Gas-Phase Hydrodeoxygenation of Benzaldehyde, Benzyl Alcohol, Phenyl Acetate, and Anisole over Precious Metal Catalysts

The aim of this work is to study the gas-phase hydrodeoxygenation (HDO) of bio-oil-related platform molecules over precious metal catalysts (Pt and Pd on alumina) at moderate temperature (325 °C) and low pressure (0.5 MPa). Bio-oils consist of a complex mixture of compounds, many of which are aromatic oxygenates, and have been modeled here by four model compounds with different oxygenated functional groups: benzaldehyde (aldehyde), benzyl alcohol (alcohol), phenyl acetate (ester), and anisole (ether). First, the stability and activity of the catalysts in the HDO of the different compounds have been studied in an isothermal fixed-bed reactor. The performance of the Pt catalyst is better than that of the corresponding Pd catalyst (highest activity and selectivity). The compound more refractory to HDO over Pt was benzyl alcohol. Both catalysts suffer from strong deactivation at the beginning of the tests, mainly by the formation of carbonaceous deposits. The deactivation is particularly strong for the HDO of benzyl alcohol over the Pd catalyst. Second, a kinetic study has been carried out varying the space time (0–1 (kg_cat s)/mol). Kinetic models, based on reaction networks derived from the product distributions, have been proposed, and the kinetic constant fit to the experimental data by least-squares regression

Consequences of Nitrogen Doping and Oxygen Enrichment on Titanium Local Order and Photocatalytic Performance of TiO₂ Anatase

Extended X-ray absorption fine structure (EXAFS) investigation of the oxygen-rich titania formed via the thermal treatment of N-doped TiO₂ has revealed that the removal of N-dopants is responsible for the creation of defect sites in the titanium environment, thus triggering at high temperatures (500–800 °C) the capture of atmospheric oxygen followed by its diffusion toward the vacant sites and formation of interstitial oxygen species. The effect of the dopants on Ti coordination number and Ti–O_int and Ti–N_int bond distances has been estimated. The photocatalytic <i>p</i>-cresol degradation tests have demonstrated that the interband states formed by the N-dopants contribute to a greater extent to the visible-light activity than the oxygen interstitials do. However, under the UV irradiation the oxygen-rich titania shows higher efficiency in the pollutant degradation, while the N-dopants in N–TiO₂ play the role of recombination sites. The presence of the surface nitrogen species in TiO₂ is highly beneficial for the application in partial photooxidation reactions, where N–TiO₂ demonstrates a superior selectivity of 5-hydroxymethyl furfural (HMF) oxidation to 2,5-furandicarbox­aldehyde (FDC). Thus, this work underlines the importance of a rational design of nonmetal doped titania for photocatalytic degradation and partial oxidation applications, and it establishes the role of bulk defects and surface dopants on the TiO₂ photooxidation performance