Direct Hydroxylation of Methane: Interplay Between Theory and Experiment

Contents
Orbital Concept for Methane Activation
	1 Introduction
	2 C–H Bond Activation of Methane
		2.1 Molecular Orbitals of Methane
		2.2 Orbital Concept for Methane Activation Based on Second-Order Perturbation
		2.3 Methane Activation by sMMO Model
	3 Reaction Mechanism for the Direct Hydroxylation of Methane
		3.1 Methane Hydroxylation by the FeO+ Species
		3.2 Methane Hydroxylation Mechanisms by sMMO
		3.3 Methane Hydroxylation Mechanisms by pMMO
	4 Conclusions
	References
Theoretical Study of the Direct Conversion of Methane by First-Row Transition-Metal Oxide Cations in the Gas Phase
	1 Introduction
	2 Electronic Structures of MO+ Ions
	3 Potential-Energy Diagrams for the Methane-To-Methanol Conversion
		3.1 Conversion of Methane to Methanol by ScO+, TiO+, and VO+
		3.2 Conversion of Methane to Methanol by CrO+ and MnO+
		3.3 Conversion of Methane to Methanol by FeO+, CoO+, and NiO+
		3.4 Conversion of Methane to Methanol by CuO+
	4 Surface Crossing and Spin–Orbit Coupling
		4.1 Crossing Seams of Potential-Energy Surfaces
		4.2 Spin–Orbit Coupling of Methane Conversion
	5 Summary
	References and Notes
Enzymatic Methane Hydroxylation: sMMO and pMMO
	1 Experimental Background
	2 History of Computational Approach
	3 Key Factors in Determining Reactivity of MMOHQ Toward Methane
	4 Proposed Mechanisms for the Methane to Methanol Conversion by MMOHQ
	5 Details in Mechanisms for the Methane Hydroxylation by MMOHQ
		5.1 Nonradical Mechanism
		5.2 Radical Rebound Mechanism
		5.3 Nonsynchronous Concerted Mechanism
	6 Mechanism for Methane Hydroxylation on pMMO
	7 Conclusions, Emerging Issues, and Challenges
	References and Notes
Mechanistic Understanding of Methane Hydroxylation by Cu-Exchanged Zeolites
	1 Introduction
	2 Methane Hydroxylation by [Cu2(μ-O)]2+ and [Cu3(μ-O)3]2+ in Zeolites
		2.1 Mechanism of C–H Activation
		2.2 Mechanism of CH3OH Formation
	3 Conclusion
	References
Oxidative Activation of Metal-Exchanged Zeolite Catalysts for Methane Hydroxylation
	1 Introduction
	2 Oxidative Activation of Fe-Exchanged Zeolites
		2.1 N2O Decomposition on FeII-ZSM-5
		2.2 H2O2 Decomposition on [FeIII–(μO)2–FeIII]-ZSM-5
	3 Oxidative Activation of Cu-Exchanged Zeolites
		3.1 N2O Decomposition on 2CuI-ZSM-5
		3.2 O2 Activation on 2[CuI2]-MOR and [CuIII2CuI(ΜO)]-MOR
	4 Conclusion
	References
Dynamics and Energetics of Methane on the Surfaces of Transition Metal Oxides
	1 Introduction
	2 Kinetics of Methane on Surface
		2.1 Langmuir Model
		2.2 Two Mechanisms: Direct Mechanism and Trapping-Mediated Mechanism
	3 Energetics of Methane on Surface
		3.1 How Strongly Methane Can be Adsorbed on the Surface?
		3.2 PdO, IrO2, and RuO2
		3.3 Adsorption of Methane on a Metal Oxide
		3.4 C–H Bond Dissociation of Methane on a Metal Oxide Surface
	4 Conclusions and Outlook
	Appendix
	References
Machine Learning Predictions of Adsorption Energies of CH4-Related Species
	1 Introduction
	2 Machine Learning Prediction of Adsorption Energies
		2.1 DFT Calculations of Adsorption Energies
		2.2 ML Methods
		2.3 ML Prediction of Adsorption Energies
		2.4 ML Prediction of ECH3–ECH2 Values for Methane Utilization
	3 Conclusion
	References
Theoretical Approach to Homogeneous Catalyst of Methane Hydroxylation: Collaboration with Computation and Experiment
	1 Introduction
	2 Computational Methods
	3 Organometallic Approaches
	4 Biomimetic Approaches
	5 Theoretical Predictions for a Methane Hydroxylation Catalyst
	6 Summary and Outlook
	References