Simultaneous removal of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and SO<Subscript>2</Subscript> by low-temperature selective catalytic reduction over modified activated carbon catalysts

A series of modified porous activated carbon (AC) catalysts prepared by impregnation were investigated for the low-temperature (≤250°C) selective catalytic reduction (SCR) of NO _x with NH₃ with simultaneous removal of SO₂. The effects of various preparation conditions and reaction conditions on NO and SO₂ conversions were observed, such as support type, active components, copper loading, calcination temperature and presence of H₂O and O₂. The modified AC catalysts were characterized by BET, XRD, TG and TPX methods. The activity test results showed that the optimal catalyst is 15% Cu/WCSAC which can provide 52% NO conversion and 68% SO₂ conversion simultaneously at 175°C with a space velocity of 30000 h^?1, and the optimal calcination temperature was 500°C. The presence of H₂O could inhibit NO conversion and promote the SO₂ conversion. The effect of O₂ (0–5%) was evaluated, and the NO and SO₂ conversions were best when the concentration of O₂ was 3%. Research demonstrated that Cu/WCSAC catalyst was a kind of potential catalysts due to the amorphous phase, high specific areas and high active ability.     

Effect of SO<Subscript>2</Subscript> on chlorination of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> mixtures

The reaction of Bi₂O₃ + Fe₂O₃ mixtures with chlorine and SO₂ at 250–700°C is studied. At 300–500°C, the degree of bismuth chloride sublimation from the oxide mixture increases in the presence of SO₂. Chemical sublimation of FeCl₃ occurs after BiCl₃ is virtually completely recovered from the solid phase.     

Study of Fe-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalyst for an enhanced NH<Subscript>3</Subscript>-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NO_X. Novel Fe-doped V₂O₅/TiO₂ catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NO_X conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H₂-TPR, NH₃-TPD) techniques showed that the iron existed in the form of Fe³⁺ and Fe²⁺ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO₂ and H₂O.     

Use of the differential charging effect in XPS to determine the nature of surface compounds resulting from the interaction of a Pt/(BaCO<Subscript>3</Subscript> + CeO<Subscript>2</Subscript>) model catalyst with SO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Changes in the chemical composition of the surface of a Pt/(BaCO₃ + CeO₂) model NO _x storage-reduction catalyst upon its interaction with SO _x (SO₂ (260 Pa) + O₂ (2600 Pa) + H₂O (525 Pa)) followed by regeneration in a mixture of CO (2100 Pa) with H₂O (525 Pa) were studied by X-ray photoelectron spectroscopy (XPS). Model catalyst samples were prepared as a thin film (about several hundreds of angstrom units in thickness) on the surface of tantalum foil coated with a layer of aluminum oxide (～100 Å). It was found that the Pt/BaCO₃ and Pt/CeO₂ catalyst constituents acquired different surface charges (differential charging) in the course of photoelectron emission; because of this, it was possible to determine the nature of surface compounds formed as a result of the interaction of the catalyst with a reaction atmosphere. It was found that barium carbonate was converted into barium sulfate as a result of reaction with SO _x on the surface of BaCO₃ at 150°C. As the treatment temperature in SO _x was increased to 300°C, the formation of sulfate on the surface of CeO₂ was observed. The sulfatization of CeO₂ was accompanied by the reduction of Ce(IV) to Ce(III). The regeneration reaction of the catalyst treated in SO _x at 300°C resulted in the consecutive decomposition of cerium(III) sulfate at ≤500°C and then barium sulfate at 600–700°C. Upon the decomposition of BaSO₄, a portion of sulfur was converted into a sulfide state, probably, because of the formation of BaS.     

Effect of Calcination Temperature on the Structure and Catalytic Properties of MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Ca<Subscript>2</Subscript>O<Subscript>3</Subscript> in the Reaction of CO and Ethane Oxidation

Effect of the calcination temperature of the MnOx/Ga2O3 system on its structural and catalytic properties in the reaction of oxidation of CO and hydrocarbons. The dependences of the catalytic activity of MnO _x /Ga₂O₃ in the reactions of CO and ethane oxidation on the calcination temperature exhibit an extremal behavior. The maximum values of activity are observed upon calcination of the system at 700°C, i.e., at the temperature that is limiting for the existence of a solid solution of manganese ions in γ-Ga₂O₃. The structural changes occurring with increasing calcination temperature are accompanied by a substantial decrease in the specific surface area of a sample. The observed rise in the specific catalytic activity (by a factor of ~7 upon an increase in the preliminary-calcination temperature from 600 to 800°C) confirms that the thermal activation effect exists for the given system.     

Perovskite LaMnO<Subscript>3</Subscript>/ZSM-5 composites for H<Subscript>2</Subscript>S reactive adsorption at high temperature

Perovskite LaMnO₃/ZSM-5 was used for reactive adsorption of hydrogen sulfide at 500–700 °C. The sorbents showed good desulphurization performance, the highest sulfur capacity of 1020 µmol S/g over 5La5Mn/ZSM-5 was obtained at 600 °C. The reducing gases (H₂ and CO) can obviously shorten the breakthrough time and reduce the sulfur capacity. Incorporating Mn ions into La₂O₃ lattice improved the sulfidation activity due to the formation of perovskite LaMnO₃ with good reducibility and structure stability.     

Performance and characterisation of CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>-WO<Subscript>3</Subscript> catalysts for selective catalytic reduction of NO with NH<Subscript>3</Subscript>

Ce-Ti-W-O _x catalysts were prepared and applied to the NH₃-selective catalytic reduction (SCR) reaction. The experimental results showed that the Ce-Ti-W-O _x catalyst prepared by the hydrothermal method exhibited higher NO conversion than those synthesised via the sol-gel and impregnating methods, while the optimal content of WO₃ and molar ratio of Ce/Ti were 20 mass % and 4: 6, respectively. Under these conditions, the catalyst exhibited the highest level of catalytic activity (the NO conversion reached values higher than 90 %) across a wide temperature range of 225–450°C, with a range of gas hourly space velocity (GHSV) of 40000–140000 h^?1. The catalyst also exhibited good resistance to H₂O and SO₂. The influences of morphology, phase structure, and surface properties on the catalytic performance were investigated by N₂ adsorption-desorption measurement, XRD, XPS, H₂-TPR, and SEM. It was found that the high efficiency of NO removal was due to the large BET surface area, the amorphous surface species, the change to element valence states, and the strong interaction between Ce, Ti, and W.     

Selective Catalytic Reduction of NO by NH<Subscript>3</Subscript> over MoO<Subscript>3</Subscript> Promoted Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

A series of MoO₃ doped Fe₂O₃ catalysts prepared by the co-precipitation method were investigated in the selective catalytic reduction of NO by NH₃ (NH₃-SCR). The catalysts displayed excellent catalytic activity from 225 to 400°C and high tolerance to SO₂/H₂O poisoning at 300°C. To characterize the catalysts the N₂-BET, XRD, Raman, NO-TPD, NH₃-TPD and in situ DRIFTS were carried out. It was found that the main reason explaining a high NH₃-SCR performance might be the synergistic effect between Fe and Mo species in the catalyst that could enhance the dispersion of Fe₂O₃ and increase NH₃ adsorption on the catalyst surface.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

K<Subscript>2</Subscript>SO<Subscript>4</Subscript>-KCl-H<Subscript>2</Subscript>O phase diagram in the area of heterogenization of homogeneous supercritical fluids

The experimental investigations of phase equilibria in the K₂SO₄-KCl-H₂O system at temperatures to 500°C and pressures to 100 MPa were directed to elucidate the phase transformation sequence that leads to the heterogenization of the supercritical fluid whose existence field propagates from the K₂SO₄-H₂O binary subsystem to the ternary system. We suggest that fluid heterogenization in the title ternary system is accompanied by the transformation of the metastable immiscibility field to stable equilibria at elevated temperatures (near 460°C) and unexpectedly high pressures (～60 MPa), despite the presence of a vapor phase.     

The mechanism of reduction of NO with H<Subscript>2</Subscript> in strongly oxidizing conditions (H<Subscript>2</Subscript>-SCR) on a novel Pt/MgO-CeO<Subscript>2</Subscript> catalyst: Effects of reaction temperature

Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments using on-line Mass Spectrometry (MS) and in situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS) have been performed to study essential mechanistic aspects of the Selective Catalytic Reduction of NO by H₂ under strongly oxidizing conditions (H₂-SCR) in the 120–300°C range over a novel 0.1 wt % Pt/MgO-CeO₂ catalyst. The N-path of reaction from NO to the N₂ gas product was probed by following the ¹⁴NO/H₂O₂ → ¹⁵NO/H₂/O₂ switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathway of reaction involves the formation of two active NO _x species different in structure, one present on MgO and the other one on the CeO₂ support surface. Inactive adsorbed NO _x species were also found on both the MgO-CeO₂ support and the Pt metal surfaces. The concentration (mol/g cat) of active NO _x leading to N₂ was found to change only slightly with reaction temperature in the 120–300°C range. This leads to the conclusion that other intrinsic kinetic reasons are responsible for the volcano-type conversion of NO versus the reaction temperature profile observed.     

V2O5/赤铁矿催化剂结构及其NH3选择性催化还原NOx性能

以水热合成针铁矿为前驱体浸渍偏钒酸铵,分别于300,400和500℃空气中焙烧,制备了不同活性组分负载量的V₂O₅/赤铁矿（V/H）催化剂,用于氨选择性催化还原（SCR）脱硝。采用X射线衍射、透射电子显微镜、比表面积分析仪、程序升温还原及程序升温脱附等方法对催化剂结构进行了表征,并用标气配制模拟烟气进行了脱硝实验。结果表明,300℃煅烧3%V/H催化剂当烟气温度为250-300℃时NO转化率均可达95%以上;当配气中单独加入水蒸气或低浓度SO₂（0.01%）时,V/H催化脱硝的活性不受影响;当系统加入高浓度的SO₂（0.03%与0.05%）或同时添加H₂O与SO₂时,SCR脱硝效率下降,其机制可能是SO₂在催化剂表面竞争吸附所致,停止添加后,催化活性迅速恢复。     

Thermoanalytical study of precursors for In<Subscript>2</Subscript>S<Subscript>3</Subscript> thin films deposited by spray pyrolysis

Thermal decomposition of precursors for In₂S₃ thin films obtained by drying aqueous solutions of InCl₃ and SC(NH₂)₂ at the In:S molar ratios of 1:3 (1) and 1:6 (2) was monitored by simultaneous TG/DTA/EGA-FTIR measurements in the dynamic 80%Ar + 20%O₂ atmosphere. XRD and FTIR were used to identify the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are complex compounds, while in 2 free SC(NH₂)₂ is also present. The thermal degradation of 1 and 2 in the temperature range of 30–900 °C consists of four mass loss steps, the total mass loss being 89.1 and 78.5%, respectively. According to XRD, In₂S₃ is formed below 300 °C, crystalline In_2.24(NCN)₃ is detected only in 1 above 520 °C and In₂O₃ is the final decomposition product at 900 °C. The gaseous species evolved include CS₂, NH₃, H₂NCN, HNCS, which upon oxidation yield also COS, SO₂, HCN and CO₂.     

The effect of platinum on the SnO<Subscript>2</Subscript> sorption properties

Chemisorption of SO₂ and O₂ at Pt-modified SnO₂ is studied by using the vacuum static method, with simultaneous recording of electrical conductivity, over the 22 to 300°C temperature range. The SnO₂ surface modification results in the increasing of SO₂ adsorption and weakening of the gas-surface bonding. The chemisorption enhances the samples’ electrical conductivity. The surface pretreatment with oxygen leads to the decreasing of the successive SO₂ chemisorption.     

Activity enhancement of acetate precursor prepared on MnO_x-CeO_2 catalyst for low-temperature NH_3-SCR: Effect of gaseous acetone addition

MnO_x-CeO_2 catalysts are developed by hydrolysis driving redox method using acetate precursor(3 Mn1 Ce-Ac) and nitrate precursor(3 Mn1 Ce-N) for the selective catalytic reduction(SCR) of NO_x by NH_3.A counterpart sample(Cop-3 Mn1 Ce) was prepared by the NH_3·H_2 O co-precipitation method for comparison purpose.Combining the results of physicochemical properties characterization and performance test,we find that the 3 Mn1 Ce-Ac catalyst with some nanorod structures is highly active for the deNOx process.The SCR activity of the 3 Mn1 Ce-Ac catalyst is more admirable than the 3 Mn1 Ce-N and the Cop-3 Mn1 Ce catalysts due to plentiful Lewis acid sites,excellent low-temperature reducibility,and superior surface area resulted from O_2 generation during the pre paration procedure.The 3 Mn1 Ce-Ac still exhibits the greatest performance for the deNOx process when gaseous acetone is in the SCR feed gas.The NO_x conversion and N_2 selectivity over the 3 Mn1 Ce-Ac are both improved by gaseous acetone above150℃ due to the inhibition of SCR undesired side reactions(NSCR C-O reactions) and "slow-SCR" process.     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Ho改性的Mn-Ce/TiO2催化剂低温脱硝性能的评价和表征

作为引起酸雨、光化学烟雾、雾霾等大气污染问题的主要根源,氮氧化物(NOx)的防治已成为亟待解决的问题.选择性催化还原技术作为最成熟有效的脱硝技术,目前已经被广泛应用于各燃煤电厂.低温脱硝催化剂具有优秀的低温活性,使得脱硝装置可以安放在脱硫装置和除尘装置下游,受到了学者广泛的研究.目前低温脱硝催化剂的研究主要是对催化剂进行改性以提高催化剂的性能,已有许多研究报道了Sn、Ni、Co、Zr、Cr、Ni等对催化剂的改性影响.Ho作为一种改性元素被应用于光催化领域,能提高TiO2的光催化能力.但Ho应用于脱硝领域的研究鲜有报道,其氧化物具有酸性位点有助于脱硝反应,因此研究Ho对低温SCR催化剂的改性作用具有重要意义.本文采用浸渍法制备Ho掺杂的Mn-Ce/TiO2催化剂,研究了Ho的掺杂对于Mn-Ce/TiO2催化剂低温脱硝性能的影响,同时还研究了烟气中的SO2和H2O对催化剂活性的影响,并利用XPS、XRD、H2-TPR、NH3-TPD等表征方法从物理性质和化学性质两方面对Ho改性的影响机理进行了研究.研究发现,Ho的掺杂能提高Mn-Ce/TiO2催化剂的脱硝能力,有助于催化剂N2选择性的提高.分析表明,Ho的掺杂有助于催化剂比表面积的提升,且能提高催化剂的酸性,有利于催化剂对NH3的吸附,从而提高催化剂的性能.XPS表征结果表明Ho掺杂后的催化剂具有更高的化学吸附氧浓度和较高的Mn4+/Mn3+比例, 使得脱硝反应更容易进行.改性后催化剂的抗水抗硫实验结果表明,Ho的掺杂能够提高催化剂的抗水抗硫性能.XRD结果表明,抗水抗硫实验后催化剂表面形成了硫酸铵盐,硫酸铵盐的形成会堵塞催化剂表面的活性位,限制脱硝反应的进行,从而影响催化剂的脱硝活性.同时,400°C下进行再生实验后的催化剂活性有所恢复,但是未能达到抗水抗硫实验前的活性,表明在抗水抗硫实验中催化剂表面形成了除硫酸铵盐以外的其他硫酸盐类.结合XPS和XRD表征结果,推断生成的盐类物质为硫酸锰和硫酸铈,从而导致再生后的催化剂的脱硝活性无法恢复到最初的活性水平.由此可以看出,硫酸盐的形成是催化剂在含硫气氛中失活的主要原因.     

Characteristics of Ag/Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/p-Si heterostructure prepared by sol-gel processing

The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi_3.25La_0.75Ti₃O₁₂ (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10⁻⁸ A/cm² within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.     

Synthesis of nanocrystalline ZnO by the thermal decomposition of [Zn(H<Subscript>2</Subscript>O)(O<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>7</Subscript>)<Subscript>2</Subscript>] in isoamyl alcohol

It was studied how the conditions of heat treatment of a [Zn(H₂O)(O₂C₅H₇)₂] solution in isoamyl alcohol at 120–140°C for 2–60 min affect the precursor decomposition mechanism and the characteristics of the obtained nanocrystalline zinc oxide. In all the cases, the product was a crystalline substance with the wurtzite structure and a size of crystallites of 14–18 nm, which was independent of the synthesis conditions. The thermal behavior and microstructure of the separated and dried nanostructured ZnO powder were investigated. It was determined how the duration and temperature of the heat treatment of the precursor solution affects the microstructure of ZnO coatings dip-coated onto glass substrates using dispersions produced at 120 and 140°C. The nanosized ZnO application procedure was shown to be promising for creating a gas-sensing layer of chemical gas sensors for detecting 1% H₂ (\(R_0 /R_{H_2 } \) was 58 ± 2 at an operating temperature of 300°C) and 4 ppm NO₂ (\(R_{NO_2 } /R_0\) were 15 ± 1 and 1.9 ± 0.1 at operating temperatures of 200 and 300°C, respectively).     

LiF-LiCl-LiVO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>-Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript> system

Phase equilibria in the LiF-LiCl-LiVO₃-Li₂SO₄-Li₂MoO₄ system have been studied by differential thermal analysis. The eutectic composition has been determined as follows (mol %): LiF, 17.4; LiCl, 42.0; LiVO₃, 17.4; Li₂SO₄, 11.6; and Li₂MoO₄, 11.6, with the melting temperature equal to 363°C and the enthalpy of melting equal to (284 ± 7) kJ/kg.