Can TiO2 promote the reduction of nitrates in water?

Monometallic palladium catalysts were synthesized using different titanium supports and tested for the reduction of nitrates from aqueous solutions using hydrogen as a reductant. The Pd/TiO2 catalysts were characterized by electron paramagnetic resonance (EPR), low-temperature Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray diffraction (XRD). The catalysts studied exhibited a high activity for nitrate removal with a lower tendency for nitrite formation than the conventional bimetallic Pd catalysts. Although ammonium formation was greater than desired, the use of a monometallic catalyst for this two-step reduction process is significant and suggests that a single site may be responsible for both reduction stages. The titanium support (particularly the Ti3+ centers generated during prereduction in the presence of Pd) appear to play an important role in the nitrate degradation process. The potential role of Pd β-hydride in generating these Ti3+ centers is discussed.