Nanosponge hierarchical micro-mesoporous MFI zeolites as a high-performance catalyst for the hydroamination of methyl acrylate with aniline

Abstract

Zeolites catalyze the hydroamination of alkenes, alkynes and dienes, yielding valuable amines, enamines and imines with high efficiency and chemoselectivity (i.e., Markovnikov or anti-Markovnikov products) thanks to the architecture of their pore system and tunable acidity. However, their micropores may impose mass-transfer constraints on reaction rates. Nevertheless, the high external surface area of hierarchical micro-mesoporous zeolites should enable them to outperform conventional zeolites. To test our hypothesis, we compared the activity of hierarchical MFI zeolites of different crystal morphologies (i.e., nanosponge, nanosheet and microcrystalline desilicated samples) with that of conventional medium- (MFI) and large-pore (MOR and Beta) zeolites in the hydroamination of methyl acrylate with aniline. The results showed that nanosponge MFI had the highest activity (TOF = 32.9 h−1), reaching 57% yield of the anti-Markovnikov product N-[2-(methoxycarbonyl)ethyl]aniline. Furthermore, our kinetic study revealed a pseudo-second-order rate law with respect to aniline over the most active nanosponge MFI catalyst, with an apparent activation energy of 68.9 kJ/mol. The high external surface of this catalyst (371 m2/g) and its developed inter-crystalline mesopores (4.8 nm) suggest a kinetic-driven hydroamination reaction. Therefore, hierarchical nanosponge aluminosilicate MFI zeolites stand out as promising heterogeneous catalysts of hydroamination reactions involving bulky substrates.