Effect of Ce doping on the structure-activity relationship of MoVO x composite metal oxides.

A series of Ce-doped MoVO x composite metal oxide catalysts were prepared by the rotary evaporation method. The effects of Ce doping ratio on the crystal phase composition, morphology and surface properties of the catalysts were investigated. The results show that the crystal phase composition of samples with different Ce doping content is also obviously different. When the doping amount is small, V0.95Mo0.97O5 is the main crystal phase, while MoO3 is dominant when the doping amount is large. The Ce-doped catalyst showed obvious rod-shaped morphology and its average single point pore diameter and the number of acidic sites increased. Compared to the un-doped MoVO x , the pore size of the sample synthesized at a Mo/Ce atomic ratio of 10/1 exhibited an increase of 41.11 nm. In addition, the effect of Ce doping on the catalytic performance of MoVO x was investigated with the selective oxidation of benzyl alcohol as a probe reaction. After doping, the MoVO x catalyst showed improved benzyl alcohol conversion and selectivity to benzaldehyde. At a Mo/Ce atomic ratio of 10/1, the conversion rate of benzyl alcohol reaches 83.26%, which is 64.56% higher than that without doping, and the highest product yield can reach 76.47%.

Facile sub-/supercritical water synthesis of nanoflake MoVTeNbO x -mixed metal oxides without post-heat treatment and their catalytic performance.

A fast and simple sub-/supercritical water synthesis method is presented in this work in which MoVTeNbO x -mixed metal oxides with various phase compositions and morphologies could be synthesized without post-heat treatment. It was demonstrated that the system temperature for synthesis had a significant influence on the physico-chemical properties of MoVTeNbO x . Higher temperatures were beneficial for the formation of a mixed crystalline phase containing TeVO4, Te3Mo2V2O17, Mo4O11 and TeO2, which are very different from the crystalline phases of conventional Mo-V-Te-Nb-mixed metal oxides. While at lower temperatures, Mo4O11 was replaced by Te. At high temperature, the as-prepared samples presented distinct nanoflake morphologies with an average size of 10-60 nm in width and exhibited excellent catalytic performances in the selective oxidation of propylene to acrylic acid. It is illustrated that the large specific surface area, presence of Mo4O11 and superficial Mo6+ and Te4+ ions are responsible for the high propylene conversion, while suitable acidic sites and superficial Nb5+ ions improved the selectivity to acrylic acid.