NOx problem

The main problem with the barium oxide approach is that sulfur dioxide competes with NOx for the basic sites, and is converted irreversibly to barium sulphate, which is quite inert. Thus, the active barium sites are quickly saturated, and the removal of NOx from the emission is severely restricted. The sulfur content of the gasoline would need to be much lower for this approach to provide a long-term solution to the NOx problem. There may also be problems associated with the thermal stabihty of the barium oxide traps during the many redox cycles, which the catalyst would be expected to ejqrerience over the lifetime of an autocatalyst. 

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