Mordenite catalysts based

This work studies a new catalyst based on Co and Pt exchanged in mordenite. It presents an... 

The analysis of the literature data shows that zeolites modified with nobel metals are among perspective catalysts for this process. The main drawbacks related to these catalysts are rather low efficiency and selectivity. The low efficiency is connected with intracrystalline diffusion limitations in zeolitic porous system. Thus, the effectiveness factor for transformation of n-alkanes over mordenite calculated basing on Thiele model pointed that only 30% of zeolitic pore system are involved in the catalytic reaction [1], On the other hand, lower selectivity in the case of longer alkanes is due to their easier cracking in comparison to shorter alkanes. 

Ethylbenzene (EB) transformation was carried out on bifonctional catalysts based on 10MR zeolites (ZSM-5, Ferrierite, ZSM-22, EU-1) and compared to Mordenite based catalysts. This work shows that monodimensional (ID) 10MR channels or large cavities are highly selective towards isomerization. For 10MR(1D) zeolites, this selectivity is attributed to microporosity blockage suggesting a pore mouth catalysis. 

H(hydrogen)-mordenite catalyst The crystallites were approximate parallelepipeds, the long dimension of which was assumed to be the pore length. Their analysis was based on straight, parallel pores in an isothermal crystallite (2 faces permeable). They measured (initial) rates of dehydration of methanol (A) to dimethyl ether in a differential reactor at 101 kPa using catalyst fractions of different sizes. Results (for two sizes) are given in the table below, together with... 

The application of zeolitic materials cls catalysts in paraffin isomerization is discussed. Particular attention is given to catalyst preparation variables such as sodium removal for zeolite Y and mordenite. Dual function catalysts based on these zeolites are compared with respect to activity. A reaction mechanism for paraffin isomerization over zeolitic dual function catalysts, on the basis of literature and own data, is presented. 

In the reaction mechanisms described above the acidity of the catalyst plays an important role. Zeolites can be converted into the H+ form and as such are powerful catalysts for acid-catalyzed reactions. We discuss below some aspects of isomerization catalyst preparation to demonstrate factors which influence the activity of catalysts based on zeolites. In this discussion we are concerned with zeolite Y and mordenite. Data on paraffin isomerization over dual function catalysts besed on other zeolites are scarce, and no data have been published showing that materials like zeolite X, zeolite L, offretite, zeolite omega, or gmelinite can be converted into catalyst bases having an isomerization activity comparable with that of H-zeolite Y or H-mordenite. 

Preparation of Dual Function Catalysts Based on Zeolite Y and Mordenite... 

Catalysts Based on Mordenite. Isomerization of paraffins over H-mordenite based catalysts has been described (6, 7,14, 0, 21). Minachev (7) reports that cyclohexane isomerization activity of Na-H-mordenite catalysts increases linearly with H+ concentration in the zeolite for 25-94% exchange. He further observed that H-mordenite is deactivated by other cations such as Li, K, Mg, Cd, Zn, and Al. This agrees with Bryant s work (6) he reported that, compared with Pd-H-mordenite, samples in which hydrogen was partly replaced by Ca or Zn had an appreciably lower n-pentane isomerization activity. 

It has been claimed that noble metal dual function catalysts based on H-mordenite are more active for paraffin isomerization than their counterparts based on H-zeolite Y (25). For both zeolites the isomerization activity depends strongly on the degree of sodium removal and comparison of low sodium Pd-H-mordenite and low sodium Pd-H-zeolite Y for isomerization of n-hexane at 250° C shows that both materials have about the same activity (Table IV), the Y sieve based material being slightly more active. 

For optimal performance of dual function isomerization catalysts based on zeolite Y or mordenite, extensive removal of sodium is necessary. The finished catalyst must be highly crystalline, and the finely dispersed metallic hydrogenation function should be well distributed throughout the catalyst particles. The proposed mechanism explains the stabilizing influence on conversion and the suppression of cracking reactions by addition of the metallic hydrogenation function to the active acidic catalyst base. 

Recently, Angelescu et a/.[92] have studied the activity and selectivity for dimerization of ethylene of various catalysts based on Ni(4,4-bipyridine)Cl2 complex coactivated with A1C1(C2H5)2 and supported on different molecular sieves such as zeolites (Y, L, Mordenite), mesoporous MCM-41 and on amorphous silica alumina. They found that this type of catalyst is active and selective for ethylene dimerization to n-butenes under mild reaction conditions (298 K and 12 atm). The complex supported on zeolites and MCM-41 favours the formation of higher amounts of n-butenes than the complex supported on silica alumina, which is more favourable for the formation of oligomers. It was also found that the concentration in 1-butene and cw-2-butene in the n-butene fraction obtained with the complex supported on zeolites and MCM-41, is higher compared with the corresponding values at thermodynamic equilibrium. 

Fig. 4A, B C show the activity change of mordenite catalysts as a function of copper content on catalyst for the reduction of NO with the sulfur content deposited on catalyst surface. Note that catalytic activity was defined as the ratio of the reaction rate for a deactivated catalyst to that for a fresh catalyst based on the first-order reaction kinetics a = k/k. The effect of sulfur compounds deposited on the catalysts due to the presence of S02 in the feed gas stream on SCR activity significantly depends on both the reaction temperatures and the copper content of the catalyst. For HM catalyst, the catalytic activity varies with its sulfur content depending on reaction temperatures, i.e., an exponential relationship at 250 °C and a linear relationship at 400 DC as shown in Fig.4A. It has already been investigated that the surface area of deactivated HM catalyst exponentially decreases with sulfur content at lower temperature of 250 °C, while it linearly decreases at higher temperature of 400 aC as shown in Fig. 1 A. Judging from these results between catalytic activity and surface area with their catalyst sulfur content at two different reaction temperatures, the decline of the catalytic activity for deactivated HM catalyst occurs simply due to the decrease of surface area.

Commercial hydroisomerization catalysts have both a noble metal based hydrogenating function and an acid function (Table 7.3). Traditionally, the acid component is provided by (i) a zeolite or by (ii) a chlorinated alumina substrate or by (iii) a sulfated zirconia carrier, the latter both being extremely intolerant of sulfur, water, and other feed contaminants. The zeolite is generally a mordenite and not a Y-zeolite. However, catalysts based on zeolite omega have been shown to be superior to mordenite-based catalysts, but no up-scale to commercial use has been reported for omega zeolite containing hydroisomerization catalysts (see below). 

Customized catalysts are also available for more specialized environmental uses. For instance, Pt/mordenite catalysts are used for the treatment of air pollutants in spray painting and coating workshops, and also to control emission in benzoic anhydride manufacturing industries. Pt-V205-S04 /mordenite is sometimes employed to purify flue gases containing sulfur compounds. Metal-based catalysts are ideal for such applications, because they work at low reactant concentrations (4-6 g/m ), high space velocities... 

At present, the major interest lies in catalysts based on synthetic X-and Y-type faujasite and synthetic mordenite. 

Paraffin isomerization over dual function catalysts based on zeolite Y and mordenite has been reviewedand a reaction mechanism was proposed in which olefin-paraffin equilibrium is established and carbonium ions are formed from both paraffins and olefins. The isomerization of n-hexane and hydrocrack-... 

While the present study has not examined the performance of zeolite based catalysts, Table V summarizes patent literature data(23b) for a mordenite and platinum/alumina mixture. Data for the Pt and SAPO-11 mixture obtained under similar conditions are presented for comparison. The mordenite catalyst is significantly less selective than SAPO-11, giving 25.6% ethylbenzene conversion with only 0.5% net xylene production. 

The efficacy of different catalysts at 50°C is given in the Fig.l. Among the catalysts used, HP A (unsupported and supported on KIO) and ion exchange resins (Amberlyst-15 and lndion-130) showed very high activities followed by sulphated zirconia, Filtrol-24 and KIO. The aluminium pillaring with SWy2 showed a little activity. Catalysts based on the zeolites such as H-ZSM-5, Y and mordenite did not show any activity. It appears that the pore sizes of these catalysts pose considerable intraparticle resistance for the reactant 2-MON to access the catalytic sites. 

In earlier work, Thomas and coworkers (1-3) found that NOx in a simulated NWP offgas (containing 2% CO, 3% CO2, 14% O2, 20% H2O and the remainder of N2) could be removed from levels of 10,000 - 30,000 ppm to 300-1,000 ppm by selective catalytic reduction with ammonia over a commercial H-mordenite catalyst (Norton NC-300) at 300-500 C. Based on these results and pilot plant tests, a conceptual process for NOx and CO removal has been designed by Westinghouse Idaho Nuclear Company, Inc. (WINCO). This process consists of three fixed bed... 

Katzer [42] concluded that the alkylation of benzene with propylene in the liquid phase on H-mordenite catalysts is an example of pore mouth catalysis. This conclusion was based on the observation that the counterdiffusion of benzene and cumene under the reaction conditions is extremely slow. 

A complete description of the peculiarities of TS-1 material and catalysts based upon it is not the objective of this chapter. An abundance of high-quality papers concerning TS-1 are available, as are papers on related materials, syntheses, characterizations and applications. " However, a few words are needed. Incorporation of titanium, in a tetrahedral coordination, into high-silica molecular sieve frameworks is the basis of the exceptional catal3hic properties of the material. By using a mental model, if an all-silica MFl framework (mordenite framework inverted, eg. silicalite-1, S-1) is the host of atomically dispersed titanium, we are in the presence of a TS-1 material. 

Catalysts based on zeolites have also been used successfully to remove NOX from the emissions of large and small-scale stationary sources. The zeolite can be extmded directly as a monohth or applied as a washcoat on preformed cordi-erite supports. The use of several zeolites—including wide-pore mor-denite— for this reaction has been patented. Up to 95% NOX conversion can be achieved with mordenite, with no promoters, and some zeolites are stable at temperatures up to 600°C. Long catalyst lives have been achieved in retrofitted coal based SCR units with low sulfur trioxide formation and good poisons resistance. Spent zeolite catalysts can be disposed of in approved landfill sites because they have negligible heavy-metal content. ... 

An active catalyst based on an extmded large-pore mordenite support has also been used. ... 

Ca.ta.lysts, A small amount of quinoline promotes the formation of rigid foams (qv) from diols and unsaturated dicarboxyhc acids (100). Acrolein and methacrolein 1,4-addition polymerisation is catalysed by lithium complexes of quinoline (101). Organic bases, including quinoline, promote the dehydrogenation of unbranched alkanes to unbranched alkenes using platinum on sodium mordenite (102). The peracetic acid epoxidation of a wide range of alkenes is catalysed by 8-hydroxyquinoline (103). Hydroformylation catalysts have been improved using 2-quinolone [59-31-4] (104) (see Catalysis). 

Zeolite samples (NaY. Na-mordenite and Na-ZSM-5) were prepared in Research Institute for Petroleum and Hydrocarbon Gases in Bratislava. A mesoporous alumina, the carrier for reforming catalyst was used. Porosity of pure mesoporous alumina evaluated by t-plot method did not show the presence of micropores within the range of accuracy of 0.001 cm3/g. Mixtures of zeolites with mesoporous alumina were prepared on the base of dried samples in 5% steps. The prepared mixtures of alumina with zeolite were homogenized in vibration mill. 

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