New redox deposition-precipitation method for preparation of supported manganese oxide catalysts

Pt-Modified Nano-Sized Mn2O3 Oxide Prepared from the Mn3O4 Phase with Tetragonal Symmetry for CO Oxidation

One of the current problems in the environmental catalysis is the design of an effective and less costly catalytic system for the oxidation of CO. The nano-sized α-Mn2O3 oxide has been prepared and modified with 0.5 wt.% Pt. The catalysts have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and diffuse-reflectance infrared spectroscopy (DRIFTS). Finely divided PtO and Pt(OH)2 are being formed on the Mn2O3 surface as a result of the strong interaction between platinum and the nano-oxide. Based on DRIFTS investigations and the model calculations, a Langmuir–Hinshelwood type of mechanism is supposed for CO oxidation on Pt/Mn2O3. The CO and oxygen are adsorbed on different types of sites. The Mars–van Krevelen mechanism is the most probable one over pure Mn2O3, thus suggesting that CO2 is adsorbed on the oxidized sites. The CO adsorption in the mixture CO + N2 or in the presence of oxygen (CO + N2 + O2) leads to a partial reduction in the Pt+ surface species and the formation of linear Pt1+−CO and Pt0−CO carbonyls. Both of them take part in the CO oxidation reaction.

Structure-Activity Relationship of Manganese Oxide Catalysts for the Catalytic Oxidation of (chloro)-VOCs

Manganese oxide catalysts, including γ-MnO2, Mn2O3 and Mn3O4, were synthesized by a precipitation method using different precipitants and calcination temperatures. The catalytic oxidations of benzene and 1,2-dichloroethane (1,2-DCE) were then carried out. The effects of the calcination temperature on the catalyst morphology and activity were investigated. It was found that the specific surface area and reducibility of the catalysts decreased with the increase in the calcination temperature, and both the γ-MnO2 and Mn3O4 were converted to Mn2O3. These catalysts showed good activity and selectivity for the benzene and 1,2-DCE oxidation. The γ-MnO2 exhibited the highest activity, followed by the Mn2O3 and Mn3O4. The high activity could be associated with the large specific surface area, abundant surface oxygen species and excellent low-temperature reducibility. Additionally, the catalysts were inevitably chlorinated during the 1,2-DCE oxidation, and a decrease in the catalytic activity was observed. It suggested that a higher reaction temperature could facilitate the removal of the chlorine species. However, the reduction of the catalytic reaction interface was irreversible.