A series of TiO2-, Al2O3-, and SiO2-supported manganese oxide catalysts were prepared, characterized, and catalytically tested for selective catalytic reduction (SCR) of NO with NH3 in the presence of excess oxygen at low temperatures (373−523 K). Various commercial supports were used in this study to find out the influence of surface area, support nature (acidic, basic), and crystalline phase on SCR activity. XRD studies reveal the presence of anatase and rutile phases for titania supports and the existence of γ-alumina in the case of alumina support. Silica support was amorphous. No independent lines corresponding to the crystalline MnO2 were observed on pure anatase and rutile samples. However, the presence of MnO2 was confirmed on other supports by XRD. BET surface area values suggest that specific surface area of the supports was decreased after impregnating with MnO2. The FT-IR and ammonia TPD studies indicate the presence of two types of acid sites on these catalysts, and the acidic strength of the catalysts is higher than the corresponding pure supports. XPS results revealed the presence of two types of manganese oxides, MnO2 (642.4 eV) and Mn2O3 (641.2 eV), on all the samples. The SCR performance of the supported Mn catalysts decreased in the following order:  TiO2 (anatase, high surface area) > TiO2 (rutile) > TiO2 (anatase, rutile) > γ-Al2O3 > SiO2 > TiO2 (anatase, low surface area). Quantitative NO conversion with 100% N2 selectivity was achieved at 393 K with Mn supported on TiO2 (anatase). TiO2-supported MnO2 catalysts showed more promising SCR activity than Al2O3- or SiO2-supported manganese oxide catalysts. Various characterization techniques suggest that Lewis acid sites, a high surface concentration of MnO2, and redox properties are important in achieving high catalytic performance at low temperatures.

A novel catalyst for low temperature selective catalytic reduction (SCR) using CO as reductant, MnO x supported on titania, has been shown to be effective for both elemental mercury capture and low temperature SCR. In low temperature (200 °C) SCR trials using an industrially relevant space velocity (50 000 h−1) and oxygen concentration (2 vol %), nearly quantitative reduction of NO x was obtained using CO as the reductant. Fresh catalyst used as an adsorbent for elemental mercury from an inert atmosphere showed remarkable mercury capture capacity, as high as 17.4 mg/g at 200 °C. The catalyst effectively captured elemental mercury after use in NO x reduction. Mercury capture efficiency was not affected by the presence of water vapor. Mercury capacity was reduced in the presence of SO2. Manganese loading and bed temperature, which influence surface oxide composition, were found to be important factors for mercury capture. X-ray photoelectron spectroscopy (XPS) results reveal that the mercury is present in its oxidized form (HgO) in spent catalyst, indicating the participation of lattice oxygen of the catalyst in the reaction. These results suggest that a single-step process integrating low temperature SCR and mercury capture from flue gas might be feasible.

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The techniques of X-ray diffraction, O2 chemisorption, FT-Raman, and X-ray photoelectron spectroscopy were utilized to characterize La2O3−TiO2 composite oxide and V2O5/La2O3−TiO2 catalyst calcined at 773 and 1073 K temperatures. The investigated La2O3−TiO2 (1:5 mole ratio) mixed oxide was obtained by a homogeneous coprecipitation method with in situ generated ammonium hydroxide. A nominal 12 wt % V2O5 was impregnated over the calcined (773 K) composite oxide by adopting a wet impregnation method from ammonium metavanadate dissolved in aqueous oxalic acid solution. The characterization results suggest that the calcined La2O3−TiO2 mixed oxide primarily consists of a mixture of TiO2 anatase and La−Ti oxides. The La2O3−TiO2 also accommodates a monolayer equivalent of vanadia in a highly dispersed state. The O 1s, Ti 2p, La 3d, and V 2p photoelectron peaks of the V2O5/La2O3−TiO2 sample are highly sensitive to the calcination temperature. The XPS line shapes and the corresponding binding energies indicate that the dispersed vanadium oxide interacts selectively with the lanthana portion of the La2O3−TiO2 mixed oxide and readily forms a LaVO4 compound. The XRD and FT-Raman techniques, in particular, provide direct evidence for the formation of LaVO4 compound. Interestingly, the presence of lanthana in V2O5/La2O3−TiO2 catalysts retards the phase transformation of anatase into rutile under the influence of vanadia.

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