Active sites nature

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

Gilson, M.K. and Honig, B.H. (1987) Calculation of the electrostatic potentials in an enzyme active site. Nature, 330, 84-86. 

Gilson, M. and B. Honig. (1987). Calculation of Electrostatic Potentials in an Enzyme Active Site. Nature. 330 84. 

As for the reaction of benzene partial oxidation, no one siqtported VPO system was tested before. Nevertheless, such catalysts could be quite suitable to estimate active sites nature and role of the catalyst composition, to study surface chemistry and hydrocarbons conversion mechanism. 

The subtle mechanistic nuances between air-CaaD and CaaD were discovered by affinity labeling with (if)-oxirane-2-carboxylate and subsequent crystallographic analysis (Figure 15(b)). ° The carboxylate side chain of (/f)-oxirane-2-carboxylate enables it to bind at the active site of air-CaaD, in a mode that results in the covalent modification of Pro-1 and the loss of catalytic activity. The affinity-labeling reaction is stereospecific, because the (5)-enantiomer of oxirane-2-carboxylate does not alkylate the enzyme. The rate of inactivation is also hindered by the presence of substrate. T aken together, these findings support the active site nature of the inactivation process and the critical contribution of Pro-1 to activity. 

It should be noted that the information examined on active sites nature was obtained without carrying out complicated quantum chemical calculations within a supermolecular approach. It is important that a clear analysis is probable on this basis of the chemical consequences of any change in composition and surface and bulk structure of oxides and their compositions (from ionic implantation to destruction of the system simulated) what allows to recognize calculations with real counting electrostatic... 

The deactivation of zeolites which occurs during the reactions of organic compounds is mainly due to the formation of secondary products heavier than the reactant(s) and the desired product(s). These secondary products remain blocked either in the pores of the zeolite, on the outer surface of the crystallites or in both positions. As has been shown in various reviews [1-4] the rate of their formation and their composition depend on numerous parameters pore structure, active sites, nature of the reactant(s), temperature... 

Gun ko, V.M., Turov, V.V., Zarko, V.I. et al. 1997a. Active site nature of pyrogenic alumina/silica and water bound to surfaces. Langmuir 13 1529-1544. 

The characterization of active sites of solid catalysts includes the determination of active sites nature, the estimation of their density (or population, i.e. the number of active sites per unit of mass or per unit of surface area), their strength and strength distribution. Active sites can be acidic, basic and, in certain cases, amphoteric. All mentioned characteristics are very important for catalysts functionality therefore, many experimental techniques are invented and adapted for their investigation. Among others, mainly spectroscopic methods (like NMR, IR, XPS, XRF...), temperature-programmed desorption is particularly important because it can be useful in the characterization of all mentioned features. 

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