Research output: Contribution to journal › Article › peer-review
Different Efficiency of Zn2+ and ZnO Species for Methane Activation on Zn-Modified Zeolite. / Gabrienko, Anton A.; Arzumanov, Sergei S.; Toktarev, Alexander V. et al.
In: ACS Catalysis, Vol. 7, No. 3, 03.03.2017, p. 1818-1830.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Different Efficiency of Zn2+ and ZnO Species for Methane Activation on Zn-Modified Zeolite
AU - Gabrienko, Anton A.
AU - Arzumanov, Sergei S.
AU - Toktarev, Alexander V.
AU - Danilova, Irina G.
AU - Prosvirin, Igor P.
AU - Kriventsov, Vladimir V.
AU - Zaikovskii, Vladimir I.
AU - Freude, Dieter
AU - Stepanov, Alexander G.
PY - 2017/3/3
Y1 - 2017/3/3
N2 - Understanding methane activation pathways on Zn-modified high-silica zeolites (ZSM-5, BEA) is of particular importance because of the possibility of methane involvement in coaromatization with higher alkanes on this type of zeolites. Herein, two samples of Zn-modified zeolite BEA containing exclusively either small zinc oxide clusters or isolated Zn2+ cations have been synthesized and thoroughly characterized by a range of spectroscopic methods (1H MAS NMR, DRIFTS, XPS, EXAFS, HRTEM) to show that only one of the Zn-species, either Zn2+ cations or ZnO small clusters, exists in the void of zeolite pores. The ability of zinc sites of different nature to promote the activation of methane C-H bond with the zeolite Brønsted acid sites (BAS) has been examined in the reactions of methane H/D hydrogen exchange with BAS and the alkylation of benzene with methane. It has been found that both ZnO and Zn2+ species promote the reaction of H/D exchange of methane with BAS. The rate of H/D exchange is higher by 2 and 3 orders of magnitude for the zeolite loaded with ZnO or Zn2+ species, respectively, compared to pure acid-form zeolite H-BEA. So, the promoting effect of Zn2+ cations is more profound than that of ZnO species for H/D exchange reaction. This implies that the synergistic effect of Zn-sites and BAS for C-H bond activation in methane is significantly higher for Zn2+ cations compared to small ZnO clusters. It has been revealed, however, that only Zn2+ cations promote the alkylation of benzene with methane, whereas ZnO species do not. The isolated Zn2+ cations provide the formation of zinc-methyl species, which are further transformed to zinc-methoxy species. The latter is the key intermediate for the performance of the alkylation reaction. Hence, while both zinc oxide clusters and Zn2+ cationic species are able to provide a synergistic effect for the activation of C-H bonds of methane displayed by the dramatic acceleration of H/D exchange reaction, only the Zn2+ cationic species perform methane activation toward the alkylation of benzene with methane. This implies that only the Zn2+ cations in Zn-modified zeolite can activate methane for the reaction of methane coaromatization with higher alkanes. (Chemical Equation Presented).
AB - Understanding methane activation pathways on Zn-modified high-silica zeolites (ZSM-5, BEA) is of particular importance because of the possibility of methane involvement in coaromatization with higher alkanes on this type of zeolites. Herein, two samples of Zn-modified zeolite BEA containing exclusively either small zinc oxide clusters or isolated Zn2+ cations have been synthesized and thoroughly characterized by a range of spectroscopic methods (1H MAS NMR, DRIFTS, XPS, EXAFS, HRTEM) to show that only one of the Zn-species, either Zn2+ cations or ZnO small clusters, exists in the void of zeolite pores. The ability of zinc sites of different nature to promote the activation of methane C-H bond with the zeolite Brønsted acid sites (BAS) has been examined in the reactions of methane H/D hydrogen exchange with BAS and the alkylation of benzene with methane. It has been found that both ZnO and Zn2+ species promote the reaction of H/D exchange of methane with BAS. The rate of H/D exchange is higher by 2 and 3 orders of magnitude for the zeolite loaded with ZnO or Zn2+ species, respectively, compared to pure acid-form zeolite H-BEA. So, the promoting effect of Zn2+ cations is more profound than that of ZnO species for H/D exchange reaction. This implies that the synergistic effect of Zn-sites and BAS for C-H bond activation in methane is significantly higher for Zn2+ cations compared to small ZnO clusters. It has been revealed, however, that only Zn2+ cations promote the alkylation of benzene with methane, whereas ZnO species do not. The isolated Zn2+ cations provide the formation of zinc-methyl species, which are further transformed to zinc-methoxy species. The latter is the key intermediate for the performance of the alkylation reaction. Hence, while both zinc oxide clusters and Zn2+ cationic species are able to provide a synergistic effect for the activation of C-H bonds of methane displayed by the dramatic acceleration of H/D exchange reaction, only the Zn2+ cationic species perform methane activation toward the alkylation of benzene with methane. This implies that only the Zn2+ cations in Zn-modified zeolite can activate methane for the reaction of methane coaromatization with higher alkanes. (Chemical Equation Presented).
KW - DRIFTS
KW - EXAFS
KW - H/D exchange
KW - MAS NMR
KW - methane activation
KW - zeolite
KW - zinc
KW - SOLID-STATE NMR
KW - IN-MODIFIED ZSM-5
KW - MODIFIED ZSM-5 ZEOLITES
KW - AROMATIC-HYDROCARBONS
KW - LIGHT ALKANES
KW - HIGH-SILICA ZEOLITES
KW - H-1 MAS NMR
KW - BRONSTED ACID SITES
KW - PROPANE AROMATIZATION
KW - HYDROGEN-EXCHANGE
UR - http://www.scopus.com/inward/record.url?scp=85015165684&partnerID=8YFLogxK
U2 - 10.1021/acscatal.6b03036
DO - 10.1021/acscatal.6b03036
M3 - Article
AN - SCOPUS:85015165684
VL - 7
SP - 1818
EP - 1830
JO - Topics in Catalysis
JF - Topics in Catalysis
SN - 1022-5528
IS - 3
ER -
ID: 10273184