Synthesis of highly crystalline nanosized HZSM-5 catalyst employing combined hydrothermal and sonochemical method: Investigation of ultrasonic parameters on physico-chemical and catalytic performance in methanol to propylene reaction

Abstract

Nanostructured HZSM-5 catalysts were synthesized using sonochemical and hydrothermal techniques. The central composite experimental design method was applied to investigate the effects of three critical preparation variables including ultrasound power, irradiation time, and sonication temperature on the structure of the prepared catalysts. The catalysts were characterized by XRD and FE-SEM techniques. The catalytic performance of the selected catalysts was also evaluated in methanol conversion to propylene reaction. The results showed that higher crystallinity and lower particle size were obtained by increasing the above-mentioned factors. The maximum relative crystallinity and minimum mean particle size were obtained as 55.5% and 62.4 nm, respectively, under the optimal conditions of ultrasound power (231 W), irradiation time (21.2 min), and sonication temperature (42.7 °C). The mean particle size of the parent and sonicated HZSM-5 nanocatalysts which were prepared using 48 and 4 h crystallization in autoclave, were 893 and 62.4 nm, respectively. The optimum sonicated catalyst showed higher selectivities to propylene (C3=, 36.8%) and lower selectivity to total heavy hydrocarbons (C5+, 16.1%) compared to the parent catalyst. These results strongly suggest that a nanocatalyst with smaller particle size and higher crystallinity can be obtained in a lower crystallization time using ultrasound method which shows better performance in methanol to propylene reaction.