Silica-alumina matrix

The earliest catalyst was made from clay later, synthetic beads from siUca-alumina were introduced. In the early 1960s, catalysts were introduced that employed up to 10% X or Y zeolite in a silica-alumina matrix. 

Source of Silica. Silica can migrate either from free silica present in the cracking catalyst or from the silica alumina matrix but not as readily from the zeolite. Figure 11 shows SEM-EDAX silicon scans of cerium/alumina steamed in the presence of these three sources of silica. Again, the bright dots represent silicon. Qualitatively the sample steamed with pure silica contains more silicon than the sample steamed with silica-alumina. The sample steamed with zeolite shows silicon at the surface of the cross-sectioned particle but little in the interior. The surface silicon comes from dusting of the particle with very finely divided zeolite. 

The heterogeneous catalysts employed in cracking are acidic materials composed of 3 to 25% (wt) of zeolites embedded in a silica-alumina matrix. Zeolites are crystalline aluminosilicates possessing a network of uniform pores whose walls hold the catalytically active acid sites. The reactant molecules pass through the pores and react within the zeolites. 

Simultaneously scientists at Esso Research and Engineering and Mobil Oil were working with X based catalysts [33-35]. Mobil Oil introduced the first zeolite based catalysts for cracking gas oils in 1962 using rare earth exchanged X in a silica-alumina matrix. This replaced the older silica-alumina catalysts. When we made Y available, the Y based catalysts largely replaced the X based catalysts in this application. 

By impregnating, with a salt solution of the element (or elements) to be determined, a powder obtained by very finely crushing the support corresponding to that of the sample this method is used for analysis of trace or minor elements in an alumina or silica alumina matrix... 

The catalyst used is a commercial catalyst known as the super-D manufactured by Crosfield Chemicals Ltd., UK. It is in the form of particulate spheroid with an average diameter of 81 microns and consists of 15-18% ion exchanged Re sodium Y-zeolites on a support silica-alumina matrix. Heat treatment of catalyst particles at 150°C for 48 hours is undertaken before cracking reaction commenced. The isopropyl benzene (cumene) has the purity higher than 99.5% which was supplied by Fissons Scientific Apparatus. 

The Plank group was large and emphasized preparation and activity testing of an enormous number of zeolite catalysts. They soon Incorporated a zeolite in an amorphous silica-alumina matrix and found that the initial activity of this catalyst was vastly superior to any amorphous silica-alumina catalyst that was utilized at that time. With this encouraging result, they quickly improved upon their catalyst formulation and a number of patents were obtained. They obtained a synergetic effect with their catalysts since they had superior activity and selectivity over that expected from the sum of the two when tested separately. 

Catalyst. The studied FCC catalyst and its main characteristics are presented in Table 1. It consists of Y-zeolite, a silica-alumina matrix and a binder. It was pretreated prior to evaluation by an ex-situ hydrothermal treatment at 1043 K for 15 h using 100% steam. For the physicochemical characterization, XRD (unit-cell size, relative cristallinity), XRF (aluminium, silicon and rare earth and metal content), N2 ad/desorption and Hg intrusion (Sbet, and pore volume) measurements were done. 

When higher-activity catalysts consisting of zeolites incorporated in a silica-alumina matrix were introduced, first to TCC units in 1962 and then to FCC... 

---