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.

The surface species formed by glycerol on γ-Al2O3, TiO2 anatase, ZrO2, MgO, and CeO2 both in the presence and in the absence of bulk water are investigated with infrared spectroscopy. The acid–base properties of the metal oxides are characterized by pyridine and CO2 adsorption/temperature-programmed desorption. The metal oxides studied provide a distribution of strengths of Lewis acid sites as well as strengths and types of basic sites which afford insight into the role of these various sites in polyol/metal oxide surface interactions. Even in the presence of bulk water, glycerol forms a bridging alkoxy bond through a primary alcohol group to two coordinatively unsaturated metal atoms and participates in a Lewis acid/base interaction between the oxygen atom of the other primary alcohol and a coordinatively unsaturated metal atom that is also involved in the alkoxy bond. These interactions only occur with metal oxides which contain strong Lewis acid sites. A quantitative correlation between the C–O stretching frequencies of the chemisorbed groups and the electronegativity of the metal atoms is established. Glycerol experiences an additional surface interaction via a hydrogen-bonding interaction between its secondary alcohol group and a relatively weak basic surface oxygen atom. Stronger base sites are blocked by adsorbed water or CO2. In the absence of strong Lewis acid sites, in the case of MgO, hydrogen-bonding interactions between glycerol and surface hydroxyls are the dominant means of interaction.

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