NMR‐Spectroscopic Evidence of Intermediate‐Dependent Pathways for Acetic Acid Formation from Methane and Carbon Monoxide over a ZnZSM‐5 Zeolite Catalyst

Abstract

Two ways: a Zn-modified ZSM-5 zeolite catalyst was developed for the reaction of methane with carbon monoxide to directly produce acetic acid under mild conditions (573-623 K), and two different intermediate-dependent reaction pathways were unambiguously identified for acetic acid formation by in situ solid-state NMR spectroscopy.

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.…”

Recent Advances in the Synthesis, Characterization and Application of Zn+‐containing Heterogeneous Catalysts

“…Excited by the special electron transfer feature in zeolite, Deng's group synthesized Zn + ‐containing ZnZSM‐5 by reacting metallic Zn vapor with HZSM‐5 zeolite in a CAVERN device or a modified glass reactor driven by heat ( Figure A) . This synthesis procedure is quite similar to that described by Chen's group, with the CAVERN device convenient for in situ NMR analysis.…”

“…Direct carbonylation of methane with CO to form higher hydrocarbons, such as acetic acid, is considered to be a more economically viable and environmental‐friendly approach for methane transformation . The ZnZSM‐5 catalyst also shows good catalytic performance for the direct carbonylation of methane into acetic acid with CO under mild conditions (573–623 K) . The carbonylation process was monitored using 13 C isotope labeled in situ solid‐state NMR spectroscopy .…”

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

“…Overall, signals of rigid molecules have always demonstrated more than one peak for the same resonance,w hich means that the same molecule exists in different molecular environments inside the zeolite framework, i.e., heterogeneity in the molecular environment of the entrapped species.T his same observation was also observed for unreacted methane (Figure 2b and 3b), as its multiple adsorbed forms were also identified and hence, further advocates for the local heterogeneity within the material. Theexistence of surface-formate species,i.e., the 13 C correlations observed at 170-173 ppm correlating with a 1 Hsignal at % 8ppm (Figure 3d), is indicative of the occurrence of CO insertion, [46][47][48][49][50][51] which is known to generate hydrocarbon pool species during the zeolite-catalyzed MTH process (see below). [28,41,42] However,i ts hould also be mentioned that these species can only be formed in the very early stages of the reaction making use of Oa toms present in the zeolite and metal oxide Mo precursor (cf.F igure 1b).…”