Denitrification catalyst is one of the essential components in the denitrification process of industrial flue gas treatment, and its use can improve denitrification efficiency and achieve ultra-low emissions. However, catalysts need to be replaced periodically during use as operating time increases, due to dust clogging, sintering, alkali metal poisoning, loss of active components, etc.
So, what are the common deactivation causes of denitrification catalyst deactivation?
1) Physical factors.
Decrease in catalyst activity due to changes in the physical properties of the catalyst itself or physical changes in the catalyst surface structure; mainly includes three types: high temperature sintering, pore blockage, and substrate abrasion.
2) Chemical factors.

The chemical activity of the active component is destroyed or inhibited after the catalyst absorbs and adsorbs the chemical components in the flue gas, which leads to the reduction of denitrification catalyst activity; mainly including: alkali metal (Na) poisoning, alkaline earth metal (Ca) poisoning, arsenic (As) poisoning, SO3 poisoning, phosphorus (P) poisoning, and the effect of water vapor (H2O).

01 Sintering
After long-term operation of SCR denitrification catalysts under high temperature conditions, TiO2 undergoes phase transition from anatase to rutile; at the same time, the active component V2O5 agglomerates to form large particles resulting in reduced dispersion. The specific surface area and activity of the catalyst will be reduced as a result.
02 Clogging
1) Surface coverage - the fly ash in the flue gas covers the surface of the catalyst monomer causing blockage (fly ash deposition).
2) Pore blockage - the internal pores of the catalyst are blocked, resulting in catalyst deactivation (ammonium salt deposition).
03 Abrasion
The intensity of catalyst abrasion is related to the airflow velocity, fly ash characteristics, impact angle and the catalyst itself characteristics.
1) Impact of the catalyst by external forces during installation or replacement.
2) Excessive flue gas flow velocity (> 8 m/s) during operation.
3) Excessive dust concentration (> 45 g/Nm3).
04 Alkali metal poisoning (Na, K)
Alkali metals can react directly with the active component of the catalyst, making the catalyst surface less acidic and reducing the reducibility of the active component, resulting in the loss of catalyst activity.
05 Alkaline earth metal poisoning (Ca)
The free CaO in the fly ash reacts with the SO3 adsorbed on the catalyst surface to form CaSO4, which scales on the catalyst surface and prevents the diffusion of the reacting material to the catalyst surface and to the catalyst interior.
06 Arsenic poisoning (As)
Arsenic (As) poisoning is caused by the presence of gaseous As2O3 in the flue gas. As2O3 is dispersed into the catalyst and solidified in the active and inactive regions, so that the diffusion of the reactant gas within the catalyst is restricted and the microscopic capillary pore channels are destroyed.
07 Sulfur poisoning (SO3)
Caused by the oxidation of SO2 in the flue gas to produce SO3. SO3 can react with CaO in the flue gas and the reducing agent NH3, and the corresponding products cover the catalyst surface and plug the pores.