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In this article, we considered all aspects of acidity (nature of acid sites, strength, density, etc.) in solid catalysts and in zeolites in particular. After reminding the definition of acidity in liquid and solid acids, we emphasized acidity characterization by the most used physical techniques, such as Hammett's indicator titration, microcalorimetry of adsorbed probe molecules (ammonia, pyridine or other amines for acidity characterization and CO2 or SO2 for basicity characterization), ammonia or any amine thermodesorption, IR spectroscopy of hydroxyl groups and of several probe molecules adsorbed (ammonia, pyridine, piperidine, amines, CO, H2, etc.), MAS-NMR of 27Al, 29Si, 1H elements and of 1H, 13C, 31P, etc. of adsorbed probe molecules, and model catalytic reactions. Modeling the way the acid features of zeolites influence the catalytic activity of these catalysts toward acid-catalyzed reactions (relation between ammonia desorption activation energy values and catalytic activities, reaction mechanism...

A series of partially Na-exchanged H-EU-1 zeolites, with an exchange ratio comprised between 0% and 47%, was prepared by contacting an H-EU-1 zeolite sample with NaNO 3 solutions of increasing concentrations. As expected, the final Na content of the zeolite increased with the NaNO 3 concentration and led to a progressive decrease of the Bronsted acid site concentration, without modifying the Lewis acidity or the crystallinity of the zeolite sample. Nevertheless, NH 3 -TPD experiments showed that the distribution in acid strength did not vary monotonously with the acid site concentration. At low exchange ratio ( −1 ) and proportion (from 28% to 11%) , some of those sites being located in 12-ring pockets covering the zeolite external surface. For an exchange ratio comprised between 26% and 35%, the amount (and proportion) of very strong acid sites increased significantly ( ≈ 200 μmol g −1 hence 40% of the total concentration in acid sites). This increase of the acid strength could be due to an optimal decrease of the acid site density.

RAFFINAGE+MTF; This work presents an insight on the reactivities of different geographical origin residues in hydrotreatment processes. Hydrodemetallization (HDM) and hydrodesulfurization (HDS) experiments have been performed on different vacuum residue (Arabian Light, Buzurgan, Djeno and Ural) with commercial catalysts under industrial conditions. Depending on its origin each residue appears to have a specific behavior; however, some general trends can also be highlighted. One key reactivity parameter (both for HDM and HDS reactions) seems to be the size of residue molecules that depends strongly on its origin. In fact, diffusion limitations may occur, even in the HDM section. Hydrodesulfurization (HDS) reactions are not completely controlled by diffusion; the nature of chemical structures also appears to be an important parameter for reactivity. A better knowledge of the chemical structures is therefore still necessary to understand these different reactivities. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; Fluid Catalytic Cracking (FCC) catalysts are based on combinations of two main active phases, the HY and the HZSM-5 (additive) zeolites, but previous studies only concerned the phenol influence on these pure zeolites. Therefore, n-heptane was transformed in presence of phenol over mechanical mixtures of HY and HZSM-5 zeolites, at 450 degrees C, to evaluate the FCC catalysts behaviour during phenolic-rich bio-oils/conventional FCC feedstocks co-processing. Phenol induces an additional deactivation of the zeolites mixtures from the beginning of the reaction because increases the carbon deposition, as for pure zeolites. However, mixing the zeolites, the impact of phenol on HZSM-5 seems to not be as strong as for HZSM-5 alone due to an initial preferential adsorption of phenol on HY, as suggested by the adsorption energies of phenol on these catalysts calculated by Density Functional Theory (DFT), -80 kJ mol(-1) for HY and -60 kJ mol(-1) for HZSM-5. This agrees with the initial products distribution, which points out an enhancement of 14-20% in the paraffins/olefins molar ratio and of about 40% in the amount of branched species on the effluent in presence of phenol, as for pure HY. The HZSM-5 further resistance against phenol, when mixed with HY, decreases by increasing phenol content from 1.2 wt.% to 4 wt.%. Hence, at an industrial level, the FCC catalyst should suffer a lower effect of phenol on the ZSM-5 additive function than expected, which would be certainly dependent on the amount of each zeolite in the FCC catalysts formulations and on the fraction of phenolic species in the FCC feedstock.

51-6 FIELD Section Title:Fossil Fuels, Derivatives, and Related Products 22, 67 IBB - Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Tecnico/UTL, Lisbon, Port. FIELD URL: written in English; The authors analyzed the influence of the acidity of a ZSM-5 catalyst on the catalytic transformation of various short-chain olefins (ethylene, propylene and 1-butene). Four ZMS-5 catalysts with different acid strength distributions were studied at different temps. and partial pressures. The results were fitted using a kinetic model based on a network mechanism, which details the products by type (olefins, paraffins and aroms.) and no. of C atoms. Polanyi-type equations, supported on quantum chem. calcns., were used to derive quant. relations between the NH3 adsorption energy, used as a measure of the acidity of a given acid site, and the energetics of the various steps involved in the reaction. Although the qual. aspects of the reactivity differs from olefin to olefin and according to the catalyst's acidity, the model is able to describe both activity and product distribution for all catalysts, reactants and conditions using a single reaction scheme and a single set of kinetic parameters. [on SciFinder(R)]

n-Heptane cracking was carried out at 450 °C over HBEA samples resulting from dealumination of the same parent HBEA zeolite by three different methods: steaming, treatment with solution of hydrochloric acid or ammonium hexafluorosilicate. With all the dealuminated samples, the main reaction products were C3 and C4 alkenes and alkanes (iso/n > 1) which suggests a successive isomerization-cracking process with the participation of a carbocation chain mechanism. Dealumination causes a decrease in the catalytic activity. A linear relation was found between the activity and the square of protonic acid site concentration suggesting that n-heptane cracking is a demanding reaction. A small amount of methane, ethylene and ethane can also be observed, which indicates the participation of the protolytic process in n-heptane cracking. The relative significance of this process depends very much on the method used for dealumination: it decreases with acid and ammonium hexafluorosilicate treatments that eliminates most of the extraframework Al Lewis species and increases with steaming. This suggests that Lewis acid sites play a significant role in the protolytic cracking of n-heptane.

Nine samples of dealuminated offretite have been prepared by simple or double treatment, without addition of water, at high temperature (873–1123 K) of a KHOffretite sample (K0.95H3.45Al4.4Si13.6O36). The samples were characterized by X-ray diffraction (unit cell parameters a and c, and “crystallinity” CRX), by 29Si n.m.r. (framework Si Al ratio and distribution of Al in T1 and T2 sites), by 27Al n.m.r. (framework and extraframework Al species), by i.r. spectroscopy (frequencies υ1 and υ2 of the asymmetric and symmetric TO bands), and by X.p.s. ( Si Al ratio of the outer surface). As with Y zeolites, highly dealuminated samples with a high CRX value can be obtained only through successive treatments with, intermediately, exchange of the K cations. The dealumination causes an increase in the Al T1 Al T2 ratio and of υ1 and υ2 but has practically no effect on the c parameter. Parameter a first decreases with the number of framework Al per unit cell (NAl), then remains quasi-constant for NAl ≤ 2.7. Nearly linear relationships are obtained between υ1 and υ2 and NAl, which allows an estimation of NAl to be made by i.r. spectroscopy.