Effect of additives on properties of vanadia-based catalysts for oxidative dehydrogenation of propane

BaTiO3-xNy: Highly Basic Oxide Catalyst Exhibiting Coupling of Electrons at Oxygen Vacancies with Substituted Nitride Ions

The base strength of oxide catalysts is controlled by the electron charge distribution between cations and anions, with unsaturated oxygen ions that have lone pair electrons typically acting as basic sites. Substitution of oxide ions with anions that have different valences, such as nitride and hydride ions, can often generate basic sites. It is plausible that electrons trapped at oxygen vacancy sites could provide increased electron density and shift the highest occupied molecular orbital energy levels of anions upward in the case that the oxygen vacancies couple with surface-substituted anions. The present work demonstrates that high catalytic basicity can be obtained via site-selective doping of anions at face-sharing Ti2O9 dimer sites with oxygen vacancies in BaTiO3-x. This improved basicity stems from the coupling of substituted nitride ions to electrons at oxygen vacancies. The oxynitride BaTiO3-xNy was found to contain nitride ions that have increased electronic charge density on the basis of such interactions. Enhanced surface basicity following doping with nitride ion was also confirmed by CO2 temperature-programmed desorption and infrared spectroscopy in conjunction with the adsorption of CHCl3. The strong Lewis base sites resulting from the formation of the oxynitride evidently facilitated the catalytic activation of C-H bonds to promote Knoevenagel condensation reactions between aldehydes and active methylene compounds with pKa values of up to 28.9.

Low-Temperature Propane Activation and Mineralization over a Co3O4 Sub-nanometer Porous Sheet: Atomic-Level Insights

Light alkanes make up a class of widespread volatile organic compounds (VOCs), bringing great environmental hazards and health concerns. However, the low-temperature catalytic destruction of light alkanes is still a great challenge to settle due to their high reaction inertness and weak polarity. Herein, a Co3O4 sub-nanometer porous sheet (Co3O4-SPS) was fabricated and comprehensively compared with its bulk counterparts in the catalytic oxidation of C3H8. Results demonstrated that abundant low-coordinated Co atoms on the Co3O4-SPS surface boost the activation of adsorbed oxygen and enhance the catalytic activity. Moreover, Co3O4-SPS has better surface metal properties, which is beneficial to electron transfer between the catalyst surface and the reactant molecules, promoting the interaction between C3H8 molecules and dissociated O atoms and facilitating the activation of C-H bonds. Due to these, Co3O4-SPS harvests a prominent performance for C3H8 destruction, 100% of which decomposed at 165 °C (apparent activation energy of 49.4 kJ mol-1), much better than the bulk Co3O4 (450 °C and 126.9 kJ mol-1) and typical noble metal catalysts. Moreover, Co3O4-SPS also has excellent thermal stability and water resistance. This study deepens the atomic-level insights into the catalytic capacity of Co3O4-SPS in light alkane purification and provides references for designing efficacious catalysts for thermocatalytic oxidation reactions.

Characterization and Deactivation Study of Mixed Vanadium and Potassium Oxide Supported on Microemulsion-Mediated Titania Nanoparticles as Catalyst in Oxidative Dehydrogenation of Propane

The influence of potassium addition to the vanadia supported on the microemulsion-mediated TiO2 nanoparticles in propane oxidative dehydrogenation was studied. Raman spectroscopy demonstrated that the addition of potassium caused enhanced dispersion of vanadia species on the support surface. Also, potassium existence affects the H2 temperature programmed reduction maximum reduction temperature and shifted it to 520°C, which was in accordance with its lesser catalytic activity. Nevertheless, a propylene selectivity enhancement was observed by potassium addition. In spite of the fact that the catalytic performance loss was not severe in vanadia-supported TiO2 anatase, potassium addition led to improve the catalyst lifetime. After deactivation test, potassium-containing vanadia catalyst possessed lower surface area loss (i.e. from 52 to 49 m2 g−1). Average crystallite size of potassium-containing vanadia catalyst exhibited lower decrease than that of potassium-free vanadia catalyst after deactivation test. According to Raman spectra, deactivation phenomena had influenced the population of vanadia species so that monovanadates decreased and polyvanadates increased.