2 research outputs found
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 Ā°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 (0ā1 (kg<sub>cat</sub> 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 TiO<sub>2</sub> Anatase
Extended X-ray absorption
fine structure (EXAFS) investigation
of the oxygen-rich titania formed via the thermal treatment of N-doped
TiO<sub>2</sub> 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 (500ā800 Ā°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 TiāO<sub>int</sub> and TiāN<sub>int</sub> 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 NāTiO<sub>2</sub> play the role of recombination
sites. The presence of the surface nitrogen species in TiO<sub>2</sub> is highly beneficial for the application in partial photooxidation
reactions, where NāTiO<sub>2</sub> demonstrates a superior
selectivity of 5-hydroxymethyl furfural (HMF) oxidation to 2,5-furandicarboxĀaldehyde
(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 TiO<sub>2</sub> photooxidation performance