Zeta Potential Measurement in Catalyst Preparations

Oxide surfaces are covered with hydroxyl groups. In contact with water, positive or negative surface charges can be developed. The surface charge of oxide particles can be fine‐tuned by changing the calcination temperature of the oxides before dispersion in water or by variation of the suspension pH. Strong negative or positive surface charges stabilize a suspension and avoid particle aggregation. Nano‐structured catalysts suspended in water show surface charges different from those of compact TiO2. For spray drying, the cationic or anionic additives used have to be strongly attached via electrostatic forces to the surface of the suspended oxide particles. When noble metal complexes have to be brought to the support surface, the positively or negatively charged complexes must have an opposite charge relative to the surface charge. Zeta potential measurements can solve these problems. The measurement of the zeta potential as a function of the pH value is a valuable characterization method for optimization of the preparation of supported catalysts and slurries by spray drying. The effects of the calcination temperature, pH, catalyst support structure, and catalyst loading on the zeta potential have been investigated for various TiO2 samples. Hierarchical catalysts with a TiO2 layer between the TiO2 support and the catalyst have different zeta potential profiles and show an improved catalytic behavior in the oxidative dehydrogenation of propane.