Search

In this paper, the conversion of methanol and butanol and the differences in product distribution over H-SAPO-34 were investigated. Some important reaction intermediates were captured during the reaction process by using gas chromatography-mass spectrometry (GC-MS) and 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CP MAS NMR) spectroscopy. In the methanol conversion process, ethene, propene and butene are the main products, while in the butanol conversion process, butanol is mainly dehydrated to form butene, and propene and butene are the main products in the initial stage. Light olefins are generated from both methanol and butanol conversion over H-SAPO-34. Furthermore, the aromatic species were observed in both retained species analysis and 13C CP MAS NMR, indicating that similar organic species confined in the H-SAPO-34 during the conversion of alcohols. Starting from different kinds of alcohols, the acid-catalysis environment in the confined space of H-SAPO-34 can catalyze the methanol and butanol conversion to produce light olefins.

In situ solid-state nuclear magnetic resonance (ssNMR) techniques under continuous flow and batch-like conditions as well as 2D 13C-13C dipolar-based COmbined R2 Driven (CORD) spin diffusion NMR experiments were utilized to investigate the dehydration process of ethanol on molecular sieve H-SSZ-13. Kinds of intermediate species including ethanol with different adsorption orientation, diethyl ether under activated state, the surface ethoxy, triethyloxonium ion and even ethene were captured directly, and the evolution process of these intermediate species was also revealed in this paper. Moreover, it can be emphasized that the ethene species were observed in situ by ssNMR for the first time. These results enriched the fundamental research of ethanol dehydration reaction.

Methanol-to-olefins (MTO) is a prevalent industrial process for producing light olefins from the non-petroleum route. Molecular sieves are core catalysts for MTO owing to their unique pore structure and tunable acidity. Solid-state nuclear magnetic resonance (NMR) is a powerful tool to elucidate the structure and interpret the catalytic reaction mechanism of the molecular sieves. In this review, we summarize the major progresses in understanding the MTO reaction mechanism with in-situ solid-state NMR, multi-dimensional and -nuclear NMR, 129Xe NMR, and pulsed field gradient NMR (PFG NMR). In-situ solid-state NMR can monitor the dynamic changes of the reactants, intermediates and products under real reaction conditions. Multi-dimensional and multi-nuclear NMR offers rich structural information of the reaction intermediate without having to destroy the catalyst structure. Especially, 129Xe NMR is applied to sensitively probe the pore structure of fresh and deactivated catalysts. PFG NMR could determine the diffusion coefficients of molecules in pores, and elucidate the diffusion mechanism of the molecular sieve.