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[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]

[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]

[Display omitted] • Pd/TiO 2 {100} is highly active and stable for CO 2 hydrogenation into formate. • The activity is benefit from the moderate basic site and metallic Pd species. • Higher density of moderate basicity over Pd/TiO 2 {100} favors for CO 2 activation. • More metallic Pd species over Pd/TiO 2 {100} contributes to H 2 activation. • The stability is benefit from strong Pd-TiO 2 interactions. • The oxygen vacancy in the TiO 2 {100} promote the Pd-TiO 2 interactions. Pd supported on different anatase TiO 2 nanocrystals predominantly exposing either {1 0 0}, {1 0 1}, or {0 0 1} facets were tested for CO 2 hydrogenation into formate. Remarkable morphology-dependent catalysis was observed. Compared to 2%Pd/TiO 2 {1 0 1} and 2%Pd/TiO 2 {0 0 1} catalysts, 2%Pd/TiO 2 {1 0 0} is highly active and stable, affording an unprecedented turnover frequency of ca. 1369 h−1 and keeping stable after 6 cycles at 313 K. This can be associated with, on the one hand, higher density of moderate basic site and relatively more Pd(0) species over 2%Pd/TiO 2 {1 0 0} contribute to the activations of CO 2 and H 2 , respectively, favorable for the activity; On the other hand, higher oxygen vacancy concentrations in the TiO 2 {1 0 0} promote the Pd-TiO 2 interactions and result in the formation and stability of flat Pd particles over 2%Pd/TiO 2 {1 0 0}, beneficial to the stability. These results highlight the importance of oxide morphology in formate formation and open up possibilities of oxide morphology engineering for developing efficient Pd-based catalysts for CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Pd-CeO 2 interaction is related to the oxygen vacancy concentration in the CeO 2. • Higher oxygen vacancy concentration in Pd/r-CeO 2 results in higher content of Pd2+ species. • The highest content of metallic Pd species in Pd/p-CeO 2 accounts for the best activity. • Hydrogenation of bidentate carbonate and bicarbonate species is the rate determining step. Several Pd catalysts supported on CeO 2 with different morphologies (i.e. CeO 2 rods (r-CeO 2), cubes (c-CeO 2) and polyhedra (p-CeO 2)) were tested for the CO 2 hydrogenation into formate. Remarkable morphology - dependent Pd-CeO 2 interaction was observed, which was related to the oxygen vacancies in the CeO 2. The r-CeO 2 with the highest concentration of oxygen vacancy resulted in smaller Pd particles and more positively-charged Pd species in the Pd/r-CeO 2 catalyst. The best performance was obtained over the Pd/p-CeO 2 catalyst, giving a turnover frequency of 746 h−1 at 40 °C. The enhanced activity was due to the highest content of metallic Pd species in the catalyst, which was responsible for the facile activation of H 2. Moreover, in situ spectroscopic results revealed that the hydrogenation of the carbonaceous intermediates was the rate - determining step. This work demonstrates oxide morphology engineering as a powerful strategy in developing efficient Pd - based catalysts for CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]