Shule Zhang

Selective catalytic oxidation of NO with O2 over Ce-doped MnOx/TiO2 catalysts

Abstract A series of Ce-doped MnO x /TiO 2 catalysts were prepared by impregnation method and used for catalytic oxidation of NO in the presence of excess O2. The sample with the Ce doping concentration of Ce/Mn=1/3 and calcined at 300°C shows a superior activity for NO oxidation to NO 2 . On Ce(1)Mn(3)Ti catalyst, 58% NO conversion was obtained at 200°C and 85% NO conversion at 250°C with a GHSV of 41000 h −1 , which was much higher than that over MnO x /TiO 2 catalyst (48% at 250°C). Characterization results implied that the higher activity of Ce(1)Mn(3)Ti could be attributed to the enrichment of well-dispersed MnO x on the surface and the abundance of Mn 3+ and Ti 3+ species. The addition of Ce into MnO x /TiO 2 could improve oxygen storage capacity and facilitate oxygen mobility of the catalyst as shown by PL and ESR, so that its activity for NO oxidation could be enhanced. The effect of H 2 O and SO 2 on the catalyst activity was also investigated.

Size- and shape-controlled synthesis and catalytic performance of iron–aluminum mixed oxide nanoparticles for NOX and SO2 removal with hydrogen peroxide

A novel, simple, reproducible and low-cost strategy is introduced for the size- and shape-controlled synthesis of iron-aluminum mixed oxide nanoparticles (NIAO(x/y)). The as-synthesized NIAO(x/y) catalyze decomposition of H2O2 yielding highly reactive hydroxyl radicals (OH) for NOX and SO2 removal. 100% SO2 removal is achieved. NIAO(x/y) with Fe/Al molar ratio of 7/3 (NIAO(7/3)) shows the highest NOX removal of nearly 80% at >170°C, whereas much lower NOX removal (<63%) is obtained for NIAO(3/7). The melting of aluminum oxides in NIAO(7/3) promotes the formation of lamellar products, thus improving the specific surface areas and mesoporous distribution, benefiting the production of OH radicals. Furthermore, the NIAO(7/3) leads to the minor increase of points of zero charges (PZC), apparent enhancement of FeOH content and high oxidizing ability of Fe(III), further improving the production of OH radicals. However, the NIAO(3/7) results in the formation of aluminum surface-enriched spherical particles, thus decreasing the surface atomic ratio of iron oxides, decreasing OH radical production. More importantly, the generation of FeOAl causes the decline of active sites. Finally, the catalytic decomposition of H2O2 on NIAO(x/y) is proposed. And the well catalytic stability of NIAO(7/3) is obtained for evaluation of 30 h.

Low-temperature selective catalytic reduction of NO over manganese supported on TiO2 nanotubes

Abstract Titanate nanotubes were synthesized hydrothermally from commercial TiO2 nanoparticles in the presence of NaOH; after calcination at 400°C, TiO2 nanotubes were obtained, which were used as the support to prepare manganese catalyst (MnOx/TiNT) by wet impregnation for the low-temperature selective catalytic reduction (SCR) of NO. The results of Brunauer, Emmett and Teller study, transmission electron microscopy, X-ray diffraction, and thermogravimetric measurements showed that TiO2 nanotubes exist in a well-defined TiO2 anatase phase after calcination at 400°C and that manganese particles are highly dispersed on the wall of TiO2 nanotubes. The effects of active-component loading, space velocity, oxygen content, [NH3]/[NO] ratio, and NO concentration on the SCR performance of MnOx/TiNT were investigated in a simulated flue gas. Under the reaction conditions of 150°C, [NH3]/[NO] of 1.2, [O2] of 3%, [NO] of 0.06%, gas hour space velocity of 23613.8 h−1, and Mn loading of 5–15%, NO conversion exceeds 95%. The catalyst is deactivated in the presence of H2O at 180°C, but its activity can be recovered almost completely by cutting off H2O. Moreover, higher resistance to H2O is observed at higher temperatures. The presence of SO2 can also deactivate the catalyst gradually; however, the catalyst shows better resistance to SO2 in the presence of H2O than in its absence. The SCR activity of the MnOx/TiNT catalyst that is deactivated by SO2 increases gradually after cutting off H2O and SO2 but cannot be restored to its initial level.

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.

Highly efficient simulated solar-light photocatalytic oxidation of gaseous NO with porous carbon nitride from copolymerization with thymine and mechanistic analysis

We synthesized novel and efficient porous carbon nitride (CN) photocatalysts by facial supramolecular approach using cyanuric acid (C), melamine (M) and thymine (T) as starting material. The T-modified CNs display excellent photophysical and photochemical properties: high specific surface area, strong light adsorption as well as low recombination rate of photoinduced electron–hole pairs. They exhibit tremendous enhanced photocatalytic activity on photocatalytic oxidation (PCO) of NO (∼400 ppm) under simulated solar-light irradiation, wherein the CM + 2.5 mol%-T possesses the highest photoactivity (93.3% in 40 min). The enhanced photocatalytic performance is ascribed to the synergic effect of large specific surface area and high separation and transfer efficiency of photoinduced electron–hole pairs. In the PCO of NO process, the main reaction product is NO3−, which was confirmed by Ion Chromatography. In addition, the mechanism of PCO is also intuitively analyzed by trapping experiment. The results indicate that ˙O2− plays a leading role in the PCO of NO process.

Z-scheme CaIn2S4/Ag3PO4 nanocomposite with superior photocatalytic NO removal performance: fabrication, characterization and mechanistic study

The development of the economy benefits from fossil fuels, but their consumption inevitably results in environmental pollution. For example, nitric oxide (NO) removal from coal-fired flue gas is a significant aspect of atmospheric pollution control. Based on its unique advantages to resolve atmospheric pollution, photocatalytic oxidation (PCO) is regarded as an effective technique to remove NO. Herein, we have first fabricated Z-scheme CaIn2S4/Ag3PO4 nanocomposites and studied their performance in the PCO of NO (400 ppm) with the assistance of H2O2. The results indicate that the CaIn2S4/Ag3PO4 nanocomposites exhibit superior photocatalytic performance, and the PCO efficiency of NO can reach 83.61%. The excellent photocatalytic ability belongs to the low recombination rate of the photoinduced electron–hole pairs. The production and participation of more active species is another critical factor due to the injected H2O2. FTIR and ion chromatography results reveal that NO3− is the final product. Furthermore, the fluorescence spectra combined with the electron spin resonance and the trapping experiment suggest that ˙OH and ˙O2− might play a predominant role in NO removal.

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.

Selective denitrification of flue gas by O3 and ethanol mixtures in a duct: Investigation of processes and mechanisms

A novel selective denitrification process, referred as O3-ethanol oxidation method, was developed by injecting O3 and ethanol mixtures into the simulated flue gas duct. The organic radicals, generated through the ethanol oxidation by O3, can oxidize NO into NO2, and finally into important industrial raw, namely, nitrate organics or aqueous nitrate acids. The residual ethanol in the tail can be recycled. The CO3(2-), HCO3(-) and SO2 in the flue gas hardly exhibit any effect on the NOX removal. Compared to the conventional O3 oxidation method, the present method shows higher selective oxidation of NO, higher NO(X) removal and less O3 consumption as well as proves lower initial investment and operating costs with more compact equipment.