Potassium and cobalt double-doped ferrierites as a new class of soot oxidation catalysts

Abstract

Research efforts to develop an effective soot oxidation catalyst have intensified in recent years due to the increased awareness of the highly harmful effect of soot particles on the human health and the environment. Large-scale application of a developed catalyst calls for a cheap support material allowing for an effective dispersion and thus a decrease in the active phase loading. Zeolites, widely used in catalysis as active phase carriers, possess advantageous characteristics such as a uniform porous structure and large surface area. Furthermore, they are characterized by high availability, good price, and are environmentally friendly. Cobalt-based materials provide promising soot oxidation catalyst phases, and alkali doping can further enhance their activity. This study focuses on the optimization of the potassium loading in the potassium and cobalt double-doped ferrierites towards a new class of cheap and environmentally friendly soot combustion catalysts. The potassium doping of the ferrierite-supported cobalt spienel was optimized in the range of 0–14 wt%. The obtained materials were characterized in terms of their composition (XRF, XPS, XRD, Raman spectroscopy), morphology (SEM, TEM/EDX/FFT), and reducibility (H2-TPR), and tested in the process of soot oxidation in tight and loose contact modes. The strong promotional effect of potassium was discussed in terms of a significant modification of the catalyst electronic properties (work function studies) and supported by the potassium surface state studies by the alkali thermal desorption method (SR-TAD). It was found that the optimal potassium promoter dispersion leads to the lowest catalyst work function and its highest activity in soot combustion. The effect of nitric oxide was also investigated for selected catalysts. The opposite effect of NO on the activity of undoped and K-doped catalysts was discussed on the basis of in-depth spectroscopic studies. An enhanced formation of nitrate species was found on the surface of the K-containing catalyst which led to the stronger inhibiting effect of NO.