Direct synthesis of Al-rich ZSM-5 nanocrystals with improved catalytic performance in aromatics formation from methane and methanol
Shaojie Li, Xianxuan Ren, Brahim Mezari, Yujie Liu, Peerapol Pornsetmetakul, Anna Liutkova, Nikolay Kosinov, Emiel J. M. Hensen
Abstract
Nanosized ZSM-5 (<100 nm) zeolites with high acidity (Si/Al < 15) can bring distinct advantages as catalysts for obtaining aromatics in C1 chemistry. Synthesis of such nanosized zeolites in a cheap and scalable manner remains a challenge. Herein, nanosized ZSM-5 (20–50 nm) with high acidity (Si/Al = 11) was hydrothermally synthesized in high yield using p-phenylenedimethylene-bis(tripropylammonium) dichloride (Pr3N-benzyl-NPr3) as the sole organic structure-directing agent (OSDA). By investigating the solid products formed during zeolite synthesis, it was found that crystallization follows a solid-state transformation mechanism. An in-depth NMR study combined with TGA measurements reveals that, after early electrostatic interaction between condensed aluminosilicate and the ammonium groups of OSDA, ZSM-5 crystallizes around the OSDA. Owing to its high acidity and shortened diffusion paths, such nanosized ZSM-5 demonstrates, compared to bulk ZSM-5, enhanced aromatics formation in methanol dehydration and non-oxidative dehydroaromatization of methane reactions.