The VK-WSX formulation was developed to offer higher activity in SO₂ gasses that are more than 90% converted. Typically VK-WSX is used in the last bed of a WSA converter. For this service, VK-WSX is more active than VK-WSA and even more active than cesium-promoted VK-WH catalyst. The high activity is the result of carefully optimizing the alkali-metal promoter content to the specific conditions in WSA converters in combination with a unique support material. VK-WSX is a non-cesium catalyst; yet it can operate effectively at temperatures as low as 370°C/700°F, enabling very high conversion rates to be reached.

The high surface area of the 9 mm Daisy contributes to the high activity, and the high void fraction ensures a low pressure drop.