Catalyst Deactivation Examples

2.1 Sintering of the Catalytic Component Next slide (Fig. 5.2) Sintering by growth of catalyst crystals This condition can be measured by selective chemisorptions techniques in which a thermally aged catalyst adsorbs much less adsorbate than when it was fresh. Stabilizer Certain rare-earth oxides such as CeO2 and La2O3 have been effective in reducing sintering rates of Pt in the automobile exhaust catalytic converter. It may fix the catalytic components to the surface minimizing mobility and crystal growth.

2.2 Carrier Sintering Within a given crystal structure, such as γ-Al2O3, the loss of surface area is associated with loss of H2O and a gradual loss of the internal pore structure network, as shown in the next slide (Fig. 5.3) Second slide (Fig. 5.4) Conversion profiles for various deactivation modes

Example 1

2. Thermally Induced Deactivation A perfectly dispersed (100% dispersion) catalyst is one in which every atom (or molecule) of active component is available to the reactants. This is shown is Fig. 5.1 (next slide).

Second mechanism for carrier change in crystal structure γ-Al2O3 → α-Al2O3 150 m2/g < 5 m2/g Anatase TiO2 Rutile TiO2 60 m2/g < 10 m2/g Stabilizer BaO, La2O3, SiO2, or ZrO2 can retard the rate of sintering in certain carriers. They are believed to form solid solutions with the carrier surface, decreasing their surface reactivity, which leads to sintering.