Deactivation of the Vanadia Catalyst in the Selective Catalytic Reduction Process

Abstract

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-alkali metal oxides; weak poisons-oxides of alkaline earth metals, arsenic, lead phosphorus and chlorides of strong alkaline metals. SO₂ is a promoter due to its acidity. HCI, although acidic, reacts with both NH₃ (forming NH₄CI) and V₂O₅ (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.