Examinando por Autor "García, R.A."

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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.
Synthesis and characterization of SBA-15 materials functionalized with olefinic groups and subsequent modification through oxidation procedures
(ELSEVIER, 2010) van Grieken, R.; Iglesias, J.; Morales, V.; García, R.A.
The synthesis of alkenyl-SBA-15 materials has been carried out through different methodologies. The direct-synthesis method used for the functionalization of SBA-15 involving the co-condensation of the alkenyl-silicon precursor together with silicon alkoxides is clearly superior than any other post-synthetic pathway, even if acid catalysts are used to drive the post-synthetic grafting of olefin groups. The direct-synthesis methodology has been deeply studied within this work, involving the influence of the silica precursor prehydrolysis time, and the loading of different olefin-silanes on the quality of the mesostructure. Small olefinic functionalities, like vinyl groups, can be incorporated in a very efficient manner up to achieve organic loadings as high as 50% mole of the olefin precursor to TEOS. The modification of these alkenyl groups through oxidation can be accomplished through post-synthetic oxidation of the olefinic group or even through an in-situ methodology where the oxidant ¿ hydrogen peroxide ¿ is added together with the rest of the precursor into the synthesis gel to lead complete oxidation of the double bonds towards glycolic functionalities. The resultant materials show potential as hydrophilic adsorbents and catalytic supports.