Toluene heterogeneous catalysis

Very recently, ultrafme metal oxides have attracted much research interests in terms of materials science and heterogeneous catalysis[10-12]. These new catalytic materials are expected to have unique catalytic properties because of their nano-scale particle sizes. In this work, a novel catalyst for selective oxidation of toluene to benzaldehyde, i.e. ultrafme complex molybdenum based oxide particles, has been developed. It has been found that the reactivity of lattice oxygen ions can be improved by decreasing the oxide particle size to nano-scale and that the ultrafme oxide particles exhibit unique catalytic properties for selective oxidation. Our results have revealed that the ultrafme complex oxide particles are potentially new catalytic materials for selective oxidation reactions. 

Asymmetric heterogeneous catalysis has been demonstrated by the enantioselec-tive and racemic hydrogenation of ethyl pyruvate over Pt-Al203 catalyst. Higher reaction rate and enantioselectivity (75%) were observed in nonpolar solvent (toluene) whereas in a polar solvent (ethanol) they decreased substantially (Scheme 13.5) [58]. 

In contrast to homogeneous hydrogenations (the PdAu system is most similar), incorporation of Cu into Pt nanoparticles had a substantial poisoning effect on toluene hydrogenation catalysis Pt [36], As Table 4.4 shows, catalytic rates, which were normalized per total mole of Pt, drop by more than two orders of magnitude as the Cu content of the particles increases. This also contrasts with heterogeneous CO oxidation studies for the same catalysts, which showed enhanced activily upon Cu incorporation. The disparate catalysis data were interpreted in terms of a surface enrichment in Cu under the hydrogenation reaction conditions, driven by the lower heat of sublimation of Cu [36, 97, 98]. 

Catalytic dehydrogenation Toluene 88% Gas-solid heterogenous catalysis 2005/[41]... 

Heterogeneous Reactions. Historically, it has been the practice in many gas-solid catalyzed reactions to write the rale law in terms of partial pressures rather than concentrations. In heterogeneous catalysis it is the weight of catalyst that is important, rather than the reactor volume. Consequently, we use -rJI in order to write the rate law in terms of mol per kg of catalyst per time in order to design PBRs. An example of a heterogeneous reaction and corresponding rate law is the hydrodemethylation of toluene (T) to form benzene (B) and methane (M) carri out over a solid catalyst. 

The low temperature limitation of homogeneous catalysis has been overcome with heterogeneous catalysts such as modified Ziegler-Natta (28) sohd-supported protonic acids (29,30) and metal oxides (31). Temperatures as high as 80°C in toluene can be employed to yield, for example, crystalline... 

Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

BTF is a suitable solvent for conducting heterogeneous reactions with phase transfer catalysis. The reaction of benzyl chloride with sodium cyanide (in toluene and BTF) or potassium cyanide (in acetonitrile and BTF) using two different phase transfer catalysts [70] gave similar yields (12.1 12.2). Aromatic nucleophilic substitution of chloro-2,4-dinitro benzene using potassium fluoride and... 

Benzylic oxidation of aromatic side-chains is also a well established technology in the bulk chemicals arena, e. g. toluene to benzoic acid and p-xylene to ter-ephthalic acid [1,2]. These processes involve homogeneous catalysis by, e. g., cobalt compounds, however, and also fall outside the scope of this book. Ammoxi-dation of methyl-substituted aromatic and heteroaromatic compounds is performed over heterogeneous catalysts in the gas phase but this reaction is treated elsewhere (Section 9.5). Transition metal-substituted molecular sieves have been widely studied as heterogeneous catalysts for oxidation of aromatic side-chains in the liquid phase, but there are serious doubts about their heterogeneity [5,6]. Here again, a cursory examination of the literature reveals that supported palladium seems to be the only heterogeneous catalyst with synthetic utility [4]. 

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