Local atomic structure and enhanced catalytic activity of W doped CeWTiOx catalysts

Abstract

The effect of W doping on the crystallinity, local atomic structure and catalytic activity of CeTiOx was investigated. W-doped CeTiOx had broader, lower-intensity XRD peaks than those of CeTiOx. Crystals were observed by TEM in CeTiOx but not in W-doped CeTiOx. The CeWTiOx SAED pattern showed diffuse ring patterns, which indicated that crystallization of CeWTiOx was inhibited by introduction of W, which existed in an amorphous phase. The local atomic structures of CeTiOx and W-doped CeTiOx were identified at the atomic level via extended X-ray absorption fine structure analysis. In the tungsten-doped catalyst, the Ce–O distance decreased from 1.80 ​Å to 1.53 ​Å but the Ce–Ce distance increased from 3.52 ​Å to 3.83 ​Å. The W-doped catalyst exhibited increased oxygen vacancies and formed weak Ce–O bonds, which was confirmed by H2-TPR. The increased Ce–Ce distance could be explained by repulsion between Ce and Ti ions (Ce3+, Ce4+, Ti3+, Ti4+) and highly oxidized W ions (W5+, W6+).