Influence of support on the activity of Mn supported catalysts for SCR of NO with ammonia

In this work four different supports of varying degree of Bronsted and Lewis acid sites and textural properties were used to evaluate the influence of degree of ammonia interaction and Mn species formation in the catalysts and its effect on NOx conversion. A series of Mn deposited on TiO2, ferrierite (FER), Engelhard titanium silicate (ETS-10) and Montmorillonite (Mont-K10) were prepared by impregnation method. The catalysts were characterized by different techniques. FTIR analysis showed only Mn/FER catalyst to possess significant amount of Bronsted and Lewis acid sites. No correlation was found between surface area, type and amount of acid sites and NOx conversion of the catalysts. XRD analysis of catalysts showed predominantly MnO2 species, especially in Mn/FER catalyst, and Mn2O3 species was not detected. However, the Raman studies indicated the presence of MnO2 and Mn2O3 bands. TPR revealed lower onset reduction temperatures of MnOx species in Mn/FER compared with other catalysts. Among different catalysts tested, Mn/FER showed highest NOx conversion between 160 and 400 °C. Based on the obtained results, it was concluded that even though acid sites are needed to activate NH3, its amount and strength were found to have less influence than the redox properties, arising from MnO2 active species.

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► Mn/FER is more active for NOx reduction with NH3 compared to other Mn supported catalysts.
► Mn species on FER is well dispersed as evident from higher NOx storage and minimal decrease in BET surface area and easy reducibility.
► Raman spectra and TPR experiments lead to the conclusion that loading Mn on FER and Mont-K10 led to material rich in MnO2.
► Strong acid sites and dispersed and easily reducible MnO2 species are both responsible for increased activity at low as well as at high temperatures.