Selective catalytic oxidation of NO with O_2 over Ce-doped MnO_x/TiO_2 catalysts

A series of Ce-doped MnOx/TiO2 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=l/3 and calcined at 300 ℃ shows a superior activity for NO oxidation to NO2. On Ce（1）Mn（3）Ti catalyst, 58% NO conversion was obtained at 200 ℃ and 85% NO conversion at 250 ℃ with a GHSV of 41000 h-1, which was much higher than that over MnOx/TiO2 catalyst （48% at 250 ℃）. Characterization results implied that the higher activity of Ce（1）Mn（3）Ti could be attributed to the enrichment of well-dispersed MnO2 on the surface and the abundance of Mn3＋ and Zi3＋ species. The addition of Ce into MnO2/TiO2 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 H2O and SO2 on the catalyst activity was also investigated.

Highly efficient K-doped Mn-Ce catalysts with strong K-Mn-Ce interaction for toluene oxidation

In this study,K_(x)-Mn-Ce catalysts prepared by sol-gel method were investigated for toluene oxidation.Compared with Mn-Ce,the catalytic performance of K_(x)-Mn-Ce was further improved.X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM)and Raman analyses demonstrate that K ions enter the lattice of CeO_(2) and disperse uniformly.The results of X-ray photoelectron spectroscopy(XPS),H_(2)-temperature programmed reduction(H_(2)-TPR).and O_(2)-temperature programmed desorption(O_(2)-TPD)analyses indicate that there is a strong interaction between K,Mn and Ce;the charge co mpensation effect would be induced when K ions enter the lattice of CeO_(2),which leads to more oxygen vacancies due to the generation of more Ce^(3+).Toluene-TPD shows that K-doping enhances the activation ability of toluene.Among all catalysts,K0.1-Mn-Ce shows the highest concentration of Mn^(4+),Ce^(3+),Osur,and redox ability,resulting in higher low-temperature catalytic activity.Additionally,the results of stability and water resistance also prove that K0.1-Mn-Ce catalyst possesses excellent stability and water resistance.

Synergistic effect of F and triggered oxygen vacancies over F-TiO_(2) on enhancing NO ozonation

Oxidation-absorption technology is a key step for NOxremoval from low-temperature gas.Under the condition of low O_(3)concentration(O_(3)/NO molar ratio = 0.6), F-TiO_(2)(F-TiO_(2)), which is cheap and environmentally friendly, has been prepared as ozonation catalysts for NO oxidation. Catalytic activity tests performed at 120℃showed that the NO oxidation efficiency of F-TiO_(2)samples was higher than that of TiO_(2)(about 43.7%), and the NO oxidation efficiency of F-TiO_(2)-0.15 was the highest, which was 65.3%. Combined with physicochemical characteristics of catalysts and the analysis of active species, it was found that there was a synergistic effect between F sites and oxygen vacancies on F-TiO_(2), which could accelerate the transformation of monomolecular O_(3)into multi-molecule singlet oxygen(1O_(2)), thus promoting the selective oxidation of NO to NO_(2). The oxidation reaction of NO on F-TiO_(2)-0.15 follows the Eley-Rideal mechanism, that is, gaseous NO reacts with adsorbed O_(3)and finally form NO_(2).

Construction of 3D/2D indium vanadate /graphite carbon nitride with nitrogen defects Z-scheme heterojunction for improving photocatalytic carbon dioxide reduction

Indium vanadate (InVO4 ) possesses excellent potential in photocatalytic carbon dioxide (CO_(2) ) reduction, but further modifications of reducing charge recombination and increasing active sites are still needed. Herein, InVO4 /g-C3 N4 (InVO-CN) heterojunction composite photocatalysts were prepared via in situ formation of InVO4 nanoparticles on the lamellar structure of graphite carbon nitride (g-C3 N4 ) containing nitrogen (N) defects. Among these composites, 30% InVO-CN showed the best photoreduction performance for CO_(2) at normal temperature and pressure without sacrificial agent (carbon monoxide, CO: 20.14 μmol g–1 h–1;methane, CH4 : 3.46 μmol g–1 h–1 ), which were 1.8 and 2.8 times higher than these of pure g-C3 N4 and InVO4 . The excellent performance could be attributed to the enhancement of CO_(2) adsorption, and most importantly, the enhanced charge carrier separation and reduction capacity induced by the formation of Z-scheme heterojunction between InVO4 and g-C3 N4 . In this work, intimate heterojunction interfaces between materials were formed by introducing g-C3 N4 with defects in InVO4 , which provides a promising modification scheme.

Efect of chromium oxide as active site over TiO_2-PILC for selective catalytic oxidation of NO

This study introduced TiO2-pillared clays （TiO2-PILC） as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350℃, the NO conversion was 61% under conditions of GHSV = 23600 hr^-l. The BET data showed that the support particles had a mesoporous structure. Hz-TPR showed that Cr（10）TiP （10 wt.% Cr doping on TiO2-PILC） clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO ＋ O2 adsorption, the intensity of evolution of superoxide ions （O2^-） increased. The content of Cr^3＋ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr^3＋ increased to 50.28%. Additionally, Oα/Oβ increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO4^2-.

Effects of synthesis methods on catalytic activities of CoOx–TiO2 for low-temperature NH3-SCR of NO

A series of cobalt doped TiO2（Co-TiO2） and Co Oxloaded 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（O-2）. The superoxide ions were crucial for the formation of low temperature SCR reaction intermediates（NO-3） by reacting with adsorbed NO molecule. Therefore, these aspects were responsible for the higher low temperature NH3-SCR activity of Co-TiO2 catalysts.

Revealing active species of CePO_(4)catalyst for selective catalytic reduction of NO_(x)with NH_(3)

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst.Herein,we tried to demonstrate the roles of amorphous and crystalline structures on CePO_(4)catalyst during selective catalytic reduction(SCR)of NO_(x)by NH_(3).Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO_(4).Both amorphous and crystalline CePO_(4)species on CePO-X samples can provide acid sites for NH_(3)adsorption,but the former can provide more acid sites.The superior redox property of surface amorphous CePO_(4)species contributes to its high NH_(3)-SCR activity at low temperature,but it also leads to the decrease of high temperature(>350℃)NH_(3)-SCR activity due to the oxidation of NH_(3).In contrast,crystalline CePO_(4)species shows high activity only at high temperature because of its poor redox property.Therefo re,it can be inferred that amo rphous and crystalline structures on CePO_(4)catalyst can be the efficient active species of NH_(3)-SCR at low and high temperature,respectively.