Hydrogenation, catalyzed by supported

Asymmetric hydrogenations catalyzed by supported transition metal complexes have included use of both chiral support materials (poly-imines, polysaccharides, and polyalcohols), and bonded chiral phosphines, although there have been only a few reports in this area. 

Thin metal films have been used as model catalysts not only in electrocatalysis (27-34) but also to study enantioselective hydrogenation catalyzed by supported platinum and palladium catalysts modified by adsorbed chiral compounds (39-44). 

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

Fig. 7 Dependence of IR band intensities on H2 partial pressure during ethene hydrogenation catalyzed by Ir4/y-Al203 at 288 K and 760 Torr (40 Torr C2H4, 50-300 Torr H2, and the balance He). The bands at 2990 (diamonds) and 2981 cnr (squares) were chosen to represent di-cr-bonded ethene and that at 1635 cnr (circles) to represent water on the y-AbOs support. These IR bands were chosen as the best ones to minimize error caused by overlap with other bands. The triangles represent the reaction rate expressed as a turnover frequency (TOF), the rate of reaction in units of molecules of ethene converted per Ir atom per second. The data indicate a correlation of the band intensities with the TOF, consistent with the suggestion that the ligands represented by the bands are reaction intermediates (but the data are not sufficient to identify the reaction intermediates) [39]...

Fig. 8 Dependence of catalytic activity measured by TOP (rate of reaction per Rh atom) (squares) and IR intensity of hydride (2020-cm mode) (diamonds) during the induction period for ethene hydrogenation catalyzed by Rhg supported on La203 at 298 K and atmospheric pressure in a flow reactor (partial pressures in feed H2, 348 Torr C2H4, 75Torr He, 337 Torr) [37]...

A number of reactions, principally of olefinic substrates, that can be catalyzed by supported complexes have been studied. These include hydrogenation, hydrosilylation, hydroformylation, polymerization, oxidative hydrolysis, acetoxylation, and carbonylation. Each of these will be considered in turn together with the possibility of carrying out several reactions consecutively using a catalyst containing more than one kind of metal complex. 

The support induced changes in hydrogenolysis reactions of alkanes can be explained to a large extent by support induced changes in the Pt-H bond strength and hydrogen adsorption site on Pt. This can easily explain the well-known compensation effect found in the kinetics of the hydrogenolysis of alkanes catalyzed by supported metal catalysts. 

These new results can explain the compensation effect and the negative order in the partial pressure of hydrogen found for the hydrogenolysis of neopentane catalyzed by supported Pt particles. The kinetics of the catalytic reaction is driven by the mode of the adsorption of hydrogen on the Pt surface. 

The rates of toluene hydrogenation catalyzed by Ir4 and by Ir6 supported on metal oxides and zeolites differ from each other, typically by factors of... 

In this section the literature representing several different catalytic reaction chemistries is summarized. The reactions include hydrogenation, CO oxidation catalyzed by supported gold, and others. 

Bond GC, Wells PB (1965) The hydrogenation of acetylene II. The reaction of acetylene with hydrogen catalyzed by alumina-supported palladium. J Catal 5 65... 

Catalytic supercritical water oxidation is an important class of solid-catalyzed reaction that utilizes advantageous solution properties of supercritical water (dielectric constant, electrolytic conductance, dissociation constant, hydrogen bonding) as well as the superior transport properties of the supercritical medium (viscosity, heat capacity, diffusion coefficient, and density). The most commonly encountered oxidation reaction carried out in supercritical water is the oxidation of alcohols, acetic acid, ammonia, benzene, benzoic acid, butanol, chlorophenol, dichlorobenzene, phenol, 2-propanol (catalyzed by metal oxide catalysts such as CuO/ZnO, Ti02, MnOz, KMn04, V2O5, and Cr203), 2,4-dichlorophenol, methyl ethyl ketone, and pyridine (catalyzed by supported noble metal catalysts such as supported platinum). ... 

Selectivities, S, Observed in Propadiene Hydrogenation Catalyzed by Some Alumina- and Pumice-Supported... 

K. Tahara, H. Tsuji, H. Kimura, T. Okazaki, Y. Itoi, S. Nishiyama, S. Tsuruya and M. Masai, "Liquid-phase hydrogenation of dicarboxylates catalyzed by supported Ru-Sn catalysts" Catal. Today, 28, 267 (1996). 

Aldol condensations can be efficiently carried out in the liquid or gas phase. These processes are in some cases catalyzed by supported transition metals, occasionally by acids, and more frequently by bases (1,9). The choice of a appropriate catalyst is necessary for obtaining the desired final product Aldol condensations catalyzed by supported metals in the presence of hydrogen yield a saturated carbonyl (10), whereas the acid-catalyzed reaction leads mainly to hydrocarbons and the base-catalyzed reaction is suitable for the synthesis of heavier a,j8-unsaturated carbonyl polymers. The majority of the heterogeneous catalysts are acidic or basic metal oxides or mixtures of metal oxides. 

Fache, E. Mercier, C. Pagnier, N. Despeyroux, B. Panster, P. (1993) Selective hydrogenation of a,P-unsaturated aldehydes catalyzed by supported aqueous-phase catalysts and supported homogeneous catalysts,/. Mol. Catal.,19,117-31. 

In what follows, the use of the PHIP technique in the studies of homogeneous catalytic processes such as hydrogenation and activation of Hj by transition metal complexes and clusters is briefly reviewed first to demonstrate the potential information content of such studies. Then, applications of PHIP to the studies of heterogeneous hydrogenations catalyzed by metal complexes immobilized on solid supports and by supported metal catalysts are discussed. 

---