Crystal Growth Kinetics as a Tool for Controlling the Catalytic Performance of a FAU-Type Basic Catalyst

Abstract

This study reports on the catalytic performance of nanosized zeolite X crystals and their precursors in the reaction of benzaldehyde with ethyl cyanoacetate. Crystal growth kinetics of FAU-type zeolite is studied at low temperature (35°C) in order to discriminate different crystallization stages. First X-ray crystalline material is detected after 6 days of hydrothermal treatment. The formation of the crystalline phase is preceded by changes in the ring structure of an aluminosilicate precursor as revealed by the combined Raman−HEXRD−solid-state NMR analyses. The set of experimental data shows that these changes are related to the reorganization of the gel structure and the formation of zeolite units. Prior to the appearance of crystalline material, the apparently amorphous solid exhibits chemical composition and short-range order organization similar to that of a crystalline FAU-type zeolite. Knoevenagel condensation was used to test the catalytic activity of a series of zeolite intermediates and nanosized zeolite crystals. The amorphous precursor obtained after 5 days of hydrothermal treatment showed the highest yield of ethyl α-cyanocinnamate. Superior catalytic performance of this material was attributed to the combination of strong basic sites and less restricted and more accessible structure of the semicrystalline zeolite units. Thus, the crystal growth kinetics of FAU-type zeolite can be used as a tool to tune the properties of a catalyst used in Knoevenagel condensation.

Titanosilicate zeolite precursors for highly efficient oxidation reactions

“…22 Inagaki et al regulated the crystal growth kinetics of zeolite Y (FAU) and found that the Xray amorphous zeolite phase, taken at the end of the induction period, showed the highest catalytic activity toward the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate. 26 Recently, Haw et al prepared X-ray amorphous ZSM-5 precursors with tetrapropylammonium hydroxide (TPAOH) as the structure directing agent, which presented superior catalytic performances in the dealkylation of 1,3,5-triisopropylbenzene, which cannot penetrate through the micropores of zeolites. 24 The above demonstrated high catalytic activities of the amorphous titanosilicate zeolites were ascribed to the more open structure of X-ray amorphous zeolites, which dramatically increased the accessibility towards the catalytic active sites and enhanced the mass transport efficiency.…”

Catalytic Properties of Nanometric Zeolite X Containing Methylammonium Cations

“…Isso facilita a entrada dos reagentes e saída dos produtos durante as reações. 2 Utilizando-se o método tplot nas isotermas da Figura 3 determinou-se que a amostra com partículas micrométricas, a Na X, possui um volume de microporos de 0,296 cm 3 g -1 enquanto que a N-NaX, com partículas nanométricas, possui um volume de microporos de 0,081 cm 3 g -1…”

“…[1][2][3] Tal modificação confere significativas mudanças nas propriedades das zeólitas, caracterizando-se principalmente pelo aumento expressivo em sua área externa e acessibilidade aos sítios catalíticos. 4 Por consequência, diferentes performances são alcançadas, mesmo em aplicações tradicionais como em separação e catálise.…”

Impact of the Zn source on the RSN-type zeolite formation

“…fully crystalline zeolite. [38][39][40] Melinte et al performed a very detail analysis of gel particles containing such voids and found that they contain shell which is impermeable for N2. 35 The majority of the mesopores exhibit diameter between 3 and 20 nm, more than 40% of the pores having a diameter between 5 and 7 nm.…”