Identification of Active Surface Species for Friedel–Crafts Acylation and Koch Carbonylation Reactions by in situ Solid‐State NMR Spectroscopy

Abstract

Finding the culprits: In situ NMR spectroscopy combined with theoretical calculations show the formation of acetyl species covalently bound to framework oxygen atoms in acid zeolites. These species, and not the usually assumed acylium cations, are the reactive intermediates in Friedel–Crafts acylation and Koch carbonylation reactions on zeolites.

Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

“…This same observation was also observed for unreacted methane (Figure b and b), as its multiple adsorbed forms were also identified and hence, further advocates for the local heterogeneity within the material. The existence of surface‐formate species, i.e., the 13 C correlations observed at 170–173 ppm correlating with a 1 H‐signal at ≈8 ppm (Figure d), is indicative of the occurrence of CO insertion, which is known to generate hydrocarbon pool species during the zeolite‐catalyzed MTH process (see below) . However, it should also be mentioned that these species can only be formed in the very early stages of the reaction making use of O atoms present in the zeolite and metal oxide Mo precursor (cf.…”

Ketene as a Reaction Intermediate in the Carbonylation of Dimethyl Ether to Methyl Acetate over Mordenite

“…Both possibilities involve very low energy barriers, and the carbocation is therefore expected to be short‐lived. It thus seems reasonable that the carbocation escaped detection in the NMR study by Corma and co‐workers 9. The ketene on the Brønsted acid site is restructured to acetyl [Eq.…”

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

“…11 Indeed, Blasco et al had confirmed the acetyl species (CH 3 CO-) rather than the acylium cation (CH 3 (CO) + ) as a stable surface species during methanol carbonylation on zeolites, which is represented by a completely different signal (170 ppm). 15 But Deng et al observed the acetyl species on MOR zeolite by its characteristic chemical shift anisotropy (CSA) parameters, because it has the same chemical shift (185 ppm) as that of the carbonyl group of MA. 16 It is a controversial issue concerning the existence of acetyl species.…”