Isomerization mordenite supports

Jao, R.-M., Leu, L.-J., and Chang, J.-R. (1996) Effects of catalyst preparation and pretreatment on light naphtha isomerization over mordenite-supported Pt catalysts. Appl Catal A., 135, 301-315. 

As indicated above (Table I), 2- and 3-valent cation forms of mordenite are considerably less active in cyclohexane isomerization than that of hydrogen. It is this property of mordenite-supported catalysts that distinguishes them sharply from zeolites of the faujasite type. Thus, in the case of faujasites, the activity of H-form (decationized form) and 2-valent modifications (such as Ca and Mg ) in acid-base reactions (cracking, isomerization, alkylation) is the same, while H-mordenite is many times as active as any cation form under study. 

Pt supported on an acidic support is a typical catalyst for the skeletal isomerization of light n-paraffins. The acidic supports can be acidic oxides, e.g., halogenated (Cl, F) alumina or sulfated zir-conia (Zr02/S04), or an appropriate zeolite, e.g., Mordenite. Pt-(C1, F)-alumina catalysts have a high performance at low temperatures and efficiently operate at temperatures between 115 and 150°C. Such low temperatures thermodynamically favor isomerization and thus, highly branched products are obtained. Zeolite supports are less active at lower temperatures and have to be operated at about... 

Historically, the earliest C8 aromatic isomerization catalysts tended to use amorphous supports with a halogen such as chloride or fluoride. Due to water sensitivity and corrosion issues, these were replaced by large-pore zeolites such as mordenite. The larger pore size was more favorable toward bimolecular transalkylation, whereas the chlorided alumina support tended to promote cracking. In both... 

Pt supported on zeolites, and particularly on modenite, have also been successfully commercialized for LSR isomerization. Pt/mordenite catalysts are less active than Pt/Cl-A Os, and are used at higher reaction temperatures (250°C), but they have the advantage of being more resistant to water and sulfur poisons present in the feed. 

The noble metal component may be either palladium or platinum the effect of the concentration of both metals on methylpentane as well as on dimethylbutane selectivity in C6 hydroisomerization on lanthanum and ammonium Y-zeolite with Si/Al of 2.5 has been studied by M.A. Lanewala et al. (5). They found an optimum of metal content for that reaction between 0.1 and 0.4 wt.-%. The noble metal has several functions (i) to increase the isomerization activity of the zeolite (ii) to support the saturation of the coke precursors and hence prevent deactivation, as was shown by H.W. Kouvenhoven et al. (6) for platinum on hydrogen mordenite (iii) to support the hydrodesulfurization activity of the catalysts in sulfur containing feedstocks. 

Type of Active Sites. - In heterogeneous catalysis the following type of actives sites can be distinguished (i) metallic, (ii) acid-base, (iii) red-ox type, and (iv) anchored metal-complex. The catalytic sites may contain one of the above types of active sites or can include several types of sites. In case of different type of sites the catalysts are bifunctional or multifunctional. For instance, Pt/Al203 and Pt/mordenite are typical bifunctional catalysts containing both metallic and acidic types of active sites. On the other hand, Pt or Pd supported on silicon carbide, nitride, or Pt/L-zeolite are mono-functional catalysts. There are important industrial reactions, such as isomerization and aromatization of linear hydrocarbons, which requires bifunctional catalysts, such as chlorinated... 

A study of the product selectivites of variously supported Co catalysts (kieselguhr, silica, alumina, bentonite, Y-zeolite, mordenite, and ZSM-5) was carried out by Bessel (37). AAdiereas the lower acidity supports such as silica and alumina produced mainly linear hydrocarbons, the acidic supports produced more branched products. At higher temperatures, the latter produced aromatics as well. The isomerization and aromatization are secondary, acid-promoted reactions of the FT olefins. This is then equivalent to a combination of the FT and the Mobil olefins to gasoline process. (With iron-based catalysts, this approach is unlikely to be successful because alkali promotion is essential and the alkali would neutralize the required acid sites on the zeolite support.) Calleja and coworkers (38) studied the FT performance of Co/HZSM-5 prepared by incipient wetness impregnation. Promotion with thorium, being basic, decreased the acidity of the zeolite and so less aromatics were formed and consequently more of the heavier hydrocarbons emerged from the reactor because of the depressed level of secondary reactions. 

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