Promotional effect of metal cations doping on OMS-2 catalysts for NH3-SCR reaction

Elucidating structure-performance correlations in gas-phase selective ethanol oxidation and CO oxidation over metal-doped γ-MnO2

“…There are two main peaks between 250-500 °C attributed to reduction of (i) MnO2 to Mn3O4 (via Mn2O3) and (ii) Mn3O4 to MnO [2,33], with the initial reduction starting from 125-200 °C. Evidently, except for La-γ-MnO2, all M-γ-MnO2 samples showed lower temperature for the first reduction peak than the undoped γ-MnO2, which may be ascribed to the weakening effect of the metal dopants (other than La 3+ ) on Mn-O bonds [26,32]. These results point to the improved reducibility of M-γ-MnO2 materials after metal doping.…”

“…Clearly, the nsutite structure was basically retained after metal doping, but some peaks for the doped M-γ-MnO2 shifted to lower angles. The Ca-γ-MnO2 with low doping content (0.3 mol%) showed similar 2θ shift as the Fe-γ-MnO2, suggesting that the presence of dopant in both the mixture solution and the final framework may render partial loss of nsutite structure symmetry of γ-MnO2 and some lattice expansion [31,32]. Furthermore, as shown in Table 1, the crystallize sizes of M-γ-MnO2 estimated from the Scherrer equation using the strongest (131) peak (2θ = 37.1 o ) varied by the metal dopants, with Cu-γ-MnO2 showing the biggest average crystallize size (22.8 nm).…”

“…The peak at lower temperatures (~130 °C) could be ascribed to desorption at surface Brönsted acid sites (Mn-OH and M-OH groups) for NH3-TPD and surface weak base sites (such as O2 -, OH -) species for CO2-TPD. The higher temperature peaks in the NH3-TPD and CO2-TPD curves are attributed to the stronger Lewis acid sites derived from the defective metal atoms [32,34] and the stronger base sites derived from lattice oxygen species (such as metal-O 2-pairs and defective O 2-anions) [35], respectively. Compared with the undoped γ-MnO2, doping with Fe 3+ , La 3+ , Co 2+ and Al 3+ resulted in a considerable increase of surface acidity and basicity, especially for stronger acid/base sites.…”

Oxygen Defect Engineering of β‐MnO2 Catalysts via Phase Transformation for Selective Catalytic Reduction of NO

“…For Nanorod, the strong and sharp peak centered at 330 °C (zone II) could be ascribed to the reduction of MnO 2 to Mn 2 O 3 or Mn 3 O 4 , and the weak and broad peak at 440 °C (zone III) refers to the further reduction to MnO. [36,[48][49][50] Regarding Nanorod-OD and Nanosheet-OD, the reduction peaks shift toward lower temperatures. Because the introduction of oxygen defects forms Mn 3+ O bonds, which are longer and weaker than Mn 4+ O, Mn atoms of Nanorod-OD and Nanosheet-OD are much easier to be reduced.…”

“…[39] It is worth to point out that the reduction starting at below 250 °C for Nanorod-OD and Nanosheet-OD (zone I) could be attributed to the reduction of surface adsorbed oxygen. [36,43,48] As listed in Table S2, Supporting Information, the concentration of H 2 consumption in zone I for Nanosheet-OD is larger than that for Nanorod-OD (10.7% versus 4.4%), implying the abundant surface adsorbed oxygen. The total H 2 consumptions decrease in the order of Nanorod (9.360 mmol g −1 ) > Nanorod-OD (9.102 mmol g −1 ) > Nanosheet-OD (8.264 mmol g −1 ), also reflecting the ascending order of Mn 3+ concentration.…”