Catalyst novel shapes

Metallosilicates incorporating catalytically active metal such as V-silicate (l 7) and Cu-silicate (ij ) could also be prepared by the rapid crystallization method. These novel catalytic materials are expected as oxidation catalysts involving shape selective function. 

Tada M, Sasaki T, Shido T, Iwasawa Y (2002) Novel SiO -attached molecular-imprinting rh-monomer catalysts for shape-selective hydrogenation of alkenes preparation, characterization, and performance. Phys Chem Chem Phys 4 4561... 

Tada, M. Sasaki, T. Iwasawa, Y. Novel Si02-attached molecular-imprinting Rh-mono-mer catalysts for shape-selective hydrogenation of alkenes preparation, characterization and performance. Phys. Chem. Chem. Phys. 2002, 4, 4561-4574. 

Clusters are intennediates bridging the properties of the atoms and the bulk. They can be viewed as novel molecules, but different from ordinary molecules, in that they can have various compositions and multiple shapes. Bare clusters are usually quite reactive and unstable against aggregation and have to be studied in vacuum or inert matrices. Interest in clusters comes from a wide range of fields. Clusters are used as models to investigate surface and bulk properties [2]. Since most catalysts are dispersed metal particles [3], isolated clusters provide ideal systems to understand catalytic mechanisms. The versatility of their shapes and compositions make clusters novel molecular systems to extend our concept of chemical bonding, stmcture and dynamics. Stable clusters or passivated clusters can be used as building blocks for new materials or new electronic devices [4] and this aspect has now led to a whole new direction of research into nanoparticles and quantum dots (see chapter C2.17). As the size of electronic devices approaches ever smaller dimensions [5], the new chemical and physical properties of clusters will be relevant to the future of the electronics industry. 

Vorlop et al. described a novel cross-linked and subsequently poly(vinyl alcohol-entrapped PaHNL for synthesis of (//(-cyanohydrins. These immobilized lens-shaped biocatalysts have a well-defined macroscopic size in the millimeter range, show no catalyst leaching, and can be recycled efficiently. Furthermore, this immobilization method is cheap and the entrapped (/ )-oxynitrilases gave similar good results compared with those of free enzymes. The (//(-cyanohydrin was obtained in good yields and with high enantioselectivity of up to >99% ee [55],... 

The microwave technique has been also found to be the best method for preparing strongly basic zeolites (ZSM-5, L, Beta, etc.) by direct dispersion of MgO and KF. This novel procedure enabled the preparation of shape-selective, solid, strongly base catalysts by a simple, cost-effective, and environmentally friendly process [11, 12]. New solid bases formed were efficient catalysts for dehydrogenation of 2-propanol and isomerization of cis-2-butene. 

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). 

C, 10-50 atm). Xylene benzene ratios of 1-10 may be obtained. Metal catalysts were later replaced by zeolites.210,211,326-328 The most recent development is the Mobil selective toluene disproportionation process,329 which takes advantage of the high para shape selectivity of a zeolite catalyst.210 The catalyst activated by a novel procedure ensures a p-xylene content of up to 95%. After the successful com-mercialization at an Enichem refinery in Italy, the process is now licensed. The catalysts and technologies applied in toluene disproportionation may be also used for transalkylation324,325,331 [Eq. (5.74)] ... 

Fig. 50. Novel catalyst shapes for residuum processing, (a) UNOCAL s cloverleaf shape, (b) AKZO Chemie/Ketjen s asymmetric quadralobe, (c) Chevron s Bumpy Oval, (d) W. R. Grace s Minilith.

Bochmann has also produced a novel class of large dianionic borates XV based on the non-labile fefra-cyano Ni and Pd(II) metallates [K12 M(CN) i 2. 215a The metals in these WCAs are strictly square planar and as such the anion assumes a flat rather than spherical shape, with a torus of fluorination on the periphery of the plane. The bis-trityl salts of these dianions afford catalysts that are not as productive as those formed from the XIV class (X = CN), although they are still much more active than borane activated catalysts. The lower activity was attributed to the inherently greater cation/anion attraction in a monocation/dianion pair. 

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