Catalysts aluminophosphates

DeNOx catalyst, aluminophosphate DeNOx catalyst, Fe-zeolites DeNOx catalyst, MCM-22 DeNOx on Cu-MFl DeNOx SCR... 

There are numerous stmctures that are similar to 2eofites, such as aluminophosphate molecular sieves, AlPOs, but these have not found catalytic apphcations. Zeofites can be modified by incorporation of cations in the crystalline lattice which are not exchangeable ions, but can play catalytic roles. For example, sificahte, which has the stmcture of ZSM-5 but without Al, incorpora ting Ti in the lattice is a commercial catalyst for oxidation of phenol with H2O2 to give diphenols the catalytic sites may be isolated Ti cations (85). 

An example of novel basic catalysts the aluminophosphate oxynitrides or "AlPONs"... 

New aluminophosphate oxynitrides solid basic catalysts have been synthesised by activation under ammonia of an AIPO4 precursor. When the nitrogen content increases, XPS points out two types of nitrogen phosphorus bonding. The conversions in Knoevenagel condensation are related to the surface nitrogen content. Platinum supported on aluminophosphate oxynitride is an active catalyst for isobutane dehydrogenation. 

Four mmoles of malononitrile and benzaldehyde were introduced in a batch stirred tank reactor at 323 K with toluene as solvent (30 ml). Then 0.05 g of aluminophosphate oxynitride was added. Samples were analysed by gas chromatography (Intersmat Delsi DI200) using a capillary column (CPSilSCB-25 m). Care was taken to avoid mass or heat transfer limitations. Before the reaction no specific catalyst pretreatment was done. 

To evaluate properties of basic catalysts, the Knoevenagel condensation over aluminophosphate oxynitrides was investigated [13]. In this reaction usually catalysed by amines, the solid catalysts function by abstraction of a proton from an acid methylene group, which is followed by nucleophilic attack on the carbonyl by the resultant carbanion, re-protonation of oxygen and elimination of water. The condensation between benzaldehyde and malononitrile is presented below. 

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. 

The liquid-phase autoxidation of cyclohexane is carried out in the presence of dissolved cobalt salts. A lot of heterogeneous catalysts were developed for this process but most catalysts lacked stability. The incorporation of cobalt ions in the framework of aluminophosphate and aluminosilicate structures opens perspectives for heterogenization of this process. CoAPO (cobalt aluminophosphate) molecular sieves were found to be active heterogeneous catalysts of this oxidation.133 Site isolation was critical to get active catalysts.134... 

Fig. 10. X-ray elemental map in the electron microscope of metal-substituted aluminophosphate (MAPO-36 (with M = Zn)) catalyst. The map shows a uniform distribution of the elements in the sample.

The catalysts for xylene isomerization with EB dealkylahon are dominated by MFI zeolite. The de-ethylation reaction is particularly facile over this zeolite. There have been several generations of catalyst technology developed by Mobil, now ExxonMobil [84]. The features in their patents include selectivation and two-catalyst systems in which the catalysts have been optimized separately for deethylation of EB and xylene isomerization [85-87]. The crystallite size used for de-ethylation is significantly larger than in the second catalyst used for xylene isomerization. Advanced MHAI is one example. The Isolene process is offered by Toray and their catalyst also appears to be MFI zeoUte-based, though some patents claim the use of mordenite [88, 89]. The metal function favored in their patents appears to be rhenium [90]. Bimetallic platinum catalysts have also been claimed on a variety of ZSM-type zeolites [91]. There are also EB dealkylation catalysts for the UOP Isomar process [92]. The zeolite claimed in UOP patents is MFI in combination with aluminophosphate binder [93]. 

The use of transition-metal-substituted aluminophosphates (AIPOs) as catalysts for free-radical auto-oxidations of hydrocarbons, a type IIaRH reaction, has been explored by several groups [60-62]. In a series of elegant contributions, Thomas... 

The aluminophosphate molecular sieve, AIPO4-5, itself has limited potential as catalyst, since its stnjcture is neutral and has neither catbn exchange capacities nor acidity [1-3]. There are two possibilities for utilizing the molecular sieves one is rrwdification of the framework by substitution of metal atoms such as silicon [3-6] and/or transition metals [5-11], and the other is introducing active site by impregnation. 

The aluminophosphate molecular sieves have an interesting property for potential use as catalyst supports, due to their excellent thermal stabilities and unique structures. AIPO4-5 is known to retain its structure after calcination at 1000°C and have uni-directional channels with pore size of 8 A bounded by 12-membered rings [2]. To utilize molecular sieves as catalyst support, chemical interactions between the molecular sieve and active component, chemical stabilities, and surface structures must be determined. However, iittle attempt has been made to clarify the surface structures or properties of catalytically active components supported on the aluminophosphate molecular sieves. 

Since the synthesis of aluminophosphate (AIPO4) molecular sieves (Wilson et al 1982), other novel catalyst materials have been developed by the... 

Antonelli and co-workers have recently demonstrated that room temperature stoichiometric ammonia synthesis is possible with their mesoporous titanium and niobium oxide catalysts. In this study, they proposed that the ammonia species are formed via the reaction activated nitrogen with the underlying moisture of the support. Reversible, inter-conversion of and NH2 species via exposure to moist air for aluminophosphate oxynitride catalysts has been observed by FTIR and XPS by Marquez and co-workers. There has been a lot of interest in the literature in the development of novel routes for the low temperature stoichiometric conversion of nitrogen to ammonia, e.g.. However, in principle this could be realised by the nitridation of Li, followed by hydrolysis, although the kinetics would be very slow. 

Catalysis. - Aluminophosphate molecular sieves (A1PO) form a family of synthetic zeotypes, containing many three dimensional framework structures. Metal substituted aluminophosphates (MAPO) have important applications as catalysts and HFEPR has been used to determine the catalytically active sites. Two very detailed papers on various MAPO have been reported recently22,23 using both echo-detected HFEPR at 95 GHz and 3H and 31P ENDOR. 

Pd-containing aluminophosphate molecular sieves have been used to carry out crossed aldol condensations between an aldehyde and a ketone by using a 0.5 % Pd/ MnAPSO-31 catalyst in a vapour-phase fixed bed reactor.[14] Thanks to the excess of the ketone with respect to the aldehyde (4 1), it is possible to get high selectivity to the desired product, i.e. 70 % of heptan-2-one from n-butyraldehyde and acetone and 89 % of pentan-2-one from acetaldehyde and acetone, the major by-product being, in both cases, MIBK from acetone self-condensation. 

The method of choice for the synthesis of unsaturated arylsulfones is the Knoevenagel condensation of arylsulfonylalkanes with aldehydes. The condensation between aldehydes and phenylsulfonyl acetonitrile, has been performed in the presence of various solid base catalysts (MgO, Cs-exchanged X zeolite, Al-Mg mixed oxide, and aluminophosphate oxynitride) at 373 K in the absence of solvents.1641 The most active catalyst for this transformation was the aluminophosphate oxynitride, but MgO and the Al-Mg mixed oxide also were found to have excellent activity, yielding the Knoevenagel adduct in yields of 86 and 71 %, respectively, after 2 h in a batch reactor. 

Generally, the issue of whether a truly solid Cr catalyst has been created for the aforementioned reactions is unresolved. This point is illustrated most clearly by all the work that has been devoted, in vain, to Cr molecular sieves (55-57). Particularly the silicates Cr-silicalite-1 and Cr-sihcahte-2 and the aluminophosphate Cr-AlPO-5 have been investigated. These materials have been employed, among others, for alcohol oxidation with t-BuOOH, for allylic (aut)oxidation of olefins, for the autoxidation of ethylbenzene and cyclohexane, and even for the catalytic decomposition of cyclohexyl hydroperoxide to give mainly cyclohexanone ... 

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