Multifunctional solid catalyst

In conclusion, there is interest for bioethanol upgrading to fuel additives and some research is active in this direction, but much more effort is needed to demonstrate the validity and the viability of the concept of preparing oxygenated diesel fuel additives from bioethanol and glycerol. The key to success is to develop selective multifunctional solid catalysts, in which interest is more general, because similar multifunctionality is necessary in the catalytic synthesis of fine chemicals [67]. There is, thus, the possibility of cross-fertilization between the two research areas. 

On the Way to Redox-Molecular Sieves as Multifunctional Solid Catalysts for the One-Step Conversion of Olefins to Aldehydes or Ketones... 

Another example for the use of a multifunctional solid catalyst is the Aldox process for the production of 2-ethyIhexanol (Eq. 6-10). 

Electrodes and solid catalysts applied in the synthesis of chemicals or in emission control are, generally, hierarchical systems comprising dimensions ranging from millimeter to nanometer scale, allowing for mass and heat transport within a reactor, molecular transport of reactants and products through a pore system, and chemical reactions on nanostructured, frequently multifunctional surface sites as illustrated in Figure 4.2.2. Catalyst preparation always yields a catalyst precursor, whereas the active phase is only formed in contact with the feed of the substrate molecules in... 

Model of Multifunctional Porous Solid Catalyst Systems... 

In the case of the multifunctional porous catalysts, such as are familiar in hydrocarbon reactions, the situation is somewhat different from that in the model above. In the model above, the diffusion problem is confined to a volume of space where catalytic activities (the sources and sinks) occur only at its boundaries. In the present case a volume element of (porous solid) space is permeated by both diffusive resistance as well as distributed catalytic sources or sinks. 

Immobilization of active species on a solid is a powerful tool for the realization of site isolation because it is difficult for immobilized active species to access, or interferes with each other. Immobilization of solid catalysts also allows easy recovery of the catalysts as well as their reuse, which would be a pivotal contribution to the development of economically and environment firiendly chemical processes. The use of multifunctional surfaces of solid catalysts, and some exquisite catalyst systems that combine acid and base solids, which were designed based on the concept of site isolation, have been recently demonstrated. 

Some successful attempts to immobilize catalysts for the oxidation of alcohols to carbonyl compounds involve the attachment of TEMPO-derivatives to a solid phase. Bolm et al. were the first to immobilize l-hydroxy-2,2,6,6-tetramethylpiperi-dine to modified silica gel (SG-TMP-OH) (11) and applied in the oxidation of multifunctional alcohols [68]. Other groups further investigated the use of polymer-supported TEMPO [69]. This system allowed the oxidation of alcohols to aldehydes and ketones, respectively, using bleach to regenerate the immobilized ni-troxyl radical (Scheme 4.6). 

Scheme 4.35 Multifunctional properties of solid-phase-bound catalysts.

The unique features of zeolites, and the possibility of tuning acidic and basic sites, as well as the creation of multifunctional catalysts, open a wide field of applications in the production of fine chemicals. In this article we present new heterogeneously catalyzed processes for the synthesis of industrially relevant fragrances, flavors and aromas. The emphasis of this review article will remain mainly on solid acids. 

The necessity of molecular transport must obviously arise whenever the reaction sites X and Y are not in geometrically identical locations, and it is precisely this condition that characterizes an important requirement for the multifunctional catalyst. In the case of a catalyst solid that consists of a composite of X-sites and F-sites in a single reactor zone the physical transport of intermediates between X- and F-sites must proceed by a diffusion prccess, which then becomes an important and integral link in the chain of reaction events. 

This catalytic system, as well as systems based on Mo/V/Te/Nb mixed oxides which have been developed by Mitsubishi (65), also represent an example of catalyst characterized by multifunctional properties. The rutile structure is the matrix to host vanadium ions as solid solutions, while the antimony oxide is present as a dispersed microcrystalline oxide. Vanadium is the component which is more active in paraffin conversion, while the high selectivity to the desired product is due to the presence of dispersed, separate phase, antimony oxide. 

Another method widely used for controlled S5mthesis of multifunctional ceramics is the sol-gel, that is used for the S3mthesis of a colloidal suspension where the dispersed phase is a solid and the dispersion medium is liquid, and is called sol. Therefore, there is the formation of a dual phase material a solid body that is occupied by a solvent, i.e., moist gel. The initiator compounds, commonly called precursors, consist of a metal surrounded by many connections and typically are inorganic salts or organic compounds. The two precursors undergo two chemical reactions at sol preparation hydrolysis and condensation, which resulted from the addition of an acid or base catalyst to form small solid particles or clusters in a liquid (aqueous solvent) [32,33]. The sol-gel method provides homogenous mixtures of cations on an atomic... 

---