Abstract
A ZSM-5 catalyst is examined in relation to the methanol-to-hydrocarbon (MTH) reaction as a function of reaction temperature and time-on-stream. The reaction profile is characterised using in-line mass spectrometry. Furthermore, the material contained within a catch-pot downstream from the reactor is analysed using gas chromatography-mass spectrometry. For a fixed methanol feed, reaction conditions are selected to define various stages of the reaction coordinate: (i) initial methanol adsorption at a sub-optimum reaction temperature (1 h at 200 °C); (ii) initial stages of reaction at an optimised reaction temperature (1 h at 350 °C); (iii) steady-state operation at an optimised reaction temperature (3 days at 350 °C); and (iv) accelerated ageing (3 days at 400 °C). Post-reaction, the catalyst samples are analysed ex situ by a combination of temperature-programmed oxidation (TPO) and spectroscopically by electron paramagnetic resonance (EPR), diffuse-reflectance infrared and inelastic neutron scattering (INS) spectroscopies. The TPO measurements provide an indication of the degree of 'coking' experienced by each sample. The EPR measurements detect aromatic radical cations. The IR and INS measurements reveal the presence of retained hydrocarbonaceous species, the nature of which are discussed in terms of the well-developed 'hydrocarbon pool' mechanism. This combination of experimental evidence, uniquely applied to this reaction system, establishes the importance of retained hydrocarbonaceous species in effecting the product distribution of this economically relevant reaction system.
Highlights
PaperAs oil reserves continue to diminish, the methanol to ole n (MTO) reaction and related methanol to gasoline (MTG) reactions over zeolitic catalysts such as ZSM-5 are anticipated to play an increasing role in the landscape of large-scale chemical and fuel manufacturing operations
Hemelsoet et al looked at the MTO reaction over ZSM-5 and SAPO-34, concentrating on mechanistic aspects of the process; in particular, they examined the well-established concept of a hydrocarbon pool via a combination of kinetic measurements supplemented by theoretical simulations.[1]
Recognising that inelastic neutron scattering (INS) can supplement the already wide range of investigations on MTH chemistry over zeolitic materials, the present study extends the preliminary ZSM-5/MTH investigation of Howe and co-workers[13] by using INS to discover if the hydrocarbonaceous species retained by the zeolite is sensitive to reaction conditions
Summary
As oil reserves continue to diminish, the methanol to ole n (MTO) reaction and related methanol to gasoline (MTG) reactions over zeolitic catalysts such as ZSM-5 are anticipated to play an increasing role in the landscape of large-scale chemical and fuel manufacturing operations. Post-reaction, the catalyst samples are analysed ex situ by a combination of temperature-programmed oxidation (TPO), electron paramagnetic resonance (EPR) spectroscopy and diffuse-re ectance infrared Fourier transform spectroscopy (DRIFTS) These additional measurements facilitate comparisons to literature work as highlighted by, amongst others, Olsbye and co-workers.[5] This is the rst time that this combination of experimental techniques have been applied to the methanol to hydrocarbon reaction over a ZSM-5 catalyst. In order to ensure a balance between sensitivity and resolution,[11] two direct geometry INS spectrometers are employed to better discern the nature of the hydrocarbonaceous material retained at the catalyst surface
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