Toluene catalytic oxidation over gold catalysts supported on cerium-based high-entropy oxides

A series of cerium-based high-entropy oxide catalysts (the ratio of CeO2 and HEO is 1:1) was prepared by a solid-state reaction method, which exploit their unique structural and performance advantages. The Ce-HEO-T samples can achieve 100% toluene conversion rate above 328 oC when they were used as catalysts directly. Subsequently, the Ce-HEO-500 exhibited the lowest temperature for toluene oxidation was used as a support to deposit different amounts of Au for a further performance improvement. Among all of prepared samples, Au/Ce-HEO-500 with a moderate content of Au (0.5 wt%) exhibited the lowest temperature for complete combustion of toluene (260 oC)，which decreased nearly 70 oC compared with Ce-HEO-500 support. Moreover, it also showed excellent stability for 60 h with 98% toluene conversion rate. Most importantly, under the condition of 5 vol.% H2O vapor, the toluene conversion rate remained unchanged and even increased slightly compared with that in dry air, exhibiting excellent water resistance. Combined with the characterizations of XRD, SEM, TEM, BET, Raman, H2-TPR and XPS, it was found that the high dispersion of active Au NPs, the special high-entropy structure and the synergistic effect between Au and Ce, Co, Cu are the key factors when improving the catalytic performance in the Au/Ce-HEO-500 catalyst.</p

Kinetics and Mechanism of Direct Reaction between CO₂ and Ca(OH)₂ in Micro Fluidized Bed

Even at present it is still difficult to characterize the reaction between CO₂ and Ca­(OH)₂ at high temperature and atmospheric pressure using traditional instruments such as thermogravimetric analyzer and differential scanning calorimeter. This study was devoted to characterizing such a reaction in a newly developed micro fluidized bed reaction analyzer (MFBRA) under isothermal conditions in the temperature range of 773–1023 K. The results indicated that the MFBRA has not only a good adaptability for characterizing the above-mentioned reaction but enables as well a new insight into the mechanism of the reaction. An obvious time delay was identified for the release of the formed steam (H₂O) in comparison with the onset of its CO₂ absorption, which might be attributed to the formation of an unstable intermediate product Ca­(HCO₃)₂ in the reaction process between CO₂ and Ca­(OH)₂. The activation energy for forming Ca­(HCO₃)₂ was found to be about 40 kJ/mol, which is much lower than that of the reaction between CO₂ and CaO

NO_<i>x</i> Removal over V₂O₅/WO₃–TiO₂ Prepared by a Grinding Method: Influence of the Precursor on Vanadium Dispersion

V₂O₅/WO₃–TiO₂ (VWT) catalysts for selective catalytic reduction (SCR) of NO_<i>x</i> removal were prepared by a mechanical grinding method using different vanadium precursors. The SCR performances were evaluated in simulated flue gas and explained through characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, H₂ temperature-programmed reduction, and in situ diffuse reflectance Fourier transform spectroscopy. VO­(acac)₂–VWT catalyst prepared using a vanadyl acetylacetonate (VO­(acac)₂) precursor exhibited the highest catalytic activity and excellent resistance to SO₂ and H₂O poisoning in 200–400 °C compared to the catalysts obtained using other precursors. The VO­(acac)₂ precursor could enrich V on the surface remarkably and promote the formation and dispersion of polymeric vanadia species. Furthermore, a relatively high percentage of low-valent vanadium atoms were found on the VO­(acac)₂–VWT surface, facilitating electron transfer between V⁴⁺ and V⁵⁺. Surface-adsorbed NH₃ species on VO­(acac)₂–VWT were much more reactive. The initial geometry of vanadium precursors determined the tendency of V to accumulate and further influenced the dispersion and final form of V species