Lina Guo

Low-temperature NOx (x = 1, 2) removal with ˙OH radicals from catalytic ozonation over a RGO–CeO2 nanocomposite: the highly promotional effect of oxygen vacancies

CeO2 grown on a reduced graphene oxide nanocomposite (RGO–CeO2) was successfully synthesized by a facile alkaline hydrothermal method with the addition of ethylene glycol. For the first time, it was utilized as an ozonation catalyst for denitrification at low temperatures. The RGO–CeO2 nanocomposite, in which the content of RGO was only 2.8 wt%, exhibited much higher catalytic activities (96.8% at 40 °C) than pure nano-CeO2 (78.2% at 40 °C), which was found to exhibit a positive relationship with the concentration of ˙OH radicals. There was no correlation between the surface hydroxyl densities and the catalytic activities of RGO–CeO2, RGO and CeO2, suggesting that not all surface hydroxyl groups exhibit the same high catalytic activity. The activity of surface hydroxyl groups becomes the dominant factor for determining catalytic performance. Compared with pure nano-CeO2, the surface hydroxyl activity was enhanced for RGO–CeO2 due to the generation of more oxygen vacancies from the reduction in crystallite size and better dispersion of CeO2. The surface –OH groups at the oxygen vacancy sites were more active than the intrinsic –OH of CeO2 at promoting the generation of ˙OH radicals and being conducive to denitrification.

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.

Enhanced catalytic ozonation over reduced spinel CoMn2O4 for NOx removal: active site and mechanism analysis

In this paper, CO atmosphere reduced cobalt manganate (CoMn2O4/CO), prepared by a hydrothermal method, was successfully utilized in catalytic ozonation for NOx removal. CoMn2O4/CO shows higher activity (84%) than CoMn2O4/air (82%), Co3O4 (76%) and Mn2O3 (76%). Hydroxyl radicals (·OH) have been detected in the catalytic ozonation process, which has been confirmed to determine the catalytic performance of NOx removal. Compared to Co3O4 and Mn2O3, CoMn2O4 exhibits more surface hydroxyl groups and oxygen vacancies, both of which are critical for the ·OH generation. More importantly, more oxygen vacancies are generated when the CoMn2O4 is calcined in the reduced atmosphere. These oxygen vacancies benefit the adsorption of sufficient H2O to yield active surface –OH on the catalyst surface, promoting the adsorption of O3 on the surface –OH and thus the production of ·OH radicals. A possible mechanism for the catalytic ozonation of NOx was proposed.

Low-Temperature NOX (x = 1, 2) Removal with •OH Radicals from Catalytic Ozonation over α-FeOOH

ABSTRACT FeOOH(H), FeOOH(P) and FeOOH(O) prepared by hydrothermal, precipitant-hydrolysis and oxidation-hydrolysis methods were tested as ozonation catalysts for the low-temperature NOX (x = 1, 2) removal. FeOOH(H) exhibits higher catalytic activities than FeOOH(P) and FeOOH(O), achieving 85.6% of NOX removal efficiency with a low ozone concentration. Compared to FeOOH(P) and FeOOH(O), FeOOH(H) shows much higher BET surface areas and higher density of surface -OH, both of which are critical for the •OH radical generation over the catalysts. These radicals can be successfully transferred into the duct under the coupling effect of hydroxyl radicals and O3, oxidizing and removing the NOX (x = 1, 2). Results of ion chromatography (IC) indicate that the oxidation products are all NO3− without any NO2− in the tail solutions.