Alkaline zeolite

Bernard, J.R. (1980) Hydrocarbons aromatization on platinum alkaline zeolites, in Proceedings of the Fifth... 

Xiang and Ma [86] also recognised the problems of treating mesoporous y-alumina membranes with highly alkaline zeolite precursor solutions. They... 

XPS and IR indicate that Pd is electron deficient in acid zeolites, and has an electron excess in alkaline zeolites EXAFS gives some evidence of this in PtHL.104 Pt particles outside the channels are not significantly modified by the zeolite basicity, and hence give unselective aromatisation, like Y zeolite.174... 

P-09 - /t-Hexane aromatization over Pt-alkaline zeolites ab-initio calculations on the influence of the exchanged cations and zeolite type (L, p and Y) on electronic properties of Pt... 

Zeolites were used in various processes that convert paraffins or olefins into alkyl monoaromatics containing chiefly from six to nine carbon atoms.There are various catalysts, and they involve a base or an acid zeolite, according to the type of process. The first catalyst, identified at the end of the 1970s. is composed of Pt deposited on the L zeolite (Table 2) exchanged with large alkaline ions such as potassium or alkaline earths, such as Ba. which gives it an alkaline nature. This cataiyst is monofunctional and is conceptually different from the conventional bifunctional acid catalysts based on Pt on chlorinated alumina. It selectively dehydrocyclizes the paraffins into aromatics, particularly hexane, which is the least reactive of them. The reaction takes place on the metal, which develops a special selectivity in contact with the alkaline zeolite. This aromatization process has not been successful so far. partly because of the extreme sensitivity of the catalyst to the slightest trace of sulfur compounds. 

Alkaline earth metals in general, and sodium in particular, are detrimental to the FCC catalyst. Sodium permanently deactivates the catalyst by neutralizing its acid sites. In the regenerator it causes the zeolite to collapse, particularly in the presence of vanadium. Sodium comes from two prime sources ... 

The cations that replace the sodium ions determine the catalyst s activity and selectivity. Zeolites are synthesized in an alkaline environment such as sodium hydroxide, producing a soda-Y zeolite. These soda-Y zeolites have little stability but the sodium can be easily... 

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

The coagulant sodium aluminate (NaA102) is strongly caustic (contributing hydroxide alkalinity to the BW) and reacts with calcium and magnesium salts and any silica present to form a zeolite sludge of calcium-magnesium-aluminum silcate. 

Figure 2.5 N2 adsorption isotherms and schematized silicon dissolution (inset) upon alkaline treatment ofZSM-5 zeolites with different framework Si/AI ratios, highlighting the crucial role of framework aluminum.

Most of the papers available on desilication are devoted to the alkaline treatment of ZSM-5 zeolites. Since a large number of zeolites consist of aluminosilicate frameworks and framework Al plays a crucial role in the mesoporosity development during desilication, this methodology should be suitable for extrapolation to other... 

As shown in Table 2.1, the improved catalytic performance of alkaline-treated zeolites compared to the parent purely microporous counterparts has been demonstrated decidedly by different groups active in academia and in industry. The positive effect is reflected in the enhanced activity, selectivity, and/or lifetime (coking resistance) of the hierarchical systems. The examples listed embrace not only a variety of zeohte topologies (MFl, MOR, MTW, BEA, and AST) but also reactions involving hghter hydrocarbons as well as bulky molecules. This illustrates the potential of the desihcation treatment, although more work is to be done in optimizing the catalytic system for the wide variety of applications. 

Reactions with clay minerals can neutralize both low-pH and high-pH solutions. Neutralization of acids occurs when hydrogen ions replace Al, Mg, and Fe. In alkaline solutions, neutralization is more complex and may involve cation exchange, clay dissolution, and reaction of cations with hydroxide ions to form new minerals called zeolites.39... 

Kwak, J.H., Szanyi, J. and Peden, C.H.F. (2004) Non-thermal plasma-assisted NOx reduction over alkali and alkaline earth ion exchanged Y, FAU zeolites, Catal. Today 89, 135—41. 

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