Supports aluminophosphates

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. 

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 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. 

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. 

The in situ membrane growth technique cannot be applied using the zeolite-based ceramic porous membrane as support, under hydrothermal conditions in a solution containing sodium hydroxide. The high pH conditions will cause membrane amorphization and lead to final dissolution. Therefore, we tried to synthesize an aluminophosphate zeolite such as AlP04-5 [105] over a zeolite porous ceramic membrane. For the synthesis of the AlP04-5-zeolite-based porous membrane composite, the in situ membrane growth technique [7,13,22] was chosen. Then, the support, that is, the zeolite-based porous ceramic membrane, was placed in contact with the synthesis mixture and, subsequently, subjected to a hydrothermal synthesis process [18]. The batch preparation was as follows [106] ... 

In reporting the results of a spectroscopic study of aluminium phosphate in 1971, Peri drew attention to the isostructural nature of A1P04 and Si02 and the likely value of A1P04 as an adsorbent and catalyst support. Stable high-area A1P04 gels could readily be prepared in 1971, but at that time there was no indication in the open or patent literature that zeolitic forms of aluminophosphate could be synthesized. 

The synthesis of the fragment CpTi supported on a mesoporous aluminophosphate has been described the coordination mode of the CpTi(iv) fragment is as depicted in Scheme 414.994... 

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)... 

Besides MeAPO, several heterogeneous systems have been proposed for the oxidation of cydohexane vith various oxidants [2c], but almost all of them yield 01/ One as the main reaction products, with AA being only a minor product. Heterogeneous catalysts can be either oxides or metal cations and complexes incorporated on inorganic matrixes, such as active carbon, zeolites, aluminophosphates or conventional supports such as alumina and silica. The activity of these systems is greatly affected by the choice of solvent, which determines the polarity of the medium. In addition, the hydrophobicity of the support is important, since a hydrophobic environment rapidly expels the oxidized products from the reaction zone. When oxygen is used as the oxidant, these systems often need small amounts of hydroperoxides as co-catalysts. 

Amorphous alumincphosphates have been used as catalysts or catalyst supports for a number of years. Canpelo and his coworkers have shewn that they can be promoted by alkali metals or F ions (Ref. 25-26), but they behave like the amorphous aluminosilicates in being non-selective. The unsubstituted aluminophosphates have essentially no catalytic activity although they do dehydrate methanol to dimethyl ether (ref. 11). They can, hewever, be used as catalyst supports, and Coughlin and Rabo (ref. 27) have considered irtpregnated AlP04 s as supports for Fischer-Tropsch catalysts. 

The use of other supports such as aluminas or aluminophosphates produces a similar Cr(VI) saturation behavior, although the exact saturation levels may differ somewhat for each temperature. Addition of promoters, to improve activity or modify polymerization behavior, such as fluoride, sulfate, phosphate, titania, etc., can also affect the thermal stability of the Cr(VI) species. These subjects are addressed separately in later sections. 

Like Cr/alumina, Cr/AIPCL is considerably more responsive to H2 as a chain-terminating agent than is Cr/silica [332], Figure 163 is a plot showing the HLMI increase with H2 addition, as a function of the P/Al ratio in the support. Although 0.35 MPa of H2 added to the reactor doubles the HLMI from polymer made with Cr/silica, there is around 40-60-fold improvement in HLMI when Cr/aluminophosphate is the catalyst. However, the response to H2 is not much affected by the P/Al ratio of the support. 

The Cr/aluminophosphate catalysts exhibit a "fast kinetics profile relative to the profile of Cr/silica. That is, the polymerization rate of Cr/AIPO4 develops almost immediately with no induction time [637], The polymerization rate rises for about 10-20 min, and then declines during the rest of the 1-2-h run. Figure 168 shows an example of the reaction kinetics, when the catalyst had a P/Al atomic ratio of 0.8 and was activated at 700 °C. The rapid development of polymerization suggests that the initiation steps are faster on Cr/aluminophosphate catalysts than on Cr/silica catalysts. This difference could indicate faster reduction, or alkylation, or that the redox by-products, such as formaldehyde, are more quickly removed from the reaction diluent. These aluminophosphate supports are usually better adsorbents for polar compounds than silica activated at 700 °C, and this difference may contribute to the kinetics profile. 

Although there are many differences between chromium oxide catalysts and the organochromium catalysts, when they are bonded to the support, organochromium catalysts usually display a similar, but exaggerated, MW response in the polymer produced relative to what is observed with chromium oxide catalysts. For example, the MW of polymer produced with each type of catalyst usually decreased as the support calcination temperature was raised. Similarly, when both chromium oxide and the organochromium compounds were deposited onto aluminophosphate supports, they always yielded lower-MW polymer as the amount of phosphate in the support was raised. 

The activities of diarenechromium(O) compounds are particularly sensitive to the support [650-653]. For example, dicumenechromium(O) provides little or no activity when deposited onto calcined silica from hexane at temperatures below 100 °C. Deposited onto aluminophosphate or fluoride-treated alumina at 25 °C, however, it can be quite active. Alternatively, if the silica is first impregnated with acidic compounds or ions (e.g., Al, V, H3PO4, H2SO4) and then calcined, the dicumenechro-mium(0) is activated to produce a polymerization catalyst [648]. Numerous other reagents also "activate the silica in this way. Even some acidic carbon blacks form active catalysts when treated with dicumenechromium(O) at 25 °C. 

Bimodal Polymer from Aluminophosphate-Supported Catalysts... 

Cr(DMPD)2 is merely one of many organochromium compounds that, when deposited on aluminophosphate supports, give polymers having a bimodal MW distribution [297,640]. This behavior is typical of catalysts made with all the organochromium compounds we have investigated, with the exception of chromocene (more in Section 16.9). Figure 190 shows the MW distribution of polymers obtained from other... 

The addition of phosphoric acid to alumina, followed by calcination at 600 °C and deposition of an organochromium compound, also resulted in polymers having a bimodal MW distribution like the polymers made from coprecipitated aluminophosphates. In one experiment, even silica was treated with H3PO4 and calcined at 250-500 °C. When this support was treated with organochromium compounds, such as Cr(DMPD)2, the resultant catalyst also produced polymers having two contributions, one of which was the same low-MW product peak associated with phosphate. The data in Figure 191 present an example of this experiment. 

An example is shown in Figure 192. Two samples of an aluminophosphate support with a P/A1 atomic ratio of 0.4 were calcined at 300 and at 700 °C, then treated with dicumenechromium(O). These catalysts were tested for ethylene polymerization and the resultant polymers were analyzed. The low-MW peak was found to be larger when the support had been calcined at 700 °C. A third peak, indicative of very high-MW polymer, was also present when the support was calcined at only... 

FIGURE 199 MW distributions of polymers made with aluminophosphate support (0.9 P/Al) that was calcined at 600 °C and then impregnated with open-ring and closed-ring chromocenes. 

For example, the trimethylsilylmethyl derivative of chromium(II) is well suited to this purpose. Although it produces a highly active catalyst on aluminophosphate or fluoride-treated alumina supports, it is barely active on silica by itself. Nevertheless, when added to silica-supported Cr(II) oxide, the result is a highly active catalyst that produces branched polymer. In addition to reacting with silanol groups, the chromium alkyl may also react with chromium oxide to again produce mono-attached species, such as is shown in Scheme 44. Coordination between one Cr atom and its chromium or oxide neighbor also seems likely. 

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