TY - JOUR
T1 - Roles of Water Molecules in Modulating the Reactivity of Dioxygen-Bound Cu-ZSM-5 toward Methane
T2 - A Theoretical Prediction
AU - Yumura, Takashi
AU - Hirose, Yuuki
AU - Wakasugi, Takashi
AU - Kuroda, Yasushige
AU - Kobayashi, Hisayoshi
N1 - Funding Information:
This project was partially supported by a Grant-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (JSPS) (T.Y. at Kyoto Institute of Technology, no. 26790001) and by a Grant-in-Aid for Scientific Research on the Innovative Area "Stimuli-responsive Chemical Species for the Creation of Fundamental Molecules" (No. 2408) from the Ministry of Education, Culture, Sports, Science and Technology, Government of Japan (MEXT) (T.Y. at Kyoto Institute of Technology, no. 15H00941).
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/4/1
Y1 - 2016/4/1
N2 - We propose theoretically that the reactivity of O2-bound Cu-ZSM-5 toward methane is enhanced by the presence of one water molecule near a dinuclear copper site inside a 10-membered ring of the zeolite cavity. The current study employed density functional theory (DFT) calculations with the B3LYP functional to elucidate reaction intermediates during dioxygen activation by Cu-ZSM-5 in the presence of one water molecule attached to a dicopper site. The initial event is the formation of a hydroperoxo species bridged by the dicopper site via an H atom transfer from an attached water to the bound dioxygen. After the formation of the intermediate, the hydroperoxo O-O bond is completely cleaved to form radical oxygen containing intermediates, such as a Cu-O-Cu species bound by two OH groups (HO-Cu-O-Cu-OH), as well as a copper oxyl group containing intermediate (HO-Cu-OH-CuO). The radical oxygen containing intermediates can cleave a methane C-H bond in a homolytic fashion. Examining the barrier for the C-H bond activation obtained from DFT calculations, we found that the two types of intermediates have the power to more effectively cleave methane C-H bonds than the Cu-O-Cu intermediate that has been proposed to be formed in the absence of a water molecule. The current DFT findings propose that O2-bound Cu-ZSM-5 in the presence of one water molecule is a potential candidate for catalysts desired for methane to methanol conversion under mild conditions. Recently, techniques for controlling the number of water molecules near the active site of a ZSM-5 zeolite have been developed, and therefore the DFT findings should stimulate experimental efforts for constructing catalysts for direct methane hydroxylation. (Chemical Equation Presented).
AB - We propose theoretically that the reactivity of O2-bound Cu-ZSM-5 toward methane is enhanced by the presence of one water molecule near a dinuclear copper site inside a 10-membered ring of the zeolite cavity. The current study employed density functional theory (DFT) calculations with the B3LYP functional to elucidate reaction intermediates during dioxygen activation by Cu-ZSM-5 in the presence of one water molecule attached to a dicopper site. The initial event is the formation of a hydroperoxo species bridged by the dicopper site via an H atom transfer from an attached water to the bound dioxygen. After the formation of the intermediate, the hydroperoxo O-O bond is completely cleaved to form radical oxygen containing intermediates, such as a Cu-O-Cu species bound by two OH groups (HO-Cu-O-Cu-OH), as well as a copper oxyl group containing intermediate (HO-Cu-OH-CuO). The radical oxygen containing intermediates can cleave a methane C-H bond in a homolytic fashion. Examining the barrier for the C-H bond activation obtained from DFT calculations, we found that the two types of intermediates have the power to more effectively cleave methane C-H bonds than the Cu-O-Cu intermediate that has been proposed to be formed in the absence of a water molecule. The current DFT findings propose that O2-bound Cu-ZSM-5 in the presence of one water molecule is a potential candidate for catalysts desired for methane to methanol conversion under mild conditions. Recently, techniques for controlling the number of water molecules near the active site of a ZSM-5 zeolite have been developed, and therefore the DFT findings should stimulate experimental efforts for constructing catalysts for direct methane hydroxylation. (Chemical Equation Presented).
KW - C-H bond activation
KW - DFT calculations
KW - direct methane oxidation
KW - nanometer sized cavity
KW - zeolite
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U2 - 10.1021/acscatal.5b02477
DO - 10.1021/acscatal.5b02477
M3 - Article
AN - SCOPUS:84963739937
VL - 6
SP - 2487
EP - 2495
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 4
ER -