Low-temperature SCR

Yaccato K, Hagemeyer A, Lesik A, Volpe A, Weinberg WH. 2004. High throughput screening of low temperature SCR and SCD de-NOx catalysts in scanning mass spectrometer. Top Catal 30/31 127-132. 

Ammonia slip on large units like an FCCU translates to wasted chemical expense with no benefit to the refiner. Excess ammonia in a high temperature SCR will oxidize to create NO, which is counter to the intended purpose of the unit. Excess ammonia in a low temperature SCR will tend to form ammonium bisulfate (ABS) per Figure 17.9. 

Kim, H. H. Takashima, K, Katsura. S. and Mizuno, A. Low temperature SCR pnKess usmg pulsed corona discharge 1999 Annual meeting of lEJ, Chiba, Japan... 

The influence of the preparation method of In-modified zeolite catalysts for the SCR of NOx by methane on the structure of In species formed and the catalytic activity has been studied. The structure of the catalysts has been investigated by XPS, ISS, XAFS, FTIR, electron microscopy and TPR. Dependent on the preparation, indium may occupy zeolite cation sites or form intra- and extra-zeolite oxide aggregates. It was found that indium ions at cation sites provide a low-temperature SCR activity while clustered species are active at high temperatures. 

Besides these categories, the development of low temperature SCR catalysts for stationary applications has also been attempted at several Companies including Hitachi Zosen, Shell, Grace, Engelhard, and others. Hitachi Zosen has... 

Thomas, D., and Highfield, T. (2011) Ammonium FormateAJrea Based Diesel Exhaust Fluid for Superior Low Temperature SCR Performance, presentation at SAE Light-Duty Diesel Emissions Symposium, Detroit, November 2011. 

Yang, X., Narula, C. (2010) Simple Approach to Tuning Catalytic Activity of MFI-Zeolites for Low Temperature SCR of NOx, poster at US Department of Energy Directions in Engine Efficiency and Emissions Research (DEER) Conference, September 27-30, 2010, Detroit. 

The risk of salt formation depends on the local maximum of the product of NH3 SO3 along the catalyst. Higher vanadium content of the catalyst increases the SCR activity but also the SO conversion. Therefore, the sulfur content of the fuel limits the minimum dosing temperature as well as the low temperature SCR activity. Figure 2.15 is an estimate of the minimum temperature before catalyst for reductant dosing with regard to fuel sulfur content. 

Many SCR catalysts containing transition metals, such as Fe, Mn, Cr, Cu, have shown good activities for low-temperature SCR [2, 3, 6, 55-68]. Among these catalysts, manganese-based oxides have been extensively studied due to their excellent low-temperature SCR performance. Here, the pure manganese oxides, manganese-based mixed oxides (composite oxides), and supported manganese oxide catalysts are reviewed. 

Many other transition metals were added to further improve the low-temperature SCR performance on MnOx-Ce02 mixed oxides. Qi and Yang [66] found that the addition of Fe and Zr increased the low-temperature activity and N2 selectivity as well as the resistance to water and SO2 poisoning. Casapu et al. [75] reported that by... 

Tang X, Hao J, Yi H, Ei J (2007) Low-temperature SCR of NO with NH3 over AC/C supported manganese-based monolithic catalysts. Catal. Today 126 406-411. 

Qi G, Yang R T (2003) Performance and kinetics study for low temperature SCR of NO with NH3 over MnOx-Ce02 catalyst. J. Catal. 217 434-441. 

Ettireddy PR, Ettireddy N, Mamedov S, Boolchand P, Smirniotis PG (2007) Surface characterization studies of Ti02 supported manganese oxide catalysts for low temperature SCR of NO with NH3. Appl Catal B 76 (1-2) 123-134... 

Marban G, Valdes-SoKs T, Fueites A (2004) Mechanism of low-temperature SCR of NO with NH3 over carbon-supported Mu304. Phys Chem Chem Phys 6 (2) 453-464... 

Flura A, Can F, Courtois X, Royer S, Duprez D (2012) Silver supported over high-sutface-area zinc aluminate spinel as an active material in low-temperature SCR of NO with ethanol. Applied Catal. B 126 275-289... 

---