Correlation of Surface Characteristics with Catalytic Performance of Potassium Promoted Pd/Al2O3 Catalysts: The Case of N2O Reduction by Alkanes or Alkenes

The present study aims at investigating the role of potassium (K) promoter on the surface and catalytic behavior of Pd/Al2O3 catalysts during N2O reduction by alkanes (CH4, C3H8) or alkenes (C3H6). In this context, the surface properties of un-promoted and K-promoted catalysts were evaluated by means of X ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption and FTIR-pyridine adsorption. The results reveal that both the electronic and structural properties of Pd entities can be substantially modified by potassium ions, which are in close proximity with catalyst surface without exhibiting a tendency to accumulate. This in turn results in significant modifications on reactants/intermediates chemisorption bonds, affecting the catalytic performance of K-promoted catalysts. Indeed, it was found that potassium strongly promotes the N2O reduction by propane or propene yielding notably lower N2O light off temperatures (ca. 100 degrees C) as compared to those obtained over un-promoted catalysts. On the contrary, a slight inhibition upon K-promotion was observed, when using CH4 as reducing agent, implying that the action of the K-promoter is strongly related with the reducing agent used and its' relative interaction with the catalyst's surface. The results are discussed in terms of the correlation between the surface chemistry modifications induced by electropositive promoters and the de-N2O performance of K-promoted catalysts.