曝气生物滤池去除亚硝酸盐氮的效果及影响因素

以珠江微污染原水为对象，研究了曝气生物滤池对NO2^·-N的去除效果及温度、NH^4＋-N、NO2^·-N、CODMn浓度等对去除NO2^·-N的影响。试验结果表明：水温是影响曝气生物滤池去除NO2^·-N的主要因素，当水温〉23℃时，对NO2^·-N的去除效果较好；在水温相同的条件下，当原水NH^4＋ -N浓度较高时曝气生物滤池出水NO2^·-N浓度也较高；原水NO2^·-N浓度越高则其去除率亦越高。     

磁控溅射碳纳米管SnO2材料性能的研究

采用磁控溅射的方法制备薄膜型碳纳米管SnO2气敏元件,通过对气敏元件在不同气体中的响应进行分析,以及对气敏元件进行SEM和XRD实验,研究碳纳米管SnO2材料的气敏性能。实验表明：磁控溅射碳纳米管SnO2气敏元件对NO2气体有很高的灵敏度,对其他气体不敏感。     

Reduction of nitrogen dioxide by propene over acidic mordenites: influence of acid site concentration, formation of by-products and mechanism

The reduction of nitrogen dioxide to nitrogen by propene was studied over a variety of acidic mordenite zeolites differing in their Si : Al ratio and thus, in their concentration of acid sites. The formation of by-products was monitored applying an ion–molecule reaction (IMR) mass spectrometer. It was found that at fixed conditions the yield of nitrogen increases with increasing concentration of acid sites, confirming that acid sites are the active catalytic centres in the reaction. Apart from nitrogen and nitric oxide, acrylonitrile and ammonia are formed as nitrogen containing gas-phase products in the reaction. In separate experiments, it was shown that acrylonitrile is hydrolysed by water over the acidic zeolites to yield ammonia and acrylic acid. When acrylonitrile is used as reducing agent for nitrogen dioxide, formation of nitrogen is strongly enhanced in the presence of water. Water also has a promoting effect on the formation of nitrogen in the reaction between nitrogen dioxide and propene. Acrylonitrile and its product of hydrolysis, ammonia, are considered to be intermediates of nitrogen dioxide reduction to nitrogen by propene over acidic zeolites.     

反硝化除磷的影响因素及新工艺

介绍了反硝化除磷的概念、机理以及影响因素,主要讨论了COD、pH值、NO2-浓度、NO3-浓度以及SRT等对反硝化除磷效果的影响,综述了目前国内外对反硝化除磷工艺的研究进展.     

Storage of NO2 on BaO/TiO2 and the influence of NO

The influence of NO on the adsorption and desorption of NO₂ on BaO/TiO₂ has been studied under lean conditions. The adsorption of NO₂ involves the disproportionation of NO₂ into an adsorbed nitrate species and NO released to the gas phase with a 3:1 ratio,

BaO+3NO₂→NO+Ba(NO₃)₂.

Three different nitrate species form on the catalyst: surface nitrates on the TiO₂ support, surface nitrates on BaO, and bulk barium nitrate. The stability of the three species in different gas feeds was investigated by temperature-programmed desorption (TPD).

The reverse reaction of the NO₂ disproportionation has also been observed. If NO is added to the feed, nitrates previously formed on the sorbent will decompose into NO₂. Therefore, the above chemical equation should be considered as an equilibrium reaction. Applying this finding to the NO_x storage and reduction catalyst means that NO probably reacts with the previously formed nitrates yielding NO₂ as an intermediate product. This NO₂ is subsequently reduced by the reducing agents (hydrocarbons and CO) present during the regeneration period.     

生物滴滤塔处理低浓度氮氧化物

采用活性炭填料挂膜的生物滴滤塔净化低浓度氮氧化物废气,研究结果表明,生物净化效率可达99%。适宜的喷淋量为3L/h,适宜的气体流量为0.4～0.5m3/h。当气体流量在0.56m3/h,入口气体氮氧化物浓度为480mg/m3,停留时间18.4s时,氮氧化物的净化效率可达到96.67%。净化氮氧化物的反硝化菌大部分为副球菌属(Paracoccus)中的细菌,也有小部分硫杆菌属(Thiobacillus)中的细菌。活性炭生物净化氮氧化物废气主要发生在活性炭外表面,而活性炭内表面发生的生化反应很少。     

Selective catalytic reduction of NO and NO2 at low temperatures

The fast SCR reaction using equimolar amounts of NO and NO₂ is a powerful means to enhance the NO_x conversion over a given SCR catalyst. NO₂ fractions in excess of 50% of total NO_x should be avoided because the reaction with NO₂ only is slower than the standard SCR reaction.

At temperatures below 200 °C, due to its negative temperature coefficient, the ammonium nitrate reaction gets increasingly important. Half of each NH₃ and NO₂ react to form dinitrogen and water in analogy to a typical SCR reaction. The other half of NH₃ and NO₂ form ammonium nitrate in close analogy to a NO_x storage-reduction catalyst. Ammonium nitrate tends to deposit in solid or liquid form in the pores of the catalyst and this will lead to its temporary deactivation.

The various reactions have been studied experimentally in the temperature range 150–450 °C for various NO₂/NO_x ratios. The fate of the deposited ammonium nitrate during a later reheating of the catalyst has also been investigated. In the absence of NO, the thermal decomposition yields mainly ammonia and nitric acid. If NO is present, its reaction with nitric acid on the catalyst will cause the formation of NO₂.     

甲苯的NO2/O2硝化新工艺

采用间歇式高压反应器研究了甲苯的NO2/O2硝化反应,考察了反应条件对反应活性的影响。结果表明,适当的催化剂比表面和酸中心对此硝化反应是必要的。在HZSM-5分子筛为催化剂的情况下,NO2/甲苯配料比为2∶1(摩尔比),O2压力0.5MPa,控制反应温度为45℃,反应时间3h,反应的转化率达到100%,对硝基甲苯的选择性为45%,较混酸法高。     

低温高活性NO氧化催化剂Mn-V-Ce/TiO2的制备与性能

采用浸渍法制备了新型NO氧化催化剂Mn-V-Ce/TiO2,考察了组分配比、载体种类、焙烧温度等制备条件和反应温度、NO进口体积分数、O2含量、空速等操作条件对其催化活性的影响,对载体和催化剂分别进行了BET和XRD分析. 结果表明,10%Mn-3%V2O5-20%CeO2/TiO2在300℃焙烧6 h得到的Mn-V-Ce/TiO2具有最佳催化氧化活性,NO体积分数500′10-6,O2体积分数10%;空速8000 h-1、温度200℃或空速5000 h-1、温度175℃条件下,出口NOx的氧化度(NO2/NOx)均达到50%~60%,NOx能取得最大的吸收效率;250℃、8000 h-1时,氧化度可达74%;250℃、5000 h-1时,氧化度可达86.6%.     

NO reduction by CH4 in the presence of O2 over La2O3 supported on Al2O3

Dispersing La₂O₃ on δ- or γ-Al₂O₃ significantly enhances the rate of NO reduction by CH₄ in 1% O₂, compared to unsupported La₂O₃. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La₂O₃ precursor used, the pretreatment, and the La₂O₃ loading. The most active family of catalysts consisted of La₂O₃ on γ-Al₂O₃ prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m²) occurred between the addition of one and two theoretical monolayers of La₂O₃ on the γ-Al₂O₃ surface. The best catalyst, 40% La₂O₃/γ-Al₂O₃, had a turnover frequency at 700°C of 0.05 s⁻¹, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La₂O₃/Al₂O₃ catalysts exhibited stable activity under high conversion conditions as well as high CH₄ selectivity (CH₄ + NO vs. CH₄ + O₂). The addition of Sr to a 20% La₂O₃/γ-Al₂O₃ sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO⁼₄ to the latter Sr-promoted La₂O₃/Al₂O₃ catalyst decreased activity although sulfate increased the activity of Sr-promoted La₂O₃. Dispersing La₂O₃ on SiO₂ produced catalysts with extremely low specific activities, and rates were even lower than with pure La₂O₃. This is presumably due to water sensitivity and silicate formation. The La₂O₃/Al₂O₃ catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications.     

Cu掺杂Mn／TiO2催化氧化NO性能研究

采用溶胶凝胶法制备了栽体TiO2,在负栽Mn（Ac）：制备Mn／TiO2时掺杂cu,制备了Mn—Cu／TiO2催化剂。考虑了cu的掺杂量、活性组分负载量、焙烧温度等制备条件对其催化氧化No性能的影响。结果表明,最佳条件下制备的催化剂,在反应温度200℃、空速41000h～、No浓度为300×10-6（书）及O2含量为10％条件下,NO氧化率可迭53．08％,250℃时NO氧化率达到74．76％。在220℃以上时H2O对其影响较小,但其抗硫性能还有待进一步研究提高。     

A study of the catalytic activity of cobalt–zinc manganites for the reduction of NO by hydrocarbons

In this work the catalytic behaviour of pure zinc manganite, ZnMn₂O₄, and cobalt–zinc manganites for the reduction of NO by propane and propene is reported. The NO and N₂O decomposition as well as the reduction of N₂O by propane and propene were also investigated. The catalysts are prepared starting from carbonate monophasic precursors that are decomposed in air at 973 K for 24 h. In all cases a spinel-like phase is obtained. Pure zinc manganite is an efficient catalyst for the NO reduction with both propane and propene and the selectivity to N₂ and CO₂ was almost one. However the presence of cobalt in the catalyst enhances the catalytic activity, in particular when propene is used as reducing agent of NO. All catalysts are stable up to 873 K upon contacting with the propane containing reactant stream whereas in the case of propene they preserve the original spinel structure up to about 773 K. In fact with propene the catalysts start to lose their stability as the reaction temperature increases above 773 K and disaggregate, by reduction of the spinel framework Mn³⁺ cations to Mn²⁺, forming a complex mixture of ZnO and MnO oxides. Despite the collapsing of the spinel phase, the disaggregated polyphasic catalysts still show a good activity and selectivity. An hypothesis for explaining this unusual behaviour is formulated. Finally, the reaction mechanisms presented in literature are consequently revisited on the basis of the results found in this work.     

Dissolution kinetics of alumina in molten CaO–Al2O3–FetO–MgO–SiO2 oxide representing the RH slag in steelmaking process

In order to effectively remove alumina inclusions suspending in ultra-low C steel during RH process, the dissolution kinetics of alumina in molten CaO–Al₂O₃–Fe_tO–MgO–SiO₂ oxide was investigated. A crucible dissolution technique was used where the alumina crucible was allowed to dissolve in the slag of various conditions ((% CaO)/(% Al₂O₃), (% Fe_tO), temperature). The obtained data were interpreted using a kinetic mass transport equation to obtain the mass transport coefficient (k_m) in each condition. Increasing (% CaO)/(% Al₂O₃), (% Fe_tO), and temperature increased the dissolution rate as well as the k_m provided that the slag composition is not close to its saturation composition by alumina. In order to simulate the dissolution of alumina inclusion in the RH slag, which cannot be measured by a confocal scanning laser microscopy (CSLM) at present due to the opaqueness of the slag, the modified invariant interface approximation was employed. Along with the obtained k_m, the viscosity of slag, and a reference experiment using the CSLM, the dissolution kinetics of alumina inclusion in the Fe_tO-containing RH slag was predicted. The time required for the dissolution of alumina inclusions from liquid steel to RH slag was discussed.     

Potential rare-earth modified CeO2 catalysts for soot oxidation part II: Characterisation and catalytic activity with NO + O2

Ceria (CeO₂) and rare-earth modified ceria (CeReO_x with Re = La³⁺, Pr^3+/4+, Sm³⁺, Y³⁺) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO + O₂. The catalysts are characterised by XRD, H₂-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO₂ is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO₂ with Pr^3+/4+ and La³⁺ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO_x and to the surface area and redox properties of CePrO_x catalyst. The NO conversion to NO₂ over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO_x is the most active one. This indicates that though La³⁺ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce⁴⁺. The lattice oxygen participates in NO conversion to NO₂ and the rate of this lattice oxygen transfer is much faster on CePrO_x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO₂ and CeReO_x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100 °C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO₂ conversion. In spite of the lower surface area, the Pt/CeYO_x and Pt/CeO₂ catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO₂ over these catalysts. The activation energy for the soot oxidation with NO + O₂ is found to be around 50 kJ/mol.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

A new active zeolite structure for the selective catalytic reduction (SCR) of nitrogen oxides: ITQ7 zeolite: The influence of NO2 on this reaction

The activity of a new zeolite material, ITQ7, has been studied for the selective catalytic reduction (SCR) of NO. The pore topology of this material is similar to the structure of a beta zeolite, with a tridirectional system with 12-member rings. ITQ7 exchanged with copper or cobalt shows a catalytic behaviour very similar to a beta zeolite exchanged with copper or cobalt, probably due to its similar structure. The presence of oxygen, water, sulphur dioxide and NO₂ has been studied, obtaining the best results at low oxygen concentration and in the absence of water and SO₂. Nevertheless if NO₂ is present in the reaction mixture, the maximum activity of the catalyst shifts towards higher oxygen concentration.     

NO reduction by CH4 in the presence of excess O2 over Pd/sulfated zirconia catalysts

The selective catalytic reduction (SCR) of NO by methane in the presence of excess oxygen has been studied on a series of Pd catalysts supported on sulfated zirconia (SZ). This support is not as sensitive to structural damage by steaming as the acidic zeolites, such as H-ZSM-5 and H-Mor. In previous studies, it was shown that this type of acidic zeolites are able to stabilize Pd²⁺ ions and promote high SCR activity and selectivity, which are typically not seen in Pd catalysts. In this contribution, it has been demonstrated that SZ is able to promote the NO reduction activity in a similar way to the acidic zeolites, by stabilizing Pd²⁺ ions that is selective for NO reduction. As in the case of acidic zeolites, the stabilization of Pd²⁺ ions can occur through a transfer of Pd species from particle to particle. One of the attractive features of Pd/SZ catalysts is that they are less sensitive to water and SO₂ poisoning than Pd/H-ZSM-5 catalyst and exhibit higher reversibility after removal of water or SO₂.     

Dissolution mechanism of alumina inclusions into CaO–SiO2–Al2O3–FetO–MgO slag via a converter tapping process

Reducing the amount of inclusions during the steelmaking process as much as possible and much earlier plays a vital role in improving the quality of steel products. To reveal the dissolution mechanism of inclusions in slag during the converter tapping process, some comparison experiments were conducted by adding isolated spherical alumina balls as inclusions in CaO–SiO₂–Al₂O₃–Fe_tO–MgO slag, and Fe_tO content up to 10% was contained in slag. The results showed that the dissolution rate of alumina balls in the slag was mainly affected by the diffusion of Al₂O₃, and the diffusion coefficients of Al₂O₃ were 4.2 × 10^–11, 7.5 × 10^–11, and 1.5 × 10^–10 m²/s at 1500℃, 1550℃, and 1600℃, respectively. In addition, the upgraded diffusion-distance-controlled dissolution model (DDD-Model), in which Fe_tO content was introduced and applied in the study. The results illustrated that the Al₂O₃ inclusion apparent dissolution rate was improved by a high Fe_tO content, increasing CaO/SiO₂ and raising the temperature as soon as possible at the early stage of the converter tapping process. It is not necessary to increase the Fe_tO content in the slag to enhance the dissolution rate of the Al₂O₃ inclusion at the last tapping stage. The predicted complete dissolution time of spherical Al₂O₃ inclusions with 1000 µm in diameter based on the upgraded DDD-Model was approximately 1796 s during the actual converter tapping process.     

氮氧化物在湿法烟气脱硫过程中的作用

采用了气液鼓泡床反应器,以NaOH溶液为吸收液,在模拟烟气条件下对氮氧化物在湿法烟气脱硫过程中的作用进行了实验研究.结果表明,在吸收液为碱性的环境下,NO2的存在对脱硫率略有促进,SO2的存在则可显著增加脱硝率;在吸收液变乏且已呈酸性的环境下,NO2和SO2互相抑制彼此的脱除率;无论酸碱环境,NO和SO2对彼此脱除率的影响都很微弱.NO和NO2的存在对脱硫产物影响显著,NO2的存在促进了脱硫产物中硫酸盐的生成,碱性环境下尤其显著,而NO的存在抑制了脱硫产物中硫酸盐的生成.     

Theoretical Study of Mechanism and Kinetics of the Reaction of NO2 with s‐Triazine

The decomposition of nitramines explosives have been of great interest for a long time. However, theoretical investigations have concentrated mainly on unimolecular decomposition whereas bimolecular reactions have received only little attention. In this paper, the bimolecular reaction between NO₂ with s‐triazine (TAZ), which is an initial product during the decomposition process of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) is investigated. The structures and potential energy surface (PES) are explored at B3LYP/6‐31G(d,p) and B3P86/6‐31G(d,p) levels, and the energies are refined using the CCSD(T)/cc‐pVTZ methods. The mechanism of the reaction is analyzed. Quantum chemistry calculations reveal that the title reactions possess small barriers that can be similar to, or smaller than that of initial decomposition reactions of RDX, which suggests that bimolecular reactions are also of great importance, and should be further investigated. Moreover, the kinetics were investigated to verify the proposed mechanism of the reaction.