The doping of In2O3 significantly promoted the catalytic performance of Co3O4 for CO oxidation. The activities of In2O3–Co3O4 increased with an increase in In2O3 content, in the form of a volcano curve. Twenty-five wt % In2O3–Co3O4 (25 InCo) showed the highest CO oxidation activity, which could completely convert CO to CO2 at a temperature as low as −105 °C, whereas it was only −40 °C over pure Co3O4. The doping of In2O3 induced the expansion of the unit cell and structural distortion of Co3O4, which was confirmed by the slight elongation of the Co–O bond obtained from EXAFS data. The red shift of the UV–vis absorption illustrated that the electron transfer from O2– to Co3+/Co2+ became easier and implied that the bond strength of Co–O was weakened, which promoted the activation of oxygen. Low-temperature H2-TPR and O2-TPD results also revealed that In2O3–Co3O4 behaved with excellent redox ability. The XANES, XPS, XPS valence band, and FT-IR data exhibited that the CO adsorption strength became weaker due to the downshift of the d-band center, which correspondingly weakened the adsorption of CO2 and obviously inhibited the accumulation of surface carbonate species. In short, the doping of In2O3 induced the structural defects, modified the surface electronic structure, and promoted the redox ability of Co3O4, which tuned the adsorption strength of CO and oxygen activation simultaneously.

Selective hydrogenation of unsaturated aldehydes to unsaturated alcohols is a valuable but challenging task for synthesizing fine chemicals. We report that single Rh atoms anchored to the edges of 2D MoS2 sheets can efficiently convert crotonaldehyde to crotyl alcohol with 100% selectivity via a steric confinement effect of pocketlike active sites. Characterization results suggest that the synthesized Rh1/MoS2 single-atom catalysts (SACs) possess a unique geometric and electronic configuration, which confines the adsorption mode of the reactant molecule by a steric effect. The DFT calculations suggest that the MoS2 sheets terminate with oxidized Mo edges and the Rh1 stably anchors at the Mo cation vacancy site, which can facilely dissociate H2 to H atoms. The dissociated H atoms spill over to react with the edge O atoms to form OH species and create an HO–Mo–Rh1–Mo–OH configuration, resembling a pocketlike active site, which confines the adsorption mode of the crotonaldehyde due to steric effects. Such specific adsorption configuration yields 100% selectivity. The strategy of constructing pocketlike active centers with single metal atoms and 2D nanosheets opens new approaches to designing highly selective SACs for specific classes of catalytic transformations.

No abstract

Pd/H-ZSM-5 catalysts could completely catalyze CH 4 to CO 2 at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO x interacting with the surface Bronsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH 3 -TPD data. Density functional theory calculations suggest PdO x groups to be the active sites for methane combustion, in the form of [AlO 2 ]Pd(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO x species are two key characteristics of the active sites ([AlO 2 ]Pd(OH)-ZSM-5) for methane combustion. As a result, the PdO x species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH 4 over Pd/H-ZSM-5 catalysts.