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1671051 
Journal Article 
Cryptomelane as high-capacity sulfur dioxide absorbent for diesel emission control: A stability study 
Li, LY; King, DL 
2005 
Yes 
Industrial and Engineering Chemistry Research
ISSN: 0888-5885
EISSN: 1520-5045 
44 
19 
7388-7397 
WOS:000231768600015 
A high-capacity sulfur oxide absorbent, cryptomelane, has been described previously. Its SO2 capacity can be as high as 70 wt %, which is more than 10 times as high as the capacities of standard metal oxide-based SO2 absorbents. In this study, the stability of cryptomelane under oxidizing, inert, reducing, and lean-rich cycling conditions was determined. Cryptomelane is stable in oxidizing and inert atmospheres. However, it is unstable under reducing atmospheres, converting to lower valent manganese oxide compounds. These low-valent oxides have very low capacity toward SO2. Upon reexposing the reduced cryptomelane products to an oxidizing atmosphere, cryptomelane may re-form. Cryptomelane exposed to the types of lean-rich cycles that have been proposed for NOx traps for diesel emission control, over the temperature range 250-550 degrees C, remains stable and maintains its very high SO2 capacity. It appears possible to use cryptomelane to protect the NOx traps from sulfur oxide degradation during cyclic lean-rich operation.