Session: General Catalysis:

Bio-oil is a promising source of green energy, due to its ability to provide carbon-based fuel that is compatible with the existing global energy infrastructure. The crude bio-oil, however, is oxy-rich, which gives it poor energy density. To upgrade crude bio-oil, an energetically intensive hydrodeoxygenation (HDO) process is employed. Efforts have been made to reduce the energy requirement through introduction and optimisation of reaction catalysts. While the transition metals abundant in earth’s crust exhibit moderate yield and char formation, the rare group metals show high yield and low char; but are prohibitively expensive. Recently, carbon-based alloys have drawn the interest for their catalytic activity for HDO. Molybdenum carbide (Mo₂C) has experimentally shown promising results in the HDO process, which is postulated as being a result of the material possessing d-band characteristics similar to precious group metals; furthermore, Mo₂C has shown favourable selectivity towards the cleavage of C-O bonds.
In this study, we investigated the kinetics of HDO over an Mo₂C catalyst for a bio-oil model compound, resorcinol, using density functional theory. The conversion of resorcinol to benzene is investigated through an intermediate, phenol, by simulating a series of elementary reaction steps. Our calculations show that the adsorption of resorcinol is favorable at low temperatures. The conversion of resorcinol to phenol is likely to occur by dehydroxylation of the reactant, followed by protonation, to form phenol. The desorption of phenol is kinetically slow and would require high temperatures to occur. A subsequent iteration of dehydroxylation and protonation of phenol could further convert it to benzene with minimum energy requirement (0.99 eV). The desorption of benzene is also kinetically slow at lower temperature. Kinetic modelling shows that increase in temperature is favorable, except for the adsorption of resorcinol on the surface.

(a) Pathways investigated showing the conversion of resorcinol to benzene; black and red lettering shows reaction number and activation barrier (or reaction energy), in eV, respectively; (b) log plot of forward rate constants with temperature.

(a) Pathways investigated showing the conversion of resorcinol to benzene; black and red lettering shows reaction number and activation barrier (or reaction energy), in eV, respectively; (b) log plot of forward rate constants with temperature.

Andrew Logsdail

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