Hydrodeoxygenation of Guaiacol over Ru(0001): A DFT Study

Abstract

The hydrodeoxygenation (HDO) of aromatic oxygenates over ruthenium was studied computationally on the model system guaiacol (2-methoxyphenol) on Ru(0001) using a DFT method. In addition to the adsorption geometries of the aromatic intermediates, the study focused on the energetics of elementary reaction steps that occur during the HDO of guaiacol. Bond scissions at the aliphatic side group were calculated to have barriers of at most 69 kJ mol −1 . In contrast, barriers for the cleavage of the aromatic bonds C aryl −O were determined at more than 100 kJ mol −1 . On the basis of calculated energetics, a reaction pathway for the HDO of guaiacol is proposed in which first the methyl group of the methoxy moiety is removed to yield catecholate. Subsequently, the oxo groups are replaced by H, yielding first phenolate and, finally, benzene. For the removal of the first oxygen center of catecholate, a substantially lower barrier (106 kJ mol −1 ) than for the C aryl −O cleavage of phenolate (189 kJ mol −1 ) was calculated. This is rationalized by the strained structure of adsorbed catecholate. The high barrier for the second C aryl −O scission step is line with recent experiments that yield phenol as the main product of guaiacol HDO over Ru/C.

Hydrodeoxygenation of Lignin-Derived Phenols: From Fundamental Studies towards Industrial Applications

“…It is also interesting to note that catechol formation was more prominent in HDO of guaiacol over Ru/C catalyst at 350 • C than at 400 • C, which was probably also related to temperature dependence of adsorption, namely low desorption of catechol at lower temperature [16]. According to a DFT study for Ru(0001) surface it was concluded that catecholate is formed prior to phenolate, finally yielding phenol as the main product [74]. .…”

“…In addition to kinetic studies, also adsorption studies [48], theoretical DFT (density function theory) calculations [22,[71][72][73][74][75] and bond dissociation energy calculations [36] have been performed.…”

Theoretical Investigation of the Reaction Mechanism of the Guaiacol Hydrogenation over a Pt(111) Catalyst

“…In fact, Chiu et al 37 have investigated the guaiacol hydrodeoxygenation over Pt/C at 523 K and 623 K and low H 2 partial pressures of 0.4 bar. At the lower temperature, they observed primarily phenol (~50%), cyclohexanone (~10%), and cyclohexanol (~5%) as major reaction products, while at higher temperatures they observed primarily phenol (30%) and benzene (30%).…”

Decomposition Mechanism of Anisole on Pt(111): Combining Single-Crystal Experiments and First-Principles Calculations

“…15,16 To gain insights into the reactivity of aromatic oxygenates on noble metal surfaces, many DFT studies have been performed and published. 13,[17][18][19][20][21][22][23][24] Honkela et al showed in particular that the dissociation of phenol into phenoxy was endothermic on Pt(111) and exothermic on Rh(111) and suggested that it may explain the higher propensity of Rh to deoxygenate aromatics. 19 Vlachos and co-workers recently proposed the first DFT-elucidated mechanism of guaiacol decomposition.…”