Selective catalytic reduction hydrothermal

Both SnOz and ZrOz are important catalysts and catalyst supports. SnOz is widely used in the selective catalytic reduction of NO because of its good hydrothermal stability as well as its fine oxidative selectivity [1,2] and SnOz-based composite oxides are very active catalysts for CH4 deep oxidation [3,4], ZrOz as a catalyst or catalyst support is used in many catalytic processes [5]. Besides their wide applications in catalysis, SnOz and ZrOz are useful materials as sensors, ceramics and solid electrolytes. 

Conversion of nitrogen oxides in the presence of NH3 to yield N2 (selective catalytic reduction, SCR) Cu-ZSM-5, Cu-ZSM-ll,Cu-ZSM-12, Cu-P, Cu-SSZ-13, Cu-SAPO-34 Small-pore, highly hydrothermally stable zeolites are currently of increasing interest in the SCR process [58, 71]... 

Park J-H, Park HJ, Baik JH et al (2006) Hydrothermal stability of CuZSM5 catalyst in reducing NO by NH3 for the urea selective catalytic reduction process. Journal of Catalysis 240 47-57... 

Moliner M, Franch C, Palomares E et al (2012) Cu-SSZ-39, an active and hydrothermally stable catalyst for the selective catalytic reduction of NOx, Chemical Communications 48 8264-8266... 

NHj-SCR activity after the 14-h hydrothermal treatment of Cu-SSZ-13, Cu-SAPO-34, Cu-SSZ-16, and Cu-ZSM-5 [41 ]. Reprinted from Picket DW, D Addio E, Lauterbach JA, Lobo RF. The ammonia selective catalytic reduction activity of copper-exchanged small-pore zeolites. Appl. Catal. B 2011 102 441—448. Copyright... 

Vennestrpm PNR, Janssens TYW, Kustov A, GriU M, Puig-Molina A, Lundegaard LF, et al. Influence of lattice stability on hydrothermal deactivation of Cu-ZSM-5 and Cu-IM-5 zeolites for selective catalytic reduction of NO by NHj. J Catal 2014 309 477-90. 

As already pointed out, catalytic reduction of NOx in a highly lean environment, such as diesel exhaust, is extremely limited. The problem, of course, is that the reductant (CO or HC) is consumed by the relatively large amount of O2, leaving virtually none for the reduction of NOx. The best selectivity has been reported for Cu/ZSM-5, but only above 350 C. Further limitations are susceptibility to poisons and poor hydrothermal stability. 

Recent literature shows a growing trend to include free alumina in the formulation of fluid catalytic cracking (FCC) products. Over the last dozen years, FCC catalysts containing free alumina have been cited in the open and patent literature for benefits including (1) enhanced catalyst reactivity and selectivity (1-3). (2) more robust operation in the presence of metals in the petroleum feedstock (4-7). (3) improved attrition resistance (8.9). (4) improved hydrothermal stability against steam deactivation during regeneration (2.8). (5) increased pore volume and decreased bulk density (8), and (6) reduction of SOx emissions (10). 

Fe-Exchanged Zeolites. Since overexchanged Fe-MFI containing a ratio of Fe/Al 1 appeared to exhibit extremely high catalytic activity and strong hydrothermal durability for the selective reduction of NOx with iso-butane as... 

This paper deals with the hydrothermal deactivation, under an air + 10 vol. % H2O mixture between 923 and 1173 K, of Cu-MFI solids, catalysts for the selective reduction of NO by propane. Fresh and aged solids were characterized by various techniques and compared with a parent H-ZSM-5 solid. The catalytic activities were measured in the absence and in the presence of water. The differences between fresh and aged Cu-ZSM-5 catalysts (destruction of the framework, extent of dealumination...) were shown to be small in spite of the strong decreases in activity. Cu-ZSM-5 is more resistant to dealumination than the parent H-ZSM-5 zeolite. The rate of NO reduction into N2 increases with the number of isolated Cu VCu ions. These isolated ions partially migrate to inaccessible sites upon hydrothermal treatments. At very high aging temperatures a part of the copper ions agglomerates into CuO particles accessible to CO, but these bulk oxides are inactive. Under catalytic conditions and in the presence of water, dealumination is observed at a lower temperature (873 K) than under the (air + 10 % H2O) mixture, because of nitric acid formation linked to NO2 which is either formed in the pipes of the apparatus or on the catalyst itself... 

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