Hydrogenation catalysts early work

The pentacyanocobaltate(II) ion has long been known to catalyze alkene hydrogenation, mainly of conjugated dienes. A review of the early work is available.45 The catalyst system shows negligible activity for the hydrogenation of non-activated monoenes. A major disadvantage is that the system is inhibited by excess substrate, and the turnover numbers obtained are generally less than 2. 

Early work on the electrophilic addition of hydrogen peroxide to alkenes was performed in the presence of an acid catalyst, usually sulfuric acid364 or p-toluenesulfonic acid.363 The reaction proceeds via Markovnikov-directed protonation of the double bond (Scheme 3). Subsequent nucleophilic attack of hydrogen peroxide on the carbocation, followed by loss of a proton, furnishes the alkyl hydroperoxide.366... 

Early work by Tonkovich et al. [46] dealt with a heat exchanger/reactor containing catalyst powder for the partial oxidation of methane for distributed hydrogen production. The intention was to run the reaction safely in a micro structured reactor owing to the short residence times applied and the improved heat removal avoiding hot-spot formation. 

The early work of photoelectrochemical hydrogen production using Ti02 as catalyst, was reported by Fujishima and Honda [61]. Subsequently, the interest for the photocatalytic processes has grown significantly, although the number of the reported photocatalysts used for water splitting is still limited. 

Catalyst Description. The LPO catalyst is a triphenylphosphine modified carbonyl complex of rhodium. Triphenylphosphine, carbon monoxide, and hydrogen form labile bonds with rhodium. Exotic catalyst synthesis and complicated catalyst handling steps are avoided since the desired rhodium complex forms under reaction conditions. Early work showed that a variety of rhodium compounds might be charged initially to produce the catalyst. Final selection was made on the basis of high yield of the catalyst precursor from a commodity rhodium salt, low toxicity, and good stability to air, heat, light, and shock. 

Selective Hydrogenation of Benzene to Cyclohexene Obtaining trans substituted cyclohexanes suggested that desorbed cyclohexenes were intermediates in the hydrogenation of benzenes. The isolation of cyclohexene and substituted cyclohexenes from the hydrogenation of benzene and substituted benzenes was first reported for hydrogenations run over a Ru/C catalyst, but the maximum olefin concentrations observed in this early work were only 0.2-3.4%.7... 

One of the major reasons why this reaction is not more widely used is that the catalyst is usually deactivated before the oxidation is completed. This deactivation is thought to be caused by either the oxidation of the metal or the blocking of the metal surface by the strong adsorption of reaction by-products. A number of procedures have been employed to minimize this deactivation. Most of the early work in this area used a large amount of platinum, prepared by the hydrogenation of platinum oxide (Adam s catalyst), as the catalyst.52 These larger metal particles are more resistant to oxidation than the smaller particles present on supported platinum catalysts.63 In addition, the large quantity of catalyst ensures that some active species will still be available toward the end of the reaction. 

There are several examples of radiation-produced changes considered elsewhere which seem to result from interaction of the radiation with surface contaminants. These include the early work on platinum in which the presence of moisture was necessary for any change (i, 2,12) perhaps the work with alumina (Section III,B,2) in which a well-evacuated catalyst was insensitive to radiation and work on NiO in which the oxygen content of the catalyst increased on irradiation (Appendix II). Polymerization of residual ethylene on ZnO was suggested as an alternate explanation for the loss in hydrogenating activity observed on irradiation (Section III,B,3). 

Epoxidation with hydroperoxides is the basis for the large-scale indirect production of propylene oxide by a process that has been called the Oxirane or Halcon processes. Early work was reported by Smith in a patent issued in 1956 [457], which described soluble heteropoly acids containing transition metals such as chromium, molybdenum, and tungsten that could be employed as homogeneous catalysts for the reaction of olefins with organic hydroperoxides and hydrogen peroxide. 

Activity and selectivity of monometallic Ag catalysts can be controlled by the preparation conditions leading to micro- and meso- to macroporous catalysts which are active and selective in the hydrogenation of crotonaldehyde. In Ag catalysts modified by a second metal, bimetallic sites exhibiting surface polarity and Ag particles in close contact with a partially reduced early transition metal or a rare earth element, or Ag species stabilized and incorporated in these oxides were concluded to be the active species in the working state of these catalysts. Simultaneous introduction of both metals during the sol-gel process under optimized hydrolyzing conditions could further increase the metal-promoter interaction and lead to well-tailored new hydrogenation catalysts. 

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