国外SCR催化剂研究进展

文章简要介绍了NOx的来源、危害、控制方法以及SCR催化剂的分类和影响因素,在此基础上,还详细分析和论述了国外SCR催化剂的研究进展,并对SCR催化剂研究领域存在的问题进行了探讨.     

Transient TPSR, DRIFTS-MS and TGA studies of a Pd/ceria-zirconia catalyst in CH4 and NO2 atmospheres

In this study, the parameters governing the activity of Pd/ceria-zirconia catalysts in the selective catalytic reduction (SCR) of NO_x assisted by methane are investigated using a combination of temperature-programmed spectroscopic and thermogravimetric techniques and transient SCR conditions. By DRIFTS of adsorbed CO, it is established that Pd species on Ce_0.2Zr_0.8O₂ are mainly present in cationic form but exhibit high reducibility. As found by temperature-programmed surface reaction (TPSR) in CH₄ + NO₂ atmosphere, the CH₄-SCR reaction is initiated at 280 °C on Pd/Ce_0.2Zr_0.8O₂ and yields almost 100% N₂ above 500 °C. DRIFTS-MS and TGA experiments performed under transient SCR conditions show that DeNO_x activity is due to a surface reaction between some methane oxidation products on reduced Pd sites with ad-N_xO_y species presumably located on the support. The detrimental effect of O₂ on DeNO_x is explained by the promotion of the total combustion of methane assisted by the ceria-zirconia component at the expense of the SCR reaction above 320 °C.     

C2H2-SCR of NO over HZSM-5 affected by intracrystalline diffusion of NO x

The influence of particle size of HZSM-5 zeolite on selective catalytic reduction of NO by acetylene (C₂H₂-SCR) was investigated. The zeolite with nano-particle behaved considerable higher activity than the micro-particle one for the reaction. It was revealed that the large difference in the activity for the C₂H₂-SCR of NO arising from the particle size of zeolite was not caused by limited intracrystalline diffusion of the reductant, but that of NO₂, which was strongly supported by the adsorption results obtained over the zeolites.     

Characterization and catalytic investigation of Fe-ZSM5 for urea-SCR

Fe-ZSM5 was prepared with high iron content by solid-state ion exchange and characterized by ICP-AES, BET surface measurements, TEM, UV–vis, EPR and DRIFT spectroscopy as well as supplementing catalytic tests in order to clear up its functionality in urea-SCR. Due to the over-exchange with iron small Fe₂O₃ particles were formed, identified by UV–vis, EPR and TEM measurements, which were proved to be not active for the SCR reaction. However, the oxidation of NO to NO₂ over Fe³⁺ ions in the catalyst was realized to be a pre-requisite for the SCR reaction and the rate-determining step. DRIFT investigations under SCR conditions showed adsorbates on Fe²⁺ up to 300 °C. The high SCR activity above 300 °C can be explained by the faster reoxidation of Fe²⁺ to Fe³⁺ sites at high temperatures. The observed inhibition of the SCR reaction by excess ammonia at low and intermediate temperatures can be explained in this context by the reducing properties of ammonia converting Fe³⁺ to Fe²⁺ or by preventing the reoxidation of Fe²⁺.     

Characterisation of structured hydrolysis catalysts for urea-SCR

In the current study the performance of different substrates with respect to pressure drop, mixing between catalyst channels and urea conversion efficiency were measured. An increase of the volumetric conversion efficiency was found when structured substrates were applied. Also the use of solid-urea aerosol was compared to the AdBlue technology and found to be a promising alternative.     

Pillared smectite modified with carbon and manganese as catalyst for SCR of NOx with NH3. Part I. General characterization and catalyst screening

Carbon- and manganese-modified zirconia-pillared smectites were prepared, characterized (XRD, BET and pore analysis, XPS) and tested in selective catalytic reduction of NO_x with NH₃. Both untreated and acidic pretreated smectites were used. The acid pretreatment increased NO conversion and influenced the extent of carbon introduction into the porous system. The carbon deposit improved selectivity of the catalytic reduction to N₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study of the abatement of VOC over V2O5–WO3–TiO2 and alternative SCR catalysts

The conversion of C3 organic compounds (propane, propene, 1- and 2-propanol, allyl alcohol, propanal, acrolein, acetone and 1- and 2-chloropropane) in the presence of excess oxygen has been investigated over two V–W–TiO₂ commercial SCR catalysts differing in the V content and over Mn–TiO₂ alternative SCR catalysts. V–W–Ti catalysts show poor activity in the oxidation of hydrocarbons and oxygenates and give significant amounts of partial oxidation products. Moreover they give rise to CO in excess of CO₂. The sample higher in V is more active. Mn–TiO₂ is definitely more active in oxidation of hydrocarbons and oxygenates, and produces, at total conversion, CO₂ as the only detectable product.

V–W–Ti catalysts are very active in dehydrochlorination of the two 2-chloropropane isomers and retain the same oxidation activity also in the presence of HCl. On the contrary, Mn-based catalysts in the presence of chlorocarbons convert into dehydrochlorination catalysts but lose their catalytic activity in oxidation. V–W–Ti catalysts can be used in Cl-containing atmospheres while Mn–TiO₂ can be proposed for DeNO_x and VOC abatement in Cl-free atmospheres such as for diesel engine exhaust gas purification.     

关于大型燃煤电站锅炉选择性催化还原脱硝技术的探讨

介绍国内外脱硝技术及其应用现状,分析选择性催化还原脱硝技术(SCR)原理、反应器布置、运行控制和脱硝效率。     

Development of the efficient TiO2 photocatalyst in photoassisted selective catalytic reduction of NO with NH3

Photoassisted selective catalytic reduction (photo-SCR) of NO with NH₃ in the presence of O₂ takes place at room temperature over TiO₂ photocatalyst. From the results of photo-SCR reaction over various TiO₂, we found that JRC-TIO-11 exhibited the best activity. The reaction activity correlated to the amount of acid sites of TiO₂, but did not depend on the specific surface area and crystal diameter. The mixture of rutile and anatase shows higher activity than any of the corresponding TiO₂ single phase catalyst.     

Influence of zirconia raw materials on the development of DeNOx monolithic catalysts

Pd-zirconia-based monolithic catalysts were prepared with various commercial zirconia raw materials and a natural magnesium silicate binder, sepiolite, for the selective catalytic reduction (SCR) of NO with CH₄ in oxygen excess. The different textural properties, metastable tetragonal zirconia phase stability, surface acidity, Pd dispersion and catalytic properties of these monoliths were compared to select the most suitable structured catalyst for NO_x control in natural gas-fired power plants. The influence of operating temperature in the two reactions, NO reduction and CH₄ combustion, with the monolithic catalysts was determined. A 0.4 wt.% Pd-zirconia catalyst, manufactured from a sulphated zirconium hydroxide raw material, was selected as the most appropriate in the reaction under study, reaching a maximum NO conversion at 400 °C.