An assessment of hydrocarbon species in the methanol-to-hydrocarbon reaction over a ZSM-5 catalyst

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.

Characterization of Metal‐zeolite Composite Catalysts: Determining the Environment of the Active Phase

“…Suwardiyanto et al . have demonstrated an application of inelastic neutron scattering for intermediate hydrocarbon species during the MTH reaction over ZSM‐5.…”

Neutron spectroscopy as a tool in catalytic science

“…The infrared spectrum 74 indicates that the hydroxyl groups are largely unchanged and shows the presence of a weak peak at 2920 cm À1 , assigned to aliphatic species. The INS spectra, Fig.…”

“…After one hour on-stream at 350 1C, on-line mass spectroscopy 74 shows that the catalyst is producing predominantly olefins. The infrared spectrum 74 indicates that the hydroxyl groups are largely unchanged and shows the presence of a weak peak at 2920 cm À1 , assigned to aliphatic species.…”

“…15 shows the results of different preparation conditions. Two INS spectrometers were used for the work: 74 green traces are from an instrument with good resolution and modest sensitivity, blue from one with modest resolution and high sensitivity. The catalyst was activated by dehydration at 350 1C in flowing helium, Fig.…”

“…INS spectroscopy has also been used to investigate the working catalyst. 73,74 A series of samples 74 with different time and temperature on-stream were prepared using the react-and-quench method. These experiments used the reactor 75 that had been developed to carry out reactions on the 10 g scale required for INS rather than the 10 mg scale used in conventional microreactor studies.…”