Performance evaluation of Pd/TiO2 and Pt/TiO2 photocatalysts for hydrogen production from ethanol-water mixtures

This study compares the photocatalytic activity of Pd/TiO2 and Pt/TiO2 photocatalysts (metal loadings 0.5 wt.% and 2 wt.%) for H-2 production from ethanol-water mixtures under UV excitation. Cationic Pd(II) and Pt(IV)/Pt(II) species were deposited on Degussa P25 TiO2 (85% anatase, 15% rutile) via the deposition-precipitation with urea method. Subsequent H-2 treatment at 350 degrees C reduced the adsorbed cationic species to predominantly Pd-0 and Pt-0, respectively. TEM analyses of the Pd/TiO2 and Pt/TiO2 photocatalysts revealed supported Pd and Pt nanoparticles of size <3 nm. XPS studies confirmed that the platinum was present primarily in metallic form, whereas palladium was present as both Pd-0 and PdO or Pd(OH)(2). Photoluminescence measurements demonstrated that Pd and Pt nanoparticles suppress electron-hole pair recombination in TiO2 by acting as electron acceptors. The Pt/TiO2 and Pd/TiO2 photocatalysts exhibited high activity and stability for H-2 production, with the optimum metal loadings being 0.5 wt.% for Pt (H-2 production rate = 41 mmol h(-1) g(-1)) and 2 wt.% for Pd (H-2 production rate = 34 mmol h(-1) g(-1)). Results confirm that the presence of zero valent Pd or Pt is critical for efficient H-2 production, and that both Pt/TiO2 and Pd/TiO2 photocatalysts are promising materials for solar H-2 production from biofuels.