Authors:Hanene Najar, Mongia Zina, and Abdelhamid Ghorbel
The aim of the present work was to combine different physicochemical techniques, namely X ray diffraction, IR spectroscopy,
and multinuclear (29Si and 27Al) solid-state NMR spectroscopy, to study the aluminum distribution and to determine the silicon–aluminum ordering in the
Y-zeolite framework when the latter was submitted to acid leaching (HCl, HNO3, H2SiF6). It was shown that all acids were effective in removing Al from the framework. Moreover, the extra-framework Al extraction
from the lattice was dependent on the nature and the concentration of the acid. After the dealumination treatment, different
species (silanol nest, six-coordinated non-framework Al) were detected. The investigation showed that the breakdown of the
parent Y-zeolite mainly depends on the degree of dealumination.
Authors:M. Olguin, J. Duque, R. Pomés, M. Villafuerte-Castrejón, L. Sansores, P. Bosch, and S. Bulbulian
The present study discusses the incorporation of uranyl ion into Y-zeolite framework. The UO
sorption was measured by neutron activation analyses. The Y-zeolite framework distorts in response to the cations present in the structure. Hence, depending on the amount and the location of the exchanged cations, the features of the X-ray diffraction pattern may vary. From the Rietveld analysis of these patterns, the positions occupied by the UO
cations in the zeolite network were determined.
NH4Y and NH4LaY-type zeolite catalysts were prepared by cyclic ion-exchange of a synthetic Linde Y-zeolite. The release of ammonia and water were followed by evolved gas analysis (automatic thermogastitrimetric equipment) as well as with a continuous selective water detector.
Authors:Maria Gonçalves, Méri Vieira, Wildson Cerqueira, and Ana Teixeira
The purpose of this work was to employ the differential thermal analysis technique (DTA) to compare variations in the collapse
energy of the Y zeolite crystalline structure in a fresh sample and in the sample after temperature treatment and impregnated
with 3,000 ppm of vanadium and nickel. A small exothermic signal in the DTA curve at 950–1,150 °C indicated the collapse of
the crystalline structure. The areas of the exothermic signals in the DTA curves of the samples indicated a 20% reduction
in the exothermic area peak of sample treated 600 °C for 3 h and 25% reduction in same peak in the metal impregnated Y zeolite.
These results were compared with X-ray data leading to the conclusion that metal impregnation affects the Y zeolite crystalline
structure and that the DTA technique is a potentially useful tool for measuring the integrity of Y zeolite in catalysts.
Authors:N. Fonseca, F. Lemos, S. Laforge, P. Magnoux, and F. Ribeiro
In this work, n-decane cracking, taken as a model reaction for the catalytic cracking of Fischer–Tropsch naphta fraction, was carried out
at 350 °C over various H-Y zeolites, with different Si/Al ratios and, thus, different acid strength distributions. It was
observed that the catalytic activity does not decrease gradually with the contact time for the catalysts under study, notably
for the zeolite samples having lower activity (hence lower total acidity as well) but, in fact, the catalytic activity first
increases with contact time and then decreases. This behavior was successfully interpreted by resorting to the fundamental
view of the catalytic cracking mechanism as a series/parallel scheme. The authors combined the bi-molecular process involving
a carbenium-chain mechanism and the protolytic process involving the formation of carbonium ions to construct a simple model
to predict, in as much detail as possible, the zeolite catalytic performance of the different catalysts that were used.
Authors:Maria Gonçalves, Joyce Barreto, Wildson Cerqueira, and Ana Teixeira
This work evaluates the effect of the FCC catalyst components—Y zeolite, kaolin and alumina—on the formation of coke during
the cracking of heavy residue (HR) of petroleum. The Y zeolite, kaolin and alumina were mixed with a HR at a ratio of approximately
1:4. The effect was studied using dynamic thermogravimetry at a heating rate of 50 K min−1, with N2 (between 35 and 700 °C) and air (in the 700–1,000 °C temperature range). The HR analyzed in these conditions formed 8.1%
of coke. All the mixtures presented larger coke formation than that observed in pure HR. The Y zeolite presented fourfold
larger coke formation, while kaolin and alumina showed twofold higher formation than pure HR. The major focus of this study
was to verify the sensitivity of the TG technique in providing information about coke formation in the fluid catalytic process
Authors:J. Jiménez-Becerril, D. Estévez, and S. Bulbulian
Fluorine-18 has been determined in neutron irradiated lithium aluminosilicate. This compound was obtained by a high temperature thermal transformation of Li-exchanged Y zeolite. Fluorine-18 formed in neutron irradiated lithium aluminosilicates was swept with a gas mixture of Ar with 0.1% hydrogen.
Thermal behaviour of pure LiN3, NaN3, CsN3 and their mixture with the respective LiY-FAU, NaY-FAU, CsY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. Thermodesorption of CO2 was applied to compare the basicity of the alkali ionexchanged Y zeolites. Two of the investigated systems, the NaN3/NaY-FAU and the CsN3/CsY-FAU gave single, well defined and reproducible azide decomposition features rendering these samples to apply as catalyst precursors for preparation of zeolite with basic character.
Authors:V. Rakić, V. Dondur, R. Hercigonja, and V. Andrić
The active sites of hydrogen-exchanged Y zeolite (HY) and dealuminated (HDY) zeolites are investigated by TPD of carbon monoxide.
Only the high temperature TPD spectra of CO (TM620-690C) were observed, meaning that CO molecules interact with very strong
acid sites. The amounts of CO bonded on these sites are small (less than 1 molecule per unit cell). The strong influence of
dealumination on the coverage degree is found. The calculated values for kinetic parameters indicate chemisorption of CO in
the investigated systems (Edes240 kJ mol-1, A1011 s-1).