Theoretical Approach to Homogeneous Catalyst of Methane …
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catalysts, methane activation is performed at relatively low temperatures leading to
suppress the overoxidation reaction kinetically.
Theoretical approaches using computational chemistry play important roles in
catalytic reactions, which provide important guidelines and practical strategies for
rational catalytic design [6, 7]. Theoretical calculations often assist in the interpretation of experimental data, such as spectroscopic data, and provide mechanistic
insight into catalytic reactions. In addition, theoretical calculations sometimes give
us preliminary information of catalytic performance that is subsequently tested experimentally. As developments in hardware and software lead to faster computation, the
theoretical approach to catalyst design of methane hydroxylation might eventually
become important. Computational chemistry has been employed not only by theoreticians but also by experimental groups to support experimental data. The direct
interaction between the theoretical results and experimental data helps the development of new and improved methane hydroxylation catalysts. The feedback between
theory and experiment is especially critical for success of the catalytic design of
methane hydroxylation [6].
In this chapter, we introduce some catalytic complexes developed by the interplay with theory and experiment and several examples of successful predictions for
methane hydroxylation using computational chemistry.
2 Computational Methods
A wide range of theoretical methods is available for catalyst design in methane
hydroxylation. For molecular systems, in particular, quantum chemical calculations
using methods such as density functional theory (DFT), which is the most practical
method for reactions involving transition metal complexes, are able to predict reliable geometrical and electronic structures, thermodynamics properties, and reaction
pathways for specific reactions. A conventional approach to understanding the reaction mechanisms of catalytic system by quantum chemical calculations starts from
presuming the transition state (TS) and the reaction pathway for the each step of
desired reaction followed by optimization of the stationary points, such as reactant
complex (RC), TS, and product complex (PC) and calculating the intrinsic reaction
coordinate (IRC). Performing these tasks in all steps in the catalytic reactions, we can
find a reasonable single reaction path connected the overall reaction. These results
provide the relative energies of the RC, TS, and PC in the each reaction and the
activation energy and reaction energy in the catalytic reaction. In quantum chemical
calculations of the transition metal complexes, in particular, the electronic configurations and spin states of the desired complexes need to be considered [7]. Because
the energy levels of various spin states in the transition metal complexes, such as the
high spin or low spin state, might be in a range of a few kcal mol
−1 , the energies
and spectra of different spin states should be computed and compared with either
experimental data or a higher-level theory. In addition, in the metal-oxo and polynuclear metal complexes, there might be the open-shell or closed-shell states in the
153
catalysts, methane activation is performed at relatively low temperatures leading to
suppress the overoxidation reaction kinetically.
Theoretical approaches using computational chemistry play important roles in
catalytic reactions, which provide important guidelines and practical strategies for
rational catalytic design [6, 7]. Theoretical calculations often assist in the interpretation of experimental data, such as spectroscopic data, and provide mechanistic
insight into catalytic reactions. In addition, theoretical calculations sometimes give
us preliminary information of catalytic performance that is subsequently tested experimentally. As developments in hardware and software lead to faster computation, the
theoretical approach to catalyst design of methane hydroxylation might eventually
become important. Computational chemistry has been employed not only by theoreticians but also by experimental groups to support experimental data. The direct
interaction between the theoretical results and experimental data helps the development of new and improved methane hydroxylation catalysts. The feedback between
theory and experiment is especially critical for success of the catalytic design of
methane hydroxylation [6].
In this chapter, we introduce some catalytic complexes developed by the interplay with theory and experiment and several examples of successful predictions for
methane hydroxylation using computational chemistry.
2 Computational Methods
A wide range of theoretical methods is available for catalyst design in methane
hydroxylation. For molecular systems, in particular, quantum chemical calculations
using methods such as density functional theory (DFT), which is the most practical
method for reactions involving transition metal complexes, are able to predict reliable geometrical and electronic structures, thermodynamics properties, and reaction
pathways for specific reactions. A conventional approach to understanding the reaction mechanisms of catalytic system by quantum chemical calculations starts from
presuming the transition state (TS) and the reaction pathway for the each step of
desired reaction followed by optimization of the stationary points, such as reactant
complex (RC), TS, and product complex (PC) and calculating the intrinsic reaction
coordinate (IRC). Performing these tasks in all steps in the catalytic reactions, we can
find a reasonable single reaction path connected the overall reaction. These results
provide the relative energies of the RC, TS, and PC in the each reaction and the
activation energy and reaction energy in the catalytic reaction. In quantum chemical
calculations of the transition metal complexes, in particular, the electronic configurations and spin states of the desired complexes need to be considered [7]. Because
the energy levels of various spin states in the transition metal complexes, such as the
high spin or low spin state, might be in a range of a few kcal mol
−1 , the energies
and spectra of different spin states should be computed and compared with either
experimental data or a higher-level theory. In addition, in the metal-oxo and polynuclear metal complexes, there might be the open-shell or closed-shell states in the