Dual Active Sites on Molybdenum/ZSM‐5 Catalyst for Methane Dehydroaromatization: Insights from Solid‐State NMR Spectroscopy

Abstract

Methane dehydroaromatization (MDA) on Mo/ZSM‐5 zeolite catalyst is promising for direct transformation of natural gas. Understanding the nature of active sites on Mo/ZSM‐5 is a challenge for applications. Herein, using 1H{95Mo} double‐resonance solid‐state NMR spectroscopy, we identify proximate dual active sites on Mo/ZSM‐5 catalyst by direct observation of internuclear spatial interaction between Brønsted acid site and Mo species in zeolite channels. The acidic proton–Mo spatial interaction is correlated with methane conversion and aromatics formation in the MDA process, an important factor in determining the catalyst activity and lifetime. The evolution of olefins and aromatics in Mo/ZSM‐5 channels is monitored by detecting their host–guest interactions with both active Mo sites and Brønsted acid sites via 1H{95Mo} double‐resonance and two‐dimensional 1H–1H correlation NMR spectroscopy, revealing the intermediate role of olefins in hydrocarbon pool process during the MDA reaction.

Enhancing AsH3 Detoxification via Electron-Deficient [NiIII–OH (μ-O)] in a Nickel-Modified NaY Zeolite: A Pathway toward As0 Products

“…Based on the 1 H NMR spectra of NaY-H and 1Ni/NaY-H (Figure b), four overlapping signals were found in both deconvoluted spectra. The signal near 0.8 ppm was identified as a silanol, while the peak at 2.6 ppm represented H bonds in Al–OH groups . Then, two H signals were detected for the bridged Si–(OH)–Al groups of the B acid sites.…”

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis

“…More recently, the spatial interaction between Mo active sites and Brønsted acid sites has been identified by using 1 H− 95 Mo double-resonance SSNMR spectroscopy, presenting the direct spectroscopic evidence on the synergic bifunctionality of Mo sites and Brønsted acid sites in Mo-exchanged ZSM-5 zeolites for methane dehydromatization reaction. 368 Besides the characterization of extra-framework metal sites, SSNMR correlation spectroscopy is also a powerful tool for detecting the framework and framework-associated atoms in zeolites. 370,371 For instance, the 2D 1 H− 27 Al correlation SSNMR demonstrates that there exist two types of framework Al sites in HZSM-5 zeolites (Figure 22a).…”

Detection of remote proton–nitrogen correlations by 1H-detected 14N overtone solid-state NMR at fast MAS

“…[39][40][41] The RESPDOR sequence has been widely used to detect the spatial proximity/interaction between 1 H and a quadrupolar nucleus such as 14 N, 42,43 63 Cu, 44 65 Zn, 45 71 Ga, 46 79 Br, 47 and 95 Mo. 48 Here we use the 14 N OT (|Dm| = 2) transitions [49][50][51][52][53][54][55] instead of the fundamental 14 N transitions (|Dm| = 1), where m denotes the energy level. A number of methods for detecting 1 H-14 N OT correlations have been studied.…”