Catalytically additional catalyst supports

Deposition of Catalytically Active Species on Additional Catalyst Supports... 

The above example outlines a general problem in immobilized molecular catalysts - multiple types of sites are often produced. To this end, we are developing techniques to prepare well-defined immobilized organometallic catalysts on silica supports with isolated catalytic sites (7). Our new strategy is demonstrated by creation of isolated titanium complexes on a mesoporous silica support. These new materials are characterized in detail and their catalytic properties in test reactions (polymerization of ethylene) indicate improved catalytic performance over supported catalysts prepared via conventional means (8). The generality of this catalyst design approach is discussed and additional immobilized metal complex catalysts are considered. 

Besides the conductive additive, TEG may sometimes be a very effective catalyst support, for example, in the catalytic active composite with conducting polymers for the new air-metal batteries, which we proposed [6],... 

Concerning the Fischer-Tropsch synthesis, carbon nanomaterials have already been successfully employed as catalyst support media on a laboratory scale. The main attention in literature has been paid so far to subjects such as the comparison of functionalization techniques,9-11 the influence of promoters on the catalytic performance,1 12 and the investigations of metal particle size effects7,8 as well as of metal-support interactions.14,15 However, research was focused on one nanomaterial type only in each of these studies. Yu et al.16 compared the performance of two different kinds of nanofibers (herringbones and platelets) in the Fischer-Tropsch synthesis. A direct comparison between nanotubes and nanofibers as catalyst support media has not yet been an issue of discussion in Fischer-Tropsch investigations. In addition, a comparison with commercially used FT catalysts has up to now not been published. 

Catalyst Supports—CNTs have a very high surface area. Each carbon atom is exposed to the interior and exterior surface. Because of the chemist s ability to connect almost any moiety to their surface, a number of CNTs have been shown to act as outstanding catalyst supports when catalysts have been attached to them. Because of their high strength, they perform well to the rigors of being a catalysts support. Their ability to conduct electricity and heat suggests additional ways CNTs can be used to assist catalytic behavior. 

Alumina is one of the most widely used catalyst supports in the petroleum industry because it is robust, porous, relatively inexpensive, and—what is especially important—it is capable of contributing acid-catalyzed activity that can be tailored to suit the requirements of a diverse array of catalytic processes. These include reforming (52, 55), hydrotreating (84, 55), and paraffin isomerization (56-55). Since pure alumina is relatively inactive for the skeletal isomerization reactions that are necessary in such processes, its acid activity is promoted through the addition of catalyst components such as fluoride, chloride, phosphate, silica, or boria. After a discussion of pure alumina itself, we will review pertinent studies of surface acidity and catalytic activity of the promoted aluminas. 

These results strongly pointed toward the involvement of the acidic hydroxyl groups in the catalytic reaction as suggested by Benesi (157), since the maximum activity was obtained when the zeolite was completely deammoniated. In addition, catalysts which had been dehydroxylated by high-temperature calcination demonstrated low activity. Thus, Benesi proposed that the Brtfnsted acid sites rather than the Lewis acids were the seat of activity for toluene disproportionation. This conclusion was supported by the enhancement in toluene disproportionation activity observed when the dehydroxylated (Lewis acid) Y zeolite was exposed to small quantities of water. As discussed previously, Ward s IR studies (156) indicated a substantial increase in Brdnsted acidity upon rehydration of dehydroxylated Y sieve. 

Catalytic visbreaking has been proposed in which the severity of thermal decomposition is increased by the addition of a selenium-, tellurium-, or sulfur containing catalyst supported on a porous substrate (Yan, 1991). 

Ray et al.29 used V205/Cr2 03 catalysts supported on A1203 for the ammoxidation of xylenes. The maximum yields increased from 40% for o-xylene to 70% for m-xylene and, using a catalyst with boria addition, to 89% for p-xylene. From t.p.r. and e.s.r. measurements the authors conclude that a new compound VCr04 is present which is responsible for the catalytic activity. 

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