Silica to alumina ratio

Catalyst acid properties depend on several parameters, including method of preparation, dehydration temperature, silica-to-alumina ratio, and the ratio of Bronsted to Lewis acid sites. 

The exact nature of the zeolite is determined by the reaction conditions, the silica to alumina ratio and the base used. For example zeolite /3, a class of zeolites with relatively large pores, in the range of 0.7 nm, of which mordenite is an example, are usually made using tetraethylammonium hydroxide as the base. This acts as a template for the formation of 12-membered ring apertures (Figure 4.3). 

The ZSM-5 zeolite had a SAR (silica-to-alumina ratio) value of 38 and were supplied by CENPES/PETROBRAS. These samples, as received, were submitted to two ion exchange processes with ammonium chloride solution at 323K for sodium content reduction, followed by calcinations at 773K under dry air flow for transformation to its acid form. 

Mixed matrix membranes with low silica-to-alumina ratio molecular sieves and methods for making and using these membranes. US Patent 7138006 B2. 

Six kinds of zeolites decatlonlzed-mordenltes and Na-mordenltes with different silica to alumina ratios were used In the present study (Table 1) decatlonlzed mordenltes were prepared from corresponding Na forms. These zeolites were supplied by the Catalysis Society of Japan as reference catalysts. 

The surface silicon concentration at the first saturation was found to decrease with the silica to alumina ratio of zeolite, shown in Table 1. A relatively small concentration on silica was remarkable. Saturated silicon concentration therefore seemed to be correlated with the aluminum concentration of zeolites. 

Because of the consecutive reaction by produced water, the deposition on HN was hardly saturated at 593 K however, it was saturated at room temperature. The saturated silicon concentration on the HM thus measured at room temperature (Table 1) decreased with the silica to alumina ratio of zeolite, similar to that on the NaM. 

In the first line of research, large pore high silica to alumina ratio zeolites obtained by synthesis,... 

The effect of ZSM-5 as an octane additive to a cracking catalyst was studied in both a small fixed-bed reactor and a fluidized-bed pilot plant. Analyses of the products of these tests were used to determine the reaction chemistry. It was found that by maximizing the ratio of isomerization activity to hydrogen transfer activity, gasoline octane was increased with a minimum of yield loss. This could be accomplished by increasing the silica-to-alumina ratio of the additive zeolite. 

In two reaction series, with substantially different silica to alumina ratios, the zeolite synthesized changed from Y to ZK-4 as the TMA/Na ratio increased. 

Commercial zeolite based hydroisomerization catalysts comprise alumina bound and platinum impregnated dealuminated mordenite. The activity and selectivity of the hydroisomerization of n-paraffins is strongly influenced by acid leaching. The influence of silica to alumina ratio has been studied for pentane isomerization over platinum mordenite many times since one of the first papers published (6). 

The effect of silica to alumina ratios in the alkylation of aromatics is difficult to study separately because upon changing the Si/Al ratio in the thesis gel both the ratio in the zeolite and the crystal size are changed [97], as well as the crystallinity and morphology. If the Si/Al ratio is changed in a post-treatment stq> by dealumination, vsdiich can be done either by add washing or by steaming, extra framework aluminium ecies are fr>rmed. These edes can block pores and thereby modify the diffiisivities of the reactants and products in the pores and can form a complex with remaining fr-amework aluminium t diich may result in a modified addity of the catalyst. 

Zeolite composition was determined by X ray fluorescence, in a XRF Phillips PW 1407 spectrometer. The fimnework silica to alumina ratio (SAR) was determined by FTIR in the structure vibration region by means of the fi uency shift of a characteristic band around 800 cm with a Nicolet 60SXR spectrometer. The textural characteristics of the zeolites, such as BET specific area, micropore volume (t-plot) and mesopore area (BJH), were evaluated by physisorption of N2 at 77K in a Micromeritics ASAP 2400 and their acid sites density by TPD of NH3 (adsorption performed at 423K with a 4.0% NH3/He mixture and TPD performed at 20K/min up to 823K). 

Zeolites Crystalline alumosilicates, three-dimensional network of silica and alumina with adjusted silica to alumina ratio Hydrophobic or hydrophilic depending on the silica/alumina ratio, cation exchanger, Br0nsted and Lewis acidity... 

In addition to size exclusion and steric inhibition, the intermolecular forces between the zeolite and sorbate molecules offer opportunities to achieve unique selectivity based on competitive sorption properties of various zeolites. Variables such as silica to alumina ratio, the nature of the cation species and the geometry of the channels have been shown to be important factors for consideration (13-14). They also can contribute to catalyst stability and reduced coking propensity, two important characteristics of commercially useful catalysts. 

Many reactions in the fine-chemical industry are performed with organic liquids or in organic solvents. When the surface of a solid-acid catalyst is hydrophilic, the presence of small amounts of water can completely block the surface of the catalyst. Carefully dried catalysts and reagents must then be employed. It may be noted that zeolites with a high silica-to-alumina ratio are hydrophobic. The (internal) surface of the zeolite is, therefore, not readily poisoned by accumulation of (traces of) water. With zeolites, moreover, use can be made of the uniform size of the pores to perform shape-selective reactions after passivation of the catalytic sites on the external surface of the zeolite crystallites. In the bulk-chemical industry several interesting reactions have been developed with zeolite catalysts [27] (cf. the review of Tanabe and Hdlderich [28]). 

Corma s group then published very interesting work on the activity of zeolites in the acylation of anisole with phenyacetyl chloride (Eq. 4) [9]. HY and WP Zeolite are active in this reaction, and modification of catalyst parameters has been examined. The amount of zeolite Na" exchanged and the silica-to-alumina ratio were examined. It was found that the rate of formation of the reaction product correlates linearly with Na exchange, indicating that all the acid sites are active in the reaction. A material does not, therefore, need to have very strong acid sites to have high activity. 

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