TiO2 is very stable material. It hardly reacts with anything (very concentrated acids only). So the first answer is - yes the catalyst is stable.

The stability of TiO2 colloids can decrease in time due to the agregation of TiO2 nanoparticles. Also materials modified with organic compounds can show lower stability, because of the degradation of the modifier. Also if the material is used in the reductive conditions Ti(IV) can be reduced to Ti(III). This process is reversible, but can cause some problems with the material activity.

Of course photocatalytic activity of TiO2 materials can decrease in time. Molecules of photodecomposited pollutands can bind to the surface and block the activity.

depends on the condition which you kept the catalyst, but the most comun reason is the poisoned of catalysts because it's exposed at atmosphere, generally TiO2 don't low its stability when it's kept well

Dear Wang

   I am agree with Marta, Prof. Lopez and Mella.

i AM aGREE WITH Marta due to aggregation and moisture it happens

As most catalysts, TiO2 becomes progresively poissoned during its use, due to strong binding of some chemicals onto its surface.

The answers above are correct. Stability is very high for TiO2

However, catalytic activity may be lowered after some time of usage

This could be due to many reasons, as described above

another reason could be smoothing of the TiO2 particle surface by stirring inside reaction

poisoning is another reason

I have fone the aging of my supporter catalyst, please look my publications about it. The photocatalysis of butylparaben And cost effective photoreactor built.

thanks

Article Photo-degradation of butyl parahydroxybenzoate by using TiO2...

Yes.

This is due to aging and blockage of catalytic sites.

The TiO2 is very stable. However it could be affected by the deposition of volatile organic compounds (VOCs). in this case it could be easily regenerated by thermal treatment.

I am agrre with the answer of Marta Buchalska and Amir Zada. Nanoparticles as all solids suffer very slow surfece modificastion with time of ageing. But also the answer of Mosses Canle López is true. Of course in this case modification of TiO2 activity  depends of the concentration of compounds in contact with titania .

TiO2 is stable compound hence used in paints. However , the stability of TiO2 colloids decreases with time due to the aggregation of the TiO2 nano-particles.

I read a lot of papers which confirm the stability after 4 and 5 cycle of photodegradation efficiency using Tio2 so is a stable catalyst