Supported acids

Pt-Re-alumina catalysts were prepared, using alumina containing potassium to eliminate the support acidity, in order to carry out alkane dehydrocyclization studies that paralleled earlier work with nonacidic Pt-alumina catalysts. The potassium containing Pt-Re catalyst was much less active than a similar Pt catalyst. It was speculated that the alkali metal formed salts of rhenic acid to produce a catalyst that was more difficult to reduce. However, the present ESCA results indicate that the poisoning effect of alkali in Pt-Re catalysts is not primarily due to an alteration in the rhenium reduction characteristics. 

Here we wish to report that the support acidity, investigated through IR spectroscopy of adsorbed CO, allows one to tune the selectivity towards different products in the hydrogenation of citral over Cu catalysts. 

By comparing gastric absorption at pH 3 and pH 6 where surface area and factors other than pH are constant, one sees that the general principle is supported acid drugs are more rapidly absorbed from acidic solution, whereas basic drugs are more rapidly absorbed from relatively alkaline solution. 

Palaniappan S, Shekhar RC (2004) Synthesis of 7-Hydroxy-4-methyl coumarin using polyaniline supported acid catalyst. J Mol Catal A Chem 209 117-124... 

Phillips H2/CO = 2 needed due to coking of the catalyst caused by high support acidity or high temperatures in particles resulting from high initial ... 

Figure 3.17 Amine catch and release purification with a silica-supported acid.

This section describes catalytic systems made by a heterogeneous catalyst (e.g., a supported metal, dispersed metals, immobilized organometaUic complexes, supported acid-base catalysts, modified zeolites) that is immobilized in a hydrophilic or ionic liquid catalyst-philic phase, and in the presence of a second liquid phase—immiscible in the first phase—made, for example, by an organic solvent. The rationale for this multiphasic system is usually ease in product separation, since it can be removed with the organic phase, and ease in catalyst recovery and reuse because the latter remains immobilized in the catalyst-philic phase, it can be filtered away, and it does not contaminate the product. These systems often show improved rates as well as selectivities, along with catalyst stabilization. 

The hydrogenation of nitrobenzene and nitrosobenzene are complex and a range of factors can influence by-product reactions, e.g. hydrogen availability, support acid/base properties (13,14). In this study we have examine competitive hydrogenation between nitrobenzene, nitrosobenzene and azobenzene. This methodology coupled with the use of deuterium has further elucidated the mechanism of these reactions. 

The several attempts, published in the literature, to describe the kinetics of vapour phase olefin (mostly ethylene) hydration can be classified into two groups according to the basic model used. One model, for reactions catalysed by phosphoric acid supported on solids, treats the kinetics as if the process were homogeneous acid catalysis and takes into account the acid strength of the supported acid. Thus, a semiempirical equation for the initial reaction rate [288]... 

In modern industrial ethyl alcohol plants, the compound is produced in two principal ways (I) by direct hydration of ethylene, or (2) by indirect hydration of ethylene. In the direct hydratiun process. H 0 is added to ethylene in the vapor phase in Lhe presence of a catalyst CH CH 4- H 0 CHiCHiOH. A supported acid catalyst usually is Used. Important factors affecting the conversion include temperature, pressure, the H 0/CH CH ratio, and the purity of (he ethylene, Further, some byproducts are formed by other reactions taking place, a primary side reaction being the dehydration of ethyl alcohol into diethyl ether 2C HjOH (C Hs)jO + HiO. To overcome these problems, a large... 

Most traditional methods use hydrochloric acid solutions as the acid reagent for the hydrolysis or alcoholysis of fi-lactams. Methanolic solutions of trimethylchloro-silane are able to generate HCI in situ, and the trick has been employed successfully for the methanolysis of fi-lactams in a route to aspartic acid derivatives [60, 61] and 2-oxazolidinones[62], respectively. Recently the use of silica-supported acid reagent has been reported as a convenient alternative. The reagent (Si02-Cl) prepared from admixing silica gel and SOCl2 in dichloromethane and subjected to dryness, is able to run the methanolysis of (1-lactams at room temperature in 20 min [63]. 

Cumene is industrially produced by propylating benzene over supported acidic catalysts such as phosphoric acid. On the other hand, the largest-scale single industrial alkylation process—that is, ethylation of benzene with ethylene—is still carried out to a significant degree in the liquid phase using acid catalysts since ethylene is less polar than propylene, it requires more forcing conditions in the protolytic initiation step [Eq. (5.71)]. 

The possible catalyst components have been classified into three groups metal oxide support, acidity enhancers, and promoters. As metal oxide supports, y-Al203, Zr02, Ti02 have been considered. Acidity enhancers SO4, BOf, POl and WO were used, for which the content of SO4-, BOf, PO ranged from 0.5-6 wt% and of WO from 0.5-36%. For promoters (water and thioresistance) the effect of Pt, Ce, Pd, Sn, Ni, Mn and Nb was explored (0.5-6 wt% for each metal). Each material contains one support, one acidity promoter and at least two metallic promoters, of which one is Pt (0.5 wt%). 

An analogous procedure has been adopted for the formation of tertiary amines, which utilised a polymer supported acid chloride 12 to scavenge the excess secondary amine, (Table... 

In this direct hydration process, a supported acid catalyst usually is used. Important factors affecting the conversion include temperature, pressure, the water/ethylene ratio, and the purity of the ethylene. Further, some by-products are formed by other reactions taking place, a primary side reaction being the dehydration of ethyl alcohol into diethyl ether ... 

Scheme 33 An example of the protection of an aldehyde 116 as its dimethyl acetal 127 performed using a solid-supported acid catalyst under EOF-driven continuous flow.

Furthermore, using the polymer-supported acid-base ambiphilic catalyst of IrH5(P-i-Pr3)2 the multi-step reaction using the conventional acid and base can be carried out as a one-pot reaction under neutral conditions. A series of gluralimides that are key compounds in medicine can be prepared readily [2] as shown in Scheme 12. 

Tempesti et al. (238) used organoboronic acids (lib) for the immobilization of Mo(VI). It is assumed that the interaction of Mo occurs through a condensation with the supported acid. Reactions reported with the bimetallic material showed an activity and selectivity comparable to those of homogeneous bimetallic analogs. In a comparable approach, Mo was anchored to immobilized phosphorus-containing acids, for example, of cellulose phosphate (11c) (239) or phosphonate resins (11a) (240). 

In Chapter 9 DFT calculations are performed in order to obtain further insight in the support induced differences in electronic properties relate to differences in the chemisorption properties of adsorbates like H, CH3 and CH2. The influence of the support acid/base... 

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