Influence of preparation methods on the physicochemical properties and catalytic performance of MnO_x-CeO_2 catalysts for NH_3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.

Doping effect of cations(Zr^(4+),Al^(3+),and Si^(4+)) on MnO_x/CeO_2 nano-rod catalyst for NH_3-SCR reaction at low temperature

Thermally stable Zr4+, Al3+, and Si4+ cations were incorporated into the lattice of CeO2 nano‐rods (i.e., CeO2‐NR) in order to improve the specific surface area. The undoped and Zr4+, Al3+, and Si4+ doped nano‐rods were used as supports to prepare MnOx/CeO2‐NR, MnOx/CZ‐NR, MnOx/CA‐NR, and MnOx/CS‐NR catalysts, respectively. The prepared supports and catalysts were comprehensively characterized by transmission electron microscopy (TEM), high‐resolution TEM, X‐ray diffraction, Raman and N2‐physisorption analyses, hydrogen temperature‐programmed reduction, ammonia temperature‐programmed desorption, in situ diffuse reflectance infrared Fourier‐transform spectroscopic analysis of the NH3 adsorption, and X‐ray photoelectron spectroscopy. Moreover, the catalytic performance and H2O+SO2 tolerance of these samples were evaluated through NH3‐selective catalytic reduction (NH3‐SCR) in the absence or presence of H2O and SO2. The obtained results show that the MnOx/CS‐NR catalyst exhibits the highest NOx conversion and the lowest N2O concentration, which result from the largest number of oxygen vacancies and acid sites, the highest Mn4+ content, and the lowest redox ability. The MnOx/CS‐NR catalyst also presents excellent resistance to H2O and SO2. All of these phenomena suggest that Si4+ is the optimal dopant for the MnOx/CeO2‐NR catalyst.

Low-Temperature SCR of NO with NH_3 on Mn-Based Catalysts Modified with Cerium

A series of Mn-based catalysts, MnOx, MnOx-CeO, Pd-Mn-Ce, MnOx/AC were prepared. And their performances for NO low-temperature SCR were investigated in this study. The NO conversion is about 90% at 100 ℃ on MnOx-CeOand almost all NO can be converted at 120 ℃. Similar results are also observed in the tests on MnOx-CeO/AC. The excellent low-temperature catalytic activity of modified Mn-based catalysts, which may be mainly due to the oxygen storage function of CeO, can improve the oxygen flow on the catalysts surface. Then the oxidation of NO to NO2 is accelerated, which is the key step of NO SCR.

Single atom gold catalysts for low-temperature CO oxidation

Low‐temperature CO oxidation is important for both fundamental studies and practical applica‐tions. Supported gold catalysts are generally regarded as the most active catalysts for low‐temperature CO oxidation. The active sites are traditionally believed to be Au nanoclusters or nanoparticles in the size range of 0.5–5 nm. Only in the last few years have single‐atom Au catalysts been proved to be active for CO oxidation. Recent advances in both experimental and theoretical studies on single‐atom Au catalysts unambiguously demonstrated that when dispersed on suitable oxide supports the Au single atoms can be extremely active for CO oxidation. In this mini‐review, recent advances in the development of Au single‐atom catalysts are discussed, with the aim of illus‐trating their unique catalytic features during CO oxidation.

One-pot synthesis of bimetallic CeCu-SAPO-34 for high-efficiency selective catalytic reduction of nitrogen oxides with NH_(3) at low temperature

NH_(3) selective catalytic reduction(SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The Ce Cu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02%(mass) Ce constituent exhibited the best catalytic activity below 300℃ and a maximum NO_(x) conversion of 99% was attained;the NO_(x) removal rates of more than 68% and 94% were achieved at 150℃ and 200℃, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH_(3)-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Br?nsted acid centers and promote the synergistic effect between CuO grains and isolated Cu^(2+) to enhance the redox cycle, which benefit the NH_(3)-SCR reaction.This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.

Ho-modified Mn-Ce/TiO_2 for low-temperature SCR of NO_x with NH_3:Evaluation and characterization

Low‐temperature selective catalytic reduction(SCR)of NO with NH3 was tested over Ho‐doped Mn–Ce/TiO2 catalysts prepared by the impregnation method.The obtained catalysts with different Ho doping ratios were characterized by Brunauer‐Emmett‐Teller(BET),X‐ray diffraction(XRD),temperature‐programmed reduction(H2‐TPR),temperature‐programmed desorption of NH3(NH3‐TPD),X‐ray photoelectron spectroscopy(XPS),and scanning electron microscopy(SEM).The catalytic activities were tested on a fixed bed.Their results indicated that the proper doping amount of Ho could effectively improve the low‐temperature denitrification performance and the SO2 resistance of Mn–Ce/TiO2 catalyst.The catalyst with Ho/Ti of 0.1 presented excellent catalytic activity,with a conversion of more than 90%in the temperature window of 140–220°C.The characterization results showed that the improved SCR activity of the Mn–Ce/TiO2 catalyst caused by Ho doping was due to the increase of the specific surface area,higher concentration of chemisorbed oxygen,higher surface Mn4+/Mn3+ratio,and higher acidity.The SO2 resistance test showed that the deactivating influence of SO2 on the catalyst was irreversible.The XRD and XPS results showed that the main reason for the catalyst deactivation was sulfates that had formed on the catalyst surface and that Ho doping could inhibit the sulfation to some extent.

La-doped Pt/TiO_2 as an efficient catalyst for room temperature oxidation of low concentration HCHO

Catalytic oxidation of formaldehyde (HCHO) is the most efficient way to purify indoor air of HCHO pollutant. This work investigated rare earth La‐doped Pt/TiO2 for low concentration HCHO oxidation at room temperature. La‐doped Pt/TiO2 had a dramatically promoted catalytic performance for HCHO oxidation. The reasons for the La promotion effect were investigated by N2 adsorption, X‐raydiffraction, CO chemisorption, X‐ray photoelectron spectroscopy, transmission electron microscopy(TEM) and high‐angle annular dark field scanning TEM. The Pt nanoparticle size was reduced to 1.7nm from 2.2 nm after modification by La, which led to higher Pt dispersion, more exposed activesites and enhanced metal‐support interaction. Thus a superior activity for indoor low concentrationHCHO oxidation was obtained. Moreover, the La‐doped TiO2 can be wash‐coated on a cordieritemonolith so that very low amounts of Pt (0.01 wt%) can be used. The catalyst was evaluated in asimulated indoor HCHO elimination environment and displayed high purifying efficiency and stability.It can be potentially used as a commercial catalyst for indoor HCHO elimination.

Mechanism explanation for SO_2 oxidation rate of Cs-Rb-V series sulfuric acid catalyst at low temperature

The reaction kinetics of SO 2 oxidation on Cs Rb V series sulfuric acid catalyst promoted by alkali salts such as cesium and rubidium was studied. A three step reaction mechanism of SO 2 oxidation was proposed, in which it was assumed that oxidation of quadrivalent vanadium complex was a controlling step. Then, a mechanism model equation was concluded according to the three step reaction mechanism. The SO 2 oxidation rate was measured with a non gradient reactor under the conditions of temperature of 380～520?℃ and space velocity of 3?600～7?200?h -1 . Through calculating with Powell nonlinear regression method, the parameters of model equation were obtained: K 1=0.152?exp(-62?073/ (RT) ), K 2=8.18?exp(-2?384/ (RT) ), K 3=0.221?exp(-18?949/ (RT) ). It was found that the model equation could fit with all the experimental reaction rate data very well. [

Influence of chromium modification on the properties of MnO_x-FeO_x catalysts for the low-temperature selective catalytic reduction of NO by NH_3

Catalytic properties of MnOx-FeOx complex oxide （hereafter denoted as Mn-Fe） catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-cbemical techniques, such as N2 physisorption, X-ray diffraction （XRD）, high-resolution transmission electron microscope （HRTEM）, in situ Fourier transform infrared spectroscopy （in situ FT-IR） and temperature-programmed reduction （TPR） and their catalytic activities were evaluated with the selective catalytic reduction （SCR） of NOx by NH3. It was found that with the addition of Cr, more NO could be removed in the low-temperature window （below 120 ℃）. Among the tested catalysts, Mn-Fe- Cr （2 ： 2 ： 1） catalyst exhibited the best catalytic performance at 80 ℃ with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that （1） the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; （2） Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate （-NH3＋）, which favored the low-temperature SCR reaction.

A comparative study of CuO/TiO_2-SnO_2,CuO/TiO_2 and CuO/SnO_2 catalysts for low-temperature CO oxidation

Nanometer SnO2 particles were synthesized by sol-gel dialytic processes and used as a support to prepare CuO supported catalysts via a deposition-precipitation method. The samples were characterized by means of TG-DTA, XRD, H2-TPR and XPS. The catalytic activity of the CuO/TiO2-SnO2 catalysts was markedly depended on the loading of CuO, and the optimum CuO loading was 8 wt.% （Tloo = 80 ℃）. The CuO/TiO2-SnO2 catalysts exhibited much higher catalytic activity than the CuO/TiO2 and CuO/SnO2 catalysts. H2-TPR result indicated that a large amount of CuO formed the active site for CO oxidation in 8 wt.% CuO/TiO2-SnO2 catalyst.

TiO_2-Supported Binary Metal Oxide Catalysts for Low-temperature Selective Catalytic Reduction of NO_x with NH_3

Binary metal oxide（MnOx-A/TiO2）catalysts were prepared by adding the second metal to manganese oxides supported on titanium dioxide（TiO2）,where,A indicates Fe2O3,WO3,MoO3,and Cr2O3.Their catalytic activity,N2 selectivity,and SO2 poisonous tolerance were investigated.The catalytic performance at low temperatures decreased in the following order：Mn-W/TiO2〉Mn-Fe/TiO2〉Mn-Cr/TiO2〉Mn-Mo/TiO2,whereas the N2 selectivity decreased in the order：Mn-Fe/TiO2〉Mn-W/TiO2〉Mn-Mo/TiO2〉Mn-Cr/TiO2.In the presence of 0.01%SO2 and 6%H2O,the NOx conversions in the presence of Mn-W/TiO2,Mn-Fe/TiO2,or Mn-Mo/TiO2 maintain 98.5%,95.8%and 94.2%, respectively,after 8 h at 120°C at GHSV 12600 h？ 1 .As effective promoters,WO3 and Fe2O3 can increase N2 selectivity and the resistance to SO2 of MnOx/TiO2 significantly.The Fourier transform infrared（FTIR）spectra of NH3 over WO3 show the presence of Lewis acid sites.The results suggest that WO3 is the best promoter of MnOx/TiO2,and Mn-W/TiO2 is one of the most active catalysts for the low temperature selective catalytic reduction of NO with NH3.

Low CO content hydrogen production from oxidative steam reforming of ethanol over CuO-CeO_2 catalysts at low-temperature

CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature.The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy,X-ray diffraction,temperature-programmed reduction,field emission scanning electron microscopy and thermo-gravimetric analysis.Over CuOCeO2 catalysts,H2 with low CO content was produced in the whole tested temperature range of 250–450 C.The non-noble metal catalyst 20CuCe showed higher H2production rate than 1%Rh/CeO2 catalyst at 300–400 C and the advantage was more obvious after 20 h testing at400 C.These results further confirmed that CuO-CeO2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.

Bifunctionality of Cu/ZnO catalysts for alcohol-assisted low-temperature methanol synthesis from syngas:Effect of copper content

Alcohol-assisted low-temperature methanol synthesis was conducted over Cu/ZnO;catalysts while varying the copper content（X）. Unlike conventional methanol synthesis, ethanol acted as both solvent and reaction intermediate in this reaction, creating a different reaction pathway. The formation of crystalline phases and characteristic morphology of the co-precipitated precursors during the co-precipitation step were important factors in obtaining an efficient Cu/ZnO catalyst with a high dispersion of metallic copper,which is one of the main active sites for methanol synthesis. The acidic properties of the Cu/ZnO catalyst were also revealed as important factors, since alcohol esterification is considered the rate-limiting step in alcohol-assisted low-temperature methanol synthesis. As a consequence, bifunctionality of the Cu/ZnO catalyst such as metallic copper and acidic properties was required for this reaction. In this respect, the copper content（X） strongly affected the catalytic activity of the Cu/ZnO;catalysts, and accordingly, the Cu/ZnO;.5 catalyst with a high copper dispersion and sufficient acid sites exhibited the best catalytic performance in this reaction.

The Preparation of Mn-Fe/CNTs Catalyst at the Low-Temperature Selective Catalytic Reduction of NO with NH₃

The metal oxide catalyst was prepared by loading MnOx and FeOx on carbon nano-tubes (CNTs) with impregnation method. Then the catalyst was characterized by BET and XPS, and the effect of adding FeOx on MnOx/CNTs catalyst at the low-temperature selective catalytic reduction of NO with NH3 was investigated. The results showed that the active components were loaded suc-cessfully and easily on the carriers by impregnation. The Mn-Fe/CNTs catalyst was chose 10% Fe(NO3)3 solution to impregnate Mn-Fe/CNTs. The species of active components loaded on the catalyst were Fe2O3. The different concentration of impregnant solution played an important role for NO conversion in SCR with NH3. With the increase of the concentration of impregnant solution, the NO conversion of catalysts was increasing initially then decreasing.

Direct decomposition of nitric oxide in low temperature over iron-based perovskite-type catalyst modified by Ru

Iron-based perovskite-type compounds modified by Ru were prepared through sol-gel process to study its catalytic activity of NOx direct decomposition at low temperature and evaluate the conversion of NO under the experimental conditions. The catalytic activity of La 0.9Ce 0.1Fe 0.8-nCo 0.2RunO3 （n=0.01,0.03,0.05,0.07,0.09）series for the NO, NO-CO two components, CO-HC-NO three components were also analyzed. The catalytic investigation evidenced that the presence of Ru is necessary for making highly activity in decomposition of nitric oxide even at low temperature（400 ℃）and La 0.9Ce 0.9Fe 0.75Co 0.2Ru 0.05O3 （n=0.05） has better activity in all the samples, the conversion of it is 58.5%. With the reducing gas（CO,C3H6）added into the gas, the catalyst displayed very high activity in decomposition of NO and the conversion of it is 80% and 92.5% separately.

No-catalyst growth of vertically-aligned AlN nanocone field electron emitter arrays with high emission performance at low temperature

The A1N nanostructures with a wide band-gap of 6.28 eV are considered as ideal cold cathode materials because of their low electron-affinity. Many methods have been devoted to fabricating A1N nanostructures, but high growth temperature over 800℃ and the use of the catalysts in most methods limit their practical application and result in their poor field-emission behaviours in uniformity. This paper reports that without any catalysts, a simple chemical vapour deposition method is used to synthesize aligned A1N nanocone arrays at 550℃ on silicon substrate or indium tin oxide glass. Field emission measurements show that these nanocones prepared at low temperature have an average turn-on field of 6 V/μm and a threshold field of 11.7 V/μm as well as stable emission behaviours at high field, which suggests that they have promising applications in field emission area.

Distinct effect of preparation methods on reaction efficiency of Mn-Ce/Al_(2)O_(3) catalysts in low-temperature NH_(3)-SCR

In this study,a series of Mn-Ce/Al_(2)O_(3) catalysts was prepared by different methods of depositionprecipitation(MnCeAl-DP),impregnation(MnCeAl-IM) and citric acid(MnCeAl-CA),and the distinct effect of preparation methods on NO_(x) removal performance at low temperature was explored.Results show that MnCeAl-DP exhibits not only the best activity but also the highest resistance against SO_(2)/H_(2)O.With the assistance of comprehensive characterizations from scanning electron microscopy(SEM),Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),H_(2)-temperature programmed reduction(H_(2)-TPR),NH_(3)-te mperature programmed deso rption(NH_(3)-TPD),and X-ray photoelectron spectroscopy(XPS),it is revealed that the MnCeAl-DP sample owns admired features of large surface area and pore volume,enriched Mn^(4+) and chemisorbed oxygen species originating from enhanced interaction between MnO_x and CeO_(2),as well as improved adsorption capacity to NH_(3) and NO.All these factors contribute to activity enhancement.Further in-situ DRIFTS studies reveal that the improvement of NH_(3)-SCR performance over MnCeAI-DP is related to the formation of abundant nitrate species,which is beneficial to the "NH_(4)NO_(3)" reaction pathway and thus enhances low-temperature activity.

Gold Catalysts Supported on Crystalline Fe_2O_3 and CeO_2/Fe_2O_3 for Low-temperature CO Oxidation

High active and stable gold catalysts supported on crystalline Fe203 and CeO2/Fe2O3 were prepared via the deposition-precipitation method. The catalyst with a Au load of 1.0% calcined at 180 ℃ showed a CO conversion of 100% at -8.9℃, while Au/CeO2/Fe2O3 converted CO completely at -16.1 ℃. Even having been calcined at 500 ℃, Au/Fe2O3 still exhibited significant catalytic activity, achieving full conversion of CO at 61.6℃. The catalyst with a low Au load of 0.5% could convert CO completely at room temperature and kept the activity unchanged for at least 150 h. N2 adsorption-desorption measurements show that the crystalline supports possessed a high specific surface area of about 200 m2/g. Characterizations of X-ray diffraction and transmission electron microscopy indicate that gold species were highly dispersed as nano or sub-nano particles on the supports. Even after the catalyst was calcined at 500 ℃, the Au particles remained in a nano-size of about 6--10 nm. X-ray photoelectron spectra reveal that the supported Au existed in metallic state Au0. The modification of Au/Fe2O3 by CeO2 proved to be beneficial to the inhibition of crystallization of Fe2O3 and the stabilization of gold particles in dispersed state, consequently promoting catalytic activity.

Applications of Enzyme-simulating Copper Complex Catalyst in Low-temperature Scouring/Bleaching of Cotton Knits

An enzyme-stimulating catalyst( PTL) with copper ions( Cu^(2+)) as the activation center and aminophosphonate as ligand was developed and applied in low-temperature scouring/bleaching of cotton knits. The optimal weight ratio of Cu^(2+) to aminophosphonate was 1 ∶75. Via orthodox and single-factor experiments,the most efficient formula for low-temperature scouring/bleaching was composed of 0. 4 g/L high-efficiency degreaser DM-1130,1. 5 g/L PTL,2. 0 g/L sodium hydroxide( NaOH),and 7. 0 g/L 30% hydrogen peroxide( H_2O_2). The PTL could not only increase the whiteness of cotton knits,but also remove pectin to enhance capillary effect.

Mn/TiO_(2)低温SCR催化剂钾中毒机理研究

Mn/TiO_(2)具有良好的低温NH3选择性催化还原NOx(SCR)的活性。烟气中存在的碱金属会从物理和化学上毒害催化剂导致Mn/TiO_(2)催化剂中毒失活。论文以暴露{101}面TiO_(2)为载体制备Mn/TiO_(2)催化剂,采用浸渍法制备K中毒催化剂,研究了Mn/TiO_(2)低温SCR催化剂钾中毒机理。实验发现,Mn/TiO_(2)催化剂脱硝效率随K中毒浓度增加而减少;新鲜Mn/TiO_(2)催化剂表面NH3-SCR反应由E-R和L-H机理共同控制;K吸附会导致催化剂比表面积降低,催化剂表面Mn4+、化学吸附氧比例降低,表面酸性位点数量减少,导致脱硝活性降低;同时K更易吸附在Mn顶位以及桥接O位附近,导致NO的吸附活化受到严重遏制,同时削弱NH3的吸附,使得L-H机理受到阻断,只能以E-R机理控制为主。