Catalysis novel catalysts

Born in Oban, Argyll, in 1960, Duncan Macquarrie studied Pure and Applied Chemistry at the University of Strathclyde, graduating with a first class degree in 1982 and a PhD in 1985. He then moved to York, where he carried out research in Phase Transfer Catalysis. He subsequently spent time in industry, where he worked in the UK and abroad, mostly in synthetic chemistry, but always with an interest in method development and catalysis. He returned to York in 1995 to take up a Royal Society University Research Fellowship, and has developed a range of novel catalysts for green chemistry. He is Associate Editor of Green Chemistry, and a National Member of Council with the Royal Society of Chemistry. 

The expected contribution of catalysis in this area will derive both from the availability, at low processing costs, of new monomers obtained from biomasses and from the development of an optimized combination of biotechnology processes with classical and new biocatalytic processes. Research priorities for catalysis in the area of polymers from renewable materials for packaging, furniture, domestic water purification and recycling include the need to develop novel catalysts, e.g., for functionalization of polymeric and dendrimeric materials, with side-chain photoactive molecular switches (to be used as smart materials), or the development of multifunctional materials, combining, for example, nanofiltration with catalytic reactivity. 

This chapter focuses on several recent topics of novel catalyst design with metal complexes on oxide surfaces for selective catalysis, such as stQbene epoxidation, asymmetric BINOL synthesis, shape-selective aUcene hydrogenation and selective benzene-to-phenol synthesis, which have been achieved by novel strategies for the creation of active structures at oxide surfaces such as surface isolation and creation of unsaturated Ru complexes, chiral self-dimerization of supported V complexes, molecular imprinting of supported Rh complexes, and in situ synthesis of Re clusters in zeolite pores (Figure 10.1). 

In this section, we discuss the high performance of the Rejo cluster/HZSM-5 catalyst, its active structure and dynamic structural transformation during the selechve catalysis, and the reaction mechanism for direct phenol synthesis from benzene and O2 on this novel catalyst [73, 107]. Detailed characterization and determination of active Re species have been conducted by XRD, Al solid-state MAS NMR, conventional XAFS and in situ time-resolved energy dispersive XAFS, which revealed the origin and prospects of high phenol selectivity on the novel Re/HZSM-5 catalyst [73]. 

While the significance of the bifunctional Brpnsted base catalysts has been illustrated in the previous sections, few examples rely solely on a Brpnsted base interaction for asymmetric catalysis. However, in the past few decades, a novel catalyst system has emerged as a powerful promoter of chiral transformations. The guanidines have gained the reputation as super bases in organic transformations. 

The EM studies show that the novel glide shear mechanism in the solid state heterogeneous catalytic process preserves active acid sites, accommodates non-stoichiometry without collapsing the catalyst bulk structure and allows oxide catalysts to continue to operate in selective oxidation reactions (Gai 1997, Gai et al 1995). This understanding of which defects make catalysts function may lead to the development of novel catalysts. Thus electron microscopy of VPO catalysts has provided new insights into the reaction mechanism of the butane oxidation catalysis, catalyst aging and regeneration. 

Enantiomerically pure bis-Gp derivatives with chiral Gp ligands have been used with success in the catalytic enantioselective opening of meso-epoxides via electron transfer (see Section 4.05.8). The structural features are of relevance for the understanding of activity and selectivity of these complexes in diastereoselective reactions and for the design of novel catalysts. A comparison of the structure of three of these bis-Gp Ti derivatives (Scheme 481) in the solid state and in solution determined by X-ray crystallography and NMR methods indicated that the structures in the crystal and in solution are the same, and that applications of these complexes in catalysis can de discussed on the basis of crystallographic data.1114 In a similar study, the 1-methylcyclohexyl-Cp, 1-butyl-1-methylbutyl-Cp, and cyclohexyl-Cp titanocene dichlorides (Scheme 481) have been prepared and their molecular structures compared. The use of these three compounds in radical addition reactions has been studied.1115... 

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. 

Several modifications of the water-soluble catalysts using co-solvents (cf. Section 4.3 and [14]), micelle forming reagents (Section 4.5 and [15]), super-critical C02-water biphasic system (cf. Section 7.4 and [16]), SAPC (Section 4.7 and [17]), and catalyst binding ligands (interfacial catalysis) [18, 24] have been proposed to overcome the lower rates observed in biphasic catalysis due to poor solubilites of reactants in water. So far endeavors were centered on innovating novel catalyst and development of the existing systems. However, limited information is available on the kinetics of biphasic hydroformylation. 

Ledoux, M. J. and Pham-Huu, G. 2001. Silicon carbide a novel catalyst support for heterogeneous catalysis. Cattech 5 226-246. 

Novel Catalysts. - One other promising option exists that might, in the long run, lead to a viable alternative to the above process concepts. Recent advances in biomimetic catalysis have resulted in the development of molecular catalysts that are selective in liquid-phase oxidation of C,-Cj aliphatic hydrocarbons under mild conditions. The catalysts have now been placed on suitable support materials for vapor-phase oxidation of methane to methanol. Significant laboratory research is still required on the properties and synthesis of these special molecular catalysts before process conditions, products, and yields can be defined, even on a laboratory scale. 

We expect that we will soon see examples of ribo- and deoxyribozymes evolved for the catalysis of complex chemical transformations. There is enough reason to assume that such synthetic enzymes will be used as catalysts in organic syntheses. The novel catalysts not only support theories of an RNA world ,... 

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