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[Display omitted] • Ir – TiO 2 interaction was dependent on Ir sizes and crystal plane of TiO 2. • Both activity and selectivity of the catalysts increased as the Ir size grew from single atom to nanoparticle. • End-on C O adsorption of crotonaldehyde was favored at the Ir-TiO x interface for Ir nanoparticles. • Crotonaldehyde adsorption geometry depends on H coverage on the catalyst surface. For the supported catalysts for the selective hydrogenation of α, β - unsaturated aldehyde with H 2 , tailoring of metal - support interfacial effect to improve reaction performance is a significant but challenging subject. In this work, we regulated both the size regimes of the Ir deposits (single atom, nanocluster and nanoparticle) and the crystal plane of anatase TiO 2 (TiO 2 (1 0 1), TiO 2 (1 0 0) and TiO 2 (0 0 1)) so as to alter the Ir-TiO x interfacial properties, in order to unravel reaction mechanism of selective hydrogenation of crotonaldehyde over the Ir/TiO 2 catalysts. Both the activity and selectivity to crotyl alcohol increased as the Ir size grew from single atom to nanoparticle, ascribed to high Ir0 content, high concentration of surface defects and prominent H-spillover effect on the Ir nanoparticles. Moreover, the in situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrated that an end-on C O adsorption mode for crotonaldehyde molecule was favored at the Ir-TiO x interface particularly at high H coverage, which thus facilitated the hydrogenation of C O bond to form crotyl alcohol. Moreover, the highest reactivity of the Ir nanoparticles was evidenced by the lowest reaction barrier. These results explicitly demonstrate that larger metal nanoparticles and adsorption geometry of the reactant at the metal - support interface are vital for improved catalytic performance, which would shed light on the ingenious catalyst design. [ABSTRACT FROM AUTHOR]

The hydrogenation of CO 2 to methane over a 20 wt% Ir/TiO 2 catalytic coating has been investigated in a tubular dielectric barrier discharge (DBD) reactor. The 1.2 µm Ir/TiO 2 coating was deposited onto the inner wall of a quartz tube by a combustion-evaporation method from a mixture containing a Ti precursor and a colloidal suspension of Ir nanoparticles (2 nm). The catalyst was characterised by XRD, SEM, TEM/EDS and CO chemisorption. The Ir(0) state in the as-synthesised film was confirmed by XPS. The CH 4 conversion increased by 1.5 times, as compared to an empty tube. A maximum CO 2 conversion rate of 2.1 μmol s−1 was achieved at a fuel production efficiency of 3.5%. Surface reactions onto the catalyst surface are responsible for enhancement of reaction rate. The results presented in this work open up new possibilities in plasma-catalysis, whereby efficient reactions can be carried out over small volumes of catalyst. [Display omitted] • The highest CO2 conversion was observed over Ir/TiO2 at the same level of energy efficiency. • The particle size and dispersion remained essentially the same after 3 h on stream in plasma. • Methane was the main reaction product in the catalytic pathway. • IrO2 phase is responsible for high catalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalytic performance of Ir/TiO 2 catalysts depended on the crystal plane of TiO 2. • Ir/TiO 2 -{1 0 1} catalyst gave 4-fold higher activity than that of Ir/TiO 2 -{0 0 1} catalyst. • The defects sites of TiO x support were responsible for the formation of crotyl alcohol. • Ir-TiO x interfacial sites may account for the formation of 1-butanol. Supported Ir/TiO 2 catalysts with the anatase TiO 2 nanocrystals exposing {1 0 1}, {1 0 0} and {0 0 1} planes were tested for selective hydrogenation of crotonaldehyde. The Ir/TiO 2 -{1 0 1} catalyst dominantly exposing {1 0 1} plane gave a initial reaction rate of 166.1 μmol g Ir -1 s−1 at 80 °C and a turnover frequency of crotyl alcohol formation of 0.022 s−1, which is 5 and 7 times respectively higher than those obtained on the Ir/TiO 2 -{0 0 1} catalyst dominantly exposing {0 0 1} plane even though they have similar Ir particle sizes (ca. 1.3 nm). The reaction behaviors were related to the surface oxygen vacancy, which served as surface acid sites and provide adsorption sites for C O bond in the CRAL molecule. Therefore, the higher concentration of oxygen vacancy in the Ir/TiO 2 -{1 0 1} accounted for the improved performance compared to the Ir/TiO 2 -{0 0 1}. However, strong adsorption of crotonaldehyde and/or products on the catalyst surface, as well as the CO poisoning via decarbonylation of crotonaldehyde, were the main reasons for the catalyst deactivation. [ABSTRACT FROM AUTHOR]

Various supported Ir/TiO2 catalysts were prepared using different Ir precursors (i.e., H2IrCl6, (NH4)2IrCl6 and Ir(acac)3) and tested for vapor phase selective hydrogenation of crotonaldehyde. The choice of Ir precursor significantly altered the Ir-TiOx interaction in the catalyst, which thus had essential influences on the geometric and electronic properties of the Ir species, reducibility, and surface acidity, and, consequently, their reaction behaviors. The Ir/TiO2-N catalyst using (NH4)2IrCl6 as the precursor gave the highest initial reaction rates and turnover frequencies of crotyl alcohol formation. Such high performance was ascribed to the high Ir dispersion and high surface concentration of Ir0 species, as well as a higher surface acidity, in the Ir/TiO2-N catalyst compared to its counterparts, indicating the synergistic roles of the Ir-TiOx interface in the reaction, as the interfacial sites were responsible for the adsorption/activation of H2 and the C=O bond in the crotonaldehyde molecule.

The catalytic performance of Ir/TiO2-FeOx, an Ir/TiO2 catalyst modified with FeOx, was investigated for the hydrogenation of o-chloronitrobenzene, FeOx was found to promote both the activity and selectivity significantly. The initial reaction rate of Ir/TiO2-FeOx(10) nanocomposite catalyst was four times as high as that of Ir/TiO2 catalyst. Especially, the accumulation of intermediates was prohibited and finally 100% selectivity to o-chloroaniline was obtained at 100% conversion. Herein, we mainly discussed the promoting effect of FeOx with using the results of powder X-ray diffraction, transmission electron microscopy, element analysis mapping, hydrogen-temperature programmed reduction, hydrogen-temperature programmed desorption, diffuse reflectance infrared fourier transform spectra and X-ray photoelectron spectroscopy analysis. The FeOx was highly dispersed and a portion of FeO species existed in the Ir/TiO2-FeOx nanocomposite catalyst. Moreover, the FeOx was certified to have a strong interaction with Ir species, which should contribute to the excellent performance of the Ir/TiO2-FeOx nanocomposite catalyst. [ABSTRACT FROM AUTHOR]

Gaseous ammonia (NH 3) in the atmosphere is potentially harmful to both human health and the environment. The selective catalytic oxidation of NH 3 (termed as NH 3 –SCO) into N 2 and H 2 O is a promising method for decreasing NH 3 emissions. A highly efficient catalyst is required for controlling NH 3 emissions by this method in practice. In this study, we prepared Ir/TiO 2 catalysts using different crystal structures of TiO 2 (rutile, P25 or anatase) as supports by a simple impregnation method and evaluated their performance in the NH 3 –SCO. We found that the Ir/TiO 2 –R (rutile) catalyst performed better than the Ir/TiO 2 –P25 (mixed–phase) and Ir/TiO 2 –A (anatase) catalyst. High–angle annular dark–field images of the aberration–corrected scanning transmission electron microscopy revealed that the Ir species were mainly atomically dispersed on the TiO 2 support in Ir/TiO 2 –R with 1 wt% Ir loading, whereas the Ir species agglomerated to form clusters or nanoparticles in Ir/TiO 2 –P25 and Ir/TiO 2 –A. The combined results of X–ray absorption fine structure, H 2 –temperature–programmed reduction, and in situ diffuse reflectance for infrared Fourier Transform spectroscopy studies suggested that atomically dispersed Ir species had stronger electronic metal–support interaction with rutile TiO 2 , which resulted in easier to adsorb and activate O 2 at the interface and thus, better low–temperature activity of the Ir/TiO 2 –R catalyst. [Display omitted] • T 100% of NH 3 is 60 °C lower on Ir/TiO 2 –R than that on Ir/TiO 2 –A catalyst. • Single–atom Ir 1 on rutile TiO 2 provides uniform and abundant active sites. • EMSI between single–atom Ir 1 and TiO 2 contribute to activation O 2 at interface. [ABSTRACT FROM AUTHOR]

Various supported Ir/TiO2 catalysts were prepared using different Ir precursors (i.e., H2IrCl6, (NH4)2IrCl6 and Ir(acac)3) and tested for vapor phase selective hydrogenation of crotonaldehyde. The choice of Ir precursor significantly altered the Ir-TiOx interaction in the catalyst, which thus had essential influences on the geometric and electronic properties of the Ir species, reducibility, and surface acidity, and, consequently, their reaction behaviors. The Ir/TiO2-N catalyst using (NH4)2IrCl6 as the precursor gave the highest initial reaction rates and turnover frequencies of crotyl alcohol formation. Such high performance was ascribed to the high Ir dispersion and high surface concentration of Ir0 species, as well as a higher surface acidity, in the Ir/TiO2-N catalyst compared to its counterparts, indicating the synergistic roles of the Ir-TiOx interface in the reaction, as the interfacial sites were responsible for the adsorption/activation of H2 and the C=O bond in the crotonaldehyde molecule. [ABSTRACT FROM AUTHOR]

Ir-based heterogeneous catalysts for photocatalytic CO 2 reduction have rarely been reported and are worthy of investigation. In this work, TiO 2 nanosheets with a higher specific surface area and more oxygen vacancies were employed to support Ir metal by impregnation (Imp) and ethylene glycol (EG) reduction methods. In comparison with Ir/TiO 2 (Imp) and TiO 2 , Ir/TiO 2 (EG) exhibited excellent photocatalytic performance toward CO 2 reduction, especially for CH 4 production on account of the oxygen defect of TiO 2 and rich surface hydroxyl groups produced from the interaction between TiO 2 nanosheets and metallic Ir. In situ ESR suggested that the oxygen defect was significant for CO 2 adsorption/activation. Furthermore, metallic Ir was beneficial for photogenerated electron transfer, surface hydroxyl generation, and adsorption of the CO intermediate, generating more available electrons and reducing agents for CH 4 production. In situ CO 2 DRIFTS confirmed the key synergistic interaction between the oxygen defect and metallic Ir in the photoreduction from CO 2 to CH 4 .