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采用沉积-沉淀法制备了固溶体CeO2-MOx(M=La3+,Ca2+)改性的Pd/γ-Al2O3催化剂,利用XRD、Raman和XPS对催化剂进行了表征.结果表明,金属(M)离子进入CeO2的晶格,形成CeO2-MOx固溶体,Raman谱上463cm-1处对应于Ce—O键的F2g对称伸缩振动强度降低.其中,样品Pd/γ-Al2O3-CeO2-CaO在615cm-1处出现一小峰,样品Pd/γ-Al2O3-CeO2-La2O3在320cm-1处出现的肩峰,都表明固溶体CeO2-MOx的形成使O2-亚晶格结构对称性降低.XPS分析表明,固溶体改性的Pd/γ-Al2O3催化剂中Pd的3d5/2结合能比正常价态的PdO的结合能高出0.5-0.6eV,形成了一种高度离子化的,与载体具有强相互作用的Pd物种.催化甲烷燃烧实验证明,固溶体CeO2-MOx(M=La3+,Ca2+)改性的Pd/γ-Al2O3催化剂的低温活性和稳定性均高于未经改性的Pd/γ-Al2O3催化剂和仅用CeO2改性的Pd/γ-Al2O3催化剂,在空速为50000h-1时,可使1%CH4-99%空气(体积分数)混合气中甲烷的10%转化温度降至254℃,转化率100%时的转化温度降至340℃.
The Pd / γ-Al2O3 catalysts modified by CeO2-MOx (M = La3 +, Ca2 +) were prepared by the deposition-precipitation method. The catalysts were characterized by XRD, Raman and XPS. The results showed that the metal , The symmetric stretching vibration intensity of F2g corresponding to the Ce-O bond at 463cm-1 in the Raman spectrum decreased, and the sample Pd / γ-Al2O3-CeO2-CaO appeared at 615cm-1 The peak at 320cm-1 of Pd / γ-Al2O3-CeO2-La2O3 sample shows that the formation of solid solution CeO2-MOx decreases the symmetry of O2- sublattice structure.XPS analysis shows that solid solution-modified Pd / γ-Al2O3 catalyst, the 3d5 / 2 binding energy of Pd is 0.5-0.6 eV higher than that of PdO with normal valence, forming a highly ionized Pd species with strong interaction with the support. The catalytic methane The combustion experiments showed that the low temperature activity and stability of the Pd / γ-Al2O3 catalyst modified by CeO2-MOx (M = La3 +, Ca2 +) were higher than those of the unmodified Pd / γ-Al2O3 catalyst and the CeO2-MOx Pd / γ-Al2O3 catalyst at a space velocity of 50000h-1, the 10% conversion temperature of methane in 1% CH4-99% air (volume fraction) The conversion temperature dropped to 340 ° C at 100%.