Cavity-controlled methanol conversion over zeolite catalysts

Abstract

The successful development and application in industry of Methanol-to-Olefins (MTO) process brought about an innovative and efficient route for olefin production via non-petrochemical resources and also attracted extreme attention of C1 chemistry and zeolite catalysis. Molecular sieve catalysts with diversified microenvironments embedding unique channel/cavity structure and acid properties, exhibit demonstrable features and advantages in shape-selective catalysis of MTO. Especially, the shape selective catalysis over 8-MR and cavity-type zeolites with acidic supercage environment and narrow pore opening manifested special host-guest interaction between the zeolite catalyst and guest reactants, intermediates and products. This caused the great differences in product distribution, catalyst deactivation, molecular diffusion, revealing the cavity-controlled methanol conversion over 8-MR and cavity-type zeolite catalyst. Furthermore, the dynamic and complicated cross-talk behaviors of catalyst material (with coke)-diffusion-reaction over this type of zeolites determine the catalytic performance of the methanol conversion. In this review, we shed light on the cavity-controlled principle in the MTO reaction including cavity-controlled active intermediates formation, cavity-controlled reaction routes with the involvement of these intermediates in the complex reaction network, cavity-controlled catalyst deactivation and cavity-controlled diffusion. All these were exhibited by the MTO reaction performances and product selectivity over 8-MR and cavity-type zeolite catalysts. Advanced strategies inspired by the cavity-controlled principle were developed, providing the great promise for the optimization and precise control of MTO process.

Evolution of Methanol Molecules within Pyridine-Modified Mordenite Unveiled by Solid-State NMR Spectroscopy

“…15,16 The catalytic behavior of zeolites is determined by both acidity and pore confinement. 17,18 For MOR zeolite, the vast difference in the local confinement effect between 12-MR and 8-MR channels has been shown to tune the reaction in different ways, either in a positive or negative manner. 19 Taking the methanol/DME carbonylation reaction as an example, studies have shown that the carbonylation reaction would preferably take place on the Bro̷ nsted acid sites (BAS) within 8-MR pores.…”

How Micropore Topology Influences the Structure and Location of Coke in Zeolite Catalysts

“…The analysis of extracted coke by mass spectromery (MS) ,,,− and the studies of the deactivation processes by different spectroscopic methods, such as UV–vis, − Raman, ,, and 13 C nuclear magnetic resonance (NMR) spectroscopies, , revealed alkylated polycyclic aromatic hydrocarbons (PAHs) as the prevailing components of coke. ,, The compounds with up to ca. 4 condensed rings are proposed to reside in the micropores, , while higher aromatics are typically considered as the components of external coke, ,− although they could also deposit in the micropores. ,, The catalyst propensity to coking and the composition of coke are strongly dependent on the framework topology, which implies that the micropore confinement also governs the deposition of coke. ,, Nonetheless, the insights on how the micropore geometry affects the coke localization are very limited and mainly focused on ZSM-5 catalysts. Density functional theory analysis indicated that the coke molecules primarily deposit in the intersection of the 10 MR channels in ZSM-5 because of the highest stabilization provided by this largest void volume .…”

“…12,19,38 The catalyst propensity to coking and the composition of coke are strongly dependent on the framework topology, which implies that the micropore confinement also governs the deposition of coke. 4,6,42 Nonetheless, the insights on how the micropore geometry affects the coke localization are very limited and mainly focused on ZSM-5 catalysts. Density functional theory analysis indicated that the coke molecules primarily deposit in the intersection of the 10 MR channels in ZSM-5 because of the highest stabilization provided by this largest void volume.…”

Evaluating the efficacy of zeolites synthesized from natural clay for the methanol-to-hydrocarbon process

“…This aspect was a crucial factor contributing to their product shape selectivity. 13 Specifically, small-pore zeolites (8-membered rings) only allowed the passage of tiny molecules like ethylene and propylene, thus often serving as catalysts in the MTO process. 14–17 On the other hand, medium-pore zeolites (10-membered rings) permitted the passage of relatively larger diameter molecules, such as benzene, toluene, and xylene (BTX).…”