A series of Mo-Mg-O catalysts with different crystalline phases (pure and mixtures) have been studied in the oxidative dehydrogenation of isobutane. X-ray diffraction, UV–Vis spectroscopy and temperature programmed reduction were applied to characterise the samples. In addition, the kinetics of the lattice oxygen exchange with labelled C18O2 was measured for all samples. It has been found that the MgMoO4 phase contains the surface active sites suitable for the adsorption of isobutane and for its dehydrogenation to isobutene with the minimum of cracking reaction. Moreover, for this reaction the migration of lattice oxygen ions is not a key parameter in the control of the catalytic properties of these materials. 相似文献
An efficient strategy for carbazole synthesis from arylureas and cyclohexanones under transition metal‐free conditions has been developed. The combined use of potassium iodide and iodine could significantly improve the reaction efficiency to provide 2,6‐disubstituted 9‐arylcarbazoles in moderate to good yields. In this kind of transformation, the whole carbazole moiety (except the nitrogen atom) comes from two equivalents of cyclohexanones.
The nanocatalysts of VOx deposited on ZrO2 supports with single monoclinic (ZrO2-M), tetragonal (ZrO2-T), and binary monoclinic-tetragonal (ZrO2-MT) phase were synthesized. VOx/ZrO2-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VOx/ZrO2-M and VOx/ZrO2-T catalysts. Among VOx/ZrO2-MT catalysts, the conversion and deactivation rate constant of VOx/ZrO2-M31T69 catalyst is 35.2% and 0.22 h−1, respectively. The promoting role of ZrO2-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VOx/ZrO2-MT catalyst improves the structural properties and dispersion of VOx. The tetragonal-monoclinic transformation on the ZrO2-MT surface facilitates VOx reduction and produces additional V3+ active sites. The highly dispersed V3+ sites on the ZrO2-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO2-MT is expected to obtain high-efficient catalysts further. 相似文献
The use of liquid organic hydrides as hydrogen carriers is a promising storage and delivery system due to the advantages of using liquid-based infrastructures and its economic feasibility compared to other conventional systems. The reversible dehydrogenation/hydrogenation of liquid organic hydrides is a key point for the development of highly performance reactors. In this study different carbon materials have been investigated as platinum supports, including carbon nanofibers, carbon black, carbon xerogel, activated carbon and ordered mesoporous carbon. To individuate the effect of the carbon support on the catalytic activity, platinum particles were synthesized by a microemulsion procedure. The analysis of the hydrogen evolution curves indicate that the support BET surface area plays a very important role on the initial catalytic activity, obtaining a maximum rate of 220 mmol gPt−1 min−1 when using an ordered mesoporous carbon with a surface area of 930 m2 g−1. Nevertheless, the analysis of catalytic activity at prolonged duration indicates a better behavior toward deactivation for supports characterized by wide pores and low graphitization degree like carbon black or carbon xerogel, despite their lower initial dehydrogenation rate (100–140 mmol gPt−1 min−1). The ultimate use in the dehydrogenation reactor as well as the operation conditions will define the best catalyst structure from the point of view of the carbon support. 相似文献