Formaldehyde (CHOH), a common volatile organic compound, causes many adverse effects on human health. The highly exposed TiO2(001) facet possesses a high photodegradation efficiency of CHOH due to its excellent ability to trap photogenerated holes and high density of surface unsaturated Ti atoms (Ti5c) to bind CHOH. However, the rapid recombination of photoinduced electron-hole pairs of TiO2(001) limits the photodegradation efficiency. We adopted a strategy of decorating TiO2(001) with g-C3N4 quantum dots (QDs), exploiting the quantum effect of g-C3N4QDs and their combined staggered band structure. This decoration improves the photocatalytic activity of TiO2(001). Moreover, the chemical configuration of g-C3N4QDs/TiO2(001) and the combination mode between the g-C3N4QDs and TiO2(001) support were explored in detail using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Following the physiochemical characteristic results, the transport mechanism of photoinduced carriers was further analyzed by ultraviolet photoelectron spectroscopy (UPS), electron paramagnetic resonance (EPR), and Heyd-Scuseria-Ernzerh (HSE) exchange-correlation functional calculations. Finally, the performance and reaction mechanism of the photodegradation of CHOH by TiO2(001) and g-C3N4QDs/TiO2(001) were thoroughly investigated. The results show that the g-C3N4QDs were composed of an N-defect tri-s-triazine supported by TiO2(001) via a strong C-O-Ti chemical bond, which accelerated the separation of photoinduced carriers through a Z-scheme route. The photodegradation and mineralization efficiencies of CHOH were significantly promoted by 30% and 60% for g-C3N4QDs/TiO2(001) compared with those of TiO2(001). The photodegradation mechanism proceeded as CHOH - dioxymethylene - formate - carbonate - CO2. This study provides a surface engineering means to design highly active modified TiO2 for CHOH photodegradation.
Cu-SSZ-13 exhibits unsatisfactory deNO x activity at low temperatures. The composite catalysts were prepared by mechanically mixing Cu-SSZ-13 and MnCeTiO x to improve the low-temperature selective catalytic reduction (SCR) activity. The optimal mass ratio of Cu-SSZ-13 and MnCeTiO x components in the composite catalysts was 1:1, where the NO x conversion was improved by around 40% in the temperature range of 150300 °C compared with Cu-SSZ-13. MnCeTiO x presented significantly stronger ability on the activation of NO to nitrates species than Cu-SSZ-13. Infrared (IR) and density functional theory (DFT) results showed that active nitrates intermediate on MnCeTiO x might migrate to Cu-SSZ-13, which assisted the oxidation of single Cu + to Cu 2+ to complete the Cu redox cycle. This avoided the low-temperature rate-determining step that the formation and oxidation of Cu + dimes in SCR over Cu-SSZ-13. The research results are beneficial to the rational design of SCR catalysts with high-performance at low temperatures.
A novel biphasic solvent consisting of diethylenetriamine (DETA), 2-amino-2-methyl-1-propanol (AMP), and pentamethyldiethylenetriamine (PMDETA) is considered as a promising CO2-capturing candidate because of its high absorption capacity, favorable phase separation behavior, fast desorption rate, and high cyclic capacity. In the present work, reaction kinetics and thermodynamics of CO2 absorption into the DETA-AMP-PMDETA biphasic solvent were studied. The kinetics process of CO2 absorption was described using the zwitterion mechanism and invoking the two-film theory. Under the fast pseudo-first-order regime, kinetics parameters, e.g., overall reaction rate constant (kov,mix), second-order rate constant (k2,mix), and enhancement factor (E), were determined. Kinetics results indicated that the CO2 reaction rate was mainly determined by DETA and AMP in the biphasic system, while PMDETA molecules would aggregate to form PMDETA clusters, which limited the absorption of CO2 to a certain extent. On the other hand, thermodynamics results showed that the regeneration heat of DETA-AMP-PMDETA biphasic solvents could be significantly reduced compared with that of MEA. In particular, the regeneration heat of the solvent 0.5 mol·L–1 (M) DETA + 1.5 M AMP + 3 M PMDETA (0.5D1.5A3P) was only 1.83 GJ·ton–1 CO2, which was approximately 52% lower than that of 30 wt % MEA. This finding suggested that the DETA-AMP-PMDETA biphasic solvent may be a good alternative to MEA to advance energy-efficient and economical CO2 capture.
The commercially available V2O5/WO3-TiO2 is a well-known catalyst for selective catalytic reduction (SCR) of NO with NH3. When alkali ions are present in the exhaust (e.g., as impurities such as dust) of a reactor containing commercial V2O5/WO3-TiO2, alkali poisoning occurs, deactivating the catalyst. Consequently, there is substantial interest in the development of better-performing and more durable NH3-SCR catalysts with an improved resistance to alkali deactivation. For the present study, the protonated (H+) form of zeolite Y, HY, was used as a support and acted as buffer zone, leading to trapping (sticking) of foreign alkali poisons in the zeolite pore structure, preventing alkali poisoning of the Fe2O3/HY catalyst. Catalytic tests showed that the Fe2O3/HY retained 100% of its original catalytic reactivity for NH3-SCR reaction even after 1000 μmol Na+ g-1 poisoning. 1000 μmol Na+ g-1 treatment indicates a 26 000-h exposure under an alkaline dust-containing condition. In contrast, upon 1000 μmol Na+ g-1 treatment, severe alkali deactivation occurred for a commercial V2O5/WO3-TiO2. The catalyst activity of Fe2O3/HY remained unchanged because of the intercalation of Na+ in the internal HY zeolite pores that impedes the blocking of Na+ poison to the external active sites of Fe2O3. The findings in this work suggest that the zeolite HY may be revealed as an attractive building block for designing an alkali poisoning-resistant catalyst.
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