Deactivation of the vanadia catalyst in the selective catalytic reduction process

Results are summarized of a comprehensive study of the effects on the SCR process of all major possible poisons encountered In the combustion gases from U.S. coals. A general rule evolved from this study is that the effect of the additive on the catalyst activity Is directly related to the basicity of the additive; poisoning Is caused by the basicity. Quantitative effects are presented, while a qualitative summary Is given as follows: strong poisons-alkall metal oxides; weak poisons-oxldes of alkaline earth metals, arsenic, lead phosphorus and chlorides of strong alkaline metals. S02 is a promoter due to Its acidity. HCI, although acidic, reacts with both NH3 (forming NH4CI) and V205 (forming VCI2 and VCI3) and consequently strongly deactivates the SCR reaction. A summary Is also given for a theoretical and experimental study of the monolithic honeycomb reactor using both undoped and poison-doped catalysts. The results showed that the reactor performance can be predicted directly from the Intrinsic catalyst activity through a model.