Lean NOx trap (LNT) technique has been proved to be very promising for lean NOx elimination. Recently, a new support K2Ti8O17 was introduced into LNT catalysts due to their large specific surface area and strong basicity. Up to now, although a lot of work has been performed on the states of barium species and their performance for NOx storage, little attention has been paid to K2CO3 used as NOx storage component, and the relationship between the existing states and NOx storage performance of K2CO3 is still unclear. In addition, most conventional LNT catalysts contain noble metals, such as Pt and Rh, greatly increasing the cost. Meanwhile, the noble metal-based LNT catalysts probably exhibit considerable selectivity of NOx to N2O due to high capability for NO dissociation. Therefore, exploration of base metal LNT catalysts is necessary. In this work, a series non-platinic LNT catalysts MOx-K2CO3/K2Ti8O17 (M = Ce, Fe, Cu, Mn and Co) were designed and prepared, which displayed rather good performance for NOx storage and reduction, even better than the Pt-containing catalyst Pt-K2CO3/K2Ti8O17. A super large NOx storage capacity of 3.32 and 3.21 mmol/g is achieved on the catalyst CoOx-K2CO3/K2Ti8O17 and MnOx-K2CO3/K2Ti8O17, respectively, which are higher than that of Pt-K2CO3/K2Ti8O17 (2.68 mmol/g). Meanwhile, NO-to-NO2 conversion of MnOx-K2CO3/K2Ti8O17 is about 10% larger than that of Pt-K2CO3/K2Ti8O17. During lean/rich cyclic tests MnOx-K2CO3/K2Ti8O17 displays a high NOx reduction percentage of 98.5% and an ultralow selectivity of NOx to N2O (0.3%).The catalysts were characterized by multiple techniques including XRD, SEM/HRTEM, EXAFS, FT-IR, CO2-TPD and in-situ DRIFTS. Due to the strong interaction between K2CO3 and K2Ti8O17, an unknown titanate phase with a K/Ti atomic ratio higher than 2/8 is identified, which is also active and regenerative for NOx storage and reduction. Several kinds of K-related species such as –OK groups, K2O, surface K2CO3 and bulk or bulk-like K2CO3 coexist. The appearance of the negative bands in in-situ DRIFT spectra of fresh catalysts around 1470/1563 cm-1 (carbonates, C=O stretch) suggests the involvement of carbonates in NOx storage.Our catalysts exhibit rather high stability,for that morphology is maintained and the active species change little after used. The as-prepared non-platinic LNT catalyst is very promising for industrial application due to its excellent catalytic performance, high stability and low cost.

New insights into the function of potassium carbonate species and the superiority of base metals to noble metals in the polytitanate nanobelt supported LNT catalysts

249th National Meeting (2015)

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New insights into the function of potassium carbonate species and the superiority of base metals to noble metals in the polytitanate nanobelt supported LNT catalysts<br />