Examinando por Autor "Linares, M."

Mostrando 1 - 2 de 2

Catalytic activity of the beta zeolite with enhanced textural properties in the Friedel-Crafts acylation of aromatic compounds
(ELSEVIER, 2008) Garcia, R.A.; Serrano, D.P.; Vicente, G.; Otero, D.; Linares, M.
Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites.
Influence of the calcination treatment on the catalytic properties of hierarchical zsm-5
(Elsevier, 2012-01) Serrano, D.P.; García, R.A.; Linares, M.; Gil, B.
The effect on the calcination conditions on the properties and catalytic performance of hierarchical and standard ZSM-5 zeolite samples have been investigated using different reactions as catalytic tests: acylation of aromatic substrates (anisole and 2- metoxynaphtalene) and rearrangement of linear and cyclic epoxides (1,2-epoxyoctane and isophorone oxide). The h-ZSM-5 material was prepared by crystallization of silanized protozeolitic units. The removal of the organics present in the as-synthesized forms of both ZSM-5 samples has been carried out using two different calcination procedures. The first one takes place under air atmosphere from room temperature to 550ºC for 5 hours, whereas the second one is performed under nitrogen at 400ºC for 4 hours, followed by treatment at 550ºC for 5 hours under air atmosphere. Clear differences are noticed related to the textural properties of the ZSM-5 samples. Thus, h- ZSM-5 presents not only higher BET surface than standard ZSM-5 zeolite, but 75% of its total area is shared by surface located outside the zeolite micropores. FTIR studies showed almost no differences between the acidic properties of the conventional zeolite calcined by both methods. However, noticeable changes were observed over the hierarchical zeolite. Thus, the concentration of Brønsted acid sites decreases by half in the case of one-step air calcination, but only a quarter when using two-step nitrogen/air calcination. These changes in the acidic properties denote that the aluminium present in hierarchical ZSM-5 is very sensitive to the calcination conditions. Furthermore, this has also significant effects on the catalytic properties of this material in both aromatic acylation and epoxide rearrangement reactions. For both types of reactions, the hierarchical sample calcined under a two-step nitrogen/air treatment presents higher activity and product yields than the same material when calcined under one-step air atmosphere. Therefore, controlling the calcination conditions is an effective method in preserving the acidic features of hierarchical ZSM-5, which in turn has a positive influence on its catalytic behaviour.