N₂O Adsorption and Photochemistry on High Area TiO₂ Powder

Abstract

The adsorption and photochemistry of N 2 O chemisorbed on TiO 2 powder has been investigated. At 157 K, nitrous oxide is molecularly adsorbed on the reduced titanium dioxide. Adsorption on the TiO 2 surface takes place through both the N and O ends of the nitrous oxide molecule. The photochemistry of the adsorbed N 2 O molecules was studied at 157 K by use of UV irradiation in the range 2.1-5.0 eV. The photoactivity of the adsorbed molecule is dependent on the N 2 O coverage. At low coverages, the adsorbed N 2 O is photodepleted to produce adsorbed nitrogen. Larger coverages of N 2 O are not photodepleted to N 2 due to the site blocking in the adsorption process. N-bonded species show a higher photoreactivity than the O-bonded species. Photoformation of NO was not observed at any N 2 O coverage.

A surface science perspective on TiO2 photocatalysis

“…In another example, Rusu and Yates. [705] showed that photocatalytic conversion of N 2 O was slightly faster if the N-end of the molecule was bound to surface Ti 4+ sites rather than if the O-end was utilized. Also, N 2 (the preferred product) was formed at low N 2 O coverages with the N-end down species.…”

“…Surface coverage has been shown to affect photocatalytic activity on TiO 2 surfaces in several examples [541,705,[717][718][719]. This author and coworkers [541] have shown that the rate of trimethyl acetate (TMA) photodecomposition on R TiO 2 (110) depended on the TMA surface coverage.…”

“…Although discussed in detail below, O 2 photodesorption is believed to result from the interaction of a VB hole with an adsorbed O δ− 2 species, resulting in a neutral O 2 molecule that readily desorbs from the surface. Other examples of molecular photodesorption from TiO 2 surfaces include alkyl halides [680][681][682]754,755,757], CO [783], N 2 O [705] and triethylamine [784]. The details of these events differ, but in each case the photodesorption event involves a charge carrier causing a charge change in the adsorbate-surface relationship that results in the adsorbate transitioning to a different potential energy surface (e.g., ion to neutral) that is more amenable to desorption.…”

“…Photoreduction studies of nitrogencontaining molecules on TiO 2 have been diverse, including those involving NO [557,788,[881][882][883][1162][1163][1164][1165], N 2 O [705,1166], NO 2 [1167], nitrate or nitrite [1168][1169][1170], and a variety of nitro-substituted aromatics [685,[1171][1172][1173][1174][1175]. As mentioned in Section 5.2, studies on NO have been approached mainly from the perspective of using ammonia or CO to perform selective catalytic reduction [557,788,[881][882][883].…”

Synthesis, characterization, and visible light activity of new nanoparticle photocatalysts based on silver, carbon, and sulfur-doped TiO2

“…Indeed, photocatalysis emerged as a new scientific area when Fujishima and Honda carried out photolysis of water into environmentally clean fuels (hydrogen and oxygen) using a titanium dioxide electrode in an electrochemical cell [1]. Ever since, heterogeneous photocatalysis by means of TiO 2 has been widely accepted and exploited as an efficient technology for killing bacteria and degrading organic and inorganic pollutants [2][3][4][5][6][7][8][9][10][11][12][13]. Moreover, titanium dioxide (TiO 2 ) has been regarded as an excellent semiconductor photocatalyst because of its performance, low cost, nontoxicity, stability, and availability.…”