Application of Inelastic Neutron Scattering to the Methanol-to-Gasoline Reaction Over a ZSM-5 Catalyst.

Russell F Howe,James Mcgregor,David Lennon,Stewart F Parker,Paul Collier

doi:10.1007/s10562-016-1742-5

Abstract

Inelastic neutron scattering (INS) is used to investigate a ZSM-5 catalyst that has been exposed to methanol vapour at elevated temperature. In-line mass spectrometric analysis of the catalyst exit stream confirms methanol-to-gasoline chemistry, whilst ex situ INS measurements detect hydrocarbon species formed in/on the catalyst during methanol conversion. These preliminary studies demonstrate the capability of INS to complement infrared spectroscopic characterisation of the hydrocarbon pool present in/on ZSM-5 during the MTG reaction.Graphical

Highlights

The conversion of alcohols to hydrocarbons was first introduced in the Mobil methanol-to-gasoline (MTG) process using an HZSM-5 catalyst, commercialised in New Zealand in 1986
We present a preliminary report on the Inelastic neutron scattering (INS) spectra of a commercial grade ZSM-5 catalyst exposed to a methanol feedstream at 623 K
The major peaks identified have m/z ratios of: 18 (H2O); and 28 (C2H4,); 41 (C3H5); 55 (C4H7, C3H3O); and 91 (C7H7). These features indicate the formation of longer-chained hydrocarbons and oxygenates; while the m/z = 91 peak is indicative of methylated benzenes, e.g. toluene, xylenes, etc. the complementary GC–MS analysis of the catch-pot liquid, collected postreaction, shows some unconverted methanol, with smaller amounts of ethanol, alongside species identified as methylated benzenes

Summary

Introduction

The conversion of alcohols to hydrocarbons was first introduced in the Mobil methanol-to-gasoline (MTG) process using an HZSM-5 catalyst, commercialised in New Zealand in 1986. Three different components of the reaction pathway can be distinguished: (1) the initial reaction steps in which methanol reacts with acid sites in the zeolite or SAPO catalysts; (2) the formation of hydrocarbon products during steady-state working conditions; and (3) the catalyst deactivation through so-called coke formation. Warringham et al [27] recently reported on sample environment details relevant to the acquisition of INS spectra of heterogeneous catalysts Against this background, it is timely to consider whether INS can be applied to look at MTG and/or MTO chemistry over zeolitic materials such as ZSM-5. Given the ability of INS to selectively probe hydrogeneous vibrational modes [15], it is enticing to discover whether the technique can provide new information on the adsorbed hydrocarbon species present at various stages of the methanol to. Further work is necessary to examine spectra at different reaction times and to better correlate catalytic performance with the vibrational spectra, this short communication demonstrates the capability of INS to positively contribute to the understanding of this economically relevant but technically challenging reaction system

Experimental

Reaction Testing

Inelastic Neutron Scattering