Dynamics and Energetics of Methane …
131
TiO 2 (110) surface, one can anticipate a good catalytic activity thereon [69], though
TiO 2 per se is not an active catalyst for the C–H bond dissociation.
The C–H bond scission of methane is one of the most important yet challenging
steps in methane conversion. But this is not the goal. For example, C–O or C–C bond
formation is necessary for the utilization of methane as a chemical building block or
chemical raw material. Indeed, it is necessary that CH 3 species be strongly bound
by the surface cus metal site when it comes to making the activation energy of the
first C–H bond dissociation of methane lower, but at the same time such a strong
binding feature would make it difficult for CH 3 to become mobile on the surface.
The activation energy for subsequent reactions would perforce become high. The
generated CH 3 species may well be doomed to over oxidation. A breakthrough to
cut the Gordian knot is really needed.
Acknowledgements This work was supported by KAKENHI grants (numbers JP17K14440 and
JP17H03117) from the Japan Society for the Promotion of Science (JSPS) and the Ministry of
Education, Culture, Sports, Science and Technology of Japan (MEXT) through the MEXT projects
Integrated Research Consortium on Chemical Sciences, Cooperative Research Program of Network
Joint Research Center for Materials and Devices and Elements Strategy Initiative to Form Core
Research Center, and by JST-CREST JPMJCR15P5 and JST-Mirai JPMJMI18A2. The computations in this work were primarily performed using the computer facilities at the Research Institute for
Information Technology, Kyushu University. Y.T. is grateful for a JSPS Grant-in-Aid for Scientific
Research on Innovative Areas (Discrete Geometric Analysis for Materials Design, grant numbers
JP18H04488 and JP20H04643, and Mixed Anion, grant number JP19H04700).
Appendix
EHMO parameters used for Ir, C, Cl, and O appear in Table 2. They are well-accepted
values used in previous studies [70, 71].
Table 2 Extended Hückel parameters
Orbital
H ii (eV)
ζ 1
(c 1 )
ζ 2
(c 2 )
Ir 6s
−11.36
2.5
Ir 6p
−4.5
2.2
Ir 5d
−12.17
5.796
(0.6351)
2.557
(0.5556)
O 2s
−32.3
2.275
O 2p
−14.8
2.275
C 2s
−21.4
1.625
C 2p
−11.4
1.625
H 1s
−13.6
1.300
131
TiO 2 (110) surface, one can anticipate a good catalytic activity thereon [69], though
TiO 2 per se is not an active catalyst for the C–H bond dissociation.
The C–H bond scission of methane is one of the most important yet challenging
steps in methane conversion. But this is not the goal. For example, C–O or C–C bond
formation is necessary for the utilization of methane as a chemical building block or
chemical raw material. Indeed, it is necessary that CH 3 species be strongly bound
by the surface cus metal site when it comes to making the activation energy of the
first C–H bond dissociation of methane lower, but at the same time such a strong
binding feature would make it difficult for CH 3 to become mobile on the surface.
The activation energy for subsequent reactions would perforce become high. The
generated CH 3 species may well be doomed to over oxidation. A breakthrough to
cut the Gordian knot is really needed.
Acknowledgements This work was supported by KAKENHI grants (numbers JP17K14440 and
JP17H03117) from the Japan Society for the Promotion of Science (JSPS) and the Ministry of
Education, Culture, Sports, Science and Technology of Japan (MEXT) through the MEXT projects
Integrated Research Consortium on Chemical Sciences, Cooperative Research Program of Network
Joint Research Center for Materials and Devices and Elements Strategy Initiative to Form Core
Research Center, and by JST-CREST JPMJCR15P5 and JST-Mirai JPMJMI18A2. The computations in this work were primarily performed using the computer facilities at the Research Institute for
Information Technology, Kyushu University. Y.T. is grateful for a JSPS Grant-in-Aid for Scientific
Research on Innovative Areas (Discrete Geometric Analysis for Materials Design, grant numbers
JP18H04488 and JP20H04643, and Mixed Anion, grant number JP19H04700).
Appendix
EHMO parameters used for Ir, C, Cl, and O appear in Table 2. They are well-accepted
values used in previous studies [70, 71].
Table 2 Extended Hückel parameters
Orbital
H ii (eV)
ζ 1
(c 1 )
ζ 2
(c 2 )
Ir 6s
−11.36
2.5
Ir 6p
−4.5
2.2
Ir 5d
−12.17
5.796
(0.6351)
2.557
(0.5556)
O 2s
−32.3
2.275
O 2p
−14.8
2.275
C 2s
−21.4
1.625
C 2p
−11.4
1.625
H 1s
−13.6
1.300