Oxynitride phosphates

A novel basic support and catalyst have been prepared by activation of aluminium phosphate with ammonia. Fine control of time and temperature allows to adjust the 0/N ratio of these oxynitride solids and thus to tune the acid-base properties. The aluminophosphate oxynitrides are active in Knoevenagel condensation, but a basicity range can not yet determined. Supporting Pt or Pt/Sn on AlPONs allows to prepare catalysts that are highly active and selective in dehydrogenation reactions. 

Following ternary phosphorus oxynitrides, which involve only phosphorus as a cationic element, quaternary and higher oxynitrides will be described. A number of other solid-state PON compounds are under study and, when considering the richness of the phosphate crystal chemistry and the additional degree of freedom given by the presence of nitrogen, it is very probable that many new nitridooxophosphate compositions will be found in the near future. 

To conclude, it is pleasant to consider the regular evolution from 0 to 4 of the number of bridging atoms in the following series of phosphate compounds, which is nicely completed by the phosphorus oxynitride PON (237). 

It must also be pointed out that other basic materials have been synthesized which present no surface oxygens and hydroxyls, but other types of active sites whose exact nature remains controversial. These type of solids are, for example, impregnated imides and nitrides on zeolites and alumina, amorphous oxynitrides obtained by treatment with ammonia or aluminium orthophosphate, zirconium phosphate, aluminium vanadate or galloaluminophosphate, and KF supported on alumina/1,3,41 One of the main advantages of these solids with respect to basic oxides is their resistance to carbon dioxide or water. 

The application of P NMR to structural studies of alkali and alkaline earth phosphate and aluminophosphate glasses, fluorophosphate glasses and phosphorus oxynitride glasses has been reviewed by Kirkpatrick and Brow (1995). 

M-SiAlON systems contain a combination of M atoms. Glass formation is found to be easier, more the types of atoms present in the nitrided glasses. Several simple silicates and phosphates which are nitrided have provided much insight into the stmcture of oxynitride glasses. 

Non-oxides KF supported on alumina Oxynitride (silicon oxynitride - SiON, aluminophosphate oxynitride -AlPON, zirconophosphate oxynitride - ZrPON) Lanthanide imide and nitride on zeolite Modified natural phosphate (NP) (calcined NaN03/NP)... 

Liquid phase aldol condensation reaction between heptanal and benzaldehyde is studied over two series of oxynitride catalysts aluminium phosphate oxynitrides AlPON and mixed aluminium gallium phosphate oxynitrides AlGaPON , with increasing nitrogen contents (0-14 wt.% for AlPON and 0 - 16 wt. % for AlGaPON ). The main products are jasminaldehyde and 2-pentyl-2-nonenal. Jasminaldehyde is formed via the cross-aldol condensation reaction between heptanal and benzaldehyde and 2-pentyl-2-nonenal is formed via the self-condensation reaction of heptanal. 

The gas-solid reaction between an amorphous precursor (of the phosphate-type in the present study) and flowing ammonia is a critical step in the preparation of oxynitride catalysts, active and selective for base-catalysed reactions [1]. 

According to Ae proposed mechanism (Scheme 1), the role of the weak basic sites (-NHx species over oxynitrides and basic oxygen or hydroxyl groups on the phosphate precursors) is to activate heptanal (I) and the role of the acid sites is to activate the carbonyl function of benzaldehyde (II). 

For the three tested catalysts, the addition of tripropylamine or benzoic acid in the reactor decreases the reaction rate. The decrease of the heptanal conversion measured after 60 min is quite significant. It decreases, for instance, from 66% to 18% over AIPO in the presence of tripropylamine, and from 66% to 32% over the same catalyst in the presence of benzoic acid. This indicates the participation of basic as well as acid sites to the reaction, over both phosphate precursors and oxynitrides. 

The effect of the poisons on the jasminaldehyde selectivity is less obvious, and discussing it seems hazardous. Indeed, we do not possess, at this stage, models at the atomic scale of the conjugated acid-base site pairs over the amorphous phosphates or their corresponding oxynitrides. Hence we can not assess whether adsorption of tripropylamine on an acid center prevents the adsorption of a reactant molecule on a neighboring basic center and reciprocally for benzoic acid. 

We showed, over two different series of Al(Ga)PON oxynitrides catalysts, that the nitridation of phosphate precursors has a positive effect on the selectivity to jasminaldehyde for the mixed aldol condensation reaction of heptanal with benzaldehyde. The influence of nitridation on the product distribution was interpreted in terms of changes in the relative density of acid and basic sites on the catalyst surface. Decreasing the acidity and increasing the basicity through nitridation enhances the simultaneous activation of benzaldeyde and heptanal and favors the cross condensation reaction between those two aldehydes, rather than the self-condensation of heptanal. 

Here we can cite aluminovanadate oxynitrides (VAION) (ref 2 in [132]). niirided phosphates ZrPON [133, 134] and AlPON [135-140] and mixed nitrided... 

Compared with oxide-, boride-, sulfide-, or phosphate-based phosphors, the study of oxynitride and nitride phosphors is at a very early stage. However, a variety of oxynitride and nitride materials with promising luminescent properties have been discovered recently [290-292]. 

Molecules of PNO can be obtained by co-condensation of O3 and PN in a noble gas matrix at low temperature [23]. Like PN(NH), (Chapter 7.2) it has a cristobalite-type crystal structure and can be obtained from P3N5 and ammonia. Solid oxynitrides are of interest because of their relationship to the condensed phosphates (Chapter 5.7). 

The so-called oxynitride glasses can be obtained by melting phosphate salts in an atmosphere of ammonia, or alternatively by melting a nitride such as Mg3N2 with sodium metaphosphate. 

Phosphorus oxynitride (PON) is the name for a family of closely related materials that have been around for over 100 years. They are not well known but are thermally very stable and may be considered as future flame retardants and for intumescent formulations since PON is analogous to ammonium polyphosphate. It can be made from inexpensive starting materials such as ammonium phosphate, melamine phosphate or urea phosphate just by prolonged and intensive heating. 

The synthesis of aluminophosphate oxynitride (ALPON) was also reported (67,68). ALPONs are prepared by heating aluminium phosphate under flowing ammonia up to 1073 K. ALPONs are active for the Knoevenagel condensations of... 

Nitridation of aluminium phosphate with pure 1 3 at temperature up to 800 C allows the preparation of aluminium phosphate oxynitride AlPON. 

Condensed phosphoramides with linear, cyclic, or cross-linked structures are produced by the reaction of POCI3 with ammonia. The higher molecular weight products are insoluble in water and on fnrther heating are converted to a cross-linked insoluble polymer, phosphorus oxynitride (PON)j (25). Phosphorus oxynitride can be made by prolonged heating of melamine phosphates (26), urea phosphate (26), or ammonium phosphate imder conditions where ammonia is retained (27). Phosphorus oxynitride is an effective flame retardant in those polymers, such as nylon 6, which can be flame retarded by exclusively char-forming condensed-phase means. However, phosphorus oxynitride is ineffective (at least by itself) in those... 

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