No abstract

The oxidant is a crucial factor affecting the performance of direct oxidation of methane to methanol (DMTM). It is still extremely challenging to realize one-pot DMTM using dioxygen. So far, hydrogen peroxide is still the most frequently reported green oxidant for DMTM with high selectivity of methanol. Aiming to achieve insights into the influence of oxidants on the DMTM performance and to improve catalysts, we computationally investigated the reaction mechanisms of DMTM using hydrogen peroxide at mono-copper sites in three kinds of Cu-exchanged zeolites with different sizes of the micropores. We identified the common advantage and limitations of hydrogen peroxide as the oxidant. In contrast to molecular oxygen, the O-O bond of hydrogen peroxide could be easily broken to produce reactive surface oxygen species, enabling the facile C-H bond activation of methane at a lower temperature. However, the radical-like mechanism for the C-H bond activation in DMTM using hydrogen peroxide makes the C-H bond breaking of methanol ineluctably superior to methane. This leads to the inevitable trade-off between selectivity and activity for DMTM. Moreover, the lower O-H bonding energy of hydrogen peroxide would also result in the significant self-decomposition of hydrogen peroxide. Despite the existence of these bottlenecks, the kinetic analysis manifests that it is still promising to improve catalysts to boost the performance of DMTM using hydrogen peroxide.

The performance of the direct oxidation of methane to methanol (DMTM) is significantly influenced by the oxidant. It is still incredibly challenging to realize one-pot DMTM using dioxygen. So far, hydrogen peroxide is still the most frequently reported green oxidant for DMTM with a high selectivity for methanol. To achieve insights into the influence of oxidants on the DMTM performance, we computationally investigated the reaction mechanisms of DMTM using hydrogen peroxide at mono-copper sites in three kinds of Cu-exchanged zeolites with different sizes of the micropores. We identified the common advantages and limitations of hydrogen peroxide as the oxidant. In contrast to dioxygen, the O-O bond of hydrogen peroxide could be easily broken to produce reactive surface oxygen species, which enables the facile C-H bond activation of methane at a lower temperature. However, because of the radical-like process for C-H bond activation at mono-copper sites, it is kinetically challenging to actualize the preferential C-H bond activation of methane as compared to that of methanol. Moreover, the lower O-H bonding energy of hydrogen peroxide would result in the self-decomposition of hydrogen peroxide. Despite the bottlenecks, the kinetic analysis shows that it is still promising to improve catalysts to boost the performance of DMTM using hydrogen peroxide.