Jun 2013, Volume 7 Issue 3

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    Junhua LI, Shubo DENG
    Junhua LI, Hong HE, Chun HU, Jincai ZHAO

    This review reports the research progress in the abatement of major pollutants in air and water by environmental catalysis. For air pollution control, the selective catalytic reduction of NOx (SCR) by ammonia and hydrocarbons on metal oxide and zeolite catalysts are reviewed and discussed, as is the removal of Hg from flue gas by catalysis. The oxidation of Volatile organic compounds (VOCs) by photo- and thermal- catalysis for indoor air quality improvement is reviewed. For wastewater treatment, the catalytic elimination of inorganic and organic pollutants in wastewater is presented. In addition, the mechanism for the procedure of abatement of air and water pollutants by catalysis is discussed in this review. Finally, a research orientation on environment catalysis for the treatment of air pollutants and wastewater is proposed.

    Zhenhe CHEN, Shubo DENG, Haoran WEI, Bin WANG, Jun HUANG, Gang YU

    Rapidly increasing concentration of CO2 in the atmosphere has drawn more and more attention in recent years, and adsorption has been considered as an effective technology for CO2 capture from the anthropogenic sources. In this paper, the attractive adsorbents including activated carbons and amine-modified materials were mainly reviewed and discussed with particular attention on progress in the adsorbent preparation and CO2 adsorption capacity. Carbon materials can be prepared from different precursors including fossil fuels, biomass and resins using the carbonization-activation or only activation process, and activated carbons prepared by KOH activation with high CO2 adsorbed amount were reviewed in the preparation, adsorption capacity as well as the relationship between the pore characteristics and CO2 adsorption. For the amine-modified materials, the physical impregnation and chemical graft of polyethylenimine (PEI) on the different porous materials were introduced in terms of preparation method and adsorption performance as well as their advantages and disadvantages for CO2 adsorption. In the last section, the issues and prospect of solid adsorbents for CO2 adsorption were summarized, and it is expected that this review will be helpful for the fundamental studies and industrial applications of activated carbons and amine-modified adsorbents for CO2 capture.

    Zhen MA, Bei ZHOU, Yu REN

    Mesoporous silicas such as MCM-41 and SBA-15 possess high surface areas, ordered nanopores, and excellent thermal stability, and have been often used as catalyst supports. Although mesoporous metal oxides have lower surface areas compared to mesoporous silicas, they generally have more diversified functionalities. Mesoporous metal oxides can be synthesized via a soft-templating or hard-templating approach, and these materials have recently found some applications in environmental catalysis, such as CO oxidation, N2O decomposition, and elimination of organic pollutants. In this review, we summarize the synthesis of mesoporous transition metal oxides using mesoporous silicas as hard templates, highlight the application of these materials in environmental catalysis, and furnish some prospects for future development.

    Farhah Amalya ISMAIL, Ahmad Zaharin ARIS

    Carbonate shells have an astonishing ability in the removal of Cd2+ in a short time period with emphasis on being a low cost adsorbent. In the present study, the sorption capacity of carbonate shells was studied for Cd2+ in batch experiments. The influence of different carbonate shell sizes and physico-chemical factors were evaluated and the results were analyzed for its correlation matrices by using Predictive Analytics Software (PASW). The mineralogy state of aqueous solution regarding the saturation index was simulated using PHREEQC to identify the Cd2+ uptake mechanism. The Cd uptake rates were calculated as well as Ca2+, HCO3- concentration, pH, ambient humidity and temperature were measured. Cd2+ removal of 91.52% was achieved after 5 h adsorption. The adsorption efficiencies were significantly influenced by pH as they increased with the increase of pH from acidic solution (5.50±0.02) to slightly alkaline (7.60±0.05). In addition, the mineralogy state of aqueous solution calculated from PHREEQC confirmed that the increment of Ca2+ and HCO3- concentrations in solution was attributed to the dissolution of carbonate shells. Moreover, the ion exchange adsorption mechanism of Cd2+ toward Ca2+ was identified as the process involved in Cd2+ uptake.

    Zeinab JAMALZADEH, Mohammad HAGHIGHI, Nazli ASGARI

    In this work, xylene removal from waste gas streams was investigated via catalytic oxidation over Pd/carbon-zeolite and Pd/carbon-CeO2 nanocatalysts. Activated carbon was obtained from pine cone chemically activated using ZnCl2 and modified by H3PO4. Natural zeolite of clinoptilolite was modified by acid treatment with HCl, while nano-ceria was synthesized via redox method. Mixed supports of carbon-zeolite and carbon-ceria were prepared and palladium was dispersed over them via impregnation method. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller surface area (BET), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) techniques. Characterization of nanocatalysts revealed a good morphology with an average particle size in a nano range, and confirmed the formation of nano-ceria with an average crystallite size below 60 nm. BET analysis indicated a considerable surface area for catalysts (~1000 m2·g-1). FTIR patterns demonstrated that the surface groups of synthesized catalysts are in good agreement with the patterns of materials applied in catalyst synthesis. The performance of catalysts was assessed in a low-pressure catalytic oxidation pilot in the temperature range of 100°C–250°C. According to the reaction data, the synthesized catalysts have been shown to be so advantageous in the removal of volatile organic compounds (VOCs), representing high catalytic performance of 98% for the abatement of xylene at 250°C. Furthermore, a reaction network is proposed for catalytic oxidation of xylene over nanocatalysts.

    Lei LI, Jian XU, Changsheng GUO, Yuan ZHANG

    Hexahedron-like BiPO4 microcrystals were sucessfully synthesized via a template-free hydrothermal method. The resulting samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV–vis spectroscopy. The BiPO4 samples were of pure monoclinic phase, and the initial amount of PO43- during synthesis did not show obvious effect on the phase properties of the materials. The hexahedron-like BiPO4 microcrystal had explicitly cut edges, and its thickness was about 1 μm. The photocatalytic performance of the BiPO4 catalysts was evaluated by photodegradation of RhB under UV light irradiation with commerial Degussa P25 TiO2 as reference. Compared with P25, the BiPO4 catalysts displayed higher photocatalytic activity, with 98.7% of RhB degraded during 60-min experiment. Cost evaluation analysis was adopted to describe the energy consumption of the degradation process, and the results suggested the potential application of this material in the field of dye-contaminated wastewater treatment or environmental matrices remediation.

    Shu-Hong LI, Yue ZHAO, Jian CHU, Wen-Wei LI, Han-Qing YU, Gang LIU, Yang-Chao TIAN

    Direct formic acid fuel cells are a promising portable power-generating device, and the development of efficient anodic catalysts is essential for such a fuel cell. In this work Pt-Bi nanoparticles supported on micro-fabricated gold wire array substrate were synthesized using an electrochemical deposition method for formic acid oxidation in fuel cells. The surface morphology and element components of the Pt-Bi/Au nanoparticles were characterized, and the catalytic activities of the three Pt-Bi/Au nanoparticle electrodes with different Pt/Bi ratios for formic acid oxidation were evaluated. It was found that Pt4Bi96/Au had a much higher catalytic activity than Pt11Bi89/Au and Pt13Bi87/Au, and Pt4Bi96/Au exhibited a current density of 2.7 mA·cm-2, which was 27-times greater than that of Pt/Au. The electro-catalytic activity of the Pt-Bi/Au electrode for formic acid oxidation increased with the increasing Bi content, suggesting that it would be possible to achieve an efficient formic acid oxidation on the low Pt-loading. Therefore, the Pt-Bi/Au electrode offers a promising catalyst with a high activity for direct oxidation of formic acid in fuel cells.

    Longli BO, Jianbo LIAO, Yucai ZHANG, Xiaohui WANG, Quan YANG

    The development of a combined process of catalytic oxidation and microwave heating for treatment of toluene waste gas was described in this work. Toluene, a typical toxic volatile organic compound, was oxidized through a fixed bed reaction chamber containing zeolite-supported copper oxide (CuO/zeolite) catalyst mixed with silicon carbide (SiC), an excellent microwave-absorbing material. The target compound was efficiently degraded on the surface of the catalyst at high reaction temperature achieved by microwave-heated SiC. A set of experimental parameters, such as microwave power, air flow and the loading size of CuO etc., were investigated, respectively. The study demonstrated these parameters had critical impact on toluene degradation. Under optimal condition, 92% toluene was removed by this combined process, corresponding to an 80%–90% TOC removal rate. Furthermore, the catalyst was highly stable even after eight consecutive 6-h runs. At last, a hypothetical degradation pathway of toluene was proposed based on the experimental data obtained from gas chromatography-mass spectrum and Fourier transform infrared spectroscopy analyses.

    Yue PENG, Junhua LI

    Motivated by the recent realization of graphene sensor to detect gas molecules that are harmful to the environment, the ammonia adsorption on graphene or graphene oxide (GO) was investigated using first-principles calculation. The optimal adsorption and orientation of the NH3 molecules on the graphene surfaces were determined, and the adsorption energies (Eb) as well as the Mulliken charge transfers of NH3 were calculated. The Eb for the graphene are small and seem to be independent of the sites and orientations. The surface epoxy or hydroxyl groups can promote the adsorption of NH3 on the GO; the enhancement of the Eb for the hydroxyl groups is greater than that for the epoxy groups on the surface. The charge transfers from the molecule to the surfaces also exhibit the same trend. The Br?nsted acid sites and Lewis acid sites could stably exist on the GO with surface hydroxyl groups and on the basal, respectively.

    Qing ZHOU, Mengqiao WANG, Aimin LI, Chendong SHUANG, Mancheng ZHANG, Xiaohan LIU, Liuyan WU

    A novel hyper-crosslinked resin (MENQ) modified with an anion exchange group was prepared using divinylbenzene (DVB) and methyl acrylate (MA) as comonomers via four steps: suspension polymerization, post-crosslinking, ammonolysis and alkylation reactions. The obtained resin had both a high specific surface area (793.34 m2·g-1) and a large exchange capacity (strong base anion exchange capacity, SEC: 0.74 mmol·g-1, weak base anion exchange capacity, WEC: 0.45 mmol·g-1). XAD-4 was selected as an adsorbent for comparison to investigate the adsorption behavior of tetracycline (TC) and humic acid (HA) onto the adsorbents. The results revealed that MENQ could effectively remove both TC and HA. The adsorption capacity of XAD-4 for TC was similar to that of MENQ, but XAD-4 exhibited poor performance for the adsorption of HA. The adsorption isotherms of TC and HA were well-fitted with the Freundlich model, which indicated the existence of heterogeneous adsorption through cation-π bonding and π–π interactions. The optimal solution condition for the adsorption of TC was at a pH of 5–6, whereas the adsorption of HA was enhanced with increasing pH of the solution.

    Xiaodong WU, Wenchao YU, Zhichun SI, Duan WENG

    V2O5-WO3/TiO2 catalyst was poisoned by impregnation with NH4Cl, KOH and KCl solution, respectively. The catalysts were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), N2 physisorption, Raman, UV-vis, NH3 adsorption, temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed oxidation of ammonia (NH3-TPO) and selective catalytic reduction of NOx with ammonia (NH3-SCR). The deactivation effects of poisoning agents follow the sequence of KCl>KOH>>NH4Cl. The addition of ammonia chloride enlarges the pore size of the titania support, and promotes the formation of highly dispersed V=O vanadyl which improves the oxidation of ammonia and the high-temperature SCR activity. K+ ions are suggested to interact with vanadium and tungsten species chemically, resulting in a poor redox property of catalyst. More importantly, potassium can reduce the Br?nsted acidity of catalysts and decrease the stability of Br?nsted acid sites significantly. The more severe deactivation of the KCl-treated catalyst can be mainly ascribed to the higher amount of potassium resided on catalyst.

    Chang-Mao HUNG, Wen-Liang LAI, Jane-Li LIN

    This work describes the environmentally friendly technology for oxidation of ammonia (NH3) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al2O3 catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H2PtCl6) and rhodium (III) nitrate (Rh(NO3)3) with γ-Al2O3 in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), three-dimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic light-scattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH3 was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al2O3 catalyst. N2 was the main product in NH3-SCO process. Further, it reveals that the oxidation of NH3 was proceeds by the over-oxidation of NH3 into NO, which was conversely reacted with the NH3 to yield N2. Therefore, the application of nanosized Pt-Rh/γ-Al2O3 catalyst can significantly enhance the catalytic activity toward NH3 oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al2O3 catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.

    Ming HUA, Lili XIAO, Bingcai PAN, Quanxing ZHANG

    The efficient removal of phosphorous from water is an important but challenging task. In this study, we validated the applicability of a new commercially available nanocomposite adsorbent, i.e., a polymer-based hydrated ferric oxide nanocomposite (HFO-201), for the further removal of phosphorous from the bioeffluent discharged from a municipal wastewater treatment plant, and the operating parameters such as the flow rate, temperature and composition of the regenerants were optimized. Laboratory-scale results indicate that phosphorous in real bioeffluent can be effectively removed from 0.92 mg·L-1 to<0.5 mg·L-1 (or even<0.1 mg·L-1 as desired) by the new adsorbent at a flow rate of 50 bed volume (BV) per hour and treatable volume of 3500–4000 BV per run. Phosphorous removal is independent of the ambient temperature in the range of 15°C–40°C. Moreover, the exhausted HFO-201 can be regenerated by a 2% NaOH+ 5% NaCl binary solution for repeated use without significant capacity loss. A scaled-up study further indicated that even though the initial total phosphorus (TP) was as high as 2 mg·L-1, it could be reduced to<0.5 mg·L-1, with a working capacity of 4.4–4.8 g·L-1 HFO-201. In general, HFO-201 adsorption is a choice method for the efficient removal of phosphate from biotreated waste effluent.

    Liqin JI, Xue BAI, Lincheng ZHOU, Hanchang SHI, Wei CHEN, Zulin HUA

    A simple solvothermal method was used to prepare monodisperse magnetite (Fe3O4) nanoparticles attached onto graphene oxide (GO) sheets as adsorbents to remove tetrabromobisphenol A (TBBPA) from an aqueous solution. These Fe3O4/GO (MGO) nanocomposites were characterized by transmission electron microscopy. The adsorption capacity at different initial pH, contact duration, and temperature were evaluated. The kinetics of adsorption was found to fit the pseudo-second-order model perfectly. The adsorption isotherm well fitted the Langmuir model, and the theoretical maximum of adsorption capacity calculated by the Langmuir model was 27.26 mg?g-1. The adsorption thermodynamics of TBBPA on the MGO nanocomposites was determined at 303 K, 313 K, and 323 K, respectively. The results indicated that the adsorption was spontaneous and endothermic. The MGO nanocomposites were conveniently separated from the media by an external magnetic field within several seconds, and then regenerated in 0.2 M NaOH solution. Thus, the MGO nanocomposites are a promising candidate for TBBPA removal from wastewater.

    Zhendong YANG, Aihua LV, Yulun NIE, Chun HU

    Fe3O4 was supported on mesoporous Al2O3 or SiO2 (50 wt.%) using an incipient wetness impregnation method, and Fe3O4/Al2O3 exhibited higher catalytic efficiency for the degradation of 2,4-dichlorophenoxyacetic acid and para-chlorobenzoic acid aqueous solution with ozone. The effect and morphology of supported Fe3O4 on catalytic ozonation performance were investigated based on the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, BET analysis and Fourier transform infrared spectroscopy. The results indicated that the physical and chemical properties of the catalyst supports especially their Lewis acid sites had a significant influence on the catalytic activity. In comparison with SiO2, more Lewis acid sites existed on the surface of Al2O3, resulting in higher catalytic ozonation activity. During the reaction process, no significant Fe ions release was observed. Moreover, Fe3O4/Al2O3 exhibited stable structure and activity after successive cyclic experiments. The results indicated that the catalyst is a promising ozonation catalyst with magnetic separation in drinking water treatment.

    Lei YUAN, Xiang ZHENG, Kaijiao DUAN, Hao HU, Jinggang WANG, Seong Ihl WOO, Zhiming LIU

    Selective catalytic reduction of NOx by H2 in the presence of oxygen has been investigated over Pt/Al2O3 catalysts pre-treated under different conditions. Catalyst preparation conditions exert significant influence on the catalytic performance, and the catalyst pre-treated by H2 or H2 then followed by O2 is much more active than that pre-treated by air. The higher surface area and the presence of metallic Pt over Pt/Al2O3 pre-treated by H2 or pretreated by H2 then followed by O2 can contribute to the formation of NO2, which then promotes the reaction to proceed at low temperatures.

    Yongfu GUO, Naiqiang YAN, Ping LIU, Shijian YANG, Juan WANG, Zan QU

    In this work, a catalytic membrane using Mn/Mo/Ru/Al2O3 as the catalyst was employed to remove elemental mercury (Hg0) from flue gas at low temperature. Compared with traditional catalytic oxidation (TCO) mode, Mn/Al2O3 membrane catalytic system had much higher removal efficiency of Hg0. After the incorporation of Mo and Ru, the production of Cl2 from the Deacon reaction and the retainability for oxidants over Mn/Al2O3 membrane were greatly enhanced. As a result, the oxidization of Hg0 over Mn/Al2O3 membrane was obviously promoted due to incorporation of Mo and Ru. In the presence of 8 ppmv HCl, the removal efficiency of Hg0 by Mn/Mo/Ru/Al2O3 membrane reached 95% at 423 K. The influence of NO and SO2 on Hg0 removal were insignificant even if 200 ppmv NO and 1000 ppmv SO2 were used. Moreover, compared with the TCO mode, the Mn/Mo/Ru/Al2O3 membrane catalytic system could remarkably reduce the demanded amount of oxidants for Hg0 removal. Therefore, the Mn/Mo/Ru/Al2O3 membrane catalytic system may be a promising technology for the control of Hg0 emission.