Effect of SiO2/Al2O3 ratio on the performance of nanocrystal ZSM-5 zeolite catalysts in methanol to gasoline conversion

Abstract

In this study, the effect of SiO2/Al2O3 ratio on the catalytic performance of nanocrystal ZSM-5 zeolite catalyst in the methanol to gasoline conversion (MTG) was investigated. A series of zeolite samples with different SiO2/Al2O3 ratios of 23, 47, 107, 217 and 411 were synthesised. Through systematically controlling the material synthesis conditions, these nanocrystal ZSM-5 zeolite samples were produced to have very similar crystal sizes and structural properties, thus providing an ideal opportunity to study the intrinsic effect of SiO2/Al2O3 ratio on the performance of the ZSM-5 samples in MTG. The MTG experimentation was carried out in a fixed-bed reactor under a set of constant conditions of temperature 375°C, pressure 1MPa and WHSV 2h−1. A steady methanol conversion was sustained with increasing the SiO2/Al2O3 ratio, and a progressive decrease in methanol conversion was found over catalysts with low SiO2/Al2O3 ratios (≤107) after 5h on stream. Decreasing the SiO2/Al2O3 ratio promoted C1-C4 selectivity and thus decreased gasoline yield. It was also found that decreasing the SiO2/Al2O3 ratio promoted aromatisation reactions and hence higher durene selectivity and more coke formation, resulting in rapid catalyst deactivation. The sample with SiO2/Al2O3 ratio of 217 showed the highest methanol conversion, gasoline yield, and very low coke formation.