Catalytic reaction systems for the direct conversion of methane to methanol have been previously developed using Cu zeolites. Among these materials, the Cu-CHA has been reported to show relatively high catalytic performance during the reaction of CH 4 −O 2 −H 2 O mixtures, although this catalytic activity varies with composition. In the present study, four Cu-CHA catalysts having different compositions and catalytic activity levels were prepared, and the redox properties and local structures of these specimens were analyzed using in situ X-ray absorption fine structure and UV−vis diffuse reflectance spectroscopies in conjunction with a CH 4 −O 2 −H 2 O reaction mixture. The relationships between the redox rates of the materials and catalytic activities (as reflected in the turnover frequency (TOF) during CH 4 oxidation) were assessed, and this analysis showed that the Cu-CHA reduction rate was highly correlated with activity. The data also suggested that the Cu 2+ reduction is associated with the activation of C−H bonds in CH 4 , which is the rate-determining step for the overall reaction. The effects of the local structure of the Cu-CHA on selectivity for CH 3 OH, the TOF value, and the Cu 2+ reduction rate were studied. Those Cu-CHA samples having high proportions of Cu 2+ ions coordinated to six-membered rings (Z 2 Cu) in the CHA framework exhibited higher selectivity than specimens having high proportions of [CuOH] + ions coordinated to eight-membered rings (ZCuOH), although the TOF values of the former Cu-CHA specimens were not higher than those of the latter because of the slower reduction rates of Cu 2+ species. The different catalyses can be attributed to the difference in Cu 2 O x active structures formed in the Z 2 Cu-rich samples and the ZCuOH-rich samples.

Direct oxidation of CH4 to CH3OH using O2 is challenging because of the high stability of CH4 and the relatively high reactivity of CH3OH. Here, Cu-CHA zeolites are tested for...

Expectations for industrial implementation of direct conversion of CH4 to CH3OH are growing with the increasing demand for energy-efficient chemical processes. In this study, catalytic production of CH3OH by direct...

Catalytic oxidation of methane to formaldehyde and methanol has attracted attention because of its advantage in energy efficiency over the conventional multistep reaction process involving endothermic steam reforming of CH 4 ; however, it is challenging to selectively obtain the partial oxidation products in the direct oxidation of CH 4 . In the present study, Co/SiO 2 with various Co loadings was tested for the CH 4 /O 2 /H 2 O gas flow reaction. As a result, Co/SiO 2 with a low loading of ≤0.1 wt % showed high selectivity for the partial oxidation reaction and mainly produced HCHO, while Co/SiO 2 with high Co loadings proceeded to complete oxidation. Structural analysis using X-ray absorption finestructure spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and scanning transmission electron microscopy suggested that single Co atoms generated at low Co loadings were effective in the selective oxidation of CH 4 to HCHO, while Co 3 O 4 nanoparticles generated at high Co loadings promoted the complete oxidation.