Effects of La, Ce, and Y Oxides on SnO2 Catalysts for CO and CH4 Oxidation

Abstract SnO 2 ‐based catalysts modified by La, Ce, and Y with a Sn/Ln (Ln=La, Ce, Y) atomic ratio of 2:1 were prepared by using a co‐precipitation method and used for CO and CH 4 oxidation. The catalysts were characterized by N 2 adsorption–desorption, XRD, energy dispersive X‐ray spectroscopy (EDS)‐SEM, H 2 temperature‐programmed reduction (TPR), X‐ray photoelectron spectroscopy (XPS), and thermogravimetric analysis differential scanning calorimetry (TGA‐DSC) techniques. All three rare earth metal oxides were found to improve the thermal stability of SnO 2 , which resulted in catalysts with much higher surface areas and smaller crystallite and particle sizes. However, only the addition of Ce resulted in a catalyst with improved activity for both CO and CH 4 oxidation. In contrast, La and Y modification resulted in samples with decreased activity for both reactions. For the Ce‐modified sample, Ce cations were found to dope into the lattice of rutile SnO 2 to form a solid‐solution structure. As a lattice impurity, ceria, the well‐known oxygen storage component (OSC), led to the formation of more defects in the matrix of SnO 2 and impeded the crystallization process, which resulted in a catalyst with a higher surface area and more active oxygen species. In contrast, XRD proved that the addition of La and Y mainly led to the formation of more stable and inert pyrochlore compounds, Sn 2 La 2 O 7 and Sn 2 Y 2 O 7 , which disrupted a major part of the active sites based on SnO 2 . Consequently, the oxidation activity was impaired, although these two samples also have higher surface areas than pure SnO 2 . The Ce‐modified sample showed not only high activity but also good reaction durability and thermal stability. Furthermore, Sn‐Ce binary oxide is a better support than SnO 2 , CeO 2 , and traditional Al 2 O 3 supports for Pd, which gives it the potential to be applied in some real after‐treatment applications.