Numerical Analysis on the Characteristics of Soot Particles in C2H4/CO2/O2/N2 Combustion

The purpose of this study is to investigate the characteristics of soot particles in C₂H₄/CO₂/O₂/N₂ combustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO₂/O₂/N₂ mixture, the key species C₂H₂, C₃H₃ responsible for formation of first aromatic ring, the typical aromatics and 4-ring aromatics total production rate all decrease greatly. In addition, with CO₂ mole fraction from 0.2 to 0.5 in the mixture, the soot particle number density, volume fraction, surface area density, which are three most important parameters to soot particle property, are suppressed obviously. Furthermore, the increasing content of CO₂ in the oxidizer influences mostly H, OH radical concentrations by two reactions: CO+OH=CO₂ H and H+O₂=O+OH, and the production rate of H, OH from the two reactions declined, which revealed that CO₂ in mixture has an inhibiting effect on soot particle generation.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

Potassium–copper and potassium–cobalt catalysts supported on alumina for simultaneous NOx and soot removal from simulated diesel engine exhaust

This paper deals with the activity of bimetallic potassium–copper and potassium–cobalt catalysts supported on alumina for the reduction of NO_x with soot from simulated diesel engine exhaust. The effect of the reaction temperature, the soot/catalyst mass ratio and the presence of C₃H₆ has been studied. In addition, the behavior of two monometallic catalysts supported on zeolite beta (Co/beta and Cu/beta), previously used for NO_x reduction with C₃H₆, as well as a highly active HC-SCR catalyst (Pt/beta) has been tested for comparison. The preliminary results obtained in the absence of C₃H₆ indicate that, at temperatures between 250 and 400 °C, the use of bimetallic potassium catalysts notably increases the rate of NO_x reduction with soot evolving N₂ and CO₂ as main reaction products. At higher temperatures, the catalysts mainly favor the direct soot combustion with oxygen. In the presence of C₃H₆, an increase in the activity for NO_x reduction has been observed for the catalyst with the highest metal content. At 450 °C, the copper-based catalysts (Cu/beta and KCu2/Al₂O₃) show the highest activity for both NO_x reduction (to N₂ and CO₂) and soot consumption. The Pt/beta catalyst does not combine, at any temperature, a high NO_x reduction with a high soot consumption rate.     

不同氧浓度下煤挥发分燃烧的化学动力学研究

燃煤有机污染物对人类健康和生态环境存在严重危害,而O₂对火焰中有机产物的形成具有明显的调控作用。鉴于煤挥发分燃烧是燃煤过程中至关重要的一环,本文以煤热解气为燃料,通过数值模拟研究了氧化剂侧O₂浓度对对冲扩散火焰中碳氢产物生成特性和机制的影响。结果表明,O₂浓度升高促进了O和OH的生成,进而提高H浓度,突显了含H和OH参与的反应的重要性。此外,乙炔(C₂H₂)、丙炔(PC₃H₄)、炔丙基(C₃H₃)、乙烯基乙炔(C₄H₄)、苯(C₆H₆)和萘(C₁₀H₈)的浓度均增大。增加O₂浓度促进了C₂H₂向PC₃H₄的转化,并使得C₃H₃更倾向于转化为丁二烯(C₄H₆),而富烯更倾向于通过苯基(C₆H₅)生成C₆H₆,因此C₆H₅作为C₆H₆前体的地位被加强。     

不同氧浓度下煤挥发分燃烧的化学动力学研究

燃煤有机污染物对人类健康和生态环境存在严重危害,而O₂对火焰中有机产物的形成具有明显的调控作用。鉴于煤挥发分燃烧是燃煤过程中至关重要的一环,本文以煤热解气为燃料,通过数值模拟研究了氧化剂侧O₂浓度对对冲扩散火焰中碳氢产物生成特性和机制的影响。结果表明,O₂浓度升高促进了O和OH的生成,进而提高H浓度,突显了含H和OH参与的反应的重要性。此外,乙炔(C₂H₂)、丙炔(PC₃H₄)、炔丙基(C₃H₃)、乙烯基乙炔(C₄H₄)、苯(C₆H₆)和萘(C₁₀H₈)的浓度均增大。增加O₂浓度促进了C₂H₂向PC₃H₄的转化,并使得C₃H₃更倾向于转化为丁二烯(C₄H₆),而富烯更倾向于通过苯基(C₆H₅)生成C₆H₆,因此C₆H₅作为C₆H₆前体的地位被加强。     

Catalytic reduction of NO by propene over LaCo1−xCuxO3 perovskites synthesized by reactive grinding

One series of LaCo_1−xCu_xO₃ perovskites with high specific surface area was prepared by the new method designated as reactive grinding. These solids were characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H₂-temperature programmed reduction (TPR), O₂-temperature programmed desorption (TPD), NO + O₂-TPD, C₃H₆-TPD, NO + O₂-temperature programmed surface reaction (TPSR) under C₃H₆/He flow as well as catalytic reduction of NO activity tests. The catalytic performance of unsubstituted sample is poor with a maximum conversion to N₂ of 19% at 500 °C at a space velocity of 55,000 h⁻¹ (3000 ppm NO, 3000 ppm C₃H₆, 1% O₂ in helium) but it is improved by incorporation of Cu into the lattice. A maximal N₂ yield of 46% was observed over LaCo_0.8Cu_0.2O₃ under the same conditions. Not only the abundance of -oxygen but also the mobility of β-oxygen of lanthanum cobaltite was remarkably enhanced by Cu substitution according to O₂-TPD and H₂-TPR studies. The better performance of Cu-substituted samples is likely to correspond to the essential nature of Cu and facility to form nitrate species in NO transformation conditions. In the absence of O₂, the reduction of NO by C₃H₆ was performed over LaCo_0.8Cu_0.2O₃, leading to a maximal conversion to N₂ of 73% accompanied with the appearance of some organo nitrogen compounds (identified as mainly C₃H₇NO₂). Subsequently, a mechanism involving the formation of an organic nitro intermediate, which further converts into N₂, CO₂ and H₂O via isocyanate, was proposed. Gaseous oxygen acts rather as an inhibitor in the reaction of NO and C₃H₆ over highly oxidative LaCo_0.8Cu_0.2O₃ due to the heavily unselective combustion of C₃H₆ by O₂.     

C2H6/C3H8影响CH4爆炸极限参数及动力学特性研究

为研究C₂H₆/C₃H₈对甲烷爆炸极限参数及动力学特性的影响,采用标准的可燃气体爆炸极限测定装置测定了不同配比的C₂H₆/C₃H₈混合气体对甲烷爆炸极限的影响规律,同时得出了氮气惰化条件下甲烷爆炸临界参数的变化规律。此外,利用Chemkin软件模拟了C₂H₆/C₃H₈混合气体对甲烷爆炸过程中中间产物浓度的影响情况,并进行了敏感性分析。结果表明,C₂H₆/C₃H₈的存在降低了甲烷的爆炸上下限,增大了甲烷的爆炸危险度;在氮气惰化过程中甲烷的爆炸上限下降,爆炸下限上升,最终爆炸上下限重合,重合点处甲烷浓度和氮气临界浓度均随C₂H₆/C₃H₈的添加而逐渐减小;此外,C₂H₆/C₃H₈混合气体使甲烷爆炸过程中CO和·H的生成量逐渐增大,而CO₂、·O和·OH的生成量则有下降趋势,通过对爆炸过程中甲烷体积的敏感性分析,发现C₂H₆/C₃H₈的存在在某种程度上促进了甲烷爆炸。对比不同配比的C₂H₆/C₃H₈混合气体,发现C₃H₈含量越高,其对甲烷爆炸过程中相关参数的影响越大,这可为工矿企业的安全生产提供一定的理论依据。     

The selective reduction of NOx with propene on Pt-beta catalyst: A transient study

The mechanism of the NO/C₃H₆/O₂ reaction has been studied on a Pt-beta catalyst using transient analysis techniques. This work has been designed to provide answers to the volcano-type activity behaviour of the catalytic system, for that reason, steady state transient switch (C₃H₆/NO/O₂ → C₃H₆/Ar/O₂, C₃H₆/Ar/O₂ → C₃H₆/NO/O₂, C₃H₆/NO/O₂ → Ar/NO/O₂, Ar/NO/O₂ → C₃H₆/NO/O₂, C₃H₆/NO/O₂ → C₃H₆/NO/Ar and C₃H₆/NO/Ar → C₃H₆/NO/O₂) and thermal programmed desorption (TPD) experiments were conducted below and above the temperature of the maximum activity (T_max). Below T_max, at 200 °C, a high proportion of adsorbed hydrocarbon exists on the catalyst surface. There exists a direct competition between NO and O₂ for Pt free sites which is very much in favour of NO, and therefore, NO reduction selectively takes place over hydrocarbon combustion. NO and C₃H₆ are involved in the generation of partially oxidised hydrocarbon species. O₂ is essential for the oxidation of these intermediates closing the catalytic cycle. NO₂ is not observed in the gas phase. Above T_max, at 230 °C, C₃H_6 ads coverage is negligible and the surface is mainly covered by O_ads produced by the dissociative adsorption of O₂. NO₂ is observed in gas phase and carbon deposits are formed at the catalyst surface. From these results, the state of Pt-beta catalyst at T_max is inferred. The reaction proceeds through the formation of partially oxidised active intermediates (C_xH_yO_zN_w) from C₃H_6 ads and NO_ads. The combustion of the intermediates with O₂(g) frees the Pt active sites so the reaction can continue. Temperature has a positive effect on the surface reaction producing active intermediates. On the contrary, formation of NO_ads and C₃H_6 ads are not favoured by an increase in temperature. Temperature has also a positive effect on the dissociation of O₂ to form O_ads, consequently, the formation of NO₂ is favoured by temperature through the oxygen dissociation. NO₂ is very reactive and produces the propene combustion without NO reduction. These facts will determine the maximum concentration of active intermediates and consequently the maximum of activity.     

NiO和Ni催化剂对苯甲酸热解机理的理论计算

在煤热解过程中加入特定的催化剂可以改变煤结构中相关化学键的结合能，使热解在相对温和的条件下进行，促使更多的小分子从煤结构上解离成为产物释放，并调节产物的产率和组成，提高转化率及产物的品质。由于煤化学结构的复杂性，从分子水平研究煤的催化热解行为非常困难。基于此，以煤的催化热解为背景，采用煤模型化合物，借助密度泛函理论(DFT)，选取苯甲酸(C₆H₅COOH)为煤基模型，以NiO和Ni为催化剂，研究催化热解过程中催化剂价态改变对煤催化剂热解的作用。DFT结果显示，苯甲酸热解的主要路径为：C₆H₅COOH \stackrel{}{\to } CO₂+C₆H₆和C₆H₅COOH \stackrel{}{\to } C₆H₆COO \stackrel{}{\to } CO₂+C₆H₆；在NiO上的分解路径为：C₆H₅COOH(g) \stackrel{}{\to } *C₆H₅COO + *H \stackrel{}{\to } *CO₂ + *C₆H₆ \stackrel{}{\to } CO₂(g) + C₆H₆(g) ；在金属Ni上的分解路径为：C₆H₅COOH(g) \stackrel{}{\to } *C₆H₅COOH \stackrel{}{\to } *C₆H₅COO + *H \stackrel{}{\to } *CO₂ + *C₆H₆ \stackrel{}{\to } CO₂(g) + C₆H₆(g) 。Ni基催化剂的加入能够促进C₆H₅COOH的热解，同时改变了苯甲酸的热解路径，但是产物不变。当NiO被还原为金属Ni时，催化效果减弱。     

Partial oxidation of light alkanes by NOx in the gas phase

Partial oxidations of CH₄, C₂H₆, C₃H₈, and iso-C₄H₁₀ with O₂ were promoted by addition of NO in the gas phase. The addition of NO increased the conversion rate of alkanes and decreased the initiation temperatures for the reactions. Moreover, selectivities and yields to oxygenates, aldehydes, ketones and alcohols, were remarkably improved by the addition of NO. The maxima of one-pass yields of oxygenates were 7% for CH₄, 11% for C₂H₆, 13% for C₃H₈, and 29% for iso-C₄H₁₀. It is suggested that NO₂ produced from NO and O₂ is the initiator for the oxidation of light alkanes. Alkyl nitrite was proposed as the reaction intermediate for the formation of oxygenates. The alkyl nitrite decomposes into oxygenates and NO that works as catalyst for the activation of O₂ and the oxidation of alkanes.     

不同CO2浓度下负直流电场对C3H8/O2/Ar/CO2预混火焰的影响规律

为了揭示电场对火焰效应与火焰传播速率的关系,在定容燃烧弹上研究了常温常压下、负直流电场（U=0、-5、-10 kV）对当量燃空比f为1.0的C₃H₈/O₂/Ar/CO₂预混火焰影响规律随混合气中CO₂掺混浓度（混合气中CO₂体积分数分别为0、10%、15%、20%）的变化关系。实验结果表明：给定加载电压,随着CO₂掺混浓度的增大,C₃H₈/O₂/Ar/CO₂预混火焰传播速率降低,规范化火焰变形率与平均火焰传播速率变化率均增大。当U=-10 kV时,CO₂掺混浓度为0、10%、15%、20%时对应的平均火焰变形率分别为1.01、1.31、1.80、3.12,平均火焰传播速度变化率分别为10.87%、17.87%、19.16%和34.63%。研究结果表明负直流电场对C₃H₈/O₂/Ar/CO₂火焰传播的促进效应随着火焰传播速率的降低而显著增强。     

Water vapor sensitivity of nanosized La(Co, Mn, Fe)1−x(Cu, Pd)xO3 perovskites during NO reduction by C3H6 in the presence of oxygen

A series of La(Co, Mn, Fe)_1−x(Cu, Pd)_xO₃ perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O₂, NO + O₂, C₃H₆, in the absence or presence of 5% H₂O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000 ppm NO, 3000 ppm C₃H₆, 1% O₂, 0 or 10% H₂O, and 50,000 h⁻¹ space velocity. The objective was to investigate the influence of H₂O addition on catalytic behavior. A good performance (100% NO conversion, 77% N₂ yield, and 90% C₃H₆ conversion) was achieved at 600 °C over LaFe_0.8Cu_0.2O₃ under a dry feed stream. With the exposure of LaFe_0.8Cu_0.2O₃ to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N₂ yield, and 86% C₃H₆ conversion. A competitive adsorption between H₂O vapor with O₂ and NO molecules at anion vacancies over LaFe_0.8Cu_0.2O₃ was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C₃H₆ + NO + O₂ reaction. This H₂O deactivation was also verified to be strictly reversible by removing steam from the feed.     

Silicone/non-silicone grafted blend composite membranes for air/vapor separation

Four types of new silicon-based graft blended polymers were developed and drawn to thin film composite membranes on high flux microporous polyetherimide support. The membranes and a 1 μm PDMS membrane as a standard were tested for the flux of the gases N₂, O₂, Ar, CH₄, CO₂, CH₃Cl, C₂H₅Cl, C₂H₆, and n-C₄H₁₀ and the vapors methanol (MeOH), t-butyl methyl ether (MTBE), 1, 1, 1-trichloroethane (Cl₃Eth), 1, 1, 2-trichlorofluoroethane (Cl₃F₃Eth), and n-hexane (n-C₆H₁₄). Methanol/argon mixtures were used to check the validity of the calculated selectivities. The results show higher performance for the newly developed membranes.     

Experimental and Modeling Study on de-NOx Characteristics of Selective Non-catalytic Reduction in O2/CO2 Atmosphere

An experimental study of thermal de-NOx using NH3 as reductant in O2/CO2 atmosphere with the effect of SO2 and different additives was performed in a drop tube furnace. Results show that the optimum te...     

Boosting selective C2H2/CH4, C2H4/CH4 and CO2/CH4 adsorption performance via 1,2,3-triazole functionalized triazine-based porous organic polymers

Nitrogen-rich porous organic polymers have shown great potentials in gas adsorption/separation, photocatalysis, electrochemistry, sensing and so on. Herein, 1,2,3-triazole functionalized triazine-based porous organic polymers (TT-POPs) have been synthesized by the copper-catalyzed azide-alkyne cycloaddition (Cu-AAC) polymerization reactions of 1,3,5-tris(4-azidophenyl)-triazine with 1,4-diacetylene benzene and 1,3,5-triacetylenebenzene, respectively. The characterizations of N₂ adsorption at 77 K show TT-POPs possess permanent porosity with BET surface areas of 666 m²·g^-1 (TT-POP-1) and 406 m²·g^-1 (TT-POP-2). The adsorption capacities of TT-POPs for CO₂, CH₄, C₂H₂ and C₂H₄, as well as the selective separation abilities of CO₂/N₂, CO₂/CH₄, C₂H₂/CH₄ and C₂H₄/CH₄ were evaluated. The gas selective separation ratio of TT-POPs was calculated by the ideal adsorbed solution theory (IAST) method, wherein the selective separation ratios of C₂H₂/CH₄ and C₂H₄/CH₄ of TT-POP-2 was 48.4 and 13.6 (298 K, 0.1 MPa), which is comparable to other adsorbents (5.6-120.6 for C₂H₂/CH₄, 10-26 for C₂H₄/CH₄). This work shows that the 1,2,3-triazole functionalized triazine-based porous organic polymer has a good application prospect in natural gas purification.     

Nitrous oxide reduction with ammonia over Co---MgO catalyst and the influence of excess oxygen

N₂O decomposition on Co---MgO was studied under high (6.67 kPa) and low (75 Pa) N₂O pressure and the effect of reductant (C₂H₆, NH₃) was studied. The activity decays because of the strong adsorption of oxygen produced, while the reductant removed the adsorbed oxygen giving a steady catalysis. The reaction between NH₃ and excess amount of O₂ produced N₂O as a main product. Although N₂O gives the same intermediate (O) as O₂ does, the former decomposition seems to proceed faster than the latter on Co---MgO. The reaction mechanism studied here was compared with the SCR (NO---NH₃ in O₂) reaction on V₂O₂-TiO₂. Since NH₃, N₂O and O₂ gives only N₂ and water, Co---MgO can be a possible catalyst used in the boiler exhaust to reduce N₂O concentration by adding ammonia.     

Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO

Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO₂ + CO). However, addition of LiCl drastically improved the yield of C₂ compounds (C₂H₆ + C₂H₄). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH₄. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH₄ to C₂H₄ through C₂H₆ (2CH₄ → C₂H₆ → C₂H₄). The study on the oxidation of C₂H₆ over the LiCl/NiO showed that the oxidative dehydrogenation of C₂H₆ to C₂H₄ occurs very selectively, which is the main reason why partial oxidation of CH₄ over LiCl/NiO gives C₂H₄ quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH₄. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni^(2+δ)+ or Ni³⁺). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH₄---CD₄ exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide.     

Study of the reaction of NOx and soot on Fe2O3 catalyst in excess of O2

This study addresses the catalytic reaction of NO_x and soot into N₂ and CO₂ under O₂-rich conditions. To elucidate the mechanism of the soot/NO_x/O₂ reaction and particularly the role of the catalyst -Fe₂O₃ is used as model sample. Furthermore, a series of examinations is also made with pure soot for reference purposes. Temperature programmed oxidation and transient experiments in which the soot/O₂ and soot/NO reaction are temporally separated show that the NO reduction occurs on the soot surface without direct participation of the Fe₂O₃ catalyst. The first reaction step is the formation of CC(O) groups that is mainly associated with the attack of oxygen on the soot surface. The decomposition of these complexes leads to active carbon sites on which NO is adsorbed. Furthermore, the oxidation of soot by oxygen provides a specific configuration of active carbon sites with suitable atomic orbital orientation that enables the chemisorption and dissociation of NO as well as the recombination of two adjacent N atoms to evolve N₂. Moreover, carbothermal reaction, high resolution transmission electron microscopy and isotopic studies result in a mechanistic model that describes the role of the Fe₂O₃ catalyst. This model includes the dissociative adsorption of O₂ on the iron oxide, surface migration of the oxygen to the contact points of soot and catalyst and then final transfer of O to the soot. Moreover, our experimental data suggest that the contact between both solids is maintained up to high conversion levels thus resulting in continuous oxygen transfer from catalyst to soot. As no coordinative interaction of soot and Fe₂O₃ catalyst is evidenced by diffuse reflectance infrared Fourier transform spectroscopy a van der Waals type interaction is supposed.     

The directed relation graph method for mechanism reduction in the oxidative coupling of methane

A detailed mechanism comprising the GRI-Mech natural gas combustion mechanism and recent updates to it that included soot formation and reactions involving acetylene by Frenklach and coworkers was chosen to describe the gas phase reactions in the oxidative coupling of methane (OCM). The complete mechanism was reduced for use under OCM conditions with the directed relation graph method. The mechanism reduction achieved reduction ratios of 0.55 for the number of species and 0.57 for the number of reactions when the differences in the concentrations of CH₄, O₂, C₂H₆, C₂H₄, and C₂H₂ between the original and reduced mechanisms were required to be less than 5%.     

Catalytic selective reduction of NO with ethylene over a series of copper catalysts on amorphous silicas

Catalytic selective reduction of NO to N₂ was studied comparing a series of Cu-based catalysts (ca. 8 wt.%) supported over amorphous pure and modified silicas: SiO₂, SiO₂-Al₂O₃, SiO₂-TiO₂, SiO₂-ZrO₂. The catalysts were prepared by the chemisorption-hydrolysis method which ensured the formation of a unique copper phase well dispersed over all supports, as confirmed by scanning electron micrographs (SEMs). Temperature-programmed reduction (TPR) analyses confirmed the presence of dispersed copper species which underwent complete reduction at a temperature of about 220°C, independently of the support. It was found that the support affects the extent of NO reduction as well as the selectivity to N₂ formation. Maximum N₂ yield was found in the range 275–300°C. The catalyst prepared over SiO₂-Al₂O₃ was the most active and selective with respect to the other silicas. Competitiveness factors (c.f.’s) as high as 13–20% in the temperature range 200–250°C could be calculated. For all catalysts, the temperature of the N₂ peak maximum did not correspond to that of the maximum C₂H₄ oxidation to CO₂, suggesting the presence of two different sites for the oxidation and the reduction activity. On the catalyst prepared on SiO₂-Al₂O₃, a kinetic interpretation of catalytic data collected at different contact times and temperatures permitted evaluating the ratio between kinetic coefficients as well as the difference between activation energies of NO reduction by C₂H₄ and C₂H₄ oxidation by O₂.