Reaction Mechanism of Ammonia Decompositon to Nitrogen and Hydrogen over Metal Loaded Titanium Oxide Photocatalyst

The reaction mechanism of ammonia decomposition to nitrogen and hydrogen over platinum loaded titanium oxide photocatalyst was investigated through various reaction tests, as well as ESR and FT-IR spectroscopies. The photoformed hole on the titanium oxide oxidizes NH3 to form amide radical (center dot NH2) and proton. The amide radicals produce hydrazine (N2H4), and it can be further decomposed to form nitrogen and hydrogen. On the other hand, the photoformed electron migrates to platinum nanoparticles through the conduction band of the titanium oxide and reduces the proton to yield hydrogen. The metals with larger work function, such as platinum, can provide more effective cocatalysts. In this photocatalytic reaction system, water molecules were essential for the continuous reaction progress. An in situ FT-IR study clarified that water restricted the accumulation of inactive byproduct, ammonium ion (NH4+), on the titanium oxide surface.