Pt-H-ZSM

The bi-functional conversion of 2,2,4-trimethylpentane over Pt/DAY has been recently reported by Jacobs et al. (104). It was compared to the corresponding conversion over Pt/H-ZSM-5 and Pt/H-ZSM-11. All three zeolites had the same chemical composition. The authors found that 2,2,4-trime-thylpentane underwent 3-scission over Pt/DAY, while the formation of feed isomers was favored over the other two catalysts. The differences in reaction products were related to differences in the pore geometry of the zeolites. A similar study was carried out with n-decane. 

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

Figure 4. Comparison of the product distributions on the Pt(1.0)/nonmetal silicate catalyst with 0.5 wt% Pt/H-ZSM-5 (Si/Al=100) catalyst in the second stage.

A further example is acid-catalyzed disproportionation with [Pt]H-ZSM-5 as catalyst. The metal perfoms the hydrogenative cleavage of more highly aggregated molecules that would otherwise cause coking of the catalyst. 

It may be, however, that no single phase zeolite catalyst is able to fulfil the role, and there has also been interest in bifunctional lean burn-deNOx catalysts where the zeolite is mixed with another catalyst. A zeolitic catalyst may be used together with a supported Pt/Al203 catalyst that is more active for NOx reduction at low temperatures. Other examples include Mn203/Ce-ZSM-5, where the manganese oxide catalyses NO oxidation to NO2, which reacts rapidly over the metal-containing zeolite, and Pt/H-ZSM-5, where the acid sites activate the hydrocarbon and promote its reaction with the NOx-... 

Weitkamp J, Jacobs PA, Martens JA. Isomerization and hydrocracking of C, through Cj n-alkanes on Pt/H-ZSM-5 zeolite. Appl Catal 1983 8 123 1. 

Fig. 2 Change of the acid sites on the physical mixture of Pt/ Si02 and H-ZSM-5 with hydrogen treatment and the following outgassing.

The recovery of the Lewis add sites and the decrease in the protonic acid sites to the original values by outgassing gas phase hydrogen are rather slow and require a high temperature. The addition of Pt/Si02 did not affect much the restoration of Ae Lewis add sites of H-ZSM-5 by outgassing gas phase hydrogen. 

Fig. 7 Cumene cracking over H-ZSM5 and the physical mixture of Pt/Si02 and H-ZSM-5 at 423K in a pulse reactor.

The catalytic activity of ln/H-ZSM-5 for the selective reduction of nitric oxide (NO) with methane was improved by the addition of Pt and Ir which catalyzed NO oxidation, even in the presence of water vapor. It was also found that the precious metal, particularly Ir loaded in/H-ZSM-5 gave a low reaction order with respect to NO, and then showed a high catalytic activity for the reduction of NO at low concentrations, if compared with ln/H-ZSM-5. The latter effect of the precious metal is attributed to the enhancement of the chemisorption of NO and also to the increase in the amount of NO2 adsorbed on in sites. 

Na-ZSM-5(a molar SiOz/AlaOa ratio=23.8) provided by Tosoh Corp. was used. ln(4wt%)/H-ZSM-5 and lr(1wt%)/H-ZSM-5 catalysts were prepared by the ion exchange method using NH4-ZSM-5 derived from the Na-ZSM-5 with aqueous solutions of ln(NOs)3 at 368 K for 8 h and lrCI(NH3)sCl2 at room temperature for 24 h, respectively. Addition of precious metals, 1wt% platinum and iridium to ln/H-ZSM-5 was carried out by impregnating the ln/NH4-ZSM-5 in aqueous solutions of Pt(NH3)4Cl2 and lrCI(NH3)5Cl2, respectively. The catalysts were calcined at 813 K for 3 h. 

Dual Function Mechanism of Alkane Aromatization over H-ZSM-5 Supported Ga, Zn, Pt Catalysts Respective Role of Acidity and Additive... 

One Interesting and industrially important process developed recently,"the cyclar process" is the catalytic aromatization of light (C3-C5) hydrocarbons over pentasil based catalysts. These new classes of solids have been widely studied (1-9). These Investigations led to the conclusion that the catalysts consisting of gallium, zinc, Pt, and modified H-ZSM-5 were more active and more selective towards aromatics than the parent H-ZSM-5 zeolite. The formation of aromatics from light alkanes comprised several main hydrocarbon reactions alkane... 

Propane reaction. In a series of experiments propane (760 torr) reacted at 773 K over H-ZSM-5 (Si/Al = 15) and H-ZSM-5 modified with Ga or Pt. The conversion of propane was maintained at around 30% by adjusting the flow rate between 1 and 10 l.h , higher flow rates being used for the most active catalysts. The catalytic activities for the different solids were normalized to that of H-ZSM-5. The data are summarized in Table 1. It is apparent that the addition of Ga, Pt, Pt-Cu to the H-ZSM-5 zeolite increased its activity for the propane conversion. 

Since it is now well accepted that the role of the additive in the H-ZSM-5 based catalysts is to Increase the rate of propane dehydrogenation it is clear that the additive should be sufficiently active to establish rapidly the thermodyneunic equilibrium propane-propene. Ga203 or ZnO exhibits with respect to Pt catalysts lower dehydrogenating properties. Nevertheless, when supported on H-ZSM-5, they were found to promote more efficiently the aromatization of propane, and also the... 

Further research has been performed and is continued to be reported, mostly with zeolites unloaded or loaded with Pt, and Ga- and Zn-promoted H-ZSM-5 or H-[Al]ZSM-5 catalysts to clarify the details of the complex transformations taking place and make further improvements. In addition, new catalysts were studied and reported. Reference should also be made to work addressing the problems of the modification of catalyst features of ZSM-5404 and the development of a new light naphtha aromatization process using a conventional fixed-bed unit.405 406... 

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