Dual-zeolite catalyst

Dual zeolite catalysts were prepared by physically blending Super-D with the catalyst containing 25 Wt.% ZSM-5 so as to achieve 1 Wt.% ZSM-5 in the physical blend. Two blends, one containing steam treated Super-D and thermally treated ZSM-5 catalyst and the other containing steam treated Super-D and steam treated ZSM-5 catalyst were prepared. Each of the blends was then intimately mixed. 

Gas Oil Cracking by the Dual Zeolite Catalyst. After the steam pre-treatment, the gas oil cracking activity of REY was about 100 times greater than the activity of the pure matrix catalyst. 

To clarify the mechanism by which gasoline composition is changed (reduction in concentration of the paraffins and an increase in concentration of olefins and aromatics) by ZSM-5 in the dual zeolite catalyst, experiments were carried out on catalysts containing only ZSM-5 dispersed in the matrix. The catalyst containing 1 Wt.% ZSM-5 was used in order to duplicate the concentration of ZSM-5 in the dual zeolite catalyst studied earlier. Experiments with the pure matrix catalyst were used to define the contribution of ZSM-5. 

A mechanism that postulates prevention of paraffin formation during gas oil cracking with the dual zeolite catalyst can explain the above data. Such a prevention could take place by more than one route. ZSM-5 present in the catalyst could prevent certain secondary reactions that lead to the formation of gasoline range... 

Previously, we have developed several techniques for platinum supported zeolite catalysts to improve the benzene product purity, including on-line sulfiding [3], precoking [6], and dual-bed catalyst system [7]. We report herein an in-depth investigation on the synergism of proton zeolite and platinum supported ZSM-12 catalyst (Pt/Z12) in a cascade dual-catalyst system. 

Whereas over the dual-bed catalyst system, namely Pt/Z12(80) HB(20), a significant improvement in benzene purity up to 94.60% was observed. This is ascribed due to selective cracking of naphthenes over acidic zeolite H-Beta at the bottom bed. 

A dual-bed catalyst system has been developed to tackle the key problems in benzene product impurity during heavy aromatics transalkylation processing over metal-supported zeolite catalysts. It was found that by introducing zeolite H-Beta as a complementary component to the conventional single-bed Pt/ZSM-12 catalyst, the cascaded dual-bed catalyst shows synergistic effect not only in catalytic stability but also in adjustments of benzene product purity and product yields and hence should represent a versatile catalyst system for heavy aromatics transalkylation. 

Paraffin isomerization of heavy alkane feeds is often used to alter the cloud or pour point of diesel or lube fractions. Catalysts for this reaction are almost always dual-function catalysts of Pt supported on a one-dimensional zeolite. Using a onedimensional zeolite allows control of the isomerized product to contain few branches, usually methyl branches (Table 12.4). 

Hydrocarbon Cracking Selectivities with Dual-Function Zeolite Catalysts... 

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... 

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. 

Hydrocracking Pd on zeolite in an amorphous matrix NiMo on silica-alumina, various other dual-function catalysts (adiabatic fixed beds)... 

Historically, the isomerization catalysts have included amorphous silica—aluminas, zeolites, and metal-loaded oxides. All of the catalysts contain acidity, which isomerizes the xylenes and if strong enough can also crack the EB and xylenes to benzene and toluene. Dual functional catalysts additionally contain a metal that is capable of converting EB to xylenes. 

Cerqueira and co-workers203 confirmed the appearance of the of the tetrahedral aluminium and phosphorus in AlPO-like crystalline structures both in beta (BEA) and in MOR zeolites treated with phosphoric acid. 31P MAS,27Al MAS and TQM AS NMR spectra permitted the species present in the samples to be assigned. Possibly, besides the the Altet-f species, other Al species are also taking part in the activity and selectivity of the catalysts. The formation of Alocl o P can also contribute to the increase in the activity by preventing further dealumination. Dual zeolite additives have no impact on the quality of naphtha when compared to MFI-based additives, which are used in the fluid catalytic cracking processes. 

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-... 

BP found that it is possible to reduce pour points catalytically. A mordenite dual-function zeolite catalyst in the hydrogen form (to confer acidity and... 

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