Hydrodeoxygenation of Guaiacol over Ceria–Zirconia Catalysts

Abstract

The hydrodeoxygenation of guaiacol is investigated over bulk ceria and ceria-zirconia catalysts with different elemental compositions. The reactions are performed in a flow reactor at 1 atm and 275-400 °C. The primary products are phenol and catechol, whereas cresol and benzene are formed as secondary products. No products with hydrogenated rings are formed. The highest conversion of guaiacol is achieved over a catalyst containing 60 mol % CeO2 and 40 mol % ZrO2 . Pseudo-first-order activation energies of 97-114 kJ mol(-1) are observed over the mixed metal oxide catalysts. None of the catalysts show significant deactivation during 72 h on stream. The important physicochemical properties of the catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction, titration of oxygen vacancies, and temperature-programmed desorption of ammonia. On the basis of these experimental results, the reasons for the observed reactivity trends are identified.

Kinetics of hydrogen activation on ceria–zirconia

“…Ce 3+ ) under typical reaction conditions for the conversion of hydrocarbon feedstocks (i.e. below 450°C, 1-30 atm) is expected to have a strong influence on the performance of these catalysts in reactions such as hydrogenation and hydrodeoxygenation [14,21,27,48].…”

“…When relationships between the synthesis conditions, the structure of the catalysts, and their performance in catalytic reactions are established, improvement of catalytic properties becomes possible [65]. This study focuses on characterizing the properties of ceria-zirconia catalysts motivated by their potential use as catalysts for hydrodeoxygenation (HDO) of oxygenates in biomass derived pyrolysis oils [21]. For this application and other catalytic processes [1,66], the ability of these materials to dissociatively adsorb hydrogen is critical (vide infra).…”

“…To provide an assessment of the magnitude of this phenomenon, we quantified the amount of exchangeable surface hydrogen on ceria, zirconia, and ceria-zirconia in a temperature range that is relevant for hydrogenation and HDO reactions (Fig. 3) [19,21].…”

“…While understanding the kinetics of H 2 -D 2 exchange over ceria and ceria-zirconia is important for the design of HDO heterogeneous catalysts [21], it is also relevant for other catalytic reactions. Ceria-zirconia catalysts show a high capacity for hydrogen-exchange that is approaching that of supported metals on metal oxide supports.…”

“…Recently, our group and others showed that oxides with vacancies can catalyze hydrodeoxygenation of biomass-derived oxygenates [21][22][23]. To design a highly efficient ceria-based catalyst for this reaction, it is important to gain quantitative insight into the amount of reactive hydrogen present on the surface under reaction conditions as well as the kinetics and types of active sites necessary for dissociative adsorption of hydrogen.…”