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A series of treatments were applied to selectively deactivate the acid sites of the supercages or of the external hemicages of a MCM-22 zeolite sample. Precoking of MCM-22 through n-heptane cracking at 450 °C does not completely suppress the activity of the supercage sites for m-xylene transformation at 350 °C. In contrast, these sites were selectively and completely deactivated after m-xylene transformation for 24 h. Among the methods that were tried to selectively deactivate the hemicage protonic sites (dealumination with ammonium hexafluorosilicate, reaction with 1,1,1,3,3,3-hexamethyldisilazane, poisoning with 2,6- or 2,4-dimethylquinoline) only the treatment with 2,4-dimethylquinoline was found to be suitable. The most selective methods were used to estimate the relative contributions of the protonic sites located in the supercages (42%), the external hemicages (22%) and the sinusoidal channels (36%) in m-xylene transformation. In the large supercages with small apertures, isomerization into a 3.5–1 para–ortho mixture is accompanied by m-xylene disproportionation; most of the bulky trimethylbenzene products trapped in these cages undergo secondary transformations in smaller molecules or into coke. In the large external hemicages, m-xylene is essentially transformed into a quasi-equimolar mixture of para- and ortho-xylenes, the only secondary products being traces of toluene and trimethylbenzenes. Lastly, in the narrow sinusoidal channels, m-xylene transformation is practically limited to isomerization into the slim para product. [Copyright &y& Elsevier]

Abstract: n-Heptane transformation was carried out at 350°C over a HMCM-22 zeolite (Si/Al=14.5) previously characterized by various techniques: X-ray diffraction, nitrogen adsorption, scanning electron microscopy, pyridine and 2,4-dimethylquinoline (2,4-DMQ) adsorption followed by FTIR. A pronounced deactivation was shown to occur in the first 10min reaction, due to a very fast initial coke formation, followed by a quasi-plateau in activity. Cracking was the main reaction. The role played by each of the three pore systems was established by selectively deactivating the supercage sites by coking then by selectively poisoning the protonic sites of the external cups with a bulky base molecule (2,4-DMQ). The supercage sites (∼70% of the inner ones) were found to be responsible for 97% of n-heptane transformation, those of the sinusoidal channels (∼20%) for only 3%, which means that these latter sites were ∼16 times less active probably because of pronounced steric constraints. Unexpectedly, the protonic sites of the external cups, which were demonstrated as able to catalyse efficiently various reactions including methylcyclohexane cracking, were found to be completely inactive. [Copyright &y& Elsevier]

Abstract: 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°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), −80kJmol−1 for HY and −60kJmol−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 1.2wt.% to 4wt.%. 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. [Copyright &y& Elsevier]

Abstract: To evaluate the possibility to partially replace the classical Fluid Catalytic Cracking (FCC) feedstocks by bio-oils derived from lignocellulosic biomass, the transformation of n-heptane was performed in the presence of small quantities of phenol over an HY zeolite, at 350 and 450°C. The results were compared with those previously obtained with methylcyclohexane. Phenol leads to a further deactivation of the zeolite due to phenol adsorption on the Brönsted and Lewis acid sites along with coke molecules from the reactants transformation. For n-heptane, the additional activity decay due to phenol is observed since the beginning of the reaction, while for methylcyclohexane it was only detected after few minutes. The increase of temperature disfavours phenol adsorption but, contrarily to methylcyclohexane, it does not prevent the phenol deactivating effect for n-heptane. Differences in the reactivity of n-heptane and methylcyclohexane molecules and IR spectroscopy data allow concluding that phenol firstly interacts with the stronger protonic sites, being then retained on the weaker acid sites. Alkylation of phenol is a reaction occurring in a lower extent under the conditions tested, being responsible for the consumption of light olefins. Finally, the adsorption of phenol favours the formation of branched molecules. Hence, the alkanes cracking should be more affected than the naphthenes cracking in the co-processing of conventional FCC feedstocks with hydrotreated bio-oils rich in phenolic compounds, being the deactivating effect certainly dependent on the quantity of bio-oils incorporated. [ABSTRACT FROM AUTHOR]