TY - JOUR

T1 - Nature of the Surface Intermediates Formed from Methane on Cu-ZSM-5 Zeolite

T2 - A Combined Solid-State Nuclear Magnetic Resonance and Density Functional Theory Study

AU - Kolganov, Alexander A.

AU - Gabrienko, Anton A.

AU - Yashnik, Svetlana A.

AU - Pidko, Evgeny A.

AU - Stepanov, Alexander G.

PY - 2020/3/19

Y1 - 2020/3/19

N2 - The intermediates formed upon the interaction of methane with Cu-modified ZSM-5 zeolites (Cu/H-ZSM-5) have been analyzed with solid-state NMR spectroscopy and DFT methods. Methane activation by Cu/H-ZSM-5 zeolites gives rise to three distinct surface methoxy-like species (-O-CH3) detected by 13C MAS NMR spectroscopy with specific chemical shifts in the range of 53-63 ppm. DFT calculations on representative cluster models of different sites potentially present in Cu/H-ZSM-5 have been used to assign these signals to (i) methanol adsorbed on two neighboring Cu sites (Cu-(HOCH3)-Cu, 62.6 ppm), (ii) methanol adsorbed on zeolite Brønsted acid sites (52.9 ppm), and (iii) lattice-bound methoxy groups (Si-O(CH3)-Al, 58.6). The formation of these methoxy-like intermediates depends on the Cu loading and, accordingly, the type of Cu species in the Cu/H-ZSM-5 zeolite. For the sample with low (0.1 wt %) Cu loading containing exclusively mononuclear isolated Cu species, only the intermediates ii and iii have been detected. The Cu-bound intermediate (i) is formed upon methane activation by multinuclear Cu sites featuring Cu-O-Cu bridging moieties present in the materials with relatively higher Cu loading (1.38 wt %). The presented results indicate that methane activation by Cu/H-ZSM-5 can be promoted by both mono- and multinuclear Cu species confined in the zeolite matrix.

AB - The intermediates formed upon the interaction of methane with Cu-modified ZSM-5 zeolites (Cu/H-ZSM-5) have been analyzed with solid-state NMR spectroscopy and DFT methods. Methane activation by Cu/H-ZSM-5 zeolites gives rise to three distinct surface methoxy-like species (-O-CH3) detected by 13C MAS NMR spectroscopy with specific chemical shifts in the range of 53-63 ppm. DFT calculations on representative cluster models of different sites potentially present in Cu/H-ZSM-5 have been used to assign these signals to (i) methanol adsorbed on two neighboring Cu sites (Cu-(HOCH3)-Cu, 62.6 ppm), (ii) methanol adsorbed on zeolite Brønsted acid sites (52.9 ppm), and (iii) lattice-bound methoxy groups (Si-O(CH3)-Al, 58.6). The formation of these methoxy-like intermediates depends on the Cu loading and, accordingly, the type of Cu species in the Cu/H-ZSM-5 zeolite. For the sample with low (0.1 wt %) Cu loading containing exclusively mononuclear isolated Cu species, only the intermediates ii and iii have been detected. The Cu-bound intermediate (i) is formed upon methane activation by multinuclear Cu sites featuring Cu-O-Cu bridging moieties present in the materials with relatively higher Cu loading (1.38 wt %). The presented results indicate that methane activation by Cu/H-ZSM-5 can be promoted by both mono- and multinuclear Cu species confined in the zeolite matrix.

KW - MOLECULAR-ORBITAL METHODS

KW - ZSM-5 ZEOLITE

KW - DIRECT CONVERSION

KW - COPPER IONS

KW - MECHANISTIC INSIGHTS

KW - CARBON-MONOXIDE

KW - METHOXY GROUPS

KW - OXO-CLUSTERS

KW - ACTIVE-SITE

KW - MFI ZEOLITE

UR - http://www.scopus.com/inward/record.url?scp=85081694425&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.0c00311

DO - 10.1021/acs.jpcc.0c00311

M3 - Article

AN - SCOPUS:85081694425

VL - 124

SP - 6242

EP - 6252

JO - ACS applied materials & interfaces

JF - ACS applied materials & interfaces

SN - 1944-8244

IS - 11

ER -