Molecular modeling approach to elucidate gas phase hydrodeoxygenation of guaiacol over a Pd(111) catalyst within DFT framework.

Abstract

Excessive amounts of oxy-functional groups in unprocessed bio-oil vitiate its quality as fuel; therefore, it has to be channelized to upgrading processes, and catalytic hydrodeoxygenation is one of the most suitable routes for the upgrading of crude bio-oil. In this computational work, catalytic hydrodeoxygenation (HDO) of guaiacol, which is an important phenolic compound of crude bio-oil, has been carried out using density functional theory (DFT) over a Pd(111) catalyst. The Pd(111) catalyst surface does not endorse direct eliminations of functional groups of guaiacol; however, it is found to perform excellently in stepwise dehydrogenation reactions of oxy-functionals of guaiacol according to present DFT results. The catechol product, formed through dehydrogenation of the methoxy group, followed by elimination of CH2 and association of the hydrogen atom, has been identified as one of the major products. The overall reaction rate is controlled by scission of CH2 from 2-methylene-oxy-phenol with an activation energy demand of 23.06kcal mol-1. Further, the kinetic analysis of each reaction step involved in HDO of guaiacol over the Pd(111) catalyst surface has also been carried out at atmospheric pressure and at a wide range of temperatures from 473 to 673K, with temperature intervals of 50K. In the kinetic analysis part, various kineticparameters, such as forward and reverse reaction rate constants, Arrhenius constants, and equilibrium rate constants, are reported. The kinetic modeling of the dominating reaction steps has revealed that even a lower temperature of 473K provides a favorable reaction environment; and the temperature increment further improves the reaction favorability.