374856 Si-Rich and Ti-Rich (Mn, Cu and Ce) Catalyst Formulations for the Selective Catalytic Reduction (SCR) of NOx with NH3: Surface Properties and Key Components in Relation with Activity of NOx Reduction

Thursday, November 20, 2014: 9:15 AM
308 (Hilton Atlanta)
Thirupathi Boningari1, Dimitrios Pappas1, Padmanabha Reddy Ettireddy2, Adam Kotrba2, Thomas Spinks2 and Panagiotis Smirniotis1, (1)Chemical Engineering Program, School of Energy, Environmental, Biological and Medicinal Engineering, University of Cincinnati, Cincinnati, OH, (2)Research and Applied Science Division, Tenneco Inc, Grass Lake, MI

A series of M/TiO2 and M/TiO2-SiO2 (with M = Mn, Cu and Ce) catalysts were prepared by adopting a wet-impregnation method and investigated for the selective catalytic reduction (SCR) of NOx in the temperature range of 100-500 oC with excess (10 vol.%) oxygen. Our XPS depth profile analysis illustrate that the surface atomic ratio of Cu1+/ Cu2+ greatly enhanced with increase in TiO2 content in the TiO2-SiO2 support, and these results are consistent with the H2-TPR results where the additional reduction peak evolved at 200 oC for copper loaded titania-rich (Cu/TiO2) catalyst. The high activity of Cu-based TiO2 formulations has been assigned to the enhancement in the formation of Cu1+ active sites, existence of surface Cu2+, Cu1+ species and the increment of reduction potentials of surface copper species. The Ce3+/Ce4+ and Ce3+/Cen+ atomic ratio (1.14 and 0.53, respectively) in Ce/TiO2 catalyst calculated from deconvoluted XPS spectra are much higher than that of Ce/TiO2-SiO2 (1:1) and Ce/TiO2-SiO2 (3:1). The existence of higher Ce3+ surface species over CeO2/TiO2 illustrates the increment of surface oxygen vacancies and thus facilitates for the adsorption of oxygen species or activates reactants in the SCR reaction. When ceria was supported on pure TiO2, the low-temperature reduction peak was broad and less defined, and the reducibility in the low temperature range was much less pronounced. On the other hand, the addition of ceria to titania with strong reciprocal interaction is generally perceived as a shift in the bulk reduction temperature to lower values, to about 500–650 °C. As bigger Ce4+ ions enter the lattice structure to proxy the Ti4+ ions with smaller ionic radii (248 and 215 pm, respectively), the lattice could become highly strained. The NOx conversions and the apparent kinetic constant of the catalyst kac, over the Cu, Mn, Ce-loaded on different supports TiO2 and TiO2-SiO2 (3:1 and 1:1) catalysts measured under steady-state conditions results demonstrated higher activity of the Ti-rich materials.

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