Unifying the Nitrogen Reduction Activity of Anatase and Rutile TiO2 Surfaces.

TiO2 is a model transition metal oxide that has been applied frequently in both photocatalytic and electrocatalytic nitrogen reduction reactions (NRR). However, the phase which is more NRR active still remains a puzzle. This work presents a theoretical study on the NRR activity of the (001), (100), (101), and (110) surfaces of both anatase and rutile TiO2 . We found that perfect surfaces are not active for NRR, while the oxygen vacancy can promote the reaction by providing excess electrons and low-coordinated Ti atoms that enhance the binding of the key intermediate (HNN*). The NRR activity of the eight facets can be unified into a single scaling line. The anatase TiO2 (101) and rutile TiO2 (101) surfaces were found to be the most and the second most active surfaces with a limiting potential of -0.91 V and -0.95 V respectively, suggesting that the TiO2 NRR activity is not very phase-sensitive. For photocatalytic NRR, the results suggest that the anatase TiO2 (101) surface is still the most active facet. We further found that the binding strength of key intermediates scale well with the formation energy of oxygen vacancy, which is determined by the oxygen coordination number and the degree of relaxation of the surface after the creation of oxygen vacancy. This work provides a comprehensive understanding of the activity of TiO2 surfaces. The results should be helpful for the design of more efficient TiO2 -based NRR catalysts.

Facilitating Catalytic Purification of Auto-Exhaust Carbon Particles via the Fe2O3{113} Facet-dependent Effect in Pt/Fe2O3 Catalysts.

The purification efficiency of auto-exhaust carbon particles in the catalytic aftertreatment system of vehicle exhaust is strongly dependent on the interface nanostructure between the noble metal component and oxide supports. Herein, we have elaborately synthesized the catalysts (Pt/Fe2O3-R) of Pt nanoparticles decorated on the hexagonal bipyramid α-Fe2O3 nanocrystals with co-exposed twelve {113} and six {104} facets. The area ratios (R) of co-exposed {113} to {104} facets in α-Fe2O3 nanocrystals were adjusted by the fluoride ion concentration in the hydrothermal method. The strong Pt-Fe2O3{113} facet interaction boosts the formation of coordination unsaturated ferric sites for enhancing adsorption/activation of O2 and NO. Pt/Fe2O3-R catalysts exhibited the Fe2O3{113} facet-dependent performance during catalytic purification of soot particles in the presence of H2O. Among the catalysts, the Pt/Fe2O3-19 catalyst exhibits the highest catalytic activities (T50 = 365 °C, TOF = 0.13 h-1), the lowest apparent activation energy (69 kJ mol-1), and excellent catalytic stability during soot purification. Combined with the results of characterizations and density functional theory calculations, the catalytic mechanism is proposed: the active sites located at the Pt-Fe2O3{113} interface can boost the key step of NO oxidation to NO2. The crystal facet engineering is an effective strategy to obtain efficient catalysts for soot purification in practical applications.

Facet Dependent Activity of Fe(III) Species Modified TiO2 for Simulated Sunlight Driven Fenton-like Reactions.

TiO2 crystals with different exposed facets are synthesized and modified facilely by depositing Fe(III) species. With more (101) facets exposed, the photoactivity of Fe-TiO2 is obviously enhanced with peroxymonosulfate (PMS) as oxidant. The degradation rate for 20 ppm Bisphenol A (BPA) on Fe-TiO2 (101) can achieve 0.219 min-1, ∼8.5 times faster than that of pure TiO2 under simulated sunlight irradiation. Photoelectrochemical measurements and density functional theory (DFT) calculations confirm that the interfacial charge transfer (IFCT) on Fe-TiO2 (101) is stronger than that on Fe-TiO2 (001) and a faster Fe(III)/Fe(II) transformation rate can be therefore achieved. As a result, the generation of ·OH and 1O2 will be accelerated with more (101) facets exposed, thus obtaining better photoactivity. Under the Fe-TiO2/PMS/Light system, BPA can be effectively degraded in a wide pH range or in the presence of multiple inorganic anions. After five cycles, 100% BPA can still be degraded within 60 min. The study provides new photocatalysts design strategy based on Fe(III)/Fe(II) redox for PMS based photocatalytic oxidation.