The chemical environment of metal nanoparticles (NPs) possesses significant influence on their catalytic performance yet is far from being well understood. Herein, tiny Pd NPs are encapsulated into the pore space of metal–organic frameworks (MOFs), UiO‐66‐X (X = H, OMe, NH2, 2OH, 2OH(Hf)), affording Pd@UiO‐66‐X composites. The surface microenvironment of the Pd NPs is readily modulated by pore wall engineering, via the functional group and metal substitution in the MOFs. Consequently, the catalytic activity of Pd@UiO‐66‐X follows the order of Pd@UiO‐66‐OH > Pd@UiO‐66‐2OH(Hf) > Pd@UiO‐66‐NH2 > Pd@UiO‐66‐OMe > Pd@UiO‐66‐H toward the hydrogenation of benzoic acid. It is found that the activity difference is not only ascribed to the distinct charge transfer between Pd and the MOF, but is also explained by the discriminated substrate adsorption energy of Pd@UiO‐66‐X (–OH < –2OH(Hf) < –NH2 < –OMe < –H), based on CO‐diffuse reflectance infrared Fourier transform spectra and density‐functional theory (DFT) calculations. The Pd@UiO‐66‐OH, featuring a high Pd electronic state and moderate adsorption energy, displays the highest activity. This work highlights the influence of the surface microenvironment of guest metal NPs, the catalytic activity of which is dominated by electron transfer and the adsorption energy, via the systematic substitution of metal and functional groups in host MOFs.

Electronic band structure and optical properties of Cr-doped ZnO were studied using the density functional method within the generalized-gradient approximation. Three configurations with the substitution of Zn by one and two Cr atoms in different positions were considered. For the pure ZnO, the Fermi level locates at the valence band maximum, while it shifts to the conduction band and exhibits metal-like characteristic after Cr atoms are introduced into the ZnO supercell. The calculated optical properties indicate that the optical energy gap is increased after Cr doping. More importantly, strong absorption in the visible-light region is found, which originates from the intraband transition of the Cr 3d bands and the conduction bands. Our calculations provide electronic structure evidence that, in addition to usage as short-wavelength optoelectronic devices, the Cr-doped ZnO system could be a potential candidate for photoelectrochemical application due to the increase in its photocatalytic activity.

No abstract

A porphyrinic metal-organic framework (MOF), PCN-222(Fe), was found to exhibit sound activity and selectivity to cyclohexanone and cyclohexanol (known as KA oil) toward cyclohexane oxidation. Remarkably, hydrophobicity engineering of the MOF pore walls led to significantly enhanced activity and selectivity to KA oil, far superior to that of the homogeneous porphyrin catalyst.

Selective semihydrogenation of alkynes has been a long-term and significant target, yet it remains a great challenge. Herein, bimetallic nanoparticles in a metal−organic framework (MOF), i.e., CuPd@ZIF-8 composite, featuring a cubic CuPd core and a porous ZIF-8 shell, have been rationally fabricated for this end. Given the unique physicochemical properties, the Cu nanocubes can not only convert solar energy into heat to accelerate the reaction but also serve as the seed for in situ formation of Pd nanoparticles (NPs) on their external surface to regulate the chemoselectivity of Pd active sites. The additional growth of the MOF shell is helpful to stabilize the CuPd core and offer regioselectivity via the steric hindrance effect. Ammonia borane provides active hydrogen species to significantly boost the hydrogenation and ensure the high selectivity. As a result, the CuPd@MOF exhibits high efficiency, featuring a turnover frequency (TOF, 6799 min −1 ) of 5−10 5 times higher than that in previous reports, and high chemo-and regioselectivity toward the semihydrogenation of alkynes, in the presence of NH 3 BH 3 as a hydrogen source, under visible-light irradiation at ambient temperature.

No abstract

Selective hydrogenation with high efficiency under ambient conditions remains a long-standing challenge. Here, a yolk−shell nanostructured catalyst, PdAg@ZIF-8, featuring plasmonic PdAg nanocages encompassed by a metal−organic framework (MOF, namely, ZIF-8) shell, has been rationally fabricated. PdAg@ZIF-8 achieves selective (97.5%) hydrogenation of nitrostyrene to vinylaniline with complete conversion at ambient temperature under visible light irradiation. The photothermal effect of Ag, together with the substrate enrichment effect of the catalyst, improves the Pd activity. The near-field enhancement effect from plasmonic Ag and optimized Pd electronic state by Ag alloying promote selective adsorption of the −NO 2 group and therefore catalytic selectivity. Remarkably, the unique yolk−shell nanostructure not only facilitates access to PdAg cores and protects them from aggregation but also benefits substrate enrichment and preferential −NO 2 adsorption under light irradiation, the latter two of which surpass the core−shell counterpart, giving rise to enhanced activity, selectivity, and recyclability.

No abstract