Mixed Anion Control of the Partial Oxidation of Methane to Methanol on the β-PtO₂Surface

Abstract

Although the C–H bond of methane is very strong, it can be easily dissociated on the (110) surface of β-PtO2. This is because a very stable Pt–C bond is formed between the coordinatively unsaturated Pt atom and CH3 on the surface. Owing to the stable nature of the Pt–C bond, CH3 is strongly bound to the surface. When it comes to methanol synthesis from methane, the Pt–C bond has to be cleaved to form a C–O bond during the reaction process. However, this is unlikely to occur on the β-PtO2 surface: The activation energy of the process is calculated to be so large as 47.9 kcal/mol. If the surface can be modified in such a way that the ability for the C–H bond activation is maintained but the Pt–C bond is weakened, a catalyst combining the functions of C–H bond cleavage and C–O bond formation can be created. For this purpose, analyzing the orbital interactions on the surface is found to be very useful, resulting in a prediction that the Pt–C bond can be weakened by replacing the O atom trans to the C atom with a N atom. This would be a sort of process to make β-PtO2 a mixed anion compound. Density functional theory simulations of catalytic reactions on the β-PtO2 surface show that the activation energy of the rate-limiting step of methanol synthesis can be reduced to 27.7 kcal/mol by doping the surface with N.

Oxidative Addition of Methane and Reductive Elimination of Ethane and Hydrogen on Surfaces: From Pure Metals to Single Atom Alloys

“…In recent years, it has been reported that reserves of methane-rich natural gas, such as tight gas, shale gas, and coalbed methane, are rapidly increasing . Much research has been conducted to convert methane into useful chemicals, such as light alkanes, olefins, alcohols, and aromatic compounds. − Currently, indirect methods are most widely used for producing value-added products from methane: methane is partially oxidized or reformed to syngas (a mixture of CO and H 2 ), from which long-chain hydrocarbons and alcohols are produced by Fischer–Tropsch synthesis. , It would be of economic interest to evaluate the possibility of using natural gas as a feedstock for chemical synthesis . Direct conversion of methane to light hydrocarbons by oxidative or nonoxidative coupling of methane (OCM or NOCM) has a potential for more efficient one-step methane upgrading, avoiding the energy-intensive syngas generation stage. , The primary products of OCM and NOCM, C 2 species (i.e., ethane or ethylene), are precursors to a variety of higher value chemical products, such as plastics and resins .…”

Partial Oxidation of Methane to Methanol on the M–O–Ag/Graphene (M = Ag, Cu) Composite Catalyst: A DFT Study

“…It can be inferred that for CH 3 OH* formation the catalytic activity follows the order of Cu−O−Ag/graphene (triplet) > Ag−O−Ag/graphene (triplet) > Ag−O−Ag/graphene (singlet) > Cu−O−Ag/graphene (singlet). Furthermore, Table3shows that Ag−O−Ag/graphene and Cu−Ag/graphene have lower reaction energies than some noble metal catalysts, such as Pt 2 O/ GO sheet (1.76 eV),66 N-doped β-PtO 2 (1.20 eV),65 and β-PtO 2 (2.08 eV) 65. And they are comparable with [Cu(μ-O)Cu] 2+ − ZSM-5,20,68 Pt 2 O 2 /GO sheet,66 Ni@C 24 N 24 ,69 and [Cu 3 (μ-O) 3 ] 2+ −MOR 70 catalysts.…”

Low-temperature selective oxidation of methane to methanol over a platinum oxide

“…This step is considered to be the rate-limiting step of the whole reaction. Such a Mars-van Krevelen-type reaction mechanism for methanol formation was also studied for the b-PtO 2 and IrO 2 surfaces: 13 the activation barriers of the methyl group transfer on the b-PtO 2 and IrO 2 surfaces were calculated to be 47.9 and 60.6 kcal mol À1 , respectively, which are much higher than that on the a-PtO 2 surface.…”

“…Note that the same process on the b-PtO 2 surface requires a larger desorption barrier of 26.1 kcal mol À1 . 13 With such a small methanol desorption barrier, methanol production is competitive with over-oxidation (Fig. S8, ESI †).…”