Water plays a critical role in the conversion of numerous renewable oxygenates to higher value products. While it is well known that condensed water can play a detrimental role in the stability of several catalysts at elevated temperatures, water is critical for the enhancement a variety of reactions relevant to the synthesis of renewable fuels and chemicals. This presentation will focus on the interesting role of water in selective ring rearrangement of furanic species.<br/> <br/>Furanic species are important components of biomass degradation, produced via hydrolysis or pyrolytic routes.  A reaction with considerable promise is the upgrading of furfural to cyclic ketones. Cyclopentanone is more stable than furfural upon storage, and is a valuable intermediate for the selective production of diesel fuel, jet fuel, and polymers. This ring rearrangement reaction, commonly referred to as the Piancatelli rearrangement, is believed to occur in the condensed aqueous phase in the presence of a homogeneous acid, with the role of the metal catalyst simply to convert furfural to furfuryl alcohol. In this contribution, we contrast the role of condensed liquid water with water vapor at elevated temperatures. At elevated temperatures, we show that water plays a critical role in ring rearrangement when contacting furfural over metals supported on reducible oxides, such as Ru/TiO<sub>2</sub>, although through a different mechanism. Ring rearrangement exhibits a positive 1.2 order dependence on water partial pressure at temperatures as high as 400°C. Carboxylic acids accelerate the rate of cyclopentenone formation from furfuryl alcohol in the condensed liquid phase by lowering the pH. However, co-feeding studies in the vapor phase reveal that these carboxylic acids compete for active sites responsible for ring rearrangement at elevated temperatures, hindering reaction rates in the absence of a condensed liquid. A kinetic analysis reveals that vapor phase rearrangement does not require furfuryl alcohol intermediates in equilibrium with the gas phase. By varying the electronic structure of the metallic nanoparticle, including Pd, Ru and Ni, a correlation is made between the carbon-metal bond strength and rate and selectivity for ring rearrangement products in the presence of water vapor. Finally, we propose a mechanism involving unique interfacial sites in the presence of water responsible for this transformation.

Influence of water on furfural ring rearrangement reactions

254th National Meeting (2017)

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