The Influence of Inserted Metal Ions on Acid Strength of OH Groups in Faujasite

The number and the strength of acid sites in catalysts have paramount importance on their efficiency. In zeolites chemistry, increased content of framework Al in zeolites gives a higher number of strong acid sites. Their strength can be a disadvantage in catalytic reactions (e.g., methanol to olefins conversion) due to undesired secondary reactions of coke formation. Here, the Faujasite type of zeolite with higher content of Al has been used for investigating the role of defects in structure and inserted (wet impregnation and thermal treatment) metal cations (Mg, Co, Ni, Zn) on the strength of OH acid sites. Desorption of deuterated acetonitrile, as a probe molecule, was used for OH groups acid strength measurements at different temperatures (150, 200, and 300 °C)

Influence of Silica Sources on the Chemical Composition of Aluminosilicate Hydrogels and the Results of Their Hydrothermal Treatment

Among the parameters that influence the outcome of a hydrothermal synthesis of molecular sieve zeolites, the effects of various silica sources are some of the least understood. Prior studies have noted that some silica sources were »active,« or »inactive,« and there have been some suggestions that aluminium impurities can contribute to a silica source’s »activity« to promote certain zeolite syntheses. However, a silica source’s activity toward promoting zeolite crystallization has not been definitively shown to be linked to any specific impurity in the silica. This study reports on the use of four different silica sources and the corresponding distribution of Na, Al, and Si between the supernatant and amorphous gel phases. It is shown that the distribution of these species was unaffected by the choice of the silica source, but did vary with batch composition. Furthermore, the degree of silicate polycondensation (DPS), measured by the molybdate method, did not vary with the choice of the silica source. The observed differences in particulate and structural properties of the products crystallized from four different silica sources were analyzed in terms of the critical processes of zeolite crystallization (gel dissolution, nucleation, crystal growth)

Zeolite A Synthesis under Dynamic Conditions, after Hydrogel Ageing

Zeolites are crystalline, microporous, alumo-silicate materials (around 400 types) which are used in many applications. Each field of usage (catalysis, ion exchange, sorption, molecular sieving, etc.) has demands regarding crystals’ structural and particulate properties. Detailed understanding of the mechanisms of crystals’ formation and growth enables the control of these properties. Hydrogels of the starting composition 3.2 Na2O × 2 SiO2 × 1.05 Al2O3 × 250 H2O were heated in stainless steel reactor at 80 °C under dynamic conditions, after ageing for tA = 0–209 h at 25 °C. Solid phase samples were characterized using microscopy (OM, SEM), PXRD and laser light scattering (LLS). Specific number of zeolite A crystals was calculated from particle size distributions. It was shown that the some particulate properties: specific number of crystals and crystal size distribution, are changing towards higher number of crystals and wider size distribution while the morphology of the crystals remains the same. Also, the crystal growth rate is higher in the systems which are treated under dynamic conditions. Obtained results were compared with data of systems crystallized under static conditions and commented on the grounds of the autocatalytic nucleation theory. (doi: 10.5562/cca2055

Micro/mesoporous aluminosilicate materials via dual templating, Part 1: synthesis and characterization

In a quest for optimal synthesis procedure of hierarchically porous zeolite by dual template method, a series of materials was prepared starting from zeolite yielding precursor with an addition of surfactant as a mesoporogen. Characterization of the obtained materials showed that all samples possess micro and mesoporous structures, which ratio depends on the amount of surfactant present in the reaction mixture. However, in the most of the samples separation of phases occurred, and crystalline zeolite phase along amorphous MCM-41 like phase were detected, except for the sample obtained from the modified precursor, where only crystalline zeolite phase was obtained, with a specific and unusual morphology. Adsorption isotherm of that sample resembles the isotherms obtained for post synthesis modified samples

Formation mechanism of three member 1 ring containing 2 microporous zincosilicate rub-17

The crystallization process of RUB-17 (RSN-type), a zeolite-type zincosilicate, was studied in order to shed light on the zeolite crystallization mechanism. The sequence of crystallization events from the formation of the initial gel to the complete transformation into a zeolite-type material was investigated. Complementary methods, including XRD, TG/dTG, Raman, 29Si MAS NMR, SEM, that allowed studying both short and long-range order in the solids were used. RSN-type structure contains 3-, 4-, 5- and 6-member rings (MRs) that allowed following the formation of different building units in the course of zeolite formation. The set of experimental data revealed that the three-member ring (3MR) was the unit preferentially formed during the induction period. At this stage of gel evolution the presence of larger rings was not detected. The latter were observed only after the appearance of long-range order in the solid proved by X-ray diffraction analysis. Hence the formation of RSN-type structure was related with the large 3MRs population during the induction stage

Influence of synthetic zeolites fertilization on Leccino olive leaf mineral composition

Na alkalnim, karbonatnim tlima, zbog formiranja teško topivih spojeva, smanjena je dostupnost cinka (Zn), mangana (Mn), i željeza (Fe). Razlog tomu je pored visokog pH i visoka koncentracija aktivnog vapna u tlu koje blokira primanje navedenih hraniva. Cilj ovog istraživanja bio je utvrditi utjecaj gnojidbe sintetskim zeolitima na mineralni sastav lišća masline Olea europaea L. sorte Leccino uzgajane na alkalnom, karbonatnom tlu. U tu svrhu provedeno je istraživanje, u vegetacijskoj komori, u trajanju od 200 dana. Gnojidba Zn, Mn i Fe obavljena je u obliku sintetskog zeolita A (ZA), u kojem su ionskom zamjenom Na ioni zamijenjeni kationima Zn2+, Mn2+ i Fe2+ (Fe3+). Temeljem rezultata istraživanja vidljivo je da je pri tretmanu zeolitima utvrđena statistički značajno veća koncentracija Mn u listu masline dok koncentracije Fe i Zn u listu masline nisu pokazale signifikantnu razliku između tretmana sa ili bez primjene zeolitaDue to the formation of precipitous compounds, availability of Zn, Mn, Fe is reduced in alkaline, calcareous soils. Beside high pH values, high active lime content is the reason for lower uptake of the above mentioned nutrients. Thus, the objective of this trial was to define the impact of synthetic zeolites fertilization on leaf mineral content of olive leaves (Olea europaea L. cv Leccino) grown in the alkaline, calcareous soil. For this purpose, an experiment was conducted in the vegetation chamber, in the period of 200 days. Fertilization with Zn, Mn, Fe was carried out in the form of synthetic zeolite A (ZA), in which the original Na+ ions from zeolite A were exchanged with Zn2+, Mn2+ and Fe2+ (Fe3+) ions from solutions. Results showed that zeolite fertilization significantly increased Mn content in olive leaf, while Fe and Zn leaf concentrations did not show any significant difference between zeolite treated and untreated olives.