Zeolite sodium-doped

For example, using an acidic H-ZSM-5 with Si/Al = 300 at 350 °C 2,5-dimethylfuran DMF is produces with 96.1 % yield at 99.8 % conversion of acetonylacetone. On the other hand, if this zeolite is doped with alkali ions in excess of their framework Al-content (Si/Al = 300, Na/Al = 7.6) then 89.1 % yield of methylcyclopentenone MCP is obtained at quantitative conversion. Only a 4.4 I yield of DMF is. observed using that basic zeolite catalyst. The number of alkali ions which are in excess of the corresponding Al content of the zeolite framework are associated with the internal silyloxy groups in the as - synthesized form of high silica zeolites. The behaviour of such a Na-ZSM-5 is very much like sodium silicalite. 

The abovementioned rate acceleration and selectivity enhancement brought about by catalysts are particularly marked when unactivated dienes and dienophiles are involved. Two molecules of 1,3-butadiene can react in a Diels-Alder reaction, one acting as diene and the other as a dienophile to produce 4-vinylcyclohexene (in 0.1% yield at 250°C in the absence of a catalyst). Cs+, Cu,+ and trivalent transition-metal exchanged montmorillonites534 as well as large-pore sodium zeolites (Na ZSM-20, NaY) and carbon molecular sieves,535 result in 20-35% yields with 95% selectivity. Large rate enhancement was observed when 1,3-cyclohexadiene underwent a similar cycloaddition536 in the presence of K10 montmorillonite doped with Fe3+ ... 

Very striking results on the interactions of molecules with a catalyst have been recently reported in zeolite catalysis because of the well ordered structure of these materials it is worth mentioning the subjects of zeolite design [10] and of acidic properties of metallosilicates [11]. In other areas where polycrystallinic or even amorphous materials arc applied, highly interesting results are now numerously emerging (such as hydrocarbon oxidation on vanadium-based catalysts [12] location of transition metal cations on Si(100) [13] CO molecules on MgO surfaces [14] CH4 and O2 interaction with sodium- and zinc-doped CaO surfaces [15] CO and NO on heavy metal surfaces [16]). An illustration of the computerized visualization of molecular dynamics of Pd clusters on MgO(lOO) and on a three-dimensional trajectory of Ar in Na mordenitc, is the recent publication of Miura et al. [17]. 

Recent work in Versailles and Santa Barbara has led to the synthesis of several nanoporous nickel(II) phosphates. A zeolitic nickel(II) phosphate, VSB-1 (Versailles/Santa Barbara-1), was prepared under simple hydrothermal conditions [22] and has a unidimensional pore system delineated by 24 NiO and PO4 poly-hedra with a free diameter of approximately 0.9 nm (Figure 18.7). It becomes microporous on calcination in air at 350 °C, yielding BET surface areas up to 160 m g and is stable in air to approximately 500 °C. The surface area appears low compared with aluminosilicate zeolites, but the density of VSB-1 is twice that of a zeolite and the channel walls are particularly thick. VSB-1 can be prepared in both ammonium and potassium forms, and exhibits ion-exchange properties that lead, for example, to the formation of the lithium and sodium derivatives. Other cations (e.g. Mn, Fe, Co, and Zn) can be substituted for Ni in VSB-1, up to a level as high as 30 atomic%. The parent compound shows canted antiferromagnetic order at Tn = 10.5 K with 6 = —71 K on doping with Fe, Tn increases to 20 K and 6 decreases to —108 K. 

In 1968 Venuto and Landis reported on the use of sodium- and rare-earth metal-doped zeolite X in the rearrangement of ethylene oxide and propylene oxide to the corresponding aldehydes [17]. In addition to the desired propanal, acetone was formed with these catalysts because of the hydride shift induced by the intermediate carbocation consecutive reactions were also observed. Such catalysts also suffer from rapid deactivation. 

Oil cracking catalysts contain identical concentrations of the following components a silica-alumina refractory material, and inert substance and sodium zeolite doped with La, Nd and Pr. The presence of REE in the zeolite increases the cracking capacity of the catalyst and its thermal stability at high temperatures [4]. 

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