Quartz catalysis mechanism

Results received in the studies of quartz-catalysis allow one to suggest that the mechanism of action of quartz catalysts is a result of as5mimetrie adsorption on the surfaee of optically active quartz. The effeetiveness of asymmetric catalysis is determined by the ability of the catal54ic system to form the labile diastereomeric complex intermediate, whieh will be determined by the extent of spatial correspondenee of the configuration of the reacting molecule to the structure of the surface of the... 

Basic Catalysis. The catalytic properties of alkali zeolites free of acidic sites have been investigated for the cracking of hexanes (25, 26). At 500 C K-Y zeolite cracks easily n-hexane and its isomers resulting in product distributions markedly different from those obtained over acidic zeolites or even by thermal cracking (pyrolysis). Free radical-type mechanism predominates on the zeolite surface. The relative rates of H atom abstraction (bimolecular) and B-scission (unimolecular) are greatly affected by the zeolite matrix. Zeolites also concentrate hydrocarbon reactants within the crystal, which enhances the rate of bimolecular reaction step. Comparison with silicalite (Al-free ZSM-5 zeolite) and quartz chips has been done in order to characterize the zeolitic effect. Silicalite behaves as inert quartz chips with no effect on the rate of H-abstraction step,... 

Catalyzed gaseous systems. The reaction between CO and CO2 at elevated temperatures ( 860-920°C) represents a classic example of carbon isotope exchange enhanced by catalysis with surfaces such as quartz, gold and silver (Brander and Urey 1945, Hayakawa 1953). In addition to rate enhancement on catalytic metal or oxide surfaces, Brander and Urey (1945) also observed an increase in rate in the presence of H2 or H20(v). They tested a variety of mechanisms to explain their experiments which involved reaction of C-enriched CO2 with normal CO as a function of temperature, gas... 

For the mechanism of asymmetric catalysis on metal-quartz catalysts there is no unifying point of view. There are the concepts of "contact activation", "specific adsorption", and "formation of specific chemical bonds" It has been proposed that on the surface of the catalyst intermediate surface diastereomers are formed which are decomposed at different rates. The data on the action of quartz-catalysts have been rather thoroughly discussed in addition positive estimations of data were given by Bonner and Harada... 

Xenides D, Maroulis G (2000) Basis set and electron correlation effects on the first and second static hyperpolarizability of SO2. Chem Phys Lett 319 618-624 Xiao Y, Lasaga AC (1994) Ab initio quantum mechanical studies of the kinetics arrd mechanisms of quartz dissolution H /HsO catalysis. Geochim Cosmochim Acta 58 5379-5400 Xiao Y, Lasaga AC (1996) Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution OH catalysis. GeocMm Cosmochim Acta 60 2283-2295 Xu SC, Zhao XS (1999) Theoretical investigation of the reaction of CIONO2 with H2O on water clusters. J Phys Chem A 103 2100-2106... 

Xiao, Y., and Lasaga, A. C. 1996. Ab-initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution OH-catalysis. Geochem. Cosmochem. Acta 60 2283. 

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