Aluminophosphate Oxynitride Research Articles

Synthesis, characterization, and base–catalytic performance of ordered mesoporous aluminophosphate oxynitride materials

The synthesis, physicochemical characterization, and catalytic evaluation of ordered mesoporous aluminophosphate oxynitride (MAPN) materials are presented here. The solid-base materials were prepared through treating aluminophosphate with an ordered mesostructure with ammonia at high temperatures. The MAPNs are well ordered, and possess high surface and pore volume. The amount of nitrogen incorporated increased with prolonged nitridation times. At the same time, the intensity of basicity is consistent with the nitrogen content, which is affirmed by Knoevenagel condensation reaction. The obtained ordered MAPN materials also possess acidity. The easy preparation and control of the nitrogen content of ordered MAPN materials, providing acidity and basicity, make them attractive as alternatives to a solid-base or acid-base catalyst, especially for the interactions of large molecules.

Synthesis of Pseudoionones by Acid and Base Solid Catalysts

The preparation of pseudoionones by aldol condensation reaction between citral and acetone have been carried out in the presence of acid (HY and beta zeolites), an acid–base (amorphous aluminophosphate) and basic catalysts such as an aluminophosphate oxynitride, MgO and different activated hydrotalcites. The results showed that acid or acid–base catalysts were not successful for performing in one pot the preparation of ionones. MgO and calcined hydrotalcites showed excellent activity and selectivity to pseudoionones, with calcined hydrotalcite more selective than MgO. Moreover, the rate of reaction can be improved by activating the hydrotalcite through rehydration. This activation can be successfully done by simply adding the optimum amount of water to the calcined hydrotalcite before reaction. The inhibiting effect of the concentration citral on the catalytic activity of rehydrated hydrotalcites that has been reported to occur at 273 K can be avoided by working at a reaction temperature of 333 K.

First evidences on the stability of nitride species in ALPON catalysts

An unexpected reversible conversion between –NH 2 and N 3− species in aluminophosphate oxynitride (ALPON) has been found during thermal treatments and subsequent exposition to moist air.

Platinum aluminophosphate oxynitride (Pt-AIPON) catalysts for the dehydrogenation of isobutane to isobutene

The catalytic dehydrogenation of isobutane to isobutene over two series of platinum-supported aluminophosphate oxynitride (Pt-AlPON) catalysts, containing different amounts of nitrogen and synthesized using two different platinum precursors, was studied. The impregnation and platinum reduction processes result in a partial loss of nitrogen and a decrease in the specific surface area of the AlPON precursors. The surface and bulk structures of the catalysts are functions of the nitrogen content of the solid. At low nitrogen contents (less than or equal to 6% w/w), the nitrogen is found mainly on the surface of the catalyst as an -NHx species. Above 6% w/w, nitridation of the bulk begins. The basicity of the solids increases with increasing nitrogen content. The conditions under which synthesis takes place influence the final nitrogen content and the surface structure of the catalysts. Dehydrogenation of isobutane to isobutene of the Pt-AlPON catalyst correlates with the basicity of the catalysts. The surface structure of the solids also influences the yield of isobutene. (C) 2000 Academic Press.

Theoretical investigations of NMR chemical shieldings on the AlPON catalyst system

Using molecular cluster models we present a theoretical ab initio study of the 27 Al and 31 P nuclear magnetic resonance (NMR) chemical shieldings aimed at obtaining short-range structural information on the aluminophosphate oxynitride (AlPON) catalyst system. We have employed orthophosphate-like molecular models with P/Al ratio equal to one and varying N/O ratios to simulate the experimentally obtained compositions. The computed NMR chemical shieldings reproduce quantitatively the observed features in the 31 P magic angle spinning NMR (MAS-NMR) spectra and permit the explanation of these modifications in terms of a progressive and preferential nitridation on the first coordination shell of the phosphorus atom leading to a mixture of [PO x N 4− x ] units in the solid. The comparison of 27 Al isotropic chemical shieldings and the experimental spectra allow us to conclude that N/O substitution does not happen in the first coordination shell of aluminum atoms. The experimentally observed broadening of the tetrahedral aluminum band can be explained by a nitridation of aluminum environment, but not by a nitridation of its first coordination shell.

Surface Stability of Amorphous Aluminophosphate Oxynitrides (AIPON)

Surface Stability of Amorphous Aluminophosphate Oxynitrides (AIPON)

The Short-Range Structure of Aluminophosphate Oxynitride Catalysts. An ab Initio and Experimental Study

In this study we combine spectroscopic data (diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS, and X-ray photoelectron spectroscopy, XPS) with ab initio SCF calculations on model systems in order to get insight into the short-range order of amorphous aluminophosphate oxynitride (AlPON) catalysts. The use of fixed P/Al = 1/1 atomic ratio and varying N/O atomic ratio in the models, allowed us to consider stoichiometries with nitrogen contents in the range 0−20 wt %, similar to those found experimentally. The observed trends in computed Koopman ionization potentials (IPs), vibrational frequencies, and thermodynamic stability are compared with experimental XPS and DRIFTS data and available information of aluminophosphate and related systems. They are used to propose a structural model for the short-range structure of amorphous aluminophosphate oxynitrides. From the XPS data it can be concluded that first nitrogen enters the phosphorus coordination sphere; this results in the formation step ...

Platinum Aluminophosphate Oxynitride (Pt−AlPON) Catalysts. Consequences of Surface Hydrolysis and Heating Processes on the Structure

Consecutive heating/cooling cycles over a platinum aluminophosphate oxynitride (Pt-AlPON) catalyst with a high nitrogen content (17.8 wt %) have been studied by diffuse reflectance infrared spectroscopy (DRIFTS). Heating steps to 500 degrees C produces the desorption of part of the nitrogenous species of the catalyst (NE4+, NH3, -NH2, -NH-) as gaseous ammonia. During the treatment at room temperature, N-2 saturated with water produces a hydrolysis reaction that transforms part of the bulk nitride ions into NH4+ surface species. These species are easily removed from the catalyst surface during the next heating step. As a result of combined successive hydrolysis/heating processes, the catalyst loses practically all its nitrogen content, reaching a structure similar to that of its AlPO4 precursor.

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

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 AlPO 4 and NH 3 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 AlPO 4, AlPON local structure is pictured as a network of PO 4 and AlO 4 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 [PO 3N] and [PO 2N 2] building units are characterised below 7.2% N and above 11% N (w/w), respectively. Also terminal –PNH 2 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 –PNH 2 reaction either as a condensation around 230–240°C or through a reaction with water around 320–340°C. Condensation depends on –PNH 2 coverage and is the preferred decomposition mechanism in high nitrogen containing AlPON.

Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides

Download options Please wait... Article information DOI https://doi.org/10.1039/A904244J Article type Paper Download Citation Phys. Chem. Chem. Phys., 1999,1, 4493-4499 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides T. Blasco, A. Corma, L. Fernández, V. Forne′s and R. Guil-López, Phys. Chem. Chem. Phys., 1999, 1, 4493 DOI: 10.1039/A904244J To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Teresa Blasco Avelino Corma Lorenzo Fernández Vicente Forne′s Rut Guil-López

Diffuse reflectance infrared spectra and their relation to the thermal stability of aluminophosphate oxynitrides as a function of nitrogen content

Amorphous aluminophosphate oxynitrides (AlPON) solids with a variable nitrogen content (2.8, 3.6, 7.2, 11, 17.5 and 20%w/w) have been prepared by nitridation of AlPO 4 using gaseous NH 3. Their thermal stability below 500°C is investigated using diffuse reflectance infrared spectroscopy and mass spectrometry. Water and ammonia, coming from AlPON surface hydrolysis upon exposure to air, are desorbed around 150°C from sites involving Al–OH. At a higher temperature (350°C) terminal –PNH 2 groups are attacked by gaseous water to produce NH 3 and additional P–OH in tetrahedral co-ordination. There is a simultaneous surface reaction between –PNH 2 groups and –PO generating P–OH (tet) but no NH 3. Besides, highly nitrided AlPON samples suffers –PNH 2 condensation around 250°C to yield gaseous NH 3 in a process thermodynamically favoured but controlled by the coverage of –PNH 2 groups.

CO2 adsorption and surface basicity evaluation of aluminophosphate oxynitride (AlPON) catalysts

Aluminophosphate oxynitrides (AlPON) are new catalysts obtained by nitridation of AlPO4 showing a high surface area and an enhanced surface basicity. In this article, surface basicity is evaluated by CO2 adsorption and related to the nitrogen content. CO2 simultaneously adsorbs linearly and as bidentate carbonate and bicarbonate species on AlPON surface. Particularly strong basic centers involving hydroxyls linked to Al cations and in the vicinity of terminal –PNH2 groups are identified. However, the influence of nitrogen content on surface basicity of AlPON is mostly through the change in the number of sites rather than on the modification of their strength. Activity results obtained for AlPON in base-catalyzed reactions are related with their capability of adsorbing CO2.

Study of aluminophosphate oxynitride (AlPON) materials by X-ray photoelectron (XPS) and diffuse reflectance Fourier transform IR spectroscopy (DRIFTS)

A series of amorphous aluminophosphate oxynitrides (AlPON) have been obtained by nitridation of AlPO4 in a tubular furnace at 750 °C under a dry NH3 stream. Bulk nitrogen content is controlled by the reaction time and quantified by alkaline digestion with molten KOH. Samples have been analysed by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance IR spectroscopy (DRIFTS). XPS results indicate that nitrogen selectively replaces oxygen atoms bonded to phosphorus in the [PO4 ] tetrahedra of AlPO4 leading to a mixture of [POxN4–x] units in AlPON. Simultaneously, an Al2O3-type phase develops. Compositions obtained by XPS are in good agreement with those expected from bulk formulation. Nitridation reaction starts at the surface of AlPO4 by breaking P–O bonds and generating terminal P–NH2 . Once surface P–NH2 saturation is achieved (above 3.6 mass% N), bulk nitridation occurs. In nitrogen saturated AlPON samples (ca. 20 mass% N) the presence of a surface P3N5 phase is proposed to be responsible for the slight surface nitrogen enrichment observed. The presence of structural (–NH–) groups, isoelectronic to (–O–), and their growing concentration with nitridation time have been detected by DRIFTS. Diffuse reflectance IR spectroscopy also suggests the presence of cyclic (P–N–P) structures.

Study of the stability of AlPON catalysts in an aqueous environment

Aluminophosphate oxynitride (AlPON) stability is studied by dispersing the solid in pure water and analysing the product by X-ray photoelectron spectroscopy (XPS), diffuse reflectance infra-red spectra (DRIFTS), thermogravimetry (TG) and X-ray absorption near edge structure (XANES). The presence of phosphate ions and the absence of A1 3+ cations in the aqueous phase indicates that no dissolution but real hydrolysis of AlPON occurs. Upon hydrolysis, AlPON loses a quite significant amount of P and N from surface. The result is a nitrogenimpoverished surface phase in which aluminum keeps its original first co-ordination sphere. This new surface phase may be ascribed to either AlPO or AlPON with a lower nitrogen content. A third possibility, phosphorous oxynitride (PON), may not be discarded due to the similarity between its P N ratio and that of hydrolysed AlPON.

Diffuse Reflectance Infrared (DRIFTS) and Mass Spectrometry Study of Thermal Stability of Aluminophosphate Oxynitrides (AlPON)

Aluminophosphate oxynitrides (AIPON) are new materials showing a very interesting catalytic behaviour. In their synthesis, impregnation and calcination stages are involved. AIPON suffers surface hydrolysis and moderate thermal decomposition. We have analysed the influence of temperature combining diffuse reflectance (DRIFTS) and mass spectrometry. Nitrogen is eliminated as NH3 in two stages. The first one, at low temperature (100-130 degrees C), is accompanied by water and corresponds to NH3 desorption from Lewis and Bronsted sites. The second stage at 330 degrees C is due to terminal (-NH2) removal upon reaction with water.

ChemInform Abstract: Surface Basicity of a New Family of Catalysts: Aluminophosphate Oxynitride (AlPON).

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Influence of nitrogen content on the acid-base properties of aluminophosphate oxynitrides

Novel basic catalysts with high specific surface areas have been synthesized by activation under ammonia of an aluminophosphate oxide precursor. The nitrogen content as well as the acid-base properties depend on both time and temperature of nitridation. The conversion and reaction rate in Knoevenagel condensation are related to the nitrogen content.

Surface basicity of a new family of catalysts: aluminophosphate oxynitride (ALPON)

A new family of basic catalysts, amorphous aluminophosphate oxynitrides (AIPONs) with variable nitrogen content, have been synthesized by nitridation of amorphous AlPO4(AIPO). The samples were analysed by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance IR spectroscopy (DRIFTS). XPS indicates that nitrogen is preferentially bonded to phosphorus in the AlPON framework. Residual surface NH4+ ions coming from the nitridation reaction were used to evaluate the Brønsted acidity of these new catalysts. The decrease in the Brønsted acidity along the series is parallel to a shift of the P—O stretching to lower wavenumbers. Malonitrile–benzaldehyde condensation was employed as a test reaction to estimate the basicity of AIPON samples. The conversion trend observed also correlates with the decrease in the frequency of the P—O stretching. Consequently, the position of the P—O stretching reflects both the reduction of the Brønsted acidity and the enhancement of the basicity of the AlPON specimen.

Application of a new hydrogenated aluminophosphate oxynitride (ALPON) as a catalytic support for the one-step synthesis of methyl isobutyl ketone from acetone

A new hydrogenated aluminophosphate oxynitride (ALPON) obtained by nitridation of AlPO 4 can be used as a support to prepare a polyfunctional catalyst with both basic and metallic sites. Ni/ ALPON catalyst was effective for the low-pressure one-step methyl isobutyl ketone (MIBK) synthesis from acetone. The selectivity of the process depended on the temperature and time-on-stream of the hydrogen reduction treatment suggesting that selective MIBK production is achieved by a fine balance between basic and metallic sites.