Photocatalytic H₂ Production from Naphthalene by Various TiO₂ Photocatalysts: Impact of Pt Loading and Formation of Intermediates

This work presents a comparative study of the efficiency of two commercial TiO₂ photocatalysts, Aeroxide P25 (ATiO₂) and Sachtleben Hombikat UV100 (HTiO₂), in H₂ production from an aqueous solution of naphthalene. The TiO₂ photocatalysts were platinized by the photodeposition method varying the platinum content of the suspension to 0.5, 1.0, and 5.0 wt%. A full physicochemical characterization for these materials was performed, showing no structural effects from the deposition method, and confirming a well dispersion of nanosized-Pt⁰ particles on the surface of both photocatalysts. Pristine ATiO₂ shows around 14% higher photocatalytic fractional conversion of naphthalene than pristine HTiO₂ after 240 min of irradiation, while both materials exhibit negligible activity for H₂ formation. The 0.5 wt% Pt- HTiO₂ increases the photocatalytic fractional conversion of naphthalene from 71% to 82% and produces 6 µmol of H₂. However, using a higher Pt content than the optimal platinization ratio of 0.5 wt% dramatically inhibits both processes. On the other hand, regardless of the fractional ratio of Pt, the platinization of ATiO₂ results in a decrease in the fractional conversion of naphthalene by 4% to 33% of the pristine value. Although the presence of Pt islands on the surface of the ATiO₂ is essential for the H₂ evolution, no dependency between the Pt ratio and the H₂ formation rate was observed since all the platinized materials show a similar H₂ formation of around 3 µmol. Based on the EPR results, the higher photocatalytic activity of the Pt-HTiO₂ is attributed to the efficient charge carrier separation and its larger surface area. The recyclability test confirms that the inhibition of the photocatalytic process is related to the deactivation of the photocatalyst surface by the adsorption of the photoformed intermediates. A strong relationship between the photocatalytic activity and the kind of the aromatic compounds was observed. The H₂ evolution and the photooxidation of the aromatic hydrocarbons exhibit higher photonic efficiencies than that of their corresponding hydroxylated compounds over the Pt-HTiO₂.