Moderating acidity of ZSM-50 by Fe-substitution for n-Heptane isomerization

Effective regulation of acid sites is essential to strengthen the reaction performance and to modulate product distribution of an isomerization reaction. In this study, ZSM-50 (Al-EUO) and Fe-substituted ZSM-50 zeolites, namely FeAl-EUO-n (n = 0.25, 0.50 and 0.75) and Fe-EUO, are synthesized by a seed-assisted hydrothermal method. The study has shown that Fe has effectively entered the Al-EUO framework as a tetrahedrally-coordinated species. More importantly, the Fe-substitution has resulted in a significant increase in the amount of surface weak- and medium-strength Brönsted acids and a reduction in the strength of strong acids of FeAl-EUO-n. This study also evaluates the catalytic performance of Pt/FeAl-EUO-n catalysts in n-heptane hydroisomerization. It shows that the introduction of Fe in ZSM-50 greatly enhances the isomer yield, achieving a maximum yield of 66.1 % at 320 °C over Pt/FeAl-EUO-0.50 compared to 16.4 % at 300°C over Pt/Al-EUO. At the same time, the fraction of multi-branched iso -heptane also increases noticeably in the reaction product.