Cracking catalysts comparing activity from acidity

Weisz and Miale compared the activity for hexane cracking of a number of zeolites (Table 4.25) with a highly active silica — alumina (10% alumina). The zeolites are at least 10 times as active as amorphous silica —alumina. The catalytic process, however, cannot utilize the activity from a pure zeolite catalyst. The catalyst must be modified to decrease the acid-strength to avoid excessive formation of coke and low molecular weight gases, at the expense of gasoline. Moreover, the catalyst must be able to withstand the thermal and hydrothermal conditions experienced in regeneration. It must also withstand breakup in the mechanical circulation systems. A detailed description of the preparation of industrial catalysts is found in the literature. 

Activated kaolinite and halloysite/endellite clays were also used as cracking catalysts. The double-layer lattice of kaolinite consists of alternating tetrahedral silica and octahedral alumina layers and the halloysite/endellite stractures have interlamellar water layers. There is very little cation exchange with natural clays of this type but after heating at 600°C to dehydrate and destroy the lattice, alumina can be extracted with acid to give catalysts comparable to activated montmorillonite. Kaolin-based cracking catalysts were therefore used to replace montmorillonite types, mainly because they did not suffer from the deactivating... 

As expected from the TPD results, Al-sapo was more active for the cracking of cumene on a per weight of catalyst basis than Al-mont. In order to compare the catalytic activity on a basis of active sites, we evaluated the number of active sites on these catalysts. TPD spectra were measured with varying the temperature of ammonia adsorption. Typical results on Al-mont are shown in Fig. 2. By integrating these spectra, the concentration of acid sites corresponding to different strength of acidity can be determined. 

Delaminated zeolites like 1TQ-2, benefiting from greater accessibility of acid sites and shorter diffusion pathways, exhibited a higher catalytic activity in cracking of 1,3-diisopropylbenzene or vacuum oil compared with MCM-22 [15]. However, it seems that a high potential of delaminated catalysts can be found in synthesis of special chemicals. Corma and Fomes showed the synthesis of 2-melhyl-2-naphthyl-4-methyl-l,3-dioxolane, which has an orange blossom fragrance [110,111],... 

This paper describes the physicochemical properties of natural rectorite samples pillared with aluminum chlorhydroxide (ACH) solutions containing (Aljj) the [A1j2 4(0H)24(H20) 2 cation. Stability, acidity, cracking activity and product selectivities from gas oil conversion will be compared to those of similarly prepared pillared montmorilIonite catalysts. 

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