Selective catalytic reduction catalyst sizing

Copper ions exchanged microporous molecular sieves, in particular Cu-ZSM-5, are active catalysts for the selective catalytic reduction of NO and N2O with hydrocarbons in the presence of O2 (HC-SCR). It has been reported that the catalytic activity may be controlled by intra-crystalline diffiisivity and by geometry-limited diffusion depending on the hydrocarbon molecular size and the zeolite pore size [1]. Therefore, it is of interest to prepare Cu-Al-MCM-41 mesoporous molecular sieves and to compare their activity with that of Cu-ZSM-5. 

It appears interesting to investigate vanadia doped sulfated Ti-pillared clay for the selective catalytic reduction of NO by anmionia and to compare their performance with sulfated Ti-pillared clay and vanadia doped Ti-pillared clay. In this work, all the catalysts were synthesized under identical conditions and were characterized by different techniques. These techniques included surface area measurement, pore size distribution, X-ray diffraction. X-ray photoelectron spectroscopy, TPD-NH3 and chemical analysis of Ti retained by the clay. The catalysts were then tested in the selective catalytic reduction of NO by ammonia in the presence of oxygen at different temperatures. 

Selective catalytic reduction (SCR) is typical performing in much cooler flue gas zones where the oxidation potential of nifrogen species is minimized. The cafalysf provides, on ifs surface, sites that permit the ammonia and NOx to react near perfect utilization. The extent of NO reduction is often limited by the local ammonia to NO ratio, the flue gas femperafure, fhe size of cafalysf, and the accepted unreacted ammonia slip. The catalyst size is limited by the available space, the resulting gas side pressure drop, the oxidation from SO2 to SO3, and so on. 

Titania-supported vanadia catalysts have been widely used in the selective catalytic reduction (SCR) of nitric oxide by ammonia (1, 2). In an attempt to improve the catalytic performance, many researchers in recent years have used different preparation methods to examine the structure-activity relationship in this system. For example, Ozkan et al (3) used different temperature-programmed methods to obtain vanadia particles exposing different crystal planes to study the effect of crystal morphology. Nickl et al (4) deposited vanadia on titania by the vapor deposition of vanadyl alkoxide instead of the conventional impregnation technique. Other workers have focused on the synthesis of titania by alternative methods in attempts to increase the surface area or improve its porosity. Ciambelli et al (5) used laser-activated pyrolysis to produce non-porous titania powders in the anatase phase with high specific surface area and uniform particle size. Solar et al have stabilized titania by depositing it onto silica (6). In fact, the new SCR catalyst developed by W. R. Grace Co.-Conn., SYNOX , is based on a titania/silica support (7). 

In order to decrease the number of bricks in the posttreatment exhaust line, some combinations can be found such as integrating catalytic treatment and filtration step. The aim of this single brick is to reduce the overall size of the posttreatment system and to reduce the cost of the final engine. One approach to achieve this goal is to coat the soot filter with a catalyst composition effective for the conversion of NO in innocuous components. With this selective catalytic reduction filtration (SCRF) concept, the catalyzed soot filter assumes two functions removal of the particulate and conversion of the NO species to N2 of the exhaust stream (Scheme 35.6). 

It is well established that ultrasmall metal clusters on supports have catalytic properties distinct from those properties of large bulk-like particles, as illustrated by the selective oxidation of propylene to propylene oxide by gold, alkene and arene hydrogenation catalysis,and CO oxidation. In these examples, the catalytic properties improve as the clusters become smaller. On the other hand, a reduction in size of the metal cluster can lead to less desirable catalytic properties as seen for ammonia synthesis on iron. Various explanations have been offered to account for the unique properties of nanoscaled metal catalysts, however, much remains to be understood. Clearly, experimental and theoretical studies will be required to develop an in-depth under-... 

A low offline injection mass flow will also reduce the potential risk and measures to be taken against trace metals and alkali compound contaminations in exhaust systems where selective catalytic reactors for NO reduction or CO catalysts are installed. A low offline injection mass flow will significantly reduce the required size, volume, and cost of washing skids and consequently the overall water and cleaner consumption. 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

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