J.A. Odriozola

Characterisation, surface hydrolysis and nitrogen stability in aluminophosphate oxynitride (AlPON) catalysts

Abstract Solid amorphous aluminophosphate oxynitride (AlPON) catalysts with a nitrogen content ranging from 0% up to 20% N (w/w) have been obtained by reaction between AlPO4 and NH3 at 800°C. Samples are analysed by X-ray photoelectron (XPS) and diffuse reflectance Fourier transform infrared (DRIFTS) spectroscopies, mass spectrometry (MS) and thermogravimetry (TG). Similar to that of AlPO4, AlPON local structure is pictured as a network of PO4 and AlO4 tetrahedra in which nitrogen preferentially replaces oxygen bonded to phosphorous, although some contribution from Al–N bonds in an AlON phase is also proposed. Nitridation stages yielding [PO3N] and [PO2N2] building units are characterised below 7.2% N and above 11% N (w/w), respectively. Also terminal –PNH2 groups are detected from early nitridation stages. Freshly prepared AlPON catalysts readily undergo hydration (10–15% by weight) and hydrolysis at atmospheric conditions. Hydration is more intense on low nitrogen containing samples and sharply decreases above 7.2% N (w/w). Ammonia is the product of both surface hydrolysis and bulk decomposition. Hydrolysis is almost independent on nitrogen content while bulk decomposition grows parallel to nitrogen percentage. Bulk decomposition below 500°C is more intense than hydrolysis and always involves terminal –PNH2 reaction either as a condensation around 230–240°C or through a reaction with water around 320–340°C. Condensation depends on –PNH2 coverage and is the preferred decomposition mechanism in high nitrogen containing AlPON.

Experimental and molecular dynamics simulation analysis of LaCrO3 precipitation in chromia scales

Experimental characterization of grain and grain boundaries of chromia scales upon addition of La has been carried out with a variety of techniques. The effect of lanthanum addition on the high temperature oxidation is explained based on simulations suggested by the experimental results. The grain boundary precipitation mechanism of perovskite phases suggested by our simulations is through the extraction of Cr atoms from the oxide scale.

The thermostabilising effect of La doping on γ-Al2O3 a molecular dynamics simulation study

Abstract Molecular dynamics simulations of the surface of γ-Al 2 O 3 have been carried out at 1000 K with three different La coverages in order to study the thermostabilising effect of rare earth cations. The system consisted originally of a γ-Al 2 O 3 sample constituted of 1440 particles from which 10, 15 and 20 aluminium cations of high coordination were replaced by lanthanum cations. The thermostabilising effect is described in terms of the hindering of migration of tetrahedral aluminium cations by the presence of highly coordinated lanthanum cations.

Thiophene hydrogenolysis using temperature-programmed surface reaction as a tool to study poison toxicity

Abstract In this work, the deactivation of a Ni/SiO 2 catalyst by thiophene and H 2 S during benzene hydrogenation at 200°C was studied. An initial toxicity approximately three times higher for thiophene than for H 2 S was found. Temperature-programmed surface reaction (TPSR) results of previously adsorbed thiophene suggest that this difference in toxicity may be explained in terms of incomplete thiophene hydrogenolysis at 200°C. TPSR results have also revealed that thiophene is hydrogenolized to a considerable extent on nickel at room temperature.