The methanol-to-hydrocarbons (MTH) process over acidic zeolites refers collectively to series of important industrial catalytic processes to produce either olefins or other hydrocarbons. Mechanistically, methanol conversion proceeds through a ‘pool’ of hydrocarbon species. For the methanol-to-olefins process, these species can be delineated broadly into ‘desired’ lighter olefins and ‘undesired’ heavier fractions that cause deactivation in a matter of hours. The catalyst selectivity and lifetime are the result of a complex interplay between various factors such as topology, acidity, operating conditions, transport phenomena, etc. The crux in further catalyst optimization is the ability to follow the formation of carbonaceous species during operation, track their reactivity and transport through the pores of the zeolite. Herein we show how advanced operando spectroscopic measurements, first principle modeling and kinetic measurements may yield crucial information on the reactivity and transport within confined environments.<br/>As a first case, we show how the combined results of an operando Kerr-gated Raman spectroscopic study with state-of-the-art operando molecular simulations, allowed to follow the formation of hydrocarbon species at various stages of methanol conversion. Polyenes are identified as crucial intermediates towards formation of polycyclic aromatic hydrocarbons, with their fate determined largely by the zeolite topology. Such advanced synergistic modeling/experimental study allowed to pinpoint the missing link between active and deactivating species.<br/>As a second case, we show how specific interactions within confined environments may also affect the transport of formed products and impact the ultimate product selectivity. Based on a combined modeling experimental study, including first-principle molecular dynamics simulations, PFG-NMR experiments and pulse-response Temporal Analysis of Products measurements, a promotional effect of the presence of Brønsted acid sites on the diffusion rate of olefins could be shown, due to the formation of favorable π-H interactions with acid protons.<br/>Both cases shown in this talk, show how a synergistic modeling experimental approach may unravel essential nanoscale insight into the nature and reactivity of complexes within confined environments which may lead to further optimization of important industrial catalysts.

How the nature, transport and reactivity of confined hydrocarbons affects the lifetime and selectivity of methanol conversion catalysts

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.