Zeolites alkali cation-exchanged

Dichlorobenzenes are commercially synthesized in the consecutive chlorination of benzene in the presence of Lewis acid such as FeCU in liquid phase. Similar to proton-exchanged zeolites, alkali-cation exchanged zeolites can catalyze the chlorination of monochlorobenzene and zeolite catalysts tend to prevent the consecutive reactions. Furthermore, the product ratio of dichlorobenzene is varied that is the selectivity of para-dichlorobenzene ( PDCB) among DCB isomers (para-selectivity) is promoted. The selectivity to para-dichlorobenzene to more than 85 % is achieved at 80.5 wt. % conversion level of chlorobenzene in zeolite K-L catalyzed reaction. The catalyst K-L shows its superiority over conventional homogeneous catalyst, FeCh. 

Polato, C.M.S., Henriques, C.A., Perez, C.A., and Monteiro, J.LF. (2004) Alkali cations exchange in MCM-22. Stud. Surf Sci. Catal., vol. 154B, Elsevier, Amsterdam, (Recent Advances in the Science and Technology of Zeolites and Related Materials), pp. 1912-1919. 

Yashina, T., Sato, K., Hayasaka, T., and Hara, N. (1972) Alkylation on synthetic zeolites III. Alkylation of toluene with methanol and formaldehyde on alkali cation exchange zeolite.. Catal, 26, 303. 

Side-Chain Alkylation. There is continued interest in the alkylation of toluene with methanol because of the potential of the process in practical application to produce styrene.430 Basic catalysts, specifically, alkali cation-exchanged zeolites, were tested in the transformation. The alkali cation acts as weak Lewis acid site, and the basic sites are the framework oxygen atoms. The base strength and catalytic activity of these materials can be significantly increased by incorporating alkali metal or alkali metal oxide clusters in the zeolite supercages. Results up to 1995 are summarized in a review.430... 

Heutral cr acidic pH values aake it possible tc start with cations which are sparingly soluble in alkaline aediua (e. g. divalent cations) or do not eziat in such a aediua (e. g. NH4 ). Hhen the NH4+ cations replace the usual alkali cations, the Materials obtained are therefore alkali-free and a siaple calcination yields the acidic fora cf the zeolite. The cation exchange step ia thus bypassed. 

Onaka and coworkers have reported highly selective V-monoalkylation of aniline and its derivatives over alkali cation exchanged X- and Y-type zeolites. The intrinsic pore structures of X and Y zeolites are assumed to be responsible for the high selectivity. Linde 3A zeolites cannot promote the alkylation of aniline because of their smaller pore structure (Scheme 3). Aniline derivatives having strong electron-withdrawing substituents, such as p-nitroaniline, which is otherwise hardly alkylated even in the presence of KOH, can be successfully alkylated in benzene. Celite coated with KF is also effective for the alkylation of amines. - ... 

Deka, R.Ch., Roy, R.K. and Hirao, K. (2004) Local reactivity descriptors to predict the strength of Lewis acid sites in alkali cation-exchanged zeolites. Chem. Phys. Lett., 389, 186-190. 

The influence of the alkali cation exchange in faujasite type zeolites on the zeolite acidity and electronegativity is presented. Correlations between the changes of these parameters and the activity and selectivity of zeolites in the hydrosul-phurization of alcohols are discussed. It was stated that for these processes in which the dissociatively adsorbed H2S takes part, the increase of the zeolite electronegativity causes the decrease in the activity. 

The aim of our study was to present the changes in properties of zeolites after alkali cation exchange and their influence on the hydrosulphurization of alcohols. 

The structure of X-type zeolites is more sensitive to the cation exchange and reaction conditions than that of Y-zeoli-tes (ref.3,4). Therefore, the major catalysts in our study were Y-type zeolites, despite the fact that X zeolites show higher activity in the reactions with H2S contribution. IR and X-ray studies of alkali cation exchanged Y zeolites indicated that no structural changes occured after the modification of... 

Fig. 1. MS/TPD spectra of pyridine preadsorbed on alkali cation exchanged Y-type zeolites temperature of activation 673 K.

The Increase in the zeolite electronegativity resulted from the alkali cation exchange causes the decrease in the thiols formation. 

The bulk chemical composition of alkali-cation exchanged zeolites was established... 

This facile loss of water was shown to be reversible by Damour (1840) and, in 1858, Eichorn showed that the zeolite chabazite contained alkali and alkaline earth metals, which were capable of being reversibly replaced, that is, the zeolite exhibited cation-exchange properties. Analysis of zeolite minerals showed them to be aluminosilicates and their easy loss of water and cation exchange was evidence for the open nature of their structures, often likened to a sponge. The description zeolitic water has been widely used to describe loosely held water in any solid. 

On the basis of an infrared study of the adsorption and reaction of methanol and dimethyl ether over alkali metal cation exchanged zeolites, we propose a reaction mechanism for the decomposition of methanol over alkali cation exchanged zeolites. Additionally, formaldehyde adsorption is performed on these molecular sieves and attempts will be made to correlate its adsorption structure with the surface reactivity. 

Ti02-Si02 mixed oxide Alkali cation exchanged EMT zeolites... 

SELECTIVE N-MOTC)ALKYLATION OF ANILINE DERIVATIVES BY USE OF ALKALI CATION EXCHANGED X- AND Y-TYPE ZEOLITES... 

In the presence of alkali cation exchanged Y-type zeolite, the reaction of aniline with dimethyl sulfate was promoted to give N-methylaniline and N,N-dimethylaniline (Table I)[3]. The order of the effectiveness of alkali cation of Y-type zeolite was K>Na >Cs in the conversion. X-Type zeolite also accelerated the reaction. 

Di or trivalent cations are able to induce the dissociation of coordinated water molecules to produce acidic species such as MOH+ (or MOH2+ for trivalent metal cations) and H+. Several infrared studies concerning rare-earth or alkali-earth metal cation exchanged Y zeolites have demonstrated the existence of such species (MOH+ or MOH2+) [3, 4, 5, 6]. However, the literature is relatively poor concerning the IR characterization of these acidic sites for LTA zeolites. The aim of the present work is to characterize 5A zeolite acidity by different techniques and adsorption tests carried on 5A zeolite samples with different ion exchange. 

The protons released are presumably available to compensate for the loss of the charge balancing cations within the zeolite. In conventional syntheses, the phtha-lonitrile condensation normally requires the nucleophilic attack of a strong base on the phthalonitrile cyano group [176, 177]. This function is presumably accommodated by the Si-O-Al (cation) basic sites within the ion-exchanged faujasite zeolites [178, 179]. The importance of this role is perhaps emphasized by the widespread use of alkali metal exchanged faujasites, particularly the more basic NaX materials of higher aluminium content [180, 181] as hosts for encapsulated phthalocyanine complexes. 

The replacement of Si4+ by Al3+ ions in the tetrahedra generates a deficit of one positive charge per aluminum ion, which must be compensated by the incorporation of extrinsic cations in the zeolite structure. The sodium or calcium ions which are most commonly found in natural or synthetic zeolites can be exchanged with other alkali, alkaline-earth, rare-earth, or transition metal ions. The zeolite open structure can accommodate not only the extraframework cations, but also various molecules provided that their size is smaller than the zeolite apertures. A key feature of cation-exchanged zeolites is the local electrostatic field associated with the cations. This has led to the view of zeolites as solid solvents (258 and references therein). 

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