Reactions of Dimethylether in Single Crystals of the Silicoaluminophosphate STA-7 Studied via Operando Synchrotron Infrared Microspectroscopy

Russell F. Howe,Mark D. Frogley,Maria Castro,Paul A. Wright,Suwardiyanto Suwardiyanto,Alex Greenaway,Gianfelice Cinque,David J. Price

doi:10.1007/s11244-018-0890-9

Abstract

Synchrotron infrared micro-spectroscopy has been applied to measure in situ the reaction of dimethylether in single crystals of the silicoaluminophosphate STA-7. The crystals are found to contain a uniform and homogeneous distribution of acidic hydroxyl groups. Dimethylether is hydrogen bonded to the hydroxyl groups at low temperatures, but evidence is found for dissociation to form surface methoxy groups above 473 K, and aromatic hydrocarbon pool species above 573 K. From time resolved infrared measurements coupled with MS analysis of evolved products it is concluded that alkene formation occurs via a direct mechanism from reaction of dimethylether with surface methoxy groups.Graphical

Highlights

The conversion of methanol to hydrocarbons over acid zeotype catalysts has intrigued the catalysis community ever since Mobil first introduced their MTG process more than 30 years ago
In this study we report the use of synchrotron infrared micro-spectroscopy to study the reactivity of dimethylether in single crystals of the acidic aluminophosphate zeotype STA-7
The brightness of the synchrotron infrared microbeam has allowed us to perform Operando infrared spectroscopy on a 2 s time scale and a 10–20 μm spatial scale. These experiments have provided insight for the first time into how the formation of olefins from dimethylether occurs in STA-7

Summary

Introduction

The conversion of methanol to hydrocarbons over acid zeotype catalysts has intrigued the catalysis community ever since Mobil first introduced their MTG (methanol to gasoline) process more than 30 years ago. Topics in Catalysis (2018) 61:199–212 stream produced by passing methanol over an alumina dehydration catalyst [1]. Later variations on this technology optimised the formation of olefins at higher temperatures and space velocities over ZSM-5 [2] or utilised smaller pore less acidic SAPO-34 zeotype to selectively produce olefins [3, 4]. There is growing evidence for a so-called direct mechanism for olefin production from methanol during the initial stages of the reaction before the hydrocarbon pool is formed [6,7,8]

Methods

Results

Conclusion