Hydrothermal Stability of HC-SCR DeNOx Catalysts

2 Hydrothermal Durability of HC-SCR DeNO Catalysts. - Among numerous HC-SCR deNOx catalysts examined, some of the catalysts exhibiting reasonable water tolerance are of particular interest for their commercial use their practical engine applications subsequently require essentially strong hydrothermal stability of the catalyst, particularly zeolite type catalyst. None of the potential SCR catalysts containing appropriate hydrothermal stability for removing NOx from mobile sources have been reported yet. This section will concentrate mainly on the time on-stream stability of potential catalysts for HC-SCR reaction. 

Cu-MFI-122 compared as a function of time on stream. The weight of catalyst was 50 mg in each case and the standard feed gas composition was NO, 2,000 ppm i-C4H,o, 2,000 ppm O2, 3%. H2O vapor (20%) and SO2 (150 ppm) were added in separate meteredfeed streams and were substituted for a portion of the He carrying gas. The calculated GHSV was 42,000 k (adopted from ref 53) 

Sachtler and coworkers have proposed a plausible reason why the overexchanged Fe-MFI catalysts can possess high deNOx activity and strong hydrothermal durability. The presence of 0x0-, hydroxo- and oxygen-bridged Fe ions as much as possible is crucial for such high catalytic properties. As already 

Catalyst Cu content SijAP CujAP Surface area (m /g) Fresh Hydrothermally-aged  

Copper ions in zeolites are mainly responsible for NO reduction activity therefore, deactivation would occur if alteration of their state or the zeolite structure were accompanied. The origin of the deactivation of Cu-exchanged zeolites due to their hydrothermal excursion has been published in several literatures. Solid state Al MAS NMR spectra of a Cu-MFI catalyst appeared to have a loss of 23% of framework aluminum after hydrothermal aging at 410°C in flowing 10% H20/90% air for 113 h. Kharas et reported the formation of 

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