New approaches to catalyst preparation

Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland. Department of Chemical Engineering, University of Calabria, Rende, Italy, skowalaklcpmain. amu. edu. pi 

A series of zincosilicates MFI was synthesized from the mixtures of even Zn/Si ratio and various silicon sources. The properties of the resulting samples differed considerably regarding their zinc content, the crystallite morphology and size and catalytic activity. The samples modified with various cations (Ca, Cu, Zn, Al, H) showed some activity for 2-propanol dehydration (no acetone was detected). The samples modified with Al cations showed the highest activity. It is likely that part of Al could attain the framework positions or facilitate a generation of separated acidic OH groups. The lower activity of the H-forms could result from the presence of hydrogen bonds between adjacent hydroxyls. 

29-P-06 - Acidity characterization of dealuminated H-ZSM-5 zeolites by isopropanol dehydration 

A series of dealuminated ZSM-5 zeolites with various framework Si/Al ratios were prepared by different methods (HCl, ammonium hexafluorosilicate, steaming). The number of acid sites that correspond to the high-temperature desorption peak of the ammonia-TPD spectra of all the dealuminated samples is in 1 1 mole analogy to the framework Al (FAl), irrespective the degree and the type of dealumination method. The catalytic activity of the H-ZSM-5 zeolites for isopropanol dehydration is linearly related to the number of acid sites that correspond to the FAl-content (Bronsted acidity). The Si-Al amorphous phase that is formed in the high-temperature steamed samples affects activity and induces different product selectivity for propene and diisopropyl ether. 

Key Laboratory of Inorganic Synthesis and Preparative Chemistry Department of Chemistry, Jilin University, Changchun 130023, China, fsxiao mail.jlu.edu.cn 

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A new approach to catalyst preparation using rate controlled temperature programme techniques... 

Tu X, Furuta N, Sumida Y, Takahashi M, Niiduma H. A new approach to the preparation of MoVNbTe mixed oxide catalysts for the oxidation of propane to acrylic acid. Catalysis Today. 2006 117(l-3) 259-264. 

Kobayashi et al. developed chiral Lewis acids derived from A -benzyldiphenylproli-nol and boron tribromide and used these successfully as catalysts in enantioselective Diels-Alder reactions [89]. The corresponding polymeric catalyst 71 was prepared and used for the Diels-Alder reaction of cyclopentadiene with methacrolein [90]. Different polymeric catalysts 72, 73, 74 were prepared from supported chiral amino alcohols and diols fimctionalized with boron, aluminum and titanium [88,90]. In these polymers copolymerization of styrene with a chiral auxiliary containing two polymerizable groups is a new approach to the preparation of crosslinked chiral polymeric ligands. This chiral monomer unit acts as chiral ligand and as a crosslink. 

We have recently suggested a new approach to the preparation of active sites in sulfated zirconia catalysts [5, 6]. In this case, the catalysts are prepared by deposition of sulfate ions on crystalline zirconium dioxide samples with highly defective structure. According to numerous reports, the monoclinic phase typical for ZrOa is not suitable for this purpose. We have shown that active materials could be obtained by impregnation of zirconia-based oxides with cubic crystalline structure. It should be noted that the cubic structure is not thermodynamically stable for pure zirconia at low temperatures. It can be stabilized by introducing different additives, in particular, alkaline-earth metal cations [7]. Recently, similar results have been obtained for ZrOa stabilized by Y2O3 [8]. 

Isomerization of unactivated vinyl cyclopropanes to cyclopentanes using nickel carbene complexes has been accomplished. The nickel carbene catalyst was generated in situ from Ni(cod)2, PPBF4 salt and base. These reactions constitute a simple protocol for the preparation of cyclopentenes by the isomerization of vinyl cyclopropanes. This result, combined with recent developments in the preparation of vinyl cyclopropanes,may provide a powerful new approach to the preparation of five-membered ring structures. 

Metal oxides belong to a class of widely used catalysts. They exhibit acidic or basic properties, which make them appropriate systems to be used as supports for highly dispersed metal catalysts or as precursors of a metal phase or sulfide, chloride, etc. Simple metal oxides range from essentially ionic compounds with the electropositive elements to covalent compounds with the nonmetals. However, taking into account the large variety of metal oxides, the principal objective of this book is to examine only metal oxides that are more attractive from the catalytic point of view, and most specifically transition metal oxides (TMO). In particular, TMO usually exhibit nonstoichiometry as a consequence of the presence of defective structures. The interaction of TMO with surfaces of the appropriate carriers develop monolayer structures of these oxides. The crystal and electronic structure, stoichiometry and composition, redox properties, acid-base character and cation valence sates are major ingredients of the chemistry investigated in the first part of the book. New approaches to the preparation of ordered TMO with extended structure of texturally well defined systems are also included. 

An interesting new approach to phosphorescent polymers has been reported by Thompson and coworkers [79]. Using a living polymerization reaction (with alkoxyamine catalyst), they have prepared the polymer 66 (Chart 4.22), which contains the electron transport oxadiazole... 

Recently, two new approaches for the preparation of metallodendritic catalysts were described. The first one involves the use of PAMAM dendrimers [11] as both template and stabilizer of metal ions. The cavities of these dendrimers can serve as host type nano-reactors for metal ion guests. This strategy is referred to as reactive encapsulation . The concept was first elegantly demonstrated by... 

Research tools and fundamental understanding New catalyst design for effective integration of bio-, homo- and heterogeneous catalysis New approaches to realize one-pot complex multistep reactions Understanding catalytic processes at the interface in nanocomposites New routes for nano-design of complex catalysis, hybrid catalytic materials and reactive thin films New preparation methods to synthesize tailored catalytic surfaces New theoretical and computational predictive tools for catalysis and catalytic reaction engineering... 

The following sections are organized into two parts. The first presents a brief overview of several approaches to preparing nanostructured supports and catalysts that are under current development. Approaches that incorporate building blocks in either part of the system (catalyst or support) will be highlighted. The second part describes a new approach to preparing nanostructured catalysts that we are currently developing in our laboratories. 

The chapter by Reetz includes many examples and explanations of methods illustrating how directed evolution has been applied to prepare new enzyme catalysts. Directed evolution of enantioselective enzymes has emerged as a fundamentally new approach to asymmetric catalysis. It involves the combination... 

Kobayashi S. Wen X, Shoda S. Specific preparation of artificial xylan a new approach to polysaccharide synthesis by using cellulase as catalyst. Macromolecules 1996 29 2698-2700. 

Silyl enol ethers are versatile reagents in organic synthesis [83]. They are used as isol-able enolate equivalents and many useful reactions have been developed using silyl enol ethers [83]. As a new approach to exploit an efficient method for combinatorial synthesis [84], silyl enol ethers were successfully immobilized on to a polymer. Polymer-supported silyl enol ethers (PSSEEs) were prepared according to Sch. 10 [85]. In aldol reactions of PSSEEs with aldehydes, it was again found that Sc(OTf)3 was an efficient catalyst [86]. An example of the preparation of a 1,3-diol library by use of PSSEEs is shown in Sch. 11. In all cases, the reactions proceeded smoothly to afford the corresponding 1,3-diols in good yields. 1,3-Diols are successfully cleaved from the... 

New approach to preparation and investigation of active sites in sulfated zirconia catalysts for skeletal isomerization of alkanes... 

Apart from the development of aliphatic hydrocarbon soluble catalysts (Fig. 1) and the investigation of new preparative routes to catalyst precursors (Scheme ) extensive modelling studies are underway in an attempt to elucidate the active species and intermediates within the catalytic cycle. New approaches to supported catalysts via unusual organic support materials are also being developed. It is anticipated that these heterogeneous systems will provide in depth information on the operation of the CSIRO catalysts and the potential for extensive control over product distributions. 

Since the late 1990s, new approaches to the dispersion of noble metal particles in polymer matrixes by means of chemical, photochemical and radiation-chemical reduction, the evaporation of metal atoms (including solvated ones) into different supports, etc. have been developed (see Section 8-1) [44]. Nevertheless, catalysts prepared from individual immobilized metal clusters have more definite, mostly predetermined, structures. For these purposes derivatives of Oss, It4, RU4, Rh4, Rh6, etc. clusters are most often used. Earlier studies [46] showed that the rate of ethylene hydrogenation promoted by tetrairidium or tetraruthenium carbonyl clusters bound to phosphynated polymers decreased with an increase of the number of donor... 

We leave to specialists the task to describe the desired new approaches in the preparation of zeolites and mesoporous materials. Much work remains to be done for the scale-up of fabrication of MCM and similar materials. The manufacture of specially structured catalysts for very compact devices, like on-board fuel cells and automobile reforming units, is certainly able to bring much information valuable for the fabrication of many specific catalysts in environmental protection, especially for reverse-flow reactors. The demands of photocatalysis also impose constraints. 

Presently, 90% of the large and middle-size production processes in the chemical industry are based on catalysis. In the comprehensive effort aiming at the development of new catalytic processes, catalyst preparation constitutes just one part amid other contributions. But this part led to conspicuous innovation, and this because the chemical engineering aspect of catalyst industrial development was considered simultaneously with the basic science aspects and the development of the whole process. This remark fully justifies the ambition of the special symposium The Science and Engineering of Catalyst Preparation. It also justifies the fact that the selection of topics in the present contribution was essentially not influenced by fashion. In our opinion, the word engineering, when catalyst preparation is considered, should certainly apply to the unit operations of catalyst manufacture. But it should also point to the comprehensive approach that includes the first steps in the discovery of an interesting catalytic reaction as well as the industrial process development. With that in mind, one must conclude that the most promising avenue is to... 

Darabi et al. introduced a different, facile, and economic approach to the preparation of quinoxalines and pyrido[2,3-l)]pyrazines with aryl substituents at the 2- and/or 3-positions by employing recyclable sihca-supported bismuth(III) chloride, providing the desired products in good-to-excellent yields (Scheme 59) (13JOMC170). A minor decrease in the activity of this new heterogeneous Lewis acid catalyst upon repeated usage was noted. A variety of substituents were tolerated under these reaction conditions. 

Mechanism The understanding of mechanisms in catalytic reactions is sometimes crucial for the creative development of new applications. In a first approach, the main interest was to develop high surface area titanium nitride as a material for catalytic applications and, therefore, evaluation of catalysts prepared under different conditions was performed. 

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