and reaction parameters such solvent, reactant, reductant, and temperature affect the extent of rhenium leaching. We have characterized catalyst deactivation by studying recyclability of the catalyst and quantifying the amount of solubilized rhenium by ICP-MS, in addition to characterization of surface and dissolved species by UV-visible and FTIR spectroscopy. We have found that both the rhenium-support interaction and the nature of the diol, which acts as a ligand and forms a complex with the oxo-rhenium site during the reaction, strongly affect the extent of catalyst leaching. The collected data provide guidance on how to control leaching through appropriate choice of reaction conditions and inform future catalyst design.

Controlling leaching of supported oxo-rhenium specied during deoxydehydration

2019 Spring National Meeting

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