The role of Pd–In interactions on the performance of PdIn-Hmordenite in the SCR of NOx with CH4
The aims of this work were to use several techniques to characterize the generated species when indium and palladium were successively exchanged in H-mordenite and to investigate the effect of the Pd/In ratio on the said species as well as to correlate the activity of the prepared solids with the formed moieties. We studied the activity of In-Hmordenite catalysts obtained by reductive solid-state ion exchange and the effect of the addition of Pd. There was a clear correlation between the maximum catalytic activity of each catalyst and its ability to form NO2 in the temperature-programmed desorption of NO (NO-TPD) experiments performed after NO adsorption. PdInHM(1/3) was the catalyst that showed the best results in activity and, after the first catalytic test, it was further activated. The temperature-programmed reduction (TPR) and NO-TPD results of this solid suggest that the amount of active species increased after the reaction and that there would be some kind of Pd–In interaction. The characterization of the fresh and used samples by CO adsorption and FTIR shows the differences between PdInHM(1/3) and PdInHM(1/6) catalysts in terms of how Pd was present on the support, and justifies the different catalytic behavior of both catalysts.
Graphical abstractThe effects of the addition of 0.5 wt% of Pd to InHMordenite were studied for the SCR of NOx with methane. A battery of characterization techniques allowed us to suggest that according to the indium loading, different Pd–In interactions are present and that the role of Pdn+ species would be to modify the balance between the different adsorbed NOx species, giving place to an optimal formulation with a In/Al = 1/3 ratio. There was a good correlation between NO-TPD experiments and the NOx conversion, wich showed an almost linear increase of the maximun NOx conversion with the NO2/NO ratio.Figure optionsDownload full-size imageDownload high-quality image (75 K)Download as PowerPoint slideHighlights► Good contribution to the identification of In and Pd species in a zeolitic matrix using a good battery of characterization techniques and detection of a probable Pd–In interaction. ► Good correlation between the catalytic activity of PdIn-Hmordenite catalysts and the desorbed NO2/NO ratio observed in NO-TPD experiments. ► Very good catalytic activity of a PdIn-Hmordenite formulation with an In/Al = 1/3 ratio for the selective catalytic reduction of NOx with methane.
Journal: Catalysis Today - Volume 172, Issue 1, 25 August 2011, Pages 124–131