CHA-Type Zeolite Prepared by Interzeolite Conversion Method Using FAU and LTL-Type Zeolite: Effect of the Raw Materials on the Crystallization Mechanism, and Physicochemical and Catalytic Properties

Formation of paired Ga sites in CHA-type zeolite frameworks via a transcription-induced method

Paired Ga sites represented by the Ga-O-Si-O-Ga sequence were firstly formed intentionally in CHA-type zeolite frameworks via the transcription of pre-formed paired Ga species in a Ga-rich amorphous silica-gallia under seed-assisted hydrothermal conditions. Such paired Ga sites behaved as ion-exchange sites for capturing divalent cation, Co2+.

Effects of Synthesis Variables on SAPO-34 Crystallization Templated Using Pyridinium Supramolecule and Its Catalytic Activity in Microwave Esterification Synthesis of Propyl Levulinate

A detailed investigation of the hydrothermal crystallization of SAPO-34 in the presence of the novel 1-propylpyridinium hydroxide ([PrPy]OH) organic structural directing agent is presented. The synthesis conditions are systematically tuned to investigate the effects of various parameters (viz. concentrations of each reactant, crystallization time, and temperature) on the nucleation and crystallization of SAPO-34. The results show that a careful variation in each of the synthesis parameters results in the formation of competing phases such as SAPO-5, SAPO-35, and SAPO-36. Pure and fully crystalline SAPO-34 can be crystallized using a precursor hydrogel of a molar ratio of 2.0 Al: 4.7 P: 0.9 Si: 6.7 [PrPy]OH: 148 H2O at 200 °C for only 19 h, which is a shorter time than that found in previous studies. The prepared SAPO-34 is also very active in the esterification of levulinic acid and 1-propanol. By using microwave heating, 91.5% conversion with 100% selectivity toward propyl levulinate is achieved within 20 min at 190 °C. Hence, the present study may open a new insight into the optimum synthesis study of other zeolites using novel pyridinium organic moieties and the opportunity of replacing conventional harmful and non-recyclable homogeneous catalysts in levulinate biofuel synthesis.

Clarification of acid site location in MSE-type zeolites by spectroscopic approaches combined with catalytic activity: comparison between UZM-35 and MCM-68

MSE-type zeolites synthesized by different organic structure-directing agents (OSDAs), UZM-35 and MCM-68, were prepared. The location of Brønsted acid sites derived from the framework Al atoms and acidic properties were investigated based on ²⁷Al MQMAS NMR and in situ IR techniques combined with the evaluation of the catalytic activity. We have successfully found a significant difference in the location of Brønsted acid sites in the MSE-type framework; 61 and 33% of acid sites were located at the 12-ring channel for MCM-68 and UZM-35, respectively. The differences in the location of the acid sites yielded their unique catalytic activities for the hydrocarbon cracking reactions, indicating that a well-chosen type of OSDAs for the synthesis is one of the possibilities for controlling the distribution of the framework Al atoms in the MSE-type framework.

Transcription-induced formation of paired Al sites in high-silica CHA-type zeolite framework using Al-rich amorphous aluminosilicate

The paired Al species pre-formed in Al-rich amorphous aluminosilicates were transcribed into high-silica CHA-type zeolite frameworks under hydrothermal conditions, which offers a new approach to creating paired Al sites in zeolite frameworks. This Al-pair-rich CHA exhibited a higher Sr²⁺ uptake than the control CHA zeolite synthesized by the conventional procedure.

On the key role of aluminium and other heteroatoms during interzeolite conversion synthesis

Interzeolite conversion, a synthesis technique for several zeolite frameworks, has recently yielded a large amount of high-performing catalytic zeolites. Yet, the mechanisms behind the success of interzeolite conversion remain unknown. Conventionally, small oligomers with structural similarity between the parent and daughter zeolites have been proposed, despite the fact these have never been observed experimentally. Moreover, recent synthesis examples contradict the theory that structural similarity between the parent and daughter zeolites enhances interzeolite conversion. In this perspective it is proposed that heteroatoms, such as aluminium, are key players in the processes that determine the successful conversion of the parent zeolite. The role of Al during parent dissolution, and all consecutive stages of crystallization, are discussed by revising a vast body of literature. By better understanding the role of Al during interzeolite conversions, it is possible to elucidate some generic features and to propose some synthetic guidelines for making advantageous catalytic zeolites. The latter analysis was also expanded to the interconversion of zeotype materials where heteroatoms such as tin are present.

The crucial roles of aluminium in driving and controlling interzeolite conversion, a useful catalyst synthesis protocol, are put under scrutiny.

Microporous Zeolites and Related Nanoporous Materials: Synthesis, Characterization and Application in Catalysis

Microporous zeolites and related nanoporous materials have been studied intensively in academic and industrial laboratories around the world [...]