Platinum Ion-Doped TiO₂: High Catalytic Activity of Pt²⁺ with Oxide Ion Vacancy in Ti⁴⁺_1–xPt²⁺_xO_2–x Compared to Pt⁴⁺ without Oxide Ion Vacancy in Ti⁴⁺_1–xPt⁴⁺_xO₂

Abstract

Ti0.97Pt2+ 0.03O1.97 and Ti0.97Pt4+ 0.03O2 have been synthesized by a solution combustion method using alanine and glycine as the fuels, respectively. Both crystallize in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are in the 2+ state in Ti0.97Pt0.03O1.97 (alanine) and 4+ state in Ti0.97Pt0.03O2 (glycine). The rate of CO oxidation occurring over Ti0.97Pt2+ 0.03O1.97 (0.76 μmol·g–1·s–1) is ∼10 times more than that over Ti0.97Pt4+ 0.03O2 at 60 °C (0.08 μmol·g–1·s–1). A large shift in 100% hydrocarbons conversion to lower temperature was observed for Pt2+ ion-substituted TiO2 relative to that for Pt4+ ion-substituted TiO2. After reoxidation of the reduced compound by H2 as well as CO, Pt ions are stabilized in mixed valences, 2+ and 4+ states. The role of oxide ion vacancy has been demonstrated by CO oxidation and H2 + O2 recombination reactions in the presence and absence of O2. We analyze the activated lattice oxygens upon substitution of Pt2+ and Pt4+ ions in TiO2, using first-principles density functional theory (DFT) calculations with supercells of Ti31Pt1O63, Ti30Pt2O62, and Ti29Pt3O61 for Pt2+ ion substitution and Ti31Pt1O64, Ti30Pt2O62, and Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to that of Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens, and these oxygens are involved in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of Pt2+ ion and oxide ion vacancy and weakly bonded lattice oxygen.

Reactivity of atomically dispersed Pt2+ species towards H2: model Pt–CeO2 fuel cell catalyst

“…in the absence of other active species such as Pt 4+ , Pt 0 , and oxygen vacancies. [11][12][13] For instance, most of the studies employed Pt-doped CeO 2 materials in the form of solid solutions, Ce 1Àx Pt x O 2Àd , prepared by the solution combustion method. 11,12 This preparation method yields oxygen vacancies as the result of charge compensation upon substitution of Ce 4+ ions by Pt 2+ in the Ce 1Àx Pt x O 2Àd solid solution.…”

Mn Ion substituted CeO2Nano spheres for Low Temperature CO Oxidation: The Promoting Effect of Mn Ions

“…It may be concluded that oxygen deficiency is more in Ce 0.80 Mn 0.20 O 2‐δ due the presence of Mn 2+ ions . The vacancy between Ce +4 and Mn +2 is one oxygen atom, which is most helpful for oxygen storage and loosing whereas Mn +3 , Mn +4 ions are not contribute the vacancy of oxygen atom . Based on above results Mn +2 content is increased from 10 % Mn ion substitution to 20 %, beyond that content of Mn +2 is decreasing.…”

“…Ce 0.90 Mn 0.10 O 2‐δ and Ce 0.80 Mn 0.20 O 2‐δ catalysts have Mn 2+ ion about 4.5 % and 15 % respectively, whereas, Ce 0.50 Mn 0.50 O 2‐δ does not have +2 oxidation state. It may be concluded that oxygen deficiency is more in Ce 0.80 Mn 0.20 O 2‐δ due the presence of Mn 2+ ions . The vacancy between Ce +4 and Mn +2 is one oxygen atom, which is most helpful for oxygen storage and loosing whereas Mn +3 , Mn +4 ions are not contribute the vacancy of oxygen atom .…”

Visible light responsive TiO2 photocatalysts for degradation of indoor acetaldehyde

“…Mukri et al reported that the presence of Pt(II) brought about its d states above the VB edge and oxygen vacancies. 32 They demonstrated that Pt(II)-substituted TiO 2 with oxygen vacancies exhibited higher photocatalytic activity for CO oxidation than Pt(IV)-substituted TiO 2 without oxygen vacancies. Kim et al mentioned that Pt dopants created energy levels above the VB edge where the trapped holes are highly localized and the oxygen vacancies were created near the Pt(II) sites.…”