Modified hierarchical birnessite-type manganese oxide nanomaterials for CO catalytic oxidation

Abstract

Hierarchical birnessite-type manganese oxide catalysts modified by transition metal (cobalt, cerium, copper, and nickel) cations were synthesized via a facile hydrothermal reaction.

Opposite Effects of Co and Cu Dopants on the Catalytic Activities of Birnessite MnO2 Catalyst for Low-Temperature Formaldehyde Oxidation

“…This suggests that the presence of dopants within the framework of δ-MnO2 influences its reduction behaviour and mobility of lattice oxygen, likely due to electronic delocalization effect of the dopants [17][18] and the formation of oxygen defects. 19,37,42 This in agreement with the observed defect formation due to doping in the Raman, XPS and HRTEM results. activity was observed over all temperature ranges and the temperature of complete conversion shifted down to 80°C from 90°C in the pristine δ-MnO2, thereby indicating the promoting effect of Co on the catalytic activity of δ-MnO2 for HCHO oxidation.…”

“…3-643.45 corresponding to Mn 3+ and Mn 4+ respectively. 6,19,37 The splitting of Co 2p1/2 (795.12 eV) and Co 2p3/2 (780.1 eV) (Figure S1) was found to be 15.02 eV, in agreement with the reported values for Co 3+ 16 .The presence of a shakeup peak at around 943 eV and a peak centered at around 933.6 eV (Fig S2 ) indicates that the doped Cu exists in Cu 2+ state. [39][40] The observed decrease in the ratio of Mn 4+ /Mn 3+ is due to the substitution of Mn 4+ by the dopants in the lattice of birnessite MnO2 and indicates the creation of oxygen vacancies.…”

“…water molecules. 11,19 As seen in Figure 4(b), and Table 2, the relative amount of surface active oxygen species increases after the addition of dopants. Relative to the pristine δ-MnO2, 0.05Co δ-MnO2 exhibited an increase in the content of surface active oxygen species compared to 0.05Cu δ-MnO2, in agreement with the decpnvolution results of Mn 2p3/2 (Table 2) and HRTEM results.…”

“…Consumed surface active oxygen species could be regenerated by the interaction of structural defects with molecular oxygen and water molecules. [18][19] The presence of oxygen vacancies could also enhance the mobility and activity of lattice oxygen to the surface, while molecular oxygen is activated into lattice oxygen at the oxygen vacant sites, thereby sustaining the whole process. 22,47 Catalyst doping and or surface modification has been demonstrated to be an effective strategy for enhancing catalytic activity, mainly through the creation of defects and enriching the surface concentration of active oxygen species.…”

Mesoporous ZnMn2O4 Nanospheres as a Nonprecious Bifunctional Catalyst for Zn–Air Batteries

“…The relative peak ratios following the OER (76% vs 24%) and ORR (88% vs 12%) processes were significantly different from those of the pristine air cathode (56% vs 44%). The O ads species are associated with defective oxides in which oxygen deficiency/occupation occurs, where oxygen species can easily be transformed into active oxygen species such as O 2– and O – via interaction of molecular oxygen with structural defects . The concentration of O ads species formed within the defect site is known to contribute significantly to the ORR and OER catalytic activities of the air cathode.…”