Low-Temperature Selective Catalytic Reduction of NO with NH_3 over Fe–Ce–O_x Catalysts

In this study, we used a simple impregnation method to prepare Fe-Ce-O x catalysts and tested them regarding their low-temperature (200-300 °C) selective catalytic reduction (SCR) of NO using NH3. We investigated the effects of Fe/Ce molar ratio, the gas hourly space velocity (GHSV), the stability and SO2/H2O resistance of the catalysts. The results showed that the FeCe(1:6)O x (Ce/Fe molar ratio is 1:6) catalyst, which has some ordered parallel channels, exhibited good SCR performance. The FeCe(1:6)O x catalyst had the highest NO conversion with an activity of 94-99% at temperatures between 200 and 300 °C at a space velocity of 28,800 h−1. The NO conversion for the FeCe(1:6)O x catalyst also reached 80-98% between 200 and 300 °C at a space velocity of 204,000 h−1. In addition, the FeCe(1:6)O x catalyst demonstrated good stability in a 10-h SCR reaction at 200-300 °C. Even in the presence of SO2 and H2O, the FeCe(1:6)O x catalyst exhibited good SCR performance.

Novel Cs-Mg-Al mixed oxide with improved mobility of oxygen species for passive NO_(x)adsorption

The development of passive NO_(x)adsorbers with cost-benefit and high NO_(x)storage capacity remains an on-going challenge to after-treatment technologies at lower temperatures associated with cold-start NO_(x)emissions.Herein,Cs_(1)Mg_(3)Al catalyst prepared by sol-gel method was cyclic tested in NO_(x)storage under 5 vol%water.At 100°C,the NO_(x)storage capacity(1219 μmol g^(-1))was much higher than that of Pt/BaO/Al_(2)O_(3)(610 μmol g^(-1)).This provided new insights for non-noble metal catalysts in low-temperature passive NO_(x)adsorption.The addition of Cs improved the mobility of oxygen species and thus improved the NO_(x)storage capacity.The XRD,XPS,IR spectra and in situ DRIFTs with NH3 probe showed an interaction between CsO_(x)and AlO_(x)sites via oxygen species formed on Cs_(1)Mg_(3)Al catalyst.The improved mobility of oxygen species inferred from O2-TPD was consistent with high NO_(x)storage capacity related to enhanced formation of nitrate and additional nitrite species by NO_(x)oxidation.Moreover,the addition of Mg might improve the stability of Cs_(1)Mg_(3)Al by stabilizing surface active oxygen species in cyclic experiments.

Low-temperature deNO_(x)performance and mechanism:a novel FeVO_(4)/CeO_(2)catalyst for iron ore sintering flue gas

Developing deNO_(x)catalysts with lower activity temperatures range significantly reduces NH_(3)selective catalytic reduction(SCR)operating costs for low-temperature industrial flue gases.Herein,a novel FeVO_(4)/CeO_(2)catalyst with great low-temperature NH_(3)-SCR and nitrogen selectivity was synthesized using a dipping method.Characterization techniques such as X-ray diffraction,Raman spectroscopy,specific surface and porosity analysis,H2 temperature-programmed reduction,NH_(3)temperature-programmed desorption,X-ray photoelectron spectroscopy,and the in situ diffused reflectance infrared Fourier transform spectroscopy were used to investigate the catalytic mechanism.An appropriate addition for FeVO_(4)in the catalyst was 5 wt.%from the results,and the active substance content reached the maximum dispersal capacity of the carrier.The NO_(x)conversion exceeded 90%,and the nitrogen selectivity was more than 98%over this catalyst at 200–350°C.The activity was kept at 88%after 7.5 h of reaction at 200°C for 7.5 h in 35 mg m^(-3)SO_(2)gas.The remarkable deNO_(x)activity,nitrogen selectivity,and sulphur resistance performances are attributed to the low redox temperature,the abundance of medium-strong acid and strong acid sites,the sufficient adsorbed oxygen,and the superior Fe^(2+)content on the surface.The Langmuir–Hinshelwood mechanism was observed on the FeVO_(4)/CeO_(2)catalyst in the NH_(3)selective catalytic reduction of NO_(x).

Low-temperature NH_(3)-SCR of NO_(x) over MnCeO_(x)/TiO_(2) catalyst:Enhanced activity and SO_(2) tolerance by modifying TiO_(2) with Al_(2)O_(3)

A series of TiO_(2)-Al_(2)O_(3) composites with Al/Ti molar ratios of 0.1,0.2,and 0.4 were synthesized by a coprecipitation method and used as supports to prepare supported MnCeO_(x) catalysts by an impregnation method.The physico-chemical properties of the samples were extensively characterized by N_(2) physisorption,X-ray diffraction,Raman spectroscopy,scanning electron micro scopy and energy-dispersive Xray spectroscopy element mapping,X-ray photoelectron spectroscopy,H_(2)-temperature programmed reduction,ammonia temperature programmed desorption,and in-situ diffuse reflectance infrared Fourier transform spectroscopy.The catalytic activity and resistance to water vapor and SO_(2) of the asprepared catalysts for the SCR of NO_(x) with NH_(3) were evaluated at 50-250℃ and GHSV of 80000 mL/(gcat·h).The results reveal that MnCeO_(x)/TiO_(2)-Al_(2)O_(3) exhibits higher activity and better SO_(2) tolerance than MnCeO_(x)/TiO_(2).Combining with the characterization results,the enhanced activity and SO_(2) tolerance of MnCeO_(x)/TiO_(2)-Al_(2)O_(3) can be mainly attributed to higher relative concentrations of Mn4+and chemisorbed oxygen species,stronger reducibility,and larger adsorption capacity for NH_(3) and NO,which originate from the larger specific surface area and pore volume,higher dispersion of Mn and Ce species compared with MnCeO_(x)/TiO_(2).Moreover,in situ DRIFTS was used to investigate the reaction mechanism,and the results indicate that the NH_(3)-SCR reaction over MnCeO_(x)/TiO_(2) and MnCeO_(x)/TiO_(2)-Al_(2)O_(3) takes place by both the E-R and L-H mechanisms.

Low-temperature selective catalytic reduction of NO with NH_(3) based on MnO_(x)-CeO_(x)/ACFN

MnO_(x)-CeO_(x)/ACFN were prepared by the impregnation method and used as catalyst for selective catalytic reduction of NO with NH_(3) at 80℃-150℃.The catalyst was characterized by N_(2)-BET,scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FT-IR).The fraction of the mesopore and the oxygen functional groups on the surface of activated carbon fiber(ACF)increased after the treatment with nitric acid,which was favorable to improve the catalytic activities of MnO_(x)-CeO_(x)/ACFN.The experimental results show that the conversion of NO is nearly 100%in the range 100℃-150℃under the optimal preparation conditions of MnO_(x)-CeO_(x)/ACFN.In addition,the effects of a series of performance parameters,including initial NH3 concentration,NO concentration and O_(2) concentration,on the conversion of NO were studied.

Investigation of the promotion effect of Mo doped CuO catalysts for the low-temperature performance of NH_(3)-SCR reaction

A novel Mo-doped CuO catalyst is developed and used for low-temperature NH_(3)-SCR reaction.Compared with the undoped CuO sample,the Mo doped CuO catalyst shows an increased SCR performance with above 80%NO_(x) conversion at 175℃.The XRD and Raman results have confirmed the incorporation of Mo metal ions into CuO lattice to form Mo-O-Cu species which may be related to the enhanced SCR activity.The XPS and UV-vis results reveal the creation of electron interaction between Cu and Mo in this Mo-O-Cu system which provides an increased amount of Lewis and Brønsted acid sites,thereby promoting the adsorption capacity of NH_(3) and NO_(x) as verified by NH_(3)-TPD and NO_(x)-TPD characterization.Besides,it also promotes the formation of oxygen vacancies,leading to the increasing of chemisorbed oxygen species,which improves the NO oxidation to NO_(2) activity.Furthermore,in situ DRIFTS technology was also used to study the reaction mechanism of this Mo doped CuO catalyst.The formed NO_(2) could react with NHx(x=3,2)species to enhance the low-temperature NH_(3)-SCR activity via the"fast-SCR"reaction pathway.The nitrate and nitrite ad-species may react with NH_(3) and NH4^(+)ad-species through the L-H pathway.