Selective catalytic oxidation of NO over iron and manganese oxides supported on mesoporous silica

The selective catalytic oxidation （SCO） of NO was studied on a catalyst consisting of iron-manganese oxide supported on mesoporous silica （MPS） with different Mn/Fe ratios. Effects of the amount of manganese and iron, oxygen, and calcination temperature on NO conversion were also investigated. It was found that the Mn-Fe/MPS catalyst with a Mn/Fe molar ratio of 1 showed the highest activity at the calcination temperature of 400 °C. The results showed that over this catalyst, NO conversion reached 70% under the condition of 280 °C and a space velocity of 5000 h-1. SO2 and H2O had no adverse impact on the reaction activity when the SCO reaction temperature was above 240 °C. In addition, the SCO activity was suppressed gradually in the presence of SO2 and H2O below 240 °C, and such an effect was reversible after heating treatment.

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.

Fabrication of highly dispersed carbon doped Cu-based oxides as superior selective catalytic oxidation of ammonia catalysts via employing citric acid-modified carbon nanotubes doping CuAl-LDHs

In this work,the CuAl-LDO/c-CNTs catalyst was fabricated via in situ oriented assembly of layered-double hydroxides(LDHs)and citric acid-modified carbon nanotubes(c-CNTs)followed by annealing treatment,and evaluated in the selective catalytic oxidation(SCO)of NH_(3)to N_(2).The CuAl-LDO/c-CNTs catalyst presented better catalytic performance(98%NH_(3)conversion with nearly 90%N_(2)selectivity at 513 K)than other catalysts,such as CuAlO_(x)/CNTs,CuAlO_(x)/c-CNTs and CuAl-LDO/CNTs.Multiple characterizations were utilized to analyze the difference of physicochemical properties among four catalysts.XRD,TEM and XPS analyses manifested that CuO and Cu_(2)O nanoparticles dispersed well on the surface of the Cu Al-LDO/c-CNTs catalyst.Compared with other catalysts,larger specific surface area and better dispersion of CuAl-LDO/c-CNTs catalyst were conducive to the exposure of more active sites,thus improving the redox capacity of the active site and NH_(3)adsorption capacity.In-situ DRIFTS results revealed that the internal selective catalytic reduction(iSCR)mechanism was found over CuAl-LDO/c-CNTs catalyst.

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-.

Gas Phase Selective Catalytic Oxidation of Toluene to Benzaldehyde on V_2O_5-Ag2O/η-Al_2O_3 Catalyst

Gas phase selective catalytic oxidation of toluene to benzatdehyde was studied on V_2O_5-Ag_2O/η-Al_2O_3 catalyst prepared by impregnation. The catalyst was characterized by XRD, XPS, TEM, and FT-IR. The catalytic results showed that toluene conversion and selectivity for benzaldehyde on catalyst sample No.4 (V/(V+Ag)=0.68) was higher than other catalysts with different V/Ag ratios. This was attributed to the higher surface area, larger pore volume and pore diameter of the catalyst sample No. 4 than the other catalysts. The XRD patterns recorded from the catalyst before and after the oxidation reaction revealed that the new phases were developed, and this suggested that silver had entered the vanadium lattice. XPS results showed that the vanadium on the surface of No.4 and No.5 sample was more than that in the bulk, thus forming a vanadium rich layer on the surface. It was noted that when the catalyst was doped by potassium promoter, the toluene conversion and selectivity for benzaldehyde were higher than those on the undoped catalyst. This was attributed to the disordered structure of V_2O_5 lattice of the K-doped catalyst and a better interracial contact between the particles.

Advances in selective catalytic oxidation of ammonia (NH_(3)-SCO): A review of catalyst structure-activity relationship and design principles

NH_(3) in ambient air directly leads to an increase in the aerosol content in the air. These substances lead to the formation of haze to various environmental problems after atmospheric circulation and diffusion. Controlling NH_(3) emissions caused by ammonia escaping from mobile and industrial sources can effectively reduce the NH_(3) content in ambient air. Among the various NH_(3) removal methods, the selective catalytic oxygen method (NH_(3)-SCO) is committed to oxidizing NH_(3) to environmentally harmless H_(2)O and N_(2);therefore, it is the most valuable and ideal ammonia removal method. In this review, the characteristics of loaded and core-shell catalysts in NH_(3)-SCO have been reviewed in the context of catalyst structure-activity relationships, and the H_(2)O resistance and SO2 resistance of the catalysts are discussed in the context of practical application conditions. Then the effects of the valence state of the active center, oxygen species on the catalyst surface, dispersion of the active center and acidic sites on the catalyst performance are discussed comprehensively. Finally, the shortcomings of the existing catalysts are summarized and the catalyst development is discussed based on the existing studies.

Experimental and theoretical studies on NO selective catalytic oxidation over α-MnO_(2)

Based on the experimental and theoretical methods,the NO selective catalytic oxidation process was proposed.The experimental results indicated that lattice oxygen was the active site for NO oxide over the α-MnO_(2)(110) surface.In the theoretical study,DFT (density functional theory) and periodic slab modeling were performed on an α-MnO_(2)(110) surface,and two possible NO oxidation mechanisms over the surface were proposed.The non-defectα-MnO_(2)(110) surface showed the highest stability,and the surface Os(the second layer oxygen atoms) position was the most active and stable site.O_(2)molecule enhanced the joint adsorption process of two NO molecules.The reaction process,including O_(2)dissociation and O=N-O-O-N=O formation,was calculated to carry out the NO catalytic oxidation mechanism over α-MnO_(2)(110).The results showed that NO oxidation over the α-MnO_(2)(110) surface exhibited the greatest possibility following the route of O=N-O-O-N=O formation.Meanwhile,the formation of O=N-O-O-N=O was the rate-determining step.

Rare earth oxide modified Cu-Mn compounds supported on TiO_2 catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Selective catalytic oxidation(SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce2O3 and La2O3 respectively.TiO2 was used as support and different ratio of O2 were tested in order to find an appropriate O2 concentration(vol.%),and the results showed that 1%O2(vol.%) was propitious to SCO of ammonia.The effects of the two rare earth oxides modified catalysts Ce2O3-Cu-Mn/TiO2 and La2O3-Cu-Mn/TiO2 on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia,1%O2(vol.%),at the temperature from 125 to 250 oC.The results revealed the beneficial role of Ce2O3 and La2O3 in catalytic activity at low temperature and lean oxygen concentration,while the modification with Ce2O3 and La2O3 led to the negative influence on N2 selectivity.For the catalysts modified with Ce showed lower NO and N2O selectivity than the catalysts modified with La,then the effects of different Ce loadings on catalytic activity and selectivity were also considered,in combination with catalysts preparation methods,which include incipient wet impregnation,sol-gel method and co-precipitation.Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others,reaching 99% ammonia at 200 oC,whereas 96% NO was detected.It also indicated that different catalyst preparation method significantly determined production distribution.

Effect of Cu-ZSM-5 catalysts with different CuO particle size on selective catalytic oxidation of N,N-Dimethylformamide

N,N-Dimethylformamide(DMF),a nitrogen-containing volatile organic compound(NVOC)with high emissions from the spray industry,has attracted increasing attention.In this study,Cu-ZSM-5 catalysts with different CuO particle sizes of 3,6,9 and 12 nm were synthesized and tested for DMF selective catalytic oxidation.The crystal structure and physicochemical properties of the catalyst were studied by various characterization methods.The catalytic activity increases with increasing CuO particle size,and complete conversion can be achieved at 300-350℃.The Cu-12 nm catalyst has the highest catalytic activity and can achieve complete conversion at 300℃.The Cu-6 nm sample has the highest N_(2)selectivity at lower temperatures,reaching 95%at 300℃.The activity of the catalysts is determined by the surface CuO cluster species,the bulk CuO species and the chemisorbed surface oxygen species.The high N_(2)selectivity of the catalyst is attributed to the ratio of isolated Cu2+and bulk CuO species,and weak acidity is beneficial to the formation of N_(2).The results in this work will provide a new design of NVOC catalytic oxidation catalysts.

Preparation and characterization of nano-rare earth composite materials:application in selectivity catalytic oxidation of ammonia and its cytotoxicity study

The manufacture,physical characterization,environmental applications and cytotoxicity properties of nanocomposites consisting of CuO/CeO2 nano-rare earth composite materials prepared using the coprecipitation method at molar ratio of 6:4 with aqueous solutions of copper nitrate and cerium nitrate were reported.The performance of the selective catalytic oxidation of ammonia to N2(NH3-SCO) over a CuO/CeO2 nano-rare earth composite materials in a tubular fixed-bed reactor(TFBR) at temperatures from 423 to 673 K in the presence of oxygen was elucidated.The catalytic redox behavior was determined by cyclic voltammetry(CV).The nanocomposite particles were characterized by TEM,with a tiny particle size around 10 nm with high dispersion phenomena.Further,cell cytotoxicity and the percentage cell survival were determined by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetra-zolium(MTS) assay on human lung MRC-5 cell line.Experimental results showed that no apparent cytotoxicity was observed when the MRC-5 was exposed to the CuO/CeO2 nanocomposite materials.

Modulate the superficial structure of La_(2)Ce_(2)O_(7) catalyst with anchoring CuO_(x) species for the selective catalytic oxidation of NH_(3)

Air contamination caused by the ammonia slip phenomenon has gradually captured the researcher’s extensive attention.An effective strategy for controlling fugitive NH_(2)is critical to improving the air quality and living environment.In the present work,CuO_(x)/La_(2)Ce_(2)O_(7)composite as a potential candidate catalyst is synthesized through the electrostatic adsorption method for the selective catalytic oxidation(SCO_(2))of NH_(2)to N.The 5%Cu Ox/La_(2)Ce_(2)O_(7)exhibits the best catalytic activity(T=243℃)and ammonia conversion efficiency.The improvement of performance is mainly attributed to the superficial connection of[Ce-O-Cu],which enhances the capturing ability of ammonia molecule and accelerates the dissociating efficiency of N–H bonding for Nevolution,simultaneously.This work provides a facile method to synthesis pyrochlore-like composite catalyst of NH_(2)-SCO_(2) for solving the problem of ammonia slip pollution in the future.

Physico-Chemical Studies of Platinum-Ruthenium Catalysts of Oxidative Conversion of Methane to Synthesis-Gas

The results of studying the interaction of H2 and O2 with Pt-, Ru- and Pt-Ru catalysts supported on 2% Ce/（θ＋α）-AlEO3, at varying the ratios and concentrations of supported elements by using the temperature-programmed desorption method are presented. It has been shown that HE is adsorbed as four forms, differing in the structure, temperature, order and activation energy of desorption： HEads, HE＋ads, Hads, Hat （Tdes 〉 873 K）. The relationship of activity and selectivity of Pt-Ru catalysts with the presence of active centers able to adsorb atomic hydrogen with desorption energy （Edes） = 60-70 kJ/mol in the catalytic oxidation of methane was determined. It was found that the O2 adsorbed as two forms differing in the structure, temperature and activation energy of desorption. It has been determined that changing the atomic ratio of elements in the catalysts significantly affect on the adsorption Of OE. The introduction of ruthenium into the platinum catalyst increases the oxygen adsorption; and the surface is stabilized in a homogeneous state. Quantum chemical calculations of the activation of C-H bonds in a molecule of methane on Ru,,Pt, （m ＋ n = 4） clusters have been carried out.

Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/y-AI203 to oxidize gaseous ammonia

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-A12O3 catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid （H2PtC16） and rhodium （Ⅲ） nitrate （Rh（NO3）3） with γ-A12O3 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 voltam- metry （CV）. The results demonstrated that at a temperature of 673K and an oxygen content of4%, approximately 99% of the NH3 was removed by catalytic oxidation over the nanosized Pt-Rh/γ-A12O3 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 ofnanosized Pt-Rh/γ-A12O3 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-A12O3 catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.