Development of a novel method for the removal of diazinon pesticide from aqueous solution and modeling by artificial neural networks (ANN)

http://digital.csic.es/bitstream/10261/162216/4/synthesisolefins.pdf

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

A facile and economical route to synthesize nano-sized ZSM-5 zeolite aggregates with mesopores was developed by a modified seed-induced method using silicate-1 (S-1) as seeds without additional templates in the presence of a trace amount of cetyltrimethylammonium bromide (CTAB). The effect of the amounts of CTAB and S-1 on the morphologies and textural properties were studied in detail, and the possible formation mechanism was proposed. The primary crystal sizes of the ZSM-5 zeolites could be adjusted and mesopores were generated in a certain range. The resulting ZSM-5 zeolites showed a uniformly conglobate morphology with particle sizes of 400–600 nm, aggregated with 20–50 nm crystallites, possessing a large external surface area and abundant inter-crystallite mesopores under the optimum synthesis conditions (CTAB to total SiO2 molar ratio was 0.02 and SiO2 in S-1 gel took up 8% to the total SiO2). The catalytic performance of nano-sized ZSM-5 zeolites in methanol to propylene reaction showed a high stability and high propylene selectivity.

Conversion of methanol to propylene over nano-sized ZSM-5 zeolite aggregates synthesized by a modified seed-induced method with CTAB

The infrared spectroscopy study of zeolite samples, obtained by steam treatment at 560-960 °C of the ZSM-5 catalyst (framework Si/Al ratio of 13), suggests an association between adsorbed molecular water and extra-framework aluminum hydroxyls generated after treatment. Moreover, infrared spectroscopy of adsorbed pyridine shows the reduction of the densities of Bronsted and Lewis sites, when treatment temperature rises, with contradicts the frequently accepted mechanism of the transformation of two bridged Si-OH-Al groups for each Lewis site generated. The gradual conversion of the octahedral extra-framework aluminum (Lewis-associated) in polymeric species with low acidity is the most probable cause of this behavior. On the other hand, the apparent decline of the acid Bronsted strength, with the increase in the temperature of the hydrothermal treatment, has two possible causes: a) the decreasing accessibility, of the pyridine molecular probe to bridged Si-OH-Al groups with the strongest Bronsted acidity, inside the channels, and b) the gradual transformation of these groups into extra framework species of weak acidity.

/pdf/ftir-study-of-the-relation-between-extra-framework-aluminum-4p4gzvyym0.pdf

FTIR study of the relation, between extra-framework aluminum species and the adsorbed molecular water, and its effect on the acidity in ZSM-5 steamed zeolite

Direct synthesis of hierarchical ZnZSM-5 with addition of CTAB in a seeding method and improved catalytic performance in methanol to aromatics reaction

Synthesis of mesoporous ZSM-5 by crystallisation of aged gels in the presence of cetyltrimethylammonium cations

ZSM-5 nuclei were prepared by ageing synthesis gels at 60 °C A cationic surfactant was added to these seeding gels, which were subsequently crystallized at 120 or 150 °C The obtained ZSM-5 zeolites possess mesopores similar to MCM-41 and their crystallinities increased with the increase of the crystallisation temperature and decreased with the decrease of the SiO 2 /Al 2 O 3 ratio Scanning electron microscopy revealed for all samples, independently of the crystallinity, the same morphology and the absence of segregated ZSM-5 crystals, thus suggesting that ZSM-5 is formed by an intraparticle transformation of the primary formed MCM-41

Marli Lansoni Gonçalves

Papers

Synthesis of mesoporous ZSM-5 by crystallisation of aged gels in the presence of cetyltrimethylammonium cations

Mesoporous ZSM-5 synthesized by simultaneous mesostructuring and crystallization of ZSM-5 nuclei