Yiqing Zeng

CeO2 supported on reduced TiO2 for selective catalytic reduction of NO by NH3

In this paper, a series of catalysts about CeO2 active sites prepared using reduced TiO2 (TiR) as supports were firstly used for selective catalytic reduction (SCR) of NO by NH3. The catalytic performance evaluation results showed that the NO removal efficiency of CeO2/TiR (CeTiR) was much higher than that of CeO2/TiO2 (CeTi). Hence, the aim of this study was to investigate the promotion mechanism of catalytic performance of CeTiR catalysts. The catalysts were characterized by XRD, BET, Raman, XPS, NH3-TPD and H2-TPR. The results of characterization revealed that CeO2 had a strong interaction with oxygen vacancies of TiR supports. The strong interaction resulted in more Ce3+ formation and better redox properties for CeTiR catalysts. In addition, it was confirmed that the better redox properties of CeTiR could be considered as the major reason of its high SCR activity via L-H mechanism but not acid properties. We expected that this study could shed some lights on the development of SCR catalysts for improving the interaction between Ti support and active species for enhancing SCR reaction.

Effects of synthesis methods on catalytic activities of CoO x –TiO 2 for low-temperature NH 3 -SCR of NO

A series of cobalt doped TiO2 (Co-TiO2) and CoOx loaded TiO2 (Co/TiO2) catalysts prepared by sol-gel and impregnation methods respectively were investigated on selective catalytic reduction with NH3 (NH3-SCR) of NO. It was found that Co-TiO2 catalyst showed more preferable catalytic activity at low temperature range. From characterization results of XRD, TEM, Raman and FT-IR, Co species were proved to be doped into TiO2 lattice by replaced Ti atoms. After being characterized and analyzed by NH3-TPD, PL, XPS, EPR and DRIFTS, it was found that the better NH3-SCR activities of Co-TiO2 catalysts, compared with Co/TiO2 catalyst, were ascribed to the formation of more oxygen vacancies which further promoted the production of more superoxide ions (O2-). The superoxide ions were crucial for the formation of low temperature SCR reaction intermediates (NO3-) by reacting with adsorbed NO molecule. Therefore, these aspects were responsible for the higher low temperature NH3-SCR activity of Co-TiO2 catalysts.

One-step hydrothermal synthesis of a novel 3D BiFeWOx/Bi2WO6 composite with superior visible-light photocatalytic activity

A novel 3D BiFeWOx/Bi2WO6 (BFW/BWO) composite has been synthesized via a facile one-pot hydrothermal process. A tight chemically bonded interface between the BFW and BWO could be constructed by this simple and environmentally benign method. The composite structures and chemical properties were investigated by XRD, FE-SEM, HR-TEM and EDS. The photocatalytic performances of the as-synthesized materials were assessed by photocatalytic oxidation (PCO) of NO under visible light illumination. The optimum BFW/BWO-1 composite exhibited 87% PCO efficiency, which was higher than that of the single phase BWO and BFW. The enhancement of the photocatalytic activity of the BFW/BWO-1 composite was ascribed to the effective separation and reduced recombination rate of the photoinduced charge carriers, evinced by transient photocurrent, EIS and PL measurements. The radical trapping experiment and DMPO spin-trapping ESR measurement revealed that H+ and ˙OH were the important active species. The tests for stability and recyclability revealed that the BFW/BWO-1 composite could be a desired photocatalyst for the oxidation of NO in the ecosystem. The kinetics and possible mechanism for the PCO of NO on the BFW/BWO-1 composites were discussed.

The effects of calcination atmosphere on the catalytic performance of Ce-doped TiO2 catalysts for selective catalytic reduction of NO with NH3

A series of well-reported Cex–Ti catalysts with a low content of Ce species were synthesized by a sol–gel method. The aim of this study was to investigate the influence of different calcination atmospheres on the formation of the Ce–O–Ti structure that comprises active sites for the selective catalytic reduction (SCR) of NO by NH3. Catalytic activity tests showed that the Cex–Ti–N (calcined under a nitrogen atmosphere) catalysts exhibited a significantly higher NO removal efficiency than Cex–Ti–A (calcined under air). Characterization results confirmed that more Ce species could incorporate into the TiO2 lattice when calcined under a nitrogen atmosphere, thus, more Ce–O–Ti structures were obtained over the Cex–Ti–N surface. This improved the NH3 adsorption and electron transfer from Ti to Ce. Therefore, N2 calcination increased the acid sites and improved the redox ability for Cex–Ti–N catalysts. In addition, it was found that the redox ability was the critical factor, which effectively promoted the low temperature SCR performance. Amongst the Cex–Ti–N catalysts, Ce5–Ti–N revealed the best SCR activity, catalytic stability and resistance to H2O and SO2. This study demonstrated the feasibility of N2 calcination in the syntheses of doped SCR catalysts and also explored the SCR reaction mechanism over the well-reported Cex–Ti catalysts. We expect that this study could shed some light on the development of feasible preparative routes for the syntheses of Metal-Ti catalysts for SCR application.

In Situ Fabrication of 3D Octahedral g-C3N4/BiFeWO x Double-Heterojunction for Highly Selective CO2 Photoreduction to CO Under Visible Light

A series of g‐C3N4/BiFeWOx composites (GN‐x/BFW) with double‐heterojunction composites as photocatalysts for efficient and stable CO2 photoreduction had been rationally designed and synthesized by the facile in situ hydrothermal method. In situ growing BFW on g‐C3N4 sheets achieved that the g‐C3N4 was embedded in the inner of BFW as well as wrapped on the surfaces of BFW. The obtained heterojunction composites greatly inhibited the recommendation of photogenerated electron/hole pairs and enhanced the light respond on the visible light due to the tight chemically bonded interface interaction. Benefiting from the unique structure, the optimized GN‐5.0 %/BFW heterostructure catalyst showed a higher performance of photoreduction CO2 to CO (43 μmol h−1 g−1) than that of pure BFW (5.2 μmol h−1 g−1) and g‐C3N4 (8.9 μmol h−1 g−1) under visible light irradiation at 10 °C. Besides, the GN‐x/BFW composites exhibited outstanding recycling photostability and structural stability. A possible Z‐scheme mechanism was proposed according to the staggered band potentials between g‐C3N4 and BFW and ESR results. Similarly, this facile synthetic method could be employed to fabricate other composites to accelerate the photocatalytic performance.