The photocatalytic degradation of formic acid was compared for a suspended system, an irnmobilized system with a coated wall and an immobilized system packed with coated glass beads. The quantum yields found for the three systems are comparable. Mass transfer limitations only occurred in the tubular reactor with the catalyst coated on the wall. The addition of air directly in this reactor increased the degradation rate by decreasing the mass transfer limitation. In the packed-bed reactor, two bead diameters were compared. Thc activity of these packed-bed reactors appeared to be comparable for low amounts of titanium dioxide, whereas the packed-bed reactor with the large beads shows a higher activity for high amount of catalyst.