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The enhancement of surface acidity for tungsten-doped CeTiOx was investigated through electronic structure. Tungsten doping increased the ratio of Ce3+ from 12.0% to 29.6%, which was confirmed by X...

Amorphous CeO2-TiO2 nanoparticles synthesized by the H2O2-modified sol-gel method were investigated in terms of the Ce-O-Ce and Ti-O-Ti linkage, local structure, and redox properties. The decrease in the crystallinity of CeO2-TiO2 by H2O2 addition was confirmed. The metal–oxygen linkage analysis showed the difference in size of the metal–oxygen network between crystalline CeO2-TiO2 and amorphous CeO2-TiO2 due to the O22− formed by H2O2. The local structure of CeO2-TiO2 was analyzed with an extended X-ray absorption fine structure (EXAFS), and the oscillation changes in the k space revealed the disordering of CeO2-TiO2. The decrease in Ce-O bond length and the Ce-O peak broadening was attributed to O22− interfering with the formation of the extended metal–oxygen network. The temperature-programmed reduction of the H2 profile of amorphous CeO2-TiO2 exhibited the disappearance of the bulk oxygen reduction peak and a low-temperature shift of the surface oxygen reduction peak. The H2 consumption increased compared to crystalline CeO2-TiO2, which indicated the improvement of redox properties by amorphization.

The redox properties of CeO2-WO3 mixed oxide supported on multi-walled carbon nanotubes (MWCNTs) and TiO2 were investigated in terms of valence state and active oxygen species. Ce–W/CNT and Ce–W/TiO2 were synthesized by impregnation method to support CeO2-WO3 mixed oxide on CNTs and TiO2. The interplanar distance of CeO2 in Ce–W/CNT was measured to be 0.316 nm by TEM and SAED pattern analysis, which was larger than that of Ce–W/TiO2 (0.310 nm), indicating the lattice expansion due to Ce3+ formation. Since the F2g and Ov peaks in Raman spectrum of Ce–W/CNT were broader than those of Ce–W/TiO2, it implied the increased oxygen vacancies of CeO2 supported on CNTs. In XPS analysis, Ce3+/(Ce4++Ce3+) ratios in Ce–W/CNT and Ce–W/TiO2 were 42.28% and 28.60%, and Oα/(Oα+Oβ) ratios were 29.07% and 17.29%, respectively. The redox properties of the catalysts were investigated by H2-TPR analysis. The reduction peak of Ce–W/CNT shifted to a lower temperature compared to Ce–W/TiO2, and H2 consumption increased by 1.91 mmol/g, increasing the redox properties. The reduction in the valence state of Ce4+ was caused by charge transfer between CNT and CeO2-WO3 mixed oxide, and the reduction promoted the formation of oxygen vacancies and active oxygen species.

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 ​A to 1.53 ​A but the Ce–Ce distance increased from 3.52 ​A to 3.83 ​A. 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+).