A new surface catalytic model for silica-based thermal protection material for hypersonic vehicles

Silica-based materials are widely employed in the thermal protection system for hypersonic vehicles, and the investigation of their catalytic characteristics is crucially important for accurate aerothermal heating prediction. By analyzing the disadvantages of Norman＇s high and low temperature models, this paper combines the two models and proposes an eight-reaction combined surface catalytic model to describe the catalysis between oxygen and silica surface. Given proper evaluation of the parameters according to many references, the recombination coefficient obtained shows good agreement with experimental data. The catalytic mechanisms between oxygen and silica surface are then analyzed. Results show that with the increase of the wall temperature, the dominant reaction contributing to catalytic coefficient varies from Langmuir Hinshelwood （LH） recombination （Tw 〈 620 K） to Eley Rideal （ER） replacement （620 K 〈 Tw 〈 1350 K）, and then to 02 desorption （Tw 〉 1350 K）. The surface coverage of chemisorption areas varies evidently with the dominant reactions in the high temperature （HT） range, while the surface coverage of physisorption areas varies within quite low temperature （LT） range （Tw 〈 250 K）. Recommended evaluation of partial parameters is also given.

Catalyst activation: Surface doping effects of group Ⅵ transition metal dichalcogenides towards hydrogen evolution reaction in acidic media

Two-dimensional(2D) transition metal dichalcogenides(TMDs) have emerged as promising alternatives to the platinum-based catalysts for hydrogen evolution reaction(HER). The edge site of these2D materials exhibits HER-active properties, whereas the large-area basal plane is inactive.Therefore, recent studies and methodologies have been investigated to improve the performance of TMD-based materials by activating inactive sites through elemental doping strategies. In this review,we focus on the metal and non-metal dopant effects on group VI TMDs such as MoS_(2) MoSe_(2) WS_(2)and WSe_(2) for promoting HER performances in acidic electrolytes. A general introduction to the HER is initially provided to explain the parameters in accessing the catalytic performance of dopedTMDs. Then, synthetic methods for doped-TMDs and their HER performances are introduced in order to understand the effect of various dopants including metallic and non-metallic elements. Finally, the current challenges and future opportunities are summarized to provide insights into developing highly active and stable doped-TMD materials and valuable guidelines for engineering TMD-based nanocatalysts for practical water splitting technologies.

Activated carbon enhanced ozonation of oxalate attributed to HO·oxidation in bulk solution and surface oxidation: Effect of activated carbon dosage and pH

Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon（AC）in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals（HOU） in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol（tBA） with low dosages of AC,while it was hardly affected by tBA when the AC dosage was greater than 0.3 g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05 g/L, but it did not work when the AC dosage was no less than 0.1 g/L. These observations indicate that HOUin bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HOU oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5 g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HOUoxidation in basic bulk solution. A mechanism involving both HOUoxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate.