Direct evidence of time-dependent crystallization evolution of SAPO-34 and SAPO-20 zeolites directed by trimethylbenzylammonium hydroxide for microwave-assisted ethanolysis of furfuryl alcohol

Abstract

Time-dependent crystallization evolution for synthesizing SAPO34 and SAPO-20 zeolites from a very active hydrogel is followed and reported where the XRD, FTIR, TGA/DTG, SEM/EDX, N₂ adsorption–desorption and TPD-NH₃ techniques are used. During the crystallization process, the hydrophobic trimethylbenzylammonium cation (BTMA⁺) has shown its ability as an effective structure-directing and pore filling agent. The resulting pure SAPO-34 and SAPO-20 show high crystallinity, where SAPO-34 exhibits higher porosity (393 m² g⁻¹, 0.24 cm³ g⁻¹) and acidity (1.20 mmol g⁻¹) than SAPO-20 (29 m² g⁻¹, 0.16 cm³ g⁻¹, 0.02 mmol g⁻¹), and these features are highly beneficial in the microwave-assisted ethanolysis of furfuryl alcohol. SAPO-34 shows outstanding catalytic activity (100% conversion, 72.5 ± 0.3% yield of ethyl levulinate) and its performance is much superior to that of SAPO-20 and other classical catalysts thanks to its medium pore size that induces molecular sieving effect. The spent SAPO-34 catalyst has high recyclability with stable activity, making it a superior and cost-effective catalyst for various selective petrochemical reactions.