Unusual decreases in activity (deactivation) often occur during the use of VOCs catalysts, resulting in the catalyst not being used properly. The following is a brief description of the causes and countermeasures for catalyst deactivation.
1. Low temperature of catalyst
If the catalyst use temperature is lower than the catalyst required temperature, then VOCs or CO will tend to coke (accumulate carbon) on the catalyst surface. The figure below shows an extreme case, if the catalyst surface is simply carbonized, it is recommended to raise the catalyst temperature to 350 oC for 4-24 hours under air atmosphere.
2. Ultra-high temperature catalyst use
If the catalyst is used at ultra-high temperature, the active components (platinum and palladium) on the catalyst surface will agglomerate and the particles will grow, making the effective active sites of the catalyst decrease and the catalyst activity decreases. In addition, the high temperature will cause the catalyst specific surface area to decrease and the catalyst carrier and co-catalyst to react in solid phase, etc., making the catalyst activity decrease. The degradation of catalyst performance due to ultra-high temperature use of catalysts is irreversible, so ultra-high temperature use must be avoided in the process of catalyst use.
3. Effect of dust on catalyst
If the VOCs gas contains dust, small particles of dust can easily enter the catalyst micropores and degrade the catalyst performance, so it is important to ensure that the dust content in the VOCs gas is relatively low. If large particles of dust are deposited on the catalyst surface, then it can be cleaned up by blowing with high pressure air.
4. Organosilicon poisoning
Oil usually refers to organosilicone oil, where the organic group is all methyl is called methyl silicone oil. When organosilane enters the pore of catalyst and reacts, the C element in organosilane is converted into CO2, H element is converted into water, and Si element is converted into SiO2. Since SiO2 is a solid, it will stay in the tiny pore of catalyst and block the pore, leading to the deactivation of catalyst. Moreover, this deactivation is irreversible. Therefore, it is important to avoid the poisoning of silicone during VOCs treatment. Organosilicon poisoning is also irreversible and must be avoided.
5. Metal organic compound poisoning
The poisoning mechanism of metal-organic compounds is similar to that of silicones.
6. Poisoning by P, F, Pb, Zn elements
These substances poisoning of catalysts, the mechanism is still unclear, I think the poisoning of such substances is also irreversible poisoning. I have done experiments that phosphoric acid can easily deactivate precious metal catalysts, but the mechanism of deactivation is not clear.
7. Cl and S poisoning
I believe that the effect of S on catalyst poisoning is very small, and Cl poisoning is basically reversible as long as it is not in high concentration and for a long time. However, when chlorine-containing organics are present, the catalyst performance can be degraded because of the strong adsorption of chlorine-containing organics on the catalyst surface. Catalyst performance can be largely recovered by subjecting the catalyst to a temperature of 350 oC in an air atmosphere (without chlorine) for 4-24 hours. Prolonged and high concentrations of prolonged poisoning can still lead to irreversible catalyst poisoning.
