Direct observation of DME carbonylation in the different channels of H-MOR zeolite by continuous-flow solid-state NMR spectroscopy

Abstract

The dynamic evolution of acetyl intermediates in the two different channels of H-mordenite (H-MOR) zeolite during dimethyl ether (DME) carbonylation is tracked by using in situ solid-state NMR spectroscopy under continuous-flow conditions. Thus, the reaction path via methyl acetate produced over active sites in 8 member ring (MR) channels, followed by diffusion into 12 MR channels, is proposed.

Insights into the Site-Selective Adsorption of Methanol and Water in Mordenite Zeolite by 129Xe NMR Spectroscopy

“…A good example for this is mordenite (MOR), which has been widely used in dimethyl ether (DME) and methanol carbonylation reactions, − methanol to olefins (MTO) reaction, , synthesis gas conversion reactions, , and other catalytic reactions. − The structure of MOR consists of straight ellipsoidal twelve-membered ring (12 MR, aperture 7 × 6.5 Å) main channels and strongly compressed eight-membered ring (8 MR, aperture 5.7 × 2.6 Å) side pockets. The unique pore confinement effect of two channels has been extensively studied both theoretically − and experimentally. − For example, Corma et al studied the activity and selectivity toward carbonylation of methanol and DME in different locations of MOR by means of DFT calculations and demonstrated that when competed with hydrocarbon formation, methanol carbonylation occurs preferentially within 8 MR channels, , which was consistent with subsequent in situ solid-state NMR experiments. , Gounder and Iglesia studied the cracking and dehydration of alkane and revealed that turnovers occurred with strong preference on acid sites contained within smaller 8 MR pockets in H-MOR, while the rate on sites located within 12 MR channels was much lower and often undetectable. Recently, we reported the conversion of syngas to ethylene with a sharp selectivity as high as 73% at CO conversion rate of 26% by employing the oxide–zeolite (OX–ZEO) catalyst concept with ZnCrO x –MOR, where high efficiency conversion is realized over the catalytic sites within the 8 MR side pockets of MOR via a ketene intermediate rather than methanol in the 8 MR or 12 MR channels .…”

“…14−17 For example, Corma et al studied the activity and selectivity toward carbonylation of methanol and DME in different locations of MOR by means of DFT calculations and demonstrated that when competed with hydrocarbon formation, methanol carbonylation occurs preferentially within 8 MR channels, 11,13 which was consistent with subsequent in situ solid-state NMR experiments. 15,16 Gounder and Iglesia 17 studied the cracking and dehydration of alkane and revealed that turnovers occurred with strong preference on acid sites contained within smaller 8 MR pockets in H-MOR, while the rate on sites located within 12 MR channels was much lower and often undetectable. Recently, we reported the conversion of syngas to ethylene with a sharp selectivity as high as 73% at CO conversion rate of 26% by employing the oxide−zeolite (OX−ZEO) catalyst concept with ZnCrOx−MOR, where high efficiency conversion is realized over the catalytic sites within the 8 MR side pockets of MOR via a ketene intermediate rather than methanol in the 8 MR or 12 MR channels.…”

Promoting Effect of Copper Loading and Mesoporosity on Cu-MOR in the Carbonylation of Dimethyl Ether to Methyl Acetate

“…For HMOR, an induction period of about 3 h was observed, where water was removed from the catalyst bed and surface acetyl groups formed by reaction of DME and methanol with bridged hydroxyl groups (i.e., Brønsted acid sites) and silanol groups on the MOR [10]. This induction period not only let the DME saturate the exchange sites with methyl groups, but it also provided time for the 12-MR channels to form aromatic precursors [16] (mostly alkyl benzenes) and light olefins (propylene, and hexene) and as a result suppressed the selectivity towards MA (see Figure S4).…”

“…Afterwards, the obtained acetyl species react with another DME molecule to produce MA and regenerate the surface methoxy groups for another catalytic cycle. The intermediate surface active acetyl species could only be identified in 8-MR side pockets by in-situ solid-state nuclear magnetic resonance (NMR) spectroscopy studies [15,16], and their formation was recently predicted from density functional theory (DFT) calculations and verified experimentally to proceed partly via initial ketene formation [17].…”

Spacial hindrance induced recovery of over-poisoned active acid sites in pyridine-modified H-mordenite for dimethyl ether carbonylation

“…Particularly, H-mordenite (H-MOR) shows a high catalytic activity for DME carbonylation to MA [23][24][25]. Researchers believe that Brønsted acid sites located at the eight-membered ring (8-MR) side pockets of H-MOR are active in DME carbonylation [26][27][28][29][30]. Unfortunately, the H-MOR catalyst is readily deactivated by coke deposition in twelve-membered ring (12-MR) channels [10], which blocks mass transfer and limits its commercial application [11].…”