RESUMEN
Activated carbon-supported CuO catalysts were prepared by an ammonia evaporation method and applied to catalyze the selective oxidation of glycerol to lactic acid. The effects of CuO loadings on the structure and catalytic performance of the catalyst were investigated. Results showed that CuO could be dispersed uniformly on the surface of activated carbon, promoting the increase of the reaction rate and accelerating the glycerol conversion significantly. As CuO loadings increased, the rate of glycerol consumption and yield to lactic acid was increased. However, too high CuO loadings would destroy the original pore structure of activated carbon and aggravate the agglomeration of CuO, resulting in a decrease in the catalytic performance of the catalyst. The best catalytic performance was obtained over 10% CuO/AC when the reaction temperature was 190 °C and the reaction time was 5 h. At this point, the selectivity to lactic acid reached 92.61%. In addition, power-function type reaction kinetic equations were used to evaluate the effect of glycerol and NaOH concentrations and the reaction temperature on the oxidation of glycerol to lactic acid over 10% CuO/AC. The activation energy of the reaction is 134.39 kJ·mol-1, which is higher than that using single CuO as the catalyst. This indicates that CuO/AC is more temperature-sensitive than CuO and can probably achieve a higher lactic acid yield at high temperatures. At the same time, it is indicated that CuO supported on activated carbon can enhance the catalytic activity of CuO effectively.
RESUMEN
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%.
RESUMEN
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.
RESUMEN
Ferroferric oxide was prepared using Fe(NO3)3 · 9H2O as the iron source under supercritical methanol conditions. Methanol was not only a solvent but also a reducing agent in the supercritical state. The effects of reaction temperature and time, and precursor concentration on product composition were investigated. In addition, ferromagnetic ferroferric oxide was synthesized in supercritical methanol with polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) as surfactants. The as-synthesized products were characterized by XRD, SEM, FTIR techniques. Results showed that the addition of PVP and PEG had notable influences on the products. The findings also showed that ferroferric oxide of a loose flocculent structure and with a variable size (from several tens to a few hundred nanometers) had been prepared in supercritical methanol at 300 °C and 17.8 MPa for 15 min. Magnetic properties of the ferroferric oxide were detected by vibrating sample magnetometer. Its saturation magnetization was 50 emu/g, which was lower than the bulk value of 92 emu/g and showed that it had ferromagnetism.
RESUMEN
Boron-doped graphene samples (BGs) with tunable boron content of 0-2.90 at% were synthesized and directly used in the gas-phase oxidation of benzyl alcohol to benzaldehyde, and showed excellent performance. XPS results indicated that the graphitic sp2 B species (BC3) is the mainly boron dopant species incorporated in the graphene lattice, which could significantly improve the content of ketone carbonyl groups (C[double bond, length as m-dash]O) on the graphene. For instance, the contents of C[double bond, length as m-dash]O jumped from 1.93 to 4.19 at% while BC3 doped into the graphene lattice was only 0.35 at%. The C[double bond, length as m-dash]O is the active site of catalytic reaction, so BG has significantly improved catalytic activity. Compared to the un-doped graphene (G), the conversion of benzyl alcohol over BGs increased 2.35 times and the selectivity of benzaldehyde increased from 77.3% to 99.2%. Aerobic-anaerobic exchange experiments revealed that the superior catalytic performance of BG was achieved only under aerobic conditions. The study of the boron-doped carbocatalyst may also provide guidance for the design of surface modified carbon-based catalysts for the selective oxidation dehydrogenation of alcohols by regulating doping elements and their types.