Catalyst uses in the hydrogenation

The platinum catalyst used in the hydrogenation was expensive and selectivity was variable. 

The nickel catalyst used in the hydrogenation of natural oils and edible fats is a special example of a catalyst which is transported in a protected state. In this case, the catalyst is protected by encapsulation in solid fat. The fat melts when the catalyst is introduced into the reactor, so releasing the active phase. Particular care must be taken to control the temperature during the transport and handling of this material. 

Poisoning is not always bad. There are situations where a catalyst is intentionally poisoned to decrease activity towards an undesirable reaction. In the hydro-desulfurization and -demetallization of a petroleum feedstock the catalyst is presulfided prior to introducing the feed to decrease its activity and minimize cracking reactions that will produce unwanted gases. Another is the use of ammonia to slightly poison a Pt catalyst used in the hydrogenation of fats and oils to decrease undesirable oversaturation. 

Spent technical palladium catalysts used in the hydrogenation of polyaromatic ketones were studied by INS to determine the surface... 

Some of the experimental results are presented in Fig. 2. The catalysts used in the hydrogenation reaction were from the same batch and the raw material (sitosterol) used was also the same. The main product was sitostanol, while sitostanone (2 in Fig. 1) was obtained in inferior quantities (below 1%). 

It should also be mentioned that in addition to the presence of Lewis-acid type surface entities there is another requirement for the preparation of selective catalysts used in the hydrogenation of a,p-unsaturated aldehydes. In this reaction both the adsorption of the substrate via its olefinic double bond and the re-adsorption of the formed crotylalcohol should be suppressed in order to increase the selectivity for the formation of the unsaturated alcohol. 

Table 27 Average crystallite size and estimated distribution of copper species in the catalysts used in the hydrogenation of dodecanoic acid (Reproduced from ref. 257 with permission)...

The reduction of the carbonyl group (and related functionalities) by catalytic methods has been successfully achieved by a number of methods. Rhodium and ruthenium complexes are the most popular catalysts used in the hydrogenation of ketones. While most catalyst systems of this type require the presence of additional chelating functionality on the substrate the recent development of highly active ruthenium(diamine) complexes allows the reduction of simple unfunctionalised ketones. Ruthenium catalysts have also been applied, with much success, to the catalytic asymmetric transfer hydrogenation of ketones in the presence of alcohols or formate. 

Alditols - A review on homogenous catalysts used in the hydrogenation of aldoses with emphasis on mechanistic aspects of their activity and modes of their deactivation has appeared, and the hydrogenation of D-fructose to D-mannitol has been described using ruthenium molecular sieves modified with chiral ligands as catalysts. ... 

It has been shown above that monometallic platinum catalysts used in the hydrogenation of crotonaldehyde usually produce the saturated aldehyde (Coloma et al., 1996). It may be possible to improve the selectivity of the process toward the hydrogenation of the carbonyl bond, by addition of a second metal. When the second metal is tin, there are three aspects of interest ... 

All the double bonds in naturally occurring fats and oils have the cis configuration. The catalyst used in the hydrogenation process... 

The catalyst used in the production of maleic anhydride from butane is vanadium—phosphoms—oxide (VPO). Several routes may be used to prepare the catalyst (123), but the route favored by industry involves the reaction of vanadium(V) oxide [1314-62-1] and phosphoric acid [7664-38-2] to form vanadyl hydrogen phosphate, VOHPO O.5H2O. This material is then heated to eliminate water from the stmcture and irreversibly form vanadyl pyrophosphate, (V(123,124). Vanadyl pyrophosphate is befleved to be the catalyticaHy active phase required for the conversion of butane to maleic anhydride (125,126). 

The catalysts used in the process are essentially nickel metal dispersed on a support material consisting of various oxide mixtures such as alumina, silica, lime, magnesia, and compounds such as calcium aluminate cements. When the catalyst is made, the nickel is present as nickel oxide which is reduced in the plant converter with hydrogen, usually the 3 1 H2 N2 synthesis gas ... 

The DKR processes for secondary alcohols and primary amines can be slightly modified for applications in the asymmetric transformations of ketones, enol esters, and ketoximes. The key point here is that racemization catalysts used in the DKR can also catalyze the hydrogenation of ketones, enol esters, and ketoximes. Thus, the DKR procedures need a reducing agent as additional additive to enable asymmetric transformations. 

The efficiency of Crabtree s catalyst as a catalyst for small molecule hydrogenation has been known for many years. Unlike many homogeneous hydrogenation catalysts, Crabtree s catalyst is able to reduce hindered olefins at favourable rates.7 It has never been reported as a catalyst for the hydrogenation of rubber except for its use in the hydrogenation of bulk PBD.8 This paper describes the first use of Crabtree s catalyst in the hydrogenation NBR. Kinetic data are presented and analyzed to understand the underlying chemistry. 

Rh and Ni complexes of this ligand were anchored to the silanol groups of silica and a USY zeolite. The catalysts were used in the hydrogenation of N-acyldehydrophenylalanine derivatives (Scheme 7.6). 

Ru3(CO)12(117)3] and [H4Ru4(CO)11(117)] as catalyst precursors in the hydrogenation of non-activated alkenes under biphasic conditions. Each cluster displays activity under moderate conditions, ca. 60 atm. H2 at 60 °C with catalytic turnovers up to ca. 500. The trinuclear clusters undergo transformations during reaction but can be used repeatedly without loss of activity.325... 

In the early 1970 s, Bayer et al. reported the first use of soluble polymers as supports for the homogeneous catalysts. [52] They used non-crosslinked linear polystyrene (Mw ca. 100 000), which was chloromethylated and converted by treatment with potassium diphenylphosphide into soluble polydiphenyl(styrylmethyl)phosphines. Soluble macromolecular metal complexes were prepared by addition of various metal precursors e.g. [Rh(PPh3)Cl] and [RhH(CO)(PPh3)3]. The first complex was used in the hydrogenation reaction of 1-pentene at 22°C and 1 atm. H2. After 24 h (50% conversion in 3 h) the reaction solution was filtered through a polyamide membrane [53] and the catalysts could be retained quantitatively in the membrane filtration cell. [54] The catalyst was recycled 5 times. Using the second complex, a hydroformylation reaction of 1-pentene was carried out. After 72 h the reaction mixture was filtered through a polyamide membrane and recycled twice. 

The metal carbonyls Cr(CO)6, Mo(CO)6, W(CO)6 and Fe(CO)5 have all been tested in the hydrogenation of acetophenone in the presence of a strong base [61, 62]. In reactions performed in either triethylamine of sodium methoxide in methanol using 5 mol% of catalyst, the Mo and Cr complexes proved to be superior. The different bases had an effect on the yield that was further demonstrated when Cr(CO)6 was used in the hydrogenation of a series of ketones under the same conditions. In most cases, the reactions were found to be better in the methoxide system, with over 98% yields obtained in reactions lasting 3 h at 120 °C. 

A PHOX analogue containing a P-O bond, the TADDOL-derived phosphite oxa-zoline catalyst 20a (Fig. 29.8) has been used in the hydrogenation of a number of substituted styrenes, as well as in asymmetric allylic alkylation [19]. However,... 

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