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Microporous and Mesoporous Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
Faujasite is a large-pore zeolite based on four sodalite cages in a tetrahedral configuration, linked by the oxygen bridges through the 6-ring windows. This leads to a structure with large cavities of diameter 1180 pm entered by 12-ring windows of diameter 740 pm, resulting in a three-dimensional network of channels, as shown in Figure 7.14. The cubic faujasite structure showing the channels that lie parallel to each of the face diagonals (oxygen bridges are included in this model).
Solid-State NMR Studies of Zeolites and Related Systems
Published in Alexis T. Bell, Alexander Pines, NMR Techniques in Catalysis, 2020
C. A. Fyfe, Κ. T. Mueller, G. T. Kokotailo
The main commercial applications of synthetic faujasite are for cracking catalysts to produce gasoline and fuel oil. Over 98% of the refineries in the world use some form of synthetic faujasite-cracking catalyst. Hydrocracking, another process using synthetic faujasite, produces kerosene, toluene, xylene, and jet fuels. ZMS-5 is used variously to produce low “pour point” lubes by dewaxing xylene and benzene from toluene, sty rene from benzene alkylation, xylene from toluene disproportionation, and in the conversion of methanol to gasoline. It has also been used to control NOx emissions with use of NH3 as a reducing agent to convert NOx to N2 and H2O. Zeolite A with Ca2+ cations (CaA) is used for air enrichment, removal of H2S from “sour” gases, and the separation of iso- and η-paraffins. Zeolites have been used as well to remove radioactive Cs+ and Sr3 + from nuclear-reactor-waste streams and ammonia from sewage and agricultural effluents.
Metal Zeolite Catalysts
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
The following principal characteristics of metal zeolite catalysts have been established in isomerization reactions.The zeolites containing univalent cations are practically inactive.Hydrogen, decationized and multivalent cationic forms of zeolites loaded with metals show high activity.The larger the charge and the smaller the radius of the zeolite cation, the higher the catalytic activity; Y zeolites containing cations with a valence 3 and 4 (0.5 wt% Pt (Pd) show lower selectivity than those containing divalent cations, the activity of some of these catalysts decreasing very rapidly.With a higher degree of exchange of Na+ by Mn+ a sharp increase in the activity of the corresponding ion-exchanged catalysts is observed after a certain threshold. The zeolite catalysts with a minimal residual sodium show the highest activity.Efficient isomerization catalysts may contain cation decationized combinations (Ca-HY, Mn-HY, La-HY, RE-HY).With an increase in SiO2/Al2O3 ratio in zeolites of faujasite types or mordenite types, the activity of the catalysts considerably increases, allowing much lower reaction temperatures.The activity, selectivity, and stability of catalysts depend on the nature and concentration of the metal component.
Esterification of acetic acid in the presence of sulfated clinoptilolite: a model study of upgrading of pyrolysis bio-oil
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Zeolites, hydrated aluminosilicates, are an important class of materials having widely industrial applications. Zeolites compose of a framework formed by SiO4 and AlO4 tetrahedra structures. Their textural and structural properties play a key role in their performance as catalyst and adsorbent. Faujasite and mordenite are large pore zeolites and use as a catalyst in hydrocarbon conversion (Aitani et al. 2019; Tamizhdurai et al. 2019; Travkina et al. 2019). There are numerous types of zeolites both synthetic and occurring naturally. Clinoptilolite, a member of the heulandite group, is one of the most important natural zeolites. Clinoptilolite is a crystalline hydrated aluminosilicate framework consisting of AlO4 and SiO4 tetrahedron (Erdogan and Ulku 2013). Natural zeolites as a catalyst have some disadvantages such as containing undesired impurities, varying chemical compositions with respect to deposit or stratum in the same deposit. Therefore, natural zeolites need modification to improve their catalytic properties. Clays and zeolites can be used as the catalyst was activated with mineral acids (Uzair et al. 2016). Treatment with sulfuric acid provides not only sulfation but also dealumination (Garcia-Basabe et al. 2010; Rivera et al. 2011).
Tailoring the reaction mixture composition for preparing zeolite coatings on aluminum supports in alkaline environments
Published in Chemical Engineering Communications, 2019
Melkon Tatlier, Lina Rustam, Gunther Munz
Some research efforts have already been made to coat aluminum substrates with zeolites. The partial support transformation method was developed for the preparation of AlPO and SAPO based zeolites on aluminum supports (Bauer et al., 2009). Thick coatings could be prepared by using this method where aluminum was used as both the support and aluminum source in the reaction leading to zeolite crystallization. In such syntheses, the reaction mixtures are generally not so alkaline and thus do not destroy the aluminum supports. A different type of example involved the multi-step formation of a zeolite Y coating on an aluminum alloy, firstly by forming a bottom layer consisting of a high-silica zeolite ZSM-5 (Munoz et al., 2005). Due to the high alkalinity of the reaction mixtures from which zeolite Y might be prepared, forming a ZSM-5 film first on the aluminum substrate offered a good corrosion protection. A similar approach was also used for obtaining layers of EMC-1 (Lauridant et al., 2013a) and Beta (Lauridant et al., 2013b) zeolites on a thicker layer of ZSM-5 synthesized first. Films of ZSM-5/MFI zeolite, alone, were also prepared on aluminum supports, especially for corrosion protection (Lauridant et al., 2012). In another study, a deposition technique was applied in the presence of triethanolamine to prepare faujasite type zeolites on aluminum alloy by using pre-aged reaction mixtures (Bonaccorsi et al., 2011). Triethanolamine may exhibit complexing action by chelating aluminate ions in the reaction mixture, however even then aluminum oxide phases, such as gibbsite, were observable in the coating together with zeolite, leading to question marks in the potential of this synthesis approach. Recently, the chelating ability of carboxylic acids for Al3+ ions in alkaline environments was used to obtain faujasite coatings on metallic aluminum by hydrothermal synthesis (Chanda et al., 2018). This was another strategy requiring the use of additional organic materials in the reaction mixtures of zeolites. However, all these methods still seem possible to be applied only for obtaining limited number of zeolites, forming from still not so highly alkaline reaction mixtures, and also present some disadvantages economically, practically, and/or regarding the quality of the coating. Thus, a more substantial understanding and practice of zeolite synthesis on aluminum supports still seem to be very beneficial for preparing coatings of various zeolites on this metal.