等速升温流态化下CaO/生物质焦的SO2/NO联合脱除特性

燃煤锅炉污染物超低排放标准对电厂脱硫和脱硝系统提出了更高的要求。CaO作为脱硫剂可以实现循环流化床锅炉烟气中SO₂的高效脱除,焦炭作为还原剂直接还原NO,同时CaO的存在对焦炭还原NO起催化作用,可以实现燃煤烟气中SO₂/NO的联合脱除。为了探究连续温度变化对CaO/生物质焦联合脱硫脱硝性能的影响,在钙循环捕集CO₂技术背景下,研究了等速升温流态化下CaO/生物质焦的SO₂/NO联合脱除特性。探究了烟气中O₂和CO₂对CaO/椰壳焦脱除SO₂/NO的影响。结果表明,O₂通过对椰壳焦表面碳原子的活化作用降低了异相还原NO温度,在300~950℃等速升温过程中CaO/椰壳焦的NO脱除效率逐渐增加,780℃以上能实现100%脱硝。O₂也提高了CaO/椰壳焦的脱硫效率。CO₂与CaO的碳酸化反应以及与椰壳焦的气化反应对同时脱除SO₂/NO有明显抑制作用。O₂和CO₂共同作用下,在500~800℃内CaO/椰壳焦的脱硝效率随温度升高而增加,脱硫效率先降低后升高。NO促进了CaO/椰壳焦脱除SO₂,而SO₂对脱硝有抑制作用。800℃时CaO/椰壳焦同时脱除SO₂和NO的效率分别为97.7%和93.9%。     

Enhancement by SO2 of initial activity for selective catalytic reduction of NO with CH3OH over \gamma-alumina

The effect of SO₂ on catalytic activity for NO reduction to N₂ by methanol in excess oxygen over $\gamma$ -alumina has been investigated. SCR activity increased initially upon exposure of a fresh $\gamma$ -alumina catalyst to SO₂ which is attributed to formation of Brønsted acid sites. Longer exposure to SO₂ leads to a decline in catalytic activity to a lower steady-state NO_x reduction activity which is independent of the SO₂ content in the feed gas.     

Promotion of the NO + O2 Reaction by Ba–Y, FAU Zeolite at 25 °C

A remarkably high inferred initial rate of NO oxidation by O₂ has been observed over Ba–Y, FAU zeolite at 25 °C in simple flow-reactor experiments. The rate of reaction at steady state was found to be lower, but still an order of magnitude greater than over alumina-supported Pt, also at 25 °C.     

Catalytic Conversion of NO and C3H6 in Exhaust Gases Over Silver Catalysts Under Stoichiometric or Excess Oxygen

The role of Ag in simultaneously catalyzing NO reduction and C₃H₆ oxidation was shown to be strongly dependent on the redox properties of its local environment. Under an atmosphere of 1,000 ppm NO, 3,000 ppm C₃H₆, and 1% O₂ and a GHSV of 30,000 h⁻¹, a perovskite La_0.88Ag_0.12FeO₃ prepared by reactive grinding is active giving a complete NO conversion and 92% C₃H₆ conversion at 500 °C. These values are much higher than the NO conversion of 55% and C₃H₆ conversion of 45% obtained over a 3 wt.% Ag/Al₂O₃ catalyst under the same conditions. Under an excess of oxygen (10% O₂) a good SCR performance with a plateau of N₂ yield above 97% over a wide temperature window of 350–500 °C along with C₃H₆ conversion of 90% at 500 °C was observed over Ag/Al₂O₃, while minor N₂ yields (∼10% at 250–350 °C) and high C₃H₆ conversions (reaching ∼100% at 450 °C) were obtained over La_0.88Ag_0.12FeO₃. Abundant molecular oxygen is desorbed from Ag substituted perovskite after 10% O₂ adsorption as verified by O₂- temperature programmed desorption (TPD). This reflects the strongly oxidative properties of La_0.88Ag_0.12FeO₃, which lead to a satisfactory NO reduction at 1% O₂ due to the ease of nitrate formation but to a significant C₃H₆ combustion above that value. The formation of nitrate species over the less oxidizing Ag/Al₂O₃ was accelerated under an excess of oxygen resulting in an excellent lean NO reduction behavior. The redox properties of silver catalysts could be adjusted via mixing perovskite with alumina for an optimal elimination of both NO and C₃H₆ over the whole range of oxygen concentration between 0 to 10%.     

Electrochemical promotion of Rh catalyst in gas-phase reduction of NO by propylene

The concept of non-faradaic electrochemical modification of catalytic activity (NEMCA) has been applied for the in situ control of catalytic activity of a rhodium film deposited on YSZ (yttria stabilized zirconia) solid electrolyte towards reduction of 1000 ppm NO by 1000 ppm C₃H₆ in presence of excess (5000 ppm) O₂ at 300 °C. A temporary heating at this feed composition results in a long-lasting deactivation of the catalyst under open circuit conditions due to partial oxidation of the rhodium surface. Positive current application (5 A) over both the active and the deactivated catalysts gives rise to an enhancement of N₂ and CO₂ production, the latter exceeding several hundred times the faradaic rate. While active rhodium exhibits a reversible behaviour, electrochemical promotion on the deactivated catalyst is composed of a reversible and an irreversible part. The reversible promotion results from the steady-state accumulation of current-generated active species at the gas exposed catalyst surface whereas the irreversible effect is due to the progressive reduction of the catalyst resulting in an increased recovery rate of lost catalytic activity. The results are encouraging with respect to application of rhodium for the catalytic removal of NO from auto-exhaust gases under lean-burn conditions.     

Characterization and Catalytic Properties of Combustion Synthesized Au/CeO2 Catalyst

Ceria-supported Au catalyst has been synthesized by the solution combustion method for the first time and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Au is dispersed as Au⁰ as well as Au³⁺ states on CeO₂ surface of 20-30 nm crystallites. On heating the as-prepared 1% Au/CeO₂ in air, the concentration of Au³⁺ ions on CeO₂ increases at the expense of Au⁰. Catalytic activities for CO and hydrocarbon oxidation and NO reduction over the as-prepared and the heat-treated 1% Au/CeO₂ have been carried out using a temperature-programmed reaction technique in a packed bed tubular reactor. The results are compared with nano-sized Au metal particles dispersed on -Al₂O₂ substrate prepared by the same method. All the reactions over heat-treated Au/CeO₂ occur at lower temperature in comparison with the as-prepared Au/CeO₂ and Au/Al₂O₂. The rate of NO + CO reaction over as-prepared and heat-treated 1% Au/CeO₂ are 28.3 and 54.0 mol g^-1 s^-1 at 250 and 300 °C respectively. Activation energy (E _a) values are 106 and 90 kJ mol^-1 for CO + O₂ reaction respectively over as-prepared and heat-treated 1% Au/CeO₂ respectively.     

SBR反应器中反硝化条件下去除苯酚工艺

基于异养反硝化原理,在序批式间歇反应器(SBR)中对反硝化同时降解苯酚的菌种进行了149 d的驯化,驯化通过逐步提高进水中苯酚和NO3--N的浓度进行.驯化结束后,进水苯酚质量浓度达到360 mg/L,葡萄糖质量浓度达到100 mg/L,NO3--N质量浓度达到240 mg/L,水力停留时间6 h,苯酚和NO3--N去除率均大于98%.反应器运行结果表明:进水苯酚质量浓度低于720 mg/L时,SBR反应器运行稳定;高浓度NO2--N(＞60 mg/L)可以严重影响微生物对苯酚以及NO3--N的去除能力,同时反应器中20.5%～23.5%的COD可被用于微生物的细胞合成.     

Can isotopic transient and formal steady-state kinetics lead to a converging surface chemistry analysis? Case study on the selective reduction of NO by CH4 over Co-ZSM-5 catalysts

The surface coverage analysis derived from two formal steady-state kinetic models is compared to values directly obtained from steady-state isotopic transient analysis (SSITKA) for the selective catalytic reduction (SCR) of NO by CH₄ over Co-ZSM-5 catalysts. It is shown that the most abundant reacting intermediates are NO _x adspecies, though no clear differentiation between the various adspecies identified by DRIFT spectroscopy was achieved. Less numerous carbon containing adspecies were identified and quantified in the reacting system, essentially as methoxy species. Nitromethane-like intermediates remained undetectable due to a very rapid transformation into N₂ and CO₂. On the basis of these converging kinetic analyses related to each elementary step of the SCR process, a microkinetic model can be derived, which allows describing transient operation, in view of a non steady-state application.     

Low temperature SCR of NO with NH3 over carbon nanotubes supported vanadium oxides

A novel multiwalled carbon nanotube (CNTs) supported vanadium catalyst was prepared. The structure of catalyst prepared was characterized by TEM, BET, FTIR, XRD and temperature-programmed desorption (TPD) methods. The results indicated that vanadium particles were highly dispersed on the wall of carbon nanotubes. The V₂O₅/CNT catalysts showed good activities in the SCR of NO with a temperature range of 373–523 K. The Lewis acid sites on the surface of V₂O₅/CNT are the active sites for the selective catalytic reduction (SCR) of NO with NH₃ at low temperatures. It was suggested that the reaction path might involve the adsorbed NH₃ species reacted with NO from gaseous phase and as well as the adsorbed NO₂ species. The diameter of CNTs showed positive effect on the activities of the catalysts. Under the reaction conditions of 463 K, 0.1 Mpa, NH₃/NO = 1, GHSV = 35,000 h⁻¹, and V₂O₅ loading of 2.35 wt%, the outer diameter of CNTs of 60–100 nm, the NO conversion was 92%.     

采用数值模拟方法研究同时氧化烟气中NO和SO2的可行性添加剂

Mechanism analysis on simultaneous oxidation of NO and SO2 with additives was presented and numerical simulation was developed to investigate the performances of three additives on oxidation of NO and SO2. The simulation result showed that reaction temperature, residence time, additive dose and NO concentration influence the oxidation process significantly. There exists an optimum reaction condition for each additive. n-C4H10 has the strongest ability to oxidize NO and SO2.