(656d) Catalytic Conversion of Furfural to Methylfuran: Investigating Reaction Mechanisms on Ni and the Effect of Boron Doping on the Activity and Selectivity of the Catalyst

Fast pyrolysis of lignocellulosic biomass is emerging as a promising route for the production of liquid transportation fuels. However, the bio-oil produced from pyrolysis has a high oxygen content (~45%) which results in a poor heating value, thus limiting its direct usability as a fuel. The catalytic hydrodeoxygenation (HDO) of bio-oil in the presence of hydrogen is an effective technique for the removal of oxygen groups from bio-oil. Furfural is one of the major bio-oil components and is a potential starting material for the production of compounds like 2-methylfuran (MF), which can be blended into transportation fuels. The challenge is to develop catalysts which can selectively break C – O bonds, while preserving the C – C bonds. In this context, hydrogenolysis of furfural (C_formyl – O cleavage) to produce MF is desirable, as the high octane number of MF allows easy blending into gasoline/diesel pools. Vapor phase HDO of furfural over Ni catalysts leads to furfuryl alcohol (via hydrogenation of formyl group) as the dominant product at low temperatures, while furans (via decarbonylation by C – C cleavage) and C4 products (via furan ring opening) dominate at higher temperatures^1-2. We investigated the potential competitive pathways for the catalytic conversion of furfural on model Ni(111) surfaces using Density Functional Theory. Our calculations show that decarbonylation (C – C cleavage) and ring opening (C_ring – O cleavage) of furfural to form furan and ring opened C4 products are kinetically favored pathways on Ni(111) surface, in agreement with experimental studies. Recent studies have suggested that the activity and selectivity of catalyst can be improved by doping boron^3-6. On Ni(111) surfaces boron binds strongly at the subsurface positions, resulting in a corrugated Ni surface, similar to a stepped surface. The presence of the subsurface, interstitial boron expands the lattice of Ni and also alters its electronic properties by donating electrons. The incorporation of B in the Ni surface was found to increase the C – C cleavage and ring opening barriers and drastically lower the C_formyl – O cleavage barriers, relative to the Ni(111) surfaces. We propose the hydrogenolysis of furfuryl alcohol to form MF to be kinetically favorable over C – C cleavage (furan formation) and ring opening (C4 products), leading to significantly enhanced MF selectivity in the vapor phase hydrogenation of furfural on boron doped Ni surfaces.

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