Silica-supported phosphoric acid

As the loading of STA on the catalyst support is decreased, incomplete anhydride conversion is observed and significant hydrolysis of the anhydride to form iso-butyric acid is observed (Table 2). Use of silica supported phosphoric acid results in lower ketone yields and significant hydrolysis of the iso-butyric anhydride. Blank reactions (catalyst and anhydride, 90°C, 30 min) indicates that hydrolysis of anhydride is observed in the presence of these catalysts and may result from either dehydroxylation of the silica support or residual water in the catalyst, ffowever this reaction is slow (42%STA/silica, 44% conversion and 70%P[3PO4/silica, 86% conversion respectively). 

Short-chain olefin oligomerization can provide gasoline, middle distillate, or lubricant oils. Typical acids used to catalyze these reactions are now solid-type catalysts such as silica-supported phosphoric acids or zeolites. 

In the case of cumene, UOP introduced a liquid-phase process in the 1940s to compete with aluminum chloride technology. The catalyst is SPA, a solid phosphoric acid catalyst in which the phosphoric acid is supported on silica. Many improvements were made to the SPA catalyst and process over the years, leading to 70% of the world s cumene being produced with SPA by the 1990s. In 1996, UOP introduced the Q-Max process, featuring a zeolitic catalyst and operating in the liquid phase (21). A new Q-Max catalyst, QZ-2001 , was introduced in 2001. 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

The reaction of u-butenes to give isobutylene is cataly zed by a wide variety of solid acids but requires relatively high temperature. Typical catalysts include alumina, halogenated alumina, amorphous silica-alumina, supported phosphoric acid, and supported tungsten or molybdemmi oxide. The most characteristic features of the skeletal isomerization of n-butenes... 

Supports and Catalysts. The preparation of the supports used in this study was discussed in detail elsewhere. The two phosphate supports, A O AIPO and 4MgO lSA O 10A1P0 were co-precipi-tated using the necessary nitrate salts, phosphoric acid, and ammonium hydroxide at a fixed pH (.] ) Niobia was precipitated by adding ammonium hydroxide to a methanolic solution of niobium chloride (8). The niobia-silica support was prepared by impregnating SiO (Davison 952) to incipient wetness with a hexane solution of niobium ethoxide. The sample was then dried and calcined to obtain a homogeneous surface phase oxide (9). 

Supported the catalysts used in this case are silica aluminas, phosphoric acid deposited on kieselguhr, or boron trifluoride deposited on modified alumina. 

Shaterian, H.R., Hosseinian, A., Ghashang, M. 2009. Reusable silica supported poly phosphoric acid catalyzed three-component synthesis of 2H-indazolo[2,l-f>]phthalazine-trione derivatives. ARKLVOC (ii) 59-67. 

The phosphate incorporation in silica supports is often achieved by impregnation with phosphoric acid [8] but in that case, the phosphate ions are only located at the pore surface. In the present work, supports with variable composition in the system Si02 - AlPO - AI2O3 are prepared by coprecipitation of all the support constituant. 

A wide variety of bases, nucleosides and nucleotides have been separated using porous layer bead ion exchangers. A representative chromatogram of the separation of ribonucleoside mono-phosphoric acids from the work of Smukler ( ) is shown in Figure 4. Recently, ion exchangers chemically bonded to small particle diameter (> 10 ym) silica have been successfully applied to the separation of nucleic acid constitutents (37). The rapid separations using such supports undoubtedly mean that they will find increasing use in the future. 

The reactor is a vessel with beds of solid catalyst. Most commercial processes use a catalyst called kieselguhr, which is phosphoric acid deposited on a silica/alumina pellet. Because of the weight of the pellets, supported beds at multiple levels in the vessel are used so the bottom layers wont be crushed.-... 

Ethylene is compressed to 1000 psi, mixed with water, and heated to 600°E The two reactants, both. in, a vapor phase, are fed down a catalyst-filled reactor. The catalyst is phosphoric acid (H3PO4) absorbed onto a porous inert support (usually diatomaceous earth or silica gel). 

Ethylamines. Mono-, di-, and triethyl amines, produced by catalytic reaction of ethanol with ammonia (330), are a significant oudet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, silica, or silica—alumina.. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethyl amine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give IV-ethylpiperidine [766-09-6] (332). 

For commercial processes, formed supports are more useful. Compared with other supports, fumed oxide supports showed new catalytic effects [41]. Some intensively investigated applications for these supports are abstracted in the following. SiC>2 pellets have been successfully introduced in a new generation of precious metal supports in vinylacetate monomer production [42]. This resulted in better selcctivities and an up to 50% higher space-time yield compared with supports based on natural alumo-silicates. In alkene hydration fumed silica pellets serve as a support for phosphoric acid. In this case, an increased catalyst lifetime and a higher space-time yield were observed [43]. Pyrogenic TiC>2 powder can be used as a starting material for the manufacture of monolithic catalysts [44] for the selective reduction of NOv with ammonia. 

Traces of unreacted silica (Si02) in the SiC will produce a fluffy white precipitate, about which little is known. Certainly it is known that when hot concentrated phosphoric acid is in contact with glass hardware, the rapid formation of a fluffy gelatinous white precipitate is seen. From an X-ray diffraction analysis of the precipitate from operating fuel-cells, it was determined that the principal component was Si3(P04)4, although metallographic and SEM/EDS analyses support the presence of the other silico-phosphate complexes in varying amounts. 

Various kinds of oxide materials, including single oxides, mixed oxides, molybdates, heteropoly-ions, clays, and zeolites, are used in catalysis they can be amorphous or crystalline, acid or basic. Furthermore the oxides can be the actual catalysts or they can act as supports on which the active catalysts have been deposited. Silica and alumina are commonly used to support both metals and other metal oxide species. Amorphous silica/alumina is a solid acid catalyst, it is also used as a support for metals, when bifunctional (acid and metal) catalysis is required, e.g., in the cracking of hydrocarbons. Other acid catalysts are those obtained by the deposition of a soluble acid on an inert support, such as phosphoric acid on silica (SPA, used in the alkylation of benzene to cumene. Section 5.2.3). They show similar properties to those of the soluble parent acids, while allowing easier handling and fixed bed operation in commercial units. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert silica or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acrylic acid were prepared from bismuth, cobalt, iron, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic silicic acids. Preferred second-stage catatysts generally7 are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity7 and productivity7 (39,45,46). 

The use of silica brick in chemical-resistant masonry is limited, because of high cost, to applications requiring a high degree of chemical resistance where traditional acid brick cannot be used, such as concentrated phosphoric acid free of fluorine. Silica brick, however, cannot be used in strong alkaline exposures or any concentrations of hydrofluoric acid. As with acid brick, its main function is to provide a barrier to abrasion and to protect other membranes or structures from chemical attack. Because brick porosity may be as high as 16%, silica brick is backed by an impermeable material and a support structure. 

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