A series of WO3/CeO2 （WOx/CeO2） catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO2 support. The resulting solid acid catalysts were characterized by X-ray diffraction （XRD）, UV-Vis ...A series of WO3/CeO2 （WOx/CeO2） catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO2 support. The resulting solid acid catalysts were characterized by X-ray diffraction （XRD）, UV-Vis spectroscopy （UV-Vis）, Raman spectroscopy （Raman）, in-situ Fourier transform infrared spectroscopy （in-situ FT-IR） of ammonia adsorption, NH3-TPD, H2 temperature- programmed reduction （H2-TPR）, NH3/NO oxidation and activity measurements for NOx reduction by NH3 （NH3-SCR）. The results show that polytungstate （WOx） species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the BriSnsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on celia, with strong interaction between CeO2 and WOx. As a result, the N2 selectivity of NH3 oxidation and NH3-SCR at high temperatures （〉 300℃） is enhanced. Therefore, a wide working temperature window in which NOx conversion exceeds 80% （NOx conversion 〉 80%） from 200 to 450℃, is achieved over 10 wt.% WOx/CeO2 catalyst. A tentative model of the NH3-SCR reaction route on WOx/CeO2 catalysts is presented.展开更多
Motivated by the recent realization ofgraphene sensor to detect gas molecules that are harmful to the environment, the ammonia adsorption on graphene or graphene oxide （GO） was investigated using first-princi- ples ...Motivated by the recent realization ofgraphene sensor to detect gas molecules that are harmful to the environment, the ammonia adsorption on graphene or graphene oxide （GO） was investigated using first-princi- ples 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 ofNH3 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 Brōnsted acid sites and Lewis acid sites could stably exist on the GO with surface hydroxyl groups and on the basal, respectively.展开更多
Vertically aligned γ-AlOOH nanosheets （NSs） have been successfully fabricated on flexible Al foils via a solvothermal route without morphology-directing agents. Three different reaction temperature （25, 80, and 1...Vertically aligned γ-AlOOH nanosheets （NSs） have been successfully fabricated on flexible Al foils via a solvothermal route without morphology-directing agents. Three different reaction temperature （25, 80, and 120 ℃） and time （30 min, 45 min, and 24 h） are discussed for the growth period, which efficiently tune the density and size of theγ-AlOOH NSs. Meanwhile, the growth speed of the nanosheets confirms that dominant growth stage is seen in the initial 45 min. Furthermore, the interlayer of the γ-AlOOH NSs displays an average height of 140 nm and superhydrophilicity. By dynamic adsorption, the as- synthesized γ-AlOOH NSs exhibit an outstanding NH3 adsorption capacity of up to 146 mg/g and stably excellent regeneration for 5 cycles. The mechanism of NH3 adsorption on the in-plane of the γ-AlOOH NSs is explained by the Lewis acid/base theory. The H-bond interactions among the NH3 molecules and the edge groups （-OH） further improve the capture ability of the nanosheets.展开更多
用Du Pont 9900计算机/热分析系统的热重分析仪(TGA)和自行改形的石英炉管,进行了分子筛催化剂的原位NH_3吸附-脱附实验,测定了样品的表面酸性。实验数据可定量表征固体催化剂的酸量及其酸强度分布。以HY分子筛为参考样品测量结果,数据...用Du Pont 9900计算机/热分析系统的热重分析仪(TGA)和自行改形的石英炉管,进行了分子筛催化剂的原位NH_3吸附-脱附实验,测定了样品的表面酸性。实验数据可定量表征固体催化剂的酸量及其酸强度分布。以HY分子筛为参考样品测量结果,数据具有良好的重复性,其相对标准偏差小于±5.0％;HZSM-5分子筛的酸性数据与文献报道的用不同方法对类似样品所取得的结果接近。还讨论了催化剂酸性与它们的催化反应活性数据的相互关系。展开更多
Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR)is crucial due to the universal presence of SO_(2)in exhaust gas.Depending on the degree of sulfati...Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR)is crucial due to the universal presence of SO_(2)in exhaust gas.Depending on the degree of sulfation,there mainly exist surface and bulk sulfates and NH_(3)-SCR activity is generally considered to suffer more from bulk sulfates.Herein,the unique function of bulk sulfates over Ce O_(2)in promoting hightemperature SCR reaction is revealed.Notably,compared with CeO_(2)dominated with surface sulfates(S-CeO_(2)-4h)and commercial V_2O_5-WO_(3)/TiO_(2),CeO_(2)with bulk sulfates(S-Ce O_(2)-72h)exhibits admirable NO conversion at the temperature range of 400-550℃.Bulk sulfates provide more Br?nsted acid sites with stronger strength for NH_(3)adsorption.Moreover,the oxidation ability of Ce O_(2)is significantly inhibited due to electron-withdrawing effect from bulk sulfates,which alleviates NH_(3)oxidation at high temperatures.More NH_(3)adsorption with high stability and limited NH_(3)oxidation capacity ensure the excellent catalytic performance for S-CeO_(2)-72h in high-temperature denitration.This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design de NO_xcatalysts employed at high temperatures.展开更多
基金the Ministry of Science and Technology, PR China for financial support of Project 2010CB732304Science and Technology Department of Zhejiang Province Project 2011C31010
文摘A series of WO3/CeO2 （WOx/CeO2） catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO2 support. The resulting solid acid catalysts were characterized by X-ray diffraction （XRD）, UV-Vis spectroscopy （UV-Vis）, Raman spectroscopy （Raman）, in-situ Fourier transform infrared spectroscopy （in-situ FT-IR） of ammonia adsorption, NH3-TPD, H2 temperature- programmed reduction （H2-TPR）, NH3/NO oxidation and activity measurements for NOx reduction by NH3 （NH3-SCR）. The results show that polytungstate （WOx） species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the BriSnsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on celia, with strong interaction between CeO2 and WOx. As a result, the N2 selectivity of NH3 oxidation and NH3-SCR at high temperatures （〉 300℃） is enhanced. Therefore, a wide working temperature window in which NOx conversion exceeds 80% （NOx conversion 〉 80%） from 200 to 450℃, is achieved over 10 wt.% WOx/CeO2 catalyst. A tentative model of the NH3-SCR reaction route on WOx/CeO2 catalysts is presented.
文摘Motivated by the recent realization ofgraphene sensor to detect gas molecules that are harmful to the environment, the ammonia adsorption on graphene or graphene oxide （GO） was investigated using first-princi- ples 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 ofNH3 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 Brōnsted acid sites and Lewis acid sites could stably exist on the GO with surface hydroxyl groups and on the basal, respectively.
文摘Vertically aligned γ-AlOOH nanosheets （NSs） have been successfully fabricated on flexible Al foils via a solvothermal route without morphology-directing agents. Three different reaction temperature （25, 80, and 120 ℃） and time （30 min, 45 min, and 24 h） are discussed for the growth period, which efficiently tune the density and size of theγ-AlOOH NSs. Meanwhile, the growth speed of the nanosheets confirms that dominant growth stage is seen in the initial 45 min. Furthermore, the interlayer of the γ-AlOOH NSs displays an average height of 140 nm and superhydrophilicity. By dynamic adsorption, the as- synthesized γ-AlOOH NSs exhibit an outstanding NH3 adsorption capacity of up to 146 mg/g and stably excellent regeneration for 5 cycles. The mechanism of NH3 adsorption on the in-plane of the γ-AlOOH NSs is explained by the Lewis acid/base theory. The H-bond interactions among the NH3 molecules and the edge groups （-OH） further improve the capture ability of the nanosheets.
基金Supported by the National Science Foundation of China(21371159)the Natural Science Foundation of Shanxi Province(2009011014)Shenzhen Strategic Emerging Industries Special Fund Program of China(GGJS20120619101655715)
文摘用Du Pont 9900计算机/热分析系统的热重分析仪(TGA)和自行改形的石英炉管,进行了分子筛催化剂的原位NH_3吸附-脱附实验,测定了样品的表面酸性。实验数据可定量表征固体催化剂的酸量及其酸强度分布。以HY分子筛为参考样品测量结果,数据具有良好的重复性,其相对标准偏差小于±5.0％;HZSM-5分子筛的酸性数据与文献报道的用不同方法对类似样品所取得的结果接近。还讨论了催化剂酸性与它们的催化反应活性数据的相互关系。
基金The financial supports from the National Natural Science Foundation of China(Nos.21976081,21972062)Major Scientific and Technological Project of Bingtuan(No.2018AA002),are greatly acknowledged。
文摘Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR)is crucial due to the universal presence of SO_(2)in exhaust gas.Depending on the degree of sulfation,there mainly exist surface and bulk sulfates and NH_(3)-SCR activity is generally considered to suffer more from bulk sulfates.Herein,the unique function of bulk sulfates over Ce O_(2)in promoting hightemperature SCR reaction is revealed.Notably,compared with CeO_(2)dominated with surface sulfates(S-CeO_(2)-4h)and commercial V_2O_5-WO_(3)/TiO_(2),CeO_(2)with bulk sulfates(S-Ce O_(2)-72h)exhibits admirable NO conversion at the temperature range of 400-550℃.Bulk sulfates provide more Br?nsted acid sites with stronger strength for NH_(3)adsorption.Moreover,the oxidation ability of Ce O_(2)is significantly inhibited due to electron-withdrawing effect from bulk sulfates,which alleviates NH_(3)oxidation at high temperatures.More NH_(3)adsorption with high stability and limited NH_(3)oxidation capacity ensure the excellent catalytic performance for S-CeO_(2)-72h in high-temperature denitration.This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design de NO_xcatalysts employed at high temperatures.
