DFT study on gas-phase hydrodeoxygenation of guaiacol by various reaction schemes

Guaiacol is an important phenolic component present in pyrolytic bio-oils; and in this work its hydrodeoxygenation (HDO) by various reaction schemes has been considered within the framework of density functional theory. In this computational study, primarily three reaction schemes for the HDO of guaiacol are considered. In the first reaction scheme (RS 1), guaiacol undergoes hydrogenolysis at O–CH3 bond site of methoxy group to produce catechol and methane followed by HDO of catechol forming phenol and water, followed by HDO of phenol producing benzene and water and finally benzene leading to cyclohexane formation. In the second reaction scheme (RS 2), guaiacol undergoes hydrogenolysis at Caromatic–O bond of methoxy group producing phenol and methanol followed by hydrotreatment of phenol to form cyclohexane along with same intermediates as in the first reaction scheme. In the third reaction scheme (RS 3), HDO of guaiacol compound at Caromatic–OH sigma bond produces anisole and water; and then anisole follows two secondary pathways to produce cyclohexane. In this computational study, the transition state optimisations, vibrational frequency and IRC calculations are carried out by B3LYP functional with 6-311+g(d,p) basis set using Gaussian 09 and Gauss View 5 software package.