NOx removal efficiency

Namihira, T., Tsukamoto, S., Wang, D. (2000) Improvement of NOx removal efficiency using short-width pulsed power, IEEE Trans. PI. Sci. 28, 434-42. 

Overexchanged Fe-MFI catalysts via an oxalate method offer high performance and hydrothermal durability for NOx reduction with iso-butane even in the presence of significant amounts of H2O and SO2 for high temperature deNOx application to the ICEs. However, this approach has hardly been reproducible. On the other hand, the CVD method can prepare such Fe-MFI catalysts on which somewhat lower NOx removal efficiency but still high durability can be achieved for the present reaction system. Not only could the technique be reproducible for the catalyst preparation, but it also depends strongly on the... 

Ammonia slip t)T)ically occurs when overstoichiometric amoimts of urea/ammonia are injected. Due to the ammonia storage capacity of the catalyst this is not emitted directly so if an appropriate control action is taken, ammonia slip can be avoided. However, up to today an inexpensive and fast NOx and/or ammonia sensor is not available to accommodate such a control action. Solutions have been proposed in the use of engine maps for predicting the NOx output [9] and/or an additional oxidation catalyst for avoiding ammonia slip [3]. The latter is detrimental to the sulfate emissions and as most of the oxidized ammonia will leave the system as NO, the overall NOx removal efficiency will be lowered. Therefore, it would be convenient if a possible overdose of ammonia will leave the system in the form of nitrogen (N2)- This would solve the SCR control problem. 

Work is continuing on the combination SCR + DPF system, wherein SCR catalyst is coated onto the DPF. This allows SCR catalyst to be placed on the vehicle without using an added component, and can get the SCR catalyst closer to the engine for faster light-ofif. Numerous reports dating to 2(X)8 show that total NOx removal efficiency is thus improved, with little to no compromise in DPF... 

Table 19.8 NOx removal efficiency and percentage of ammonia used to reduce NOx in a smart catalytic converter based on Pt-Ba-NSR and Fe-zeolite SCR catalyst...

Le Phuc N, Courtois X, Can F, Royer S, Marecot P, Duprez D (2011) NOx removal efficiency and ammonia selectivity during the NOx storage-reduction process over Pt/ BaO(Fe, Mn, Ce)/Al203 model catalysts. Part I Influence of Fe and Mn addition. Appl. Catal. B 102 353-361... 

This chapter does not intend to indicate that these observations are of general validity for the SCR-HC reaction and catalysts. Indeed, the results show that still further effort is necessary to understand the surface chemistry of this process. There are several factors affecting NOx removal efficiency with hydrocarbons, such as dispersion, coordination, and local electronic states of the metal cations. The oxide matrix surrounding the active sites is not inert, but plays both an indirect role (through electronic influence on the active centres) and a direct role (role of interface sites, surface acido-base centres — both Brpnsted and Lewis sites — and oxygen vacancies). The role of the oxide matrix shows several analogies with the role of the zeolite matrix in metal cation containing zeolites for SCR-HC [61]. 

Previous surface science studies showed that Rh is essential for NOx removal over TWC because NO dissociates more readily on metallic Rh than on Pt and Pd sites [26-28]. Nevertheless, the efficiency of Rh to selectively transform NO into N2 is restricted below the light-off temperature with a predominant formation of N20. Future practical developments are closely related to a better understanding of the formation and on the transformation of N20 over noble metals during the cold start engine. Such an aspect is still challenging over TWC and particularly under lean conditions since the extent in NO conversion is usually significantly lowered. 

Figure 1 shows the non linear dependence of 03 production efficiency on NOx and non methane hydrocarbon (NMHC) levels. The 03 production efficiency is defined as the number of 03 molecules produced per molecule of NOx removed from the atmosphere. This non linear behavior of chemistry in the atmosphere reflects the occurrence of catalytic cycles. It implies the consideration of the spatial variability of short-lived 03 precursors which present important concentration gradients between continental and oceanic areas. 

A key factor in limiting the ozone formation in the atmosphere is the efficiency of NOx removal from the atmosphere. Several reactions participate in the removal in the atmosphere, but in most of the troposphere NOx is removed by the reaction of N02 with OH ... 

Patents were filed by Babcock Wilcox [21-23] concerning the so-called SOx-NOx-Rox Box process, according to which, in line with Fig. 6b, contemporary SO2 and NOx removal (the former by adsorption on lime, the latter by catalytic reduction with ammonia) is accomplished by the use of catalytic filters, prepared as described in Section III. A schematic of the catalytic baghouse assembly is presented in Fig. 7. The results of the application of such technology to the treatment of a lab-scale atmospheric fluidized-bed coal boiler (capacity 0.5 MWe) were reported in Refs. 9 and 29. The achieved abatement efficiencies were 70-80% for SO2, 90% for NOx(NH3/NO ratio = 1 ammonia slippage = 10-15%), and 99% for particulate. Since March 1992 a 5-MWe demonstration project, funded by the U.S. Department of Energy and by the Ohio Coal Development Office,... 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

There are many ways in which CO2 is different from SO2 and NOx, but the one that seems to matter for allocation is the perceived potential for abatement. Put simply, the perception is that, with few exceptions, CO2 emissions cannot be reduced in relation to production other than by carbon capture and storage (CC S), which is available only at costs that are higher than any society is now willing to bear. At lower costs, this perception maintains that the only way of reducing CO2 emissions is to reduce output. This is a very different view of abatement potential from what characterises SO2 and NOx. In both cases, deep reduction technologies achieving 90% or better removal efficiency have... 

Using 100 cc of packed volume of catalyst loaded with ruthenium up to an extent of 0.2 wt%, 1 wt% and 2 wt% experimental studies were conducted to determine removal efficiency for NOx- Table-2 gives the experimental data obtained for the removal efficiency. It can be seen that 1 wt% loading gives the maximum efficiency. This study could lead to optimise the ruthenium content of catalyst under the operating conditions used. 

Further efforts are being made to improve the catalytic response of Ti02 for NOx removal. For example, Nakamura and coworkers [80], have used hydrogen plasma-treated Ti02 to sensitize the catalytic response in the visible wavelength region to make use of sunKght more efficiently. Anpo and coworkers have used chromium (Cr) ion-implanted... 

Shoyama, T. Yoshioka, Y. (2007). Theoretical study of methods for improving the energy efficiency of NOx removal from diesel exhaust gases by silent discharge. Electrical Engineering in Japan, Vol. 161, pp. 1-9... 

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