Theoretical Study of the Direct
Conversion of Methane by First-Row
Transition-Metal Oxide Cations
in the Gas Phase
Yoshihito Shiota and Kazunari Yoshizawa
Abstract The direct conversion of methane to methanol is a thermodynamically
favorable process compared with the available commercial process that uses synthesis
gas. This chapter reviews quantum chemical approaches, especially by means of
density functional theory (DFT) calculations, to elucidate the reaction pathway and
energetics for methane-to-methanol conversion by first-row transition-metal oxide
ions (MO
+ s, where M is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). We introduce the
electronic structures of MO
+ and the potential-energy diagrams for the methane
hydroxylation by MO
+ . In the FeO
+ /CH 4 system, surface crossing seams were
computed along the reaction pathway. Spin–orbit coupling (SOC) was calculated to
estimate the probability of spin-inversion. SOC decreases along the reaction pathway,
approaching zero in the product complex.
Keywords Density functional theory calculations · Methane activation · Spin
states · Transition state · Surface crossing
1 Introduction
The development of catalysts for the selective oxidation of saturated hydrocarbons
under mild conditions is a central research topic in modern chemistry [1–11]. Studies
on the gas-phase reactions between bare transition-metal ions and hydrocarbons have
provided a wealth of insight concerning the intrinsic interactions between the active
site of catalysts and organic substrates [12–15]. The direct conversion of CH 4 to
CH 3 OH is thermodynamically more favorable than the commercial two-step process
using synthesis gas (CO and H 2 ) [16]; it is therefore a current topic of interest in
pure and applied chemistry.
The catalytic activity of bare transition-metal monoxide cations (MO
+ ) toward
CH 4 is a key to the mechanistic aspects of direct CH 4 hydroxylation [17–30]. Schwarz
and coworkers have systematically investigated the gas-phase reactions between the
Y. Shiota (B) · K. Yoshizawa
Institute for Materials Chemistry and Engineering, Kyushu University, Motooka, Nishi-ku,
Fukuoka 819-0395, Japan
e-mail: shiota@ms.ifoc.kyushu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_2
23
Conversion of Methane by First-Row
Transition-Metal Oxide Cations
in the Gas Phase
Yoshihito Shiota and Kazunari Yoshizawa
Abstract The direct conversion of methane to methanol is a thermodynamically
favorable process compared with the available commercial process that uses synthesis
gas. This chapter reviews quantum chemical approaches, especially by means of
density functional theory (DFT) calculations, to elucidate the reaction pathway and
energetics for methane-to-methanol conversion by first-row transition-metal oxide
ions (MO
+ s, where M is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). We introduce the
electronic structures of MO
+ and the potential-energy diagrams for the methane
hydroxylation by MO
+ . In the FeO
+ /CH 4 system, surface crossing seams were
computed along the reaction pathway. Spin–orbit coupling (SOC) was calculated to
estimate the probability of spin-inversion. SOC decreases along the reaction pathway,
approaching zero in the product complex.
Keywords Density functional theory calculations · Methane activation · Spin
states · Transition state · Surface crossing
1 Introduction
The development of catalysts for the selective oxidation of saturated hydrocarbons
under mild conditions is a central research topic in modern chemistry [1–11]. Studies
on the gas-phase reactions between bare transition-metal ions and hydrocarbons have
provided a wealth of insight concerning the intrinsic interactions between the active
site of catalysts and organic substrates [12–15]. The direct conversion of CH 4 to
CH 3 OH is thermodynamically more favorable than the commercial two-step process
using synthesis gas (CO and H 2 ) [16]; it is therefore a current topic of interest in
pure and applied chemistry.
The catalytic activity of bare transition-metal monoxide cations (MO
+ ) toward
CH 4 is a key to the mechanistic aspects of direct CH 4 hydroxylation [17–30]. Schwarz
and coworkers have systematically investigated the gas-phase reactions between the
Y. Shiota (B) · K. Yoshizawa
Institute for Materials Chemistry and Engineering, Kyushu University, Motooka, Nishi-ku,
Fukuoka 819-0395, Japan
e-mail: shiota@ms.ifoc.kyushu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_2
23