La的掺杂方式对CeO2-MnOx催化氧化氯苯性能的影响

采用共沉淀法制备CeO₂-MnO_x和La₂O₃-CeO₂-MnO_x催化剂,再用沉积-沉淀法制备La₂O₃/CeO₂-MnO_x催化剂,并对催化剂的氯苯催化氧化反应活性进行检测。结果表明,La的加入可以显著提高催化剂催化氧化氯苯的活性。XRD和TPR表征结果表明,La的加入抑制CeO₂晶粒尺寸的长大,增强CeO₂的晶格应变,并促进Mn进入CeO₂的晶相,形成较好的MnCeO_x固溶体。催化剂的热稳定性评价结果表明,La的加入有效提高CeO₂-MnO_x催化剂的热稳定性。     

Contribution to solving the problem of dioxins generated during waste incineration

The production of dioxins/furans during waste incineration, and particularly the development of measures for minimizing the amount of generated pollutants, continue to command a considerable scientific as well public interest. Experiments are reported which were performed at the TAMARA municipal solid waste pilot incineration, erected on the premises of the karlsruhe Nuclear Research Centre. These experiments show that the solid waste mass flow rate and moisture content influence the dioxin/furan formation, Good removal efficiencies of dioxins/furans have been In wet cleaning. Hydrogen peroxide added to the crude gas is an interesting “killer” reagent for dioxins/furans.     

A review of catalytic processes for the destruction of PCDD and PCDF from waste gases

The current literature concerning the catalytic destruction of dioxins and of related model compounds is reviewed. Several different catalyst formulations have been tested, but V-rich vanadia-tungsta-titania catalysts seem to be mostly applied and allow reducing the dioxins concentration well below the limits of 0.1 ng TEQ/Nm³, as required by the EU directives. Other catalysts (in particular the noble metal-based ones) seem to be less efficient, due to deactivation effects and/or a considerable amount of polychlorinated by-products formation during oxidation activity. The coupled de-NO_x and dioxin destruction systems compete with activated carbon adsorption for efficiency in PCDD/F removal from gases.     

Understanding the activation mechanism induced by NOx on the performances of VOx/TiO2 based catalysts in the total oxidation of chlorinated VOCs

A previous investigation of the chlorobenzene combustion activity of VO_x/TiO₂, VO_x–WO_x/TiO₂ and VO_x–MoO_x/TiO₂ catalysts in the presence of NO pointed out the activation effect of NO. The suggested three-step mechanism based on catalytic performances data only was: (1) chlorobenzene is oxidized on the surface of the VO_x phase (as described by Mars–van Krevelen), (2) NO gets oxidized to NO₂, mainly on WO_x and MoO_x, and (3) the in situ produced NO₂ assists O₂ in the reoxidation of the VO_x phase thus speeding up the oxidation step of the Mars–van Krevelen mechanism. The latter effect macroscopically corresponds to the observed increase of chlorobenzene conversion. This contribution aims at validating this hypothetical mechanism by pointing out the favourable occurrence of an oxidation of NO to NO₂ on the WO_x and MoO_x phases and by pointing out the higher efficiency of NO₂ than O₂ to reoxidize the reduced VO_x sites. In addition, the present contribution clearly demonstrates that, in the absence of NO, the chlorobenzene total oxidation occurred following the Mars–van Krevelen mechanism. Moreover, a thorough characterization of the oxidation state of the vanadium proving that the improvement of the catalyst activity brought by the simultaneous presence of NO and O₂ is linked to the stronger reoxidation of the VO_x active phase. Furthermore, plotting all the catalytic activity data versus the mean vanadium oxidation level clearly depicts, for the first time, the strong dependence between them. Under a mean vanadium oxidation level of 4.82 the catalyst is inactive while above 4.87 the activity is stabilized at a high level of conversion independent of the vanadium oxidation level.     

An FT-IR study of the conversion of 2-chloropropane, o-dichlorobenzene and dibenzofuran on V2O5-MoO3-TiO2 SCR-DeNOx catalysts

Spectra of the adsorbed species arising from contact of a V₂O₅-MoO₃-TiO₂ model SCR catalyst with ortho-dichlorobenzene (o-DCB) and dibenzofuran (DBF) and their evolution with the temperature are presented and discussed. Dichlorobenzene adsorbs weakly probably on Lewis acid sites through the chlorine atom. A very fast nucleophilic substitution on dichlorobenzene to a chlorophenate species occurs already at RT. On the contrary, adsorption of dibenzofuran is molecular, probably through the oxygen atom on Lewis sites. The aromatic rings of both molecules tend to be later oxidized to give carboxylate species. Parallel experiments with chloropropane show that dehydrochlorination occurs readily, hydrochloric acid is adsorbed quite weakly and that propene can be further oxidized. However, heavier oxidized species like cyclic anhydrides are also formed from chloropropane. The data suggest that the dechloration step of the phenyl ring could be not critical. On the contrary, the building-up of aromatic compounds from smaller molecules is possible and the oxidation of phenyl ring can be slow near reaction conditions. The possibility that the reaction between phenate species and chlorobenzenes give the “de novo” synthesis of dioxins is envisaged.     

Hydrodechlorination and hydrogenation of aromatic compounds over palladium on alumina in hydrogen-saturated water

The catalytic transformations of 1,2-dichlorobenzene, chlorobenzene, 4-chlorobiphenyl, γ-hexachlorocyclohexane (Lindane), naphthalene and phenanthrene were studied over palladium on alumina in hydrogen-saturated water (Pd/Al₂O₃/H₂) at room temperature and ambient pressure. The chlorinated benzenes were rapidly hydrodechlorinated and Lindane was dehydrochlorinated to benzene. Partial or complete hydrogenation was observed for biphenyl and the polycyclic aromatic hydrocarbons. The phenanthrene ring was cleaved at the 9,10-position. In general dechlorination reactions were faster than hydrogenation reactions.     

Ce掺杂对Ru/TiO2催化氯苯性能的影响

采用等体积浸渍法制备了单贵金属Ru/TiO₂和双金属Ru-Ce/TiO₂系列催化剂,测试了其对氯苯的催化活性,并通过N₂吸脱附、扫描电镜(SEM)、程序升温还原(H₂-TPR)进行表征,旨在考察稀土元素Ce掺杂对Ru/TiO₂催化氯苯性能的影响。结果表明,Ce的引入可使其在降低贵金属含量的基础上仍保持高的催化效率,且极大地提高了低温催化活性。0.4%Ru-1.0%Ce/TiO₂与0.4%Ru/TiO₂相比,其T₁₀和T₉₀分别降低了50℃和60℃。H₂-TPR表明引入Ce为催化剂提供了更多的表面氧空位,形成Ru-O-Ce增强了其氧化还原能力。掺杂Ce未改变Ru/TiO₂催化剂的结构形貌,仍保持介孔结构,但若负载量过多,会堵塞部分孔道,阻碍污染物吸附及反应,降低催化性能。     

离子液体中过氧钼酸盐催化燃油深度氧化脱硫

以过氧化氢为氧化剂,[Omim]PF₆离子液体为萃取剂,[C₁₆mim]₂ Mo₂O₁₁为催化剂建立了萃取催化氧化脱硫体系（ECODS）。该反应体系在非常温和的条件下可使DBT的脱除率最高达到99.4%,大大优于单纯的萃取脱硫和萃取氧化脱硫体系。不同硫化物在该体系下的脱硫效果为：DBT >BT >TH。催化体系循环使用10次后催化反应活性未见明显下降。将此催化体系直接用于市售的汽油和柴油,可使其中硫含量降低至12.70mg/L和11.62mg/L。     

基于硫基循环抑制技术的危险废物焚烧炉二(口恶)英排放的控制

依托某危险废物焚烧炉(50 t·d^-1)开发了一套硫基循环抑制及飞灰低温热处置联用控制二(口恶)英排放的中试平台,研究了该系统对硫基的循环累积能力及对烟气中二(口恶)英合成的抑制能力.系统利用吸附剂吸附了烟气中SO₂,并在低温热处置装置中将吸附剂中SO₂脱附回烟气中,实现SO₂循环.试验结果表明,该系统能连续稳定运行,对烟气中的SO₂具有一定的富集累积能力,添加一定量外源硫基物质后系统中烟气SO₂能维持在100 mg·m^-3左右,对整体二(口恶)英排放因子的去除率达80%以上.可见,该硫基循环抑制技术对废物处理过程中二(口恶)英减排具有重要指导价值,且长期稳定运行对控制二(口恶)英低排放起关键作用,但该中试系统的相关参数需进一步优化.     

Revisiting the Behaviour of Vanadia-Based Catalysts in the Abatement of (Chloro)-Aromatic Pollutants: Towards an Integrated Understanding

For several years, the authors study VO _x /TiO₂ catalytic formulations in the context of the oxidative abatement of aromatics, possibly chlorinated, from polluted air. This paper revisits their main findings and understandings. Although VO _x /TiO₂ catalysts, when upgraded with Mo or W oxides, are already used in industrial applications, it is shown that the systematic investigation (i) of the reasons why optimized synthesis and formulations are indeed efficient, (ii) of the nature of the sites responsible for the adsorption of the pollutants and their catalytic transformation, and (iii) of the corresponding mechanisms, is a valuable approach to identify guidelines and strategies for further improving the catalysts. The origin of the beneficial effects brought by WO _x and MoO _x to VO _x /TiO₂, and by the use of a sulphated titania support, is addressed, as well as the impact on the catalysts behaviour and performances of molecules inevitably present in a combustion exhaust gas, like CO and NO _x co-pollutants and water. The behaviours of a chloro-aromatic molecule, like chlorobenzene, and an oxygen containing-heterocyclic molecule, like furan and dimethylfuran, are then compared and discussed in the debate of their selection as representative model compounds for the catalytic abatement of dioxins. In this context, it is shown that strategies developed to improve the performances of VO _x /TiO₂ formulations to abate Cl-aromatics, could be detrimental for cyclic molecules containing O-heteroatom, as entire dioxins. Finally, an integrated view of the catalytic process is presented by envisaging the case of a complex mixture, closer to the real application of gaseous effluent cleaning.     

Cooperative effect induced by the mixing of Na-ZSM-5 and Pd/H3PW12O40/SiO2 in the selective catalytic reduction of NO with aromatic hydrocarbons

Pd was loaded on the dispersed H₃PW₁₂O₄₀ (HPW) over the SiO₂ surface, and the catalyst was applied to the selective reduction of NO with aromatic hydrocarbons. The catalyst exhibited high activity in the NO reduction when branched aromatic hydrocarbons, such as toluene and xylene, were used as reductants. The catalytic activity of Pd/HPW/SiO₂ was improved remarkably by physically mixing it with Na-ZSM-5. From the temperature programmed desorption (TPD) of toluene and the analysis of the products, it was inferred that the activity was enhanced when Pd/HPW/SiO₂ and Na-ZSM-5 were mixed. In other words, aromatic hydrocarbons were partially oxidized to yield oxygenated hydrocarbons, e.g., benzaldehyde and phthalic anhydride, over Pd/Na-ZSM-5; in this reaction, a part of Pd migrated from Pd/HPW/SiO₂ to Na-ZSM-5 during the course of the physical mixing procedure. Subsequently, the oxygenated hydrocarbons reacted with NO entrapped with HPW over Pd to yield N₂.     

Pd/Ce基催化剂催化氧化氯苯的性能

采用等体积浸渍法制备Pd/Al₂O₃系列催化剂,考察不同Pd负载量对催化剂催化氯苯活性的影响,结果表明0.75%Pd/Al₂O₃催化剂活性最优,采用BET、H₂-TPR、SEM等对催化剂进行表征分析,表明添加Ce后氧化能力增强,催化氧化效率提高。对催化产物进行分析,使用离子色谱分析了无机Cl^-生成情况及其选择性,使用GC-MS定性分析了有机副产物,发现350℃时有少量苯生成。同时考察了焙烧温度、氯苯浓度、空速对催化活性的影响,结果表明焙烧温度过高或过低都会影响催化剂的活性,在550℃焙烧的催化剂活性更优,400℃时氯苯转化率为96%;氯苯入口处质量浓度在1500～6000mg/m³时,浓度升高,催化氯苯活性降低;空速在15000～30000h^-1时,空速对氯苯催化活性影响不大,但继续提高空速会明显降低催化活性。     

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 2. Ozone decomposition and deactivation of γ-Al2O3

The role of ozone was studied for two different configurations combining non-thermal plasma (NTP) and heterogeneous catalysis, namely the use of a gas phase plasma with subsequent exposure of the effluent to a catalyst in a packed-bed reactor (post-plasma treatment) and the placement of the catalyst directly in the discharge zone (in-plasma catalysis). Non-porous and porous alumina and silica were deployed as model catalysts. The oxidation of immobilised hydrocarbons, toluene as a volatile organic compound and CO as an inorganic pollutant were studied in both operational modes.

While conversion and selectivity of hydrocarbon oxidation in the case of catalytic post-plasma treatment can be fully explained by the catalytic decomposition of O₃ on γ-Al₂O₃, the conversion processes for in-plasma catalysis are more complex and significant oxidation was also measured for the other three materials (-Al₂O₃, quartz and silica gel). It became obvious that additional synergetic effects can be utilised in the case of in-plasma catalysis due to short-lived species formed in the NTP.

The capability of porous alumina for ozone decomposition was found to be correlated with its activity for oxidation of carbon-containing agents. It could be clearly shown that the reaction product CO₂ poisons the catalytic sites at the γ-Al₂O₃ surface. The catalytic activity for O₃ decomposition can be partially re-established by NTP treatment. However, for practical purposes the additional reaction pathways provided by in-plasma catalytic processes are essential for satisfactory conversion and selectivity.     

Increased combustion rate of chlorobenzene on Pt/γ-Al2O3 in binary mixtures with hydrocarbons and with carbon monoxide

The catalytic combustion of chlorobenzene on a 2 wt.% Pt/γ-Al₂O₃ catalyst in binary mixtures with various hydrocarbons (toluene, benzene, cyclohexane, cyclohexene, 1,4-cyclohexadiene, 2-butene, and ethene) and with carbon monoxide has been explored. For all binary mixtures used the (excess of) added hydrocarbon increased the rate of conversion of chlorobenzene. With 2-butene, T_50% and T_100% for chlorobenzene were reduced by 100 and 200°C, respectively. Toluene and ethene were almost equally efficient as 2-butene. Co-feeding benzene or carbon monoxide resulted in a much smaller decrease of the T_50%. The additional heat and water production in hydrocarbon combustion may contribute to some extent to the observed rate acceleration, but removal of Cl from the surface due to the hydrocarbon appears to be the major factor.

The co-feeding of hydrocarbons invariably reduced the output of polychlorinated benzenes, which are formed as byproducts in the combustion of chlorobenzene on Pt/γ-Al₂O₃. Again, especially toluene, ethene, and 2-butene were very efficient. Benzene — as well as cyclohexane, cyclohexene, and 1,4-cyclohexadiene, which were converted in situ into benzene — was much less effective, due to chlorination of the aromatic nucleus. In chlorobenzene–CO mixtures the levels of polychlorinated benzenes were almost as high as with chlorobenzene per se. Removal of Cl from the surface (mainly in the form of HCl) by (non-aromatic) hydrocarbons is responsible for reducing the formation of byproducts.     

Mn-Ce-Co-Ox/PPS催化滤料催化降解气相二英的研究

通过原位氧化法一步制备得到Mn-Ce-Co-O_x/PPS催化滤料,研究了催化剂负载量对Mn-Ce-Co-O_x/PPS催化降解呋喃的影响,进而分析了最优负载量的Mn-Ce-Co-O_x/PPS催化滤料在140~200℃对二英的催化降解规律,同时采用SEM、EDS和XRD等表征手段对复合催化滤料的结构及性能进行表征。结果如下：催化剂负载量由81.8 g/m²增加到154.2 g/m²,Mn-Ce-Co-O_x/PPS对呋喃的降解效率呈增加趋势,催化剂单层饱和负载量为120.5 g/m²。Mn-Ce-Co-O_x/PPS催化滤料在140~200℃对二英的脱除效率高达90%以上,降解效率随着反应温度升高而快速提升,200℃降解效率达到最高,为78.01%,表现出良好的催化降解性能。对17种二英同系物的降解效率进行分析,发现Mn-Ce-Co-O_x/PPS对低氯代二英同系物的降解率高于高氯代同系物的降解率。     

Catalytic hydrodehalogenation as a detoxification methodology

Catalytic hydrodehalogenation is presented as a viable approach in the non-destructive treatment of concentrated halogenated aromatic gas streams to generate reusable raw material. Nickel loaded (from 1.5 to 20.3% w/w) silica catalysts have been used to hydrotreat a range of halogenated feedstock, where 473 K≤T≤573 K: chlorobenzene, chlorotoluene, chlorophenol, bromobenzene, dichlorobenzene, dichlorophenol, trichlorophenol, pentachlorophenol. The long term (up to 800 h-on-stream) stability of these catalysts has been assessed where the changes in nickel particle size and morphology as a result of the prolonged catalytic step was probed by TEM; each catalyst irrespective of any loss of initial activity was fully selective in solely promoting dehalogenation. In the case of a polychlorinated feedstock, dechlorination can proceed in a stepwise manner to generate a partially dechlorinated product. Hydrodehalogenation appears to occur via an electrophilic mechanism where the presence of electron-donating substituents on the benzene ring enhances the rate of reaction. The reaction is shown to be structure sensitive over Ni/SiO₂ where the hydrodechlorination rates and ultimate yield of the parent aromatic from a polychlorinated reactant is favored by larger nickel particle sizes. A direct contact of the freshly activated catalyst with HCl or HBr gas induced an appreciable growth of the supported metal crystallites. Chlorobenzene hydrodechlorination was suppressed on a HCl or HBr treated Ni/SiO₂ which promoted instead the unexpected growth of highly ordered carbon filaments; this carbon growth is characterized by TEM and SEM. The dependence of the experimental hydrodechlorination and hydrodebromination rates on the gas phase aromatic partial pressure (in the range 0.02–0.1 atm) is adequately represented by a kinetic model involving a non-competitive adsorption of hydrogen and halogenated aromatic where the incoming aromatic reactant must displace the hydrogen halide from the catalyst surface.     

The promotional effect of MoO3 doped V2O5/TiO2 for chlorobenzene oxidation

A series of V₂O₅–MoO₃/TiO₂ catalysts prepared by an impregnation method was investigated on their catalytic performance of chlorobenzene oxidation. This study demonstrated that MoO₃ is a dopant, which can improve catalyst redox properties and enhance chlorobenzene oxidation catalytic activity at low temperature. Compared to V₂O₅–TiO₂ and V₂O₅–WO₃/TiO₂ catalysts, V₂O₅–MoO₃/TiO₂ catalysts showed outstanding activity on chlorobenzene oxidation, which is due to the promoting influence of MoO₃. For excellent catalytic performance and good N₂ selectivity with water, the V₂O₅–MoO₃/TiO₂ catalysts may have promising commercial potential for the synergetic control of dioxins and NO_x emitted from stationary sources.     

邻二氯苯在钒-钨-钛催化剂上的完全催化氧化

采用等体积浸渍法制备不同系列钒-钨-钛催化剂,以与二噁英TCDD化学结构式相似的邻二氯苯作为替代物,研究催化剂对邻二氯苯的去除效率,考察钒负载质量分数和钨负载质量分数对邻二氯苯催化氧化性能的影响,通过XRD和催化剂比表面积分析对催化剂的微观结构进行表征。结果表明,随着钒负载质量分数的增加,催化剂比表面积降低,催化剂性能降低;随着钨负载质量分数的增加,催化剂比表面积增加,催化剂性能提高。钨的加入有利于促进活性钒的分散,提高催化剂的比表面积,催化剂比表面积是影响催化剂性能的关键因素。     

Variation of toxic pollutants emission during a feeding cycle from an updraft fixed bed gasifier for disposing rural solid waste

The variation of toxic pollutants emission during a feeding cycle was examined by field monitoring from a batch feeding updraft fixed bed gasifier for disposing rural domestic solid waste. Results showed that the content of oxygen in flue gas gradually increased, while SO_2 and HCl in flue gas decreased with time after feeding in a whole feeding cycle. Although large amount of CO was produced during the gasifying, low CO content in flue gas could be obtained after the heat treatment with an electric heating device. The distribution characteristics of dioxin congeners in flue gas indicted the re-synthesis of dioxins after flue gas heating, and the increase of oxygen promoted the synthesis of dioxins. The emission content of dioxins could meet the standard(0.1 ng I-TEQ·m~(-3),GB18458-2014) of China when the oxygen content was controlled below 8.3%. Hence, for a batch feeding gasifier,low oxygen condition should be offered by reducing air intake at the later stage of feeding cycle in order to decrease the re-synthesis of dioxins after the flue gas heating.     

Catalytic oxidation of aromatic VOCs with Cr or Pd-impregnated Al-pillared bentonite: Byproduct formation and deactivation studies

The catalytic behavior of chromium and palladium-impregnated Al-pillared bentonite for the oxidation of aromatic VOCs, i.e. chlorobenzene or xylene, was investigated. The Cr-impregnated bentonite showed high activity for the total oxidation of cholorobenzene and xylene but the materials were completely deactivated during the reaction at 600 °C. Atomic absorption, XPS, XRD and TG analyses suggested three main causes for the deactivation, i.e. the loss of Cr due to the formation of volatile CrO₂Cl₂, a strong decrease on the surface area due to the collapse of the pillars and the formation of coke. For the Pd supported pillared bentonite, the impregnation procedure completely destroyed the Al-pillars but produced a very active and stable catalyst to oxidize aromatic contaminants. However, in the case of chlorobenzene almost 20% yield of the hazardous hexachlorobenzene was obtained likely by an oxychlorination process.