Conversion bifunctional zeolite catalysts

Another important zeolite catalyst is the so-called bifunctional catalyst. The thermal reduction of zeolites previously exchanged with metals is the method currently used for the preparation of bifunctional catalysts for hydrocarbon conversion. The bifunctional zeolite catalysts are composed of both acidic sites and metal clusters. The preparation methods of these catalysts encompass three steps ion exchange, calcinations, and reduction, (Section 3.2.1.4) [123,127],... 

Mono- as well as bifunctional zeolite catalysts are applied in the multistep conversions of ... 

Thus, to reduce the density of Bronsted acid sites in the bifunctional zeolite catalysts, introduction of both Ca + and Pd was carried out, and this was done either simultaneously (method A) or successively (method B). Best results were obtained by method B. As an example. Fig. 62 shows the conversion of ethylbenzene and the yields of ethylcyclohexane, xylenes, dimethylcyclohexanes, alkanes, benzene and diethylbenzenes over a Pd,Ca,H-ZSM-5 catalyst prepared by a two-step solid-state ion exchange. In a first step, CaCl2 was incorporated via SSIE, followed by a second step, viz., SSIE of PdCl2 into Ca,H-ZSM-5 obtained in the first step. 

Octadecane hydroprocessing behavior of Pt-containing bifunctional catalysts with TON and MTT framework types was compared, as illustrated in Figure 13.31 [28]. While the two zeolitic catalysts showed similar activities, the selectivity vs conversion performances were different. At any given conversion, the selectivity to dibranched isomers was lower and the selectivity to mono-branched isomers... 

Modeling of absorption and bifunctional conversion of n-alkanes on Pt/H-ZSM-22 zeolite catalyst. Chem. 

It is proposed that the high selectivity to isomers even at high conversion is obtained because the formation of n-hydrocarbon from the monomethyl isomers, i.e. the reverse reaction, occurs at a higher rate over the molybdenum oxycarbide catalysts than the bifunctional Pt/jS-zeolite catalyst. Over the Pt/jS-zeolite catalyst this reverse reaction would involve... 

Direct dehydroisomerisation (DHI) of n-butane into isobutene over bifunctional zeolite-based catalysts represents a potential new route for the generation of isobutene utilising cheap n-butane feedstock. Isobutene is used worldwide for production of methyl tert-butyl ether (MTBE) and polyisobutylene. It is currently obtained via extraction from refinery/cracker C4 streams or via conversions of isobutane (in one step) or n-butane (in two steps).1,2 Isobutene can also be produced via the isomerisation of n-butenes,3 although there is no evidence that this is practised commercially.2,3... 

The use of bifunctional metal/zeolite catalysts for the conversion of synthesis gas (carbon monoxide and hydrogen) to gasoline range hydrocarbons has recently attracted much attention. For example, the combination of metal oxides with the medium pore ( 6A) zeolite ZSM-5 and the use of a metal nitrate impregnated ZSM-5 catalyst have been shown to produce gasoline range hydrocar-... 

The objective of this work is to determine the influence of the porous structure (size and shape) and acidity (number and strength of the acid sites) on isomerization selectivity during the conversion of ethylbenzene on bifunctional catalysts PLAI2O3/ 10 MR zeolite. The transformation of EB was carried out on intimate mixtures of Pt/Al203 (PtA) and 10 MR zeolites (ZSM-5, ZSM-22, Ferrierite, EU-1) catalysts and compared to Mordenite reference catalyst activity. 

There are several examples of one-pot reactions with bifunctional catalysts. Thus, using a bifunctional Ru/HY catalyst, water solutions of corn starch (25 wt.%) have been hydrolyzed on acidic sites of the Y-type zeolite, and glucose formed transiently was hydrogenated on ruthenium to a mixture of sorbitol (96%), mannitol (1%), and xylitol (2%) [68]. Similarly a one-pot process for the hydrolysis and hydrogenation of inulin to sorbitol and mannitol has been achieved with Ru/C catalysts where the carbon support was preoxidized to generate acidic sites [69]. Ribeiro and Schuchardt [70] have succeeded in converting fructose into furan-2,5-dicarboxylic acid with 99% selectivity at 72% conversion in a one-pot reaction... 

Fourth, by careful choice of the zeolite support in the preparation of a bifunctional catalyst for synthesis gas conversion, the product distribution, particularly for hydrocarbons, may be controlled. This conclusion is of importance in the design of catalysts for the production of liquid transportation fuels from synthesis gas. 

With Ru-H-Beta zeolite as a bifunctional catalyst, the equimolar amounts of the two hexoses formed after hydrolysis of sucrose are converted to between 45 and 37% of D-mannitol at conversions between 20 to 100% with (62). In comparison to any other previously reported system, this represents a clear diastereoselective... 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

The metal functions can be elegantly combined with the acidic functions of the zeolitic support to obtain a very effective bifunctional catalyst. For example the selective isomerisation followed by dehydrogenation of limonene to give p-cymene (Scheme 24) can be carried out in one step over a multifunctionalised zeolite [213]. With an acidic boron zeolite (Si/B= 21) 21% selectivity to p-cymene was obtained at 100% conversion. Addition of 3 wt% Pd increased the selectivity to 70% at the same conversion. Further addition of Ce (1.5 wt% Pd, 3.5 wt% Ce) to the metal loaded zeolite led to 87% selectivity. 

Comparison data were presented, that demonstrate the use of the polysiloxane material as an advantageous substitute for organic cation exchange resins, sulfuric acid, p-toluene sulfonic acid and acidic zeolites. It is demonstrated, that materials like 1 and 2 are cost-efficient and reliable catalysts in esterification, alkylation, and condensation, whereas use of the bifunctional catalyst 3 gives excellent conversions in hydrogenolysis reactions in general. 

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