Zeolite catalysts introduction

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. 

Figure 4.11 Different types of selectivity in zeolite catalysts. (Reprinted from Introduction to Zeolite Science and Practice, Studies in Surface Science and Catalysis, Vol. 137, I.E. Maxwell, W.J.H. Stork, Introduction to Zeolite Science and Practice, Studies in Surface Science and Catalysis, Vol. 137, Hydrocarbon Processing with Zeolites, pp. 747-819. Copyright 2001. With permission from Elsevier.)...

Following their introduction to the refining industry in 1962, zeolite cracking catalysts, have virtually replaced the amorphous silica alumina cracking catalysts that had previously dominated the marketplace. To the rare earth industry the development of zeolite catalysts represented a new end use without precedent. Nearly all zeolite cracking... 

Special care has to be taken, however, that the quinoline titer truly represents the minimum amount of catalyst poison. In most cases this type of base is adsorbed by inactive as well as active sites. Demonstration of indiscriminate adsorption is furnished by the titration results of Roman-ovskii et al. (52). These authors (Fig. 13) showed that introduction of a given dose of quinoline at 430°C in a stream of carrier gas caused the activity of Y-zeolite catalyst (as measured by cumene conversion) to drop with time, reach a minimum value, then slowly rise as quinoline was desorbed. The decrease in catalytic activity with time is direct evidence for the redistribution of initially adsorbed quinoline from inactive to active centers. We have observed similar behavior in carrying out catalytic titrations of amorphous and crystalline aluminosilicates with pyridine, quinoline, and lutidine isomers. In most cases, we found that the poisoning effectiveness of a given amine can be increased either by lengthening the time interval between pulse additions or by raising the sample temperature for a few minutes after each pulse addition. 

CONTENTS Introduction, Thom H. Dunning, Jr. Electronic Structure Theory and Atomistic Computer Simulations of Materials, Richard P. Messmer, General Electric Corporate Research and Development and the University of Pennsylvania. Calculation of the Electronic Structure of Transition Metals in Ionic Crystals, Nicholas W. Winter, Livermore National Laboratory, David K. Temple, University of California, Victor Luana, Universidad de Oviedo and Russell M. Pitzer, The Ohio State University. Ab Initio Studies of Molecular Models of Zeolitic Catalysts, Joachim Sauer, Central Institute of Physical Chemistry, Germany. Ab Inito Methods in Geochemistry and Mineralogy, Anthony C. Hess, Battelle, Pacific Northwest Laboratories and Paul F. McMillan, Arizona State University. 

Friedel-Crafts alkylation of benzene was first commercialized for ethylbenzene and cumene in the 1940s. Aluminum chloride is the Friedel-Crafts catalyst, and the process is operated in the liquid phase. Several alternatives to aluminum chloride technology were developed later, but zeolitic catalysts are a rather recent introduction. UOP began using zeolitic catalysts in the 1990s. 

The recent introduction of zeolite catalysts m SCR applications (gas-fircd cogeneration plants) has to be mentioned Iron- or copper-containing zeolites guarantee high DeNOxmg performances up to temperatures of 600°C, where metal oxides become thermally unstable [12,13] The use of zeolite-based NO reduction catalysts with distinct structures has been covered in the patent literature, namely, mordenite, clinoptilotite, faujasite (both types X and Y), and pentasil [14,15]... 

Leica Cambridge Stereoscan 360). The SEM micrographs of H-ZSM-5, Zn-H-ZSM-5 and Ga-H-ZSM-5 exhibited the typical crystal form of ZSM-5 zeolite and the average crystal size was 2 pm-4 pm. The quantitative analysis of the Ga and Zn content in the ZSM-5 zeolite was performed by an X-ray fluorescence analyzer X-MET 880 (Outokumpu). The specific surface area of the synthesized zeolite catalysts was determined by nitrogen adsorption using a Sorptomatic 1900 (Carlo Erba Instmments). The specific surface area calculated by the Dubinin method was found to be 427, 445 and 372 m /g for Zn-H-ZSM-5, Ga-H-ZSM-5 and H-ZSM-5, respectively. It was observed from different characterization techniques that the introduction of Ga and Zn by this method did not destroy the structure of the ZSM-5 zeolite. 

Generally, preparation of metal-loaded zeolite catalysts involves initial introduction of the metal component by impregnation, cation exchange, or—occasionally—physical adsorption of a volatile inorganic (such as Ni(CO)4), followed by an in situ thermal decomposition or reduction step. Thus, a Pt-containing zeolite catalyst was prepared by Rabo et al. 

In summary, the research work performed at the INL demonstrated that the introduction of supercritical cosolvents during the alkylation reaction did not result in improved or sustained catalytic performance. However, supercritical fluids in general and isobutane in particular were shown to be promising regenerants of some solid acid zeolite catalysts that may be utilized in isobutane/butene alkylation reaction. 

It was shown that solid-state ion exchange is also a suitable route to preparation of active acidic or bifunctional catalysts. Introduction of Ca or Mg into mordenite [21] or La " into Y-type zeolite, mordenite or ZSM-5 [22] by solid-state reaction yielded, after brief contact with small amounts of water, acidic zeolite catalysts which were, for instance, active in disproportionation and/or dealkylation of ethylbenzene or in cracking of n-decane [43]. The contact with water was essential to generate, after solid-state ion exchange, acidic Brpnsted centres (compare, for instance. Figure 2). In the case of solid-state exchange between LaClj and NH -Y an almost 100% exchange was achieved in a one-step procedure, and the hydrated La-Y reaction product exhibited a catalytic performance (selectivity in ethylbenzene disporportionation, time-onstream behaviour) comparable to or even better than that of a conventionally produced La-Y (96) catalyst [22,23]. In fact, compared to the case of NH -Y the introduction of La " " by solid-state reaction proceeded less easily and was frequently lower than 100% with H-ZSM-5 or H-MOR. 

The introduction of ultrastable Y zeolites as the acid component (74) even if producing lower middle-distillates than amorphous catalysts, they show a better temperature performance, i.e. zeolite catalysts exhibits higher start-ofr run activity and lower deactivation rates (Fig. 16). 

Introduction of commercially interesting reactions with zeolite catalysts... 

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