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13C NMR relaxation study and CNDO/2 calculations on some organic molecules adsorbed on Y-type zeolites
No full text
Thermodynamic properties of aqueous non-electrolyte mixtures. Enthalphy of mixing and liquid-liquid equilibrium of water + aliphatic aldehydes mixtures
No full textThe liquid-liquid equilibrium, L-L, and the enthalpy of mixing, HM, for water with ethanal, propanal and butanal mixtures were determined at 298.15 K.
For all the mixtures studied, HM vs. x curves show exothermic mixing in the water-rich region which becomes endothermic at high aldehyde concentrations.
These curves have been interpreted in terms of intercomponent molecular interactions and hydrophobic stabilization of the water structure by molecules of aldehyde. The results obtained indicate that the number of alkyl groups in the aldehyde plays an important role in determining the magnitude of these effects and also influences the miscibility
Temperature-programmed desorption study of ammonia desorption-diffusion in molecular sieves
No full textLiquid-phase alkylation of phenol with t-butanol over various catalysts derived from MWW precursor
No full textThree types of MWW-based catalysts ( MCM-22, MCM-36 and ITQ-2 ) were studied in the liquid phase alkylation of phenol by tert-butanol ( TBA ). Ammonia adsorption calorimetry was applied to investigate the acid properties of zeolites with different framework topology and cristallinity. It was established that acid properties of MCM-22 family depend mainly of the solid Al-content ( the Si/Al ratio varied from 9.1 to 46.0 ).Delamination of MCM-22 precursor ( MCM-22(P)) leading to ITQ-2 results in the decrease of the total acidity and th eincrease of the intermediate acid sites concentration, while the pillaring process yielding MCM-36 affected mainly the total concentration of acid sites, the acid strenght distribution being similar to th ecorresponding MCM-22 zeolite. The catalytic activity and selectivity of zeolite-based calysts are discussed. The most active catalyst for the studied reaction was MCM-22 B ( Si/Al 15 . The results obtained with MCM-22 as catalyst revealed that, despite th expectations due to the presence of 10-MR pores in the structure of this zeolite, no enhanced selectivity to p-tert-butyl phenol is observed. This has been rationalized by the assumption that most of reactions occurring in this system take place on acid sites at or close to the external surface. This assumption is also supported by the similar catalytic selectivity of the MWW-derved structures ( viz. MCM-36 and ITQ-2 ), which expose a higher concentration of external pockets. However, it is noticeable the high catalytic activity of MCM-22 zeolites for the liquid phase alkylation of phenol by TBA that is comparable to the gas phase activity of large pore zeolites like as HY or HM
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