Cascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control, defined mainly by zeolites. However, a great deal of mechanistic understanding remains unclear: metal-based catalysts usually lead to complex product compositions that may result in unexpected zeolite reactivity. Here we present an in-depth multivariate analysis of the chemistry involved in eight different zeolite topologies when combined with a highly active Fe-based catalyst in the hydrogenation of CO2 to olefins, aromatics, and paraffins. Solid-state NMR spectroscopy and computational analysis demonstrate that the hybrid nature of the active zeolite catalyst and its preferred CO2-derived reaction intermediates (CO/ester/ketone/hydrocarbons, i.e., inorganic-organic supramolecular reactive centers), along with 10 MR-zeolite topology, act as descriptors governing the ultimate product selectivity.
The transformation of methanol-to-hydrocarbons (MTH) has significant potential as a route to synthesise low-cost fuels; however, the initial stages of the zeolite catalysed MTH process are not well understood.
The
methanol-to-hydrocarbon process is known to proceed autocatalytically
in H-ZSM-5 after an induction period where framework methoxy species
are formed. In this work, we provide mechanistic insight into the
framework methylation within H-ZSM-5 at high methanol loadings and
varying acid site densities by means of first-principles molecular
dynamics simulations. The molecular dynamics simulations show that
stable methanol clusters form in the zeolite pores, and these clusters
commonly deprotonate the active site; however, the cluster size is
dependent on the temperature and acid site density. Enhanced sampling
molecular dynamics simulations give evidence that the barrier for
methanol conversion is significantly affected by the neighborhood
of an additional acid site, suggesting that cooperative effects influence
methanol clustering and reactivity. The insights obtained are important
steps in optimizing the catalyst and engineering the induction period
of the methanol-to-hydrocarbon process.
Room temperature methoxylation is methanol loading dependent: the higher the methanol loading, the faster the methoxylation. Methanol load of ≥2 leads to methoxylation while no methoxylation is observed with ≤1 molecule per Brønsted acidic site.
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