A highly selective and robust catalyst based on Pt nanoclusters (NCs) confined inside the cavities of an amino-functionalized Zr-terephthalate metal-organic framework (MOF), UiO-66-NH 2 was developed. The Pt NCs are monodisperse and confined in the cavities of UiO-66-NH 2 even at 10.7 wt % Pt loading. This confinement was further confirmed by comparing the catalytic performance of Pt NCs confined inside and supported on the external surface of the MOF in the hydrogenation of ethylene, 1-hexene, and 1,3-cyclooctadiene. The benefit of confining Pt NCs inside UiO-66-NH 2 was also demonstrated by evaluating their performance in the chemoselective hydrogenation of cinnamaldehyde. We found that both high selectivity to cinnamyl alcohol and high conversion of cinnamaldehyde can be achieved using the MOFconfined Pt nanocluster catalyst, while we could not achieve high cinnamyl alcohol selectivity on Pt NCs supported on the external surface of the MOF. The catalyst can be recycled ten times without any loss in its activity and selectivity. To confirm the stability of the recycled catalysts, we conducted kinetic studies for the first 20 h of reaction during four recycle runs on the catalyst. Both the conversion and selectivity are almost overlapping for the four runs, which indicates the catalyst is very stable under the employed reaction conditions.

Atomically ordered intermetallic nanoparticles (iNPs) have sparked considerable interest in fuel cell applications by virtue of their exceptional electronic and structural properties. However, the synthesis of small iNPs in a controllable manner remains a formidable challenge because of the high temperature generally required in the formation of intermetallic phases. Here we report a general method for the synthesis of PtZn iNPs (3.2 ± 0.4 nm) on multiwalled carbon nanotubes (MWNT) via a facile and capping agent free strategy using a sacrificial mesoporous silica (mSiO) shell. The as-prepared PtZn iNPs exhibited ca. 10 times higher mass activity in both acidic and basic solution toward the methanol oxidation reaction (MOR) compared to larger PtZn iNPs synthesized on MWNT without the mSiO shell. Density functional theory (DFT) calculations predict that PtZn systems go through a "non-CO" pathway for MOR because of the stabilization of the OH* intermediate by Zn atoms, while a pure Pt system forms highly stable COH* and CO* intermediates, leading to catalyst deactivation. Experimental studies on the origin of the backward oxidation peak of MOR coincide well with DFT predictions. Moreover, the calculations demonstrate that MOR on smaller PtZn iNPs is energetically more favorable than larger iNPs, due to their high density of corner sites and lower-lying energetic pathway. Therefore, smaller PtZn iNPs not only increase the number but also enhance the activity of the active sites in MOR compared with larger ones. This work opens a new avenue for the synthesis of small iNPs with more undercoordinated and enhanced active sites for fuel cell applications.

Uniform ceria nanocrystals with good crystallinity and high surface areas were prepared by a facile alcohothermal method with the addition of bases (KOH or NaOH), using Ce(III) or Ce(IV) salt as a starting material. The as-prepared nanocrystals were characterized by means of powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), nitrogen adsorption, thermogravimetry and differential thermal analysis (TG-DTA), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and ultraviolet and visible spectroscopy (UV-vis). The ceria crystals had controllable sizes from 2.6 to 6.9 nm estimated by the PXRD line broadening analysis. TEM and HRTEM micrographs showed that the as-prepared ceria nanocrystals have a relatively high degree of crystallinity and low degree of conglomeration under high base concentrations. BET specific surface areas of the as-synthesized ceria nanocrystals were very high (103-238 m 2 g -1 ). XPS spectra indicated that the cerium in the nanocrystals was predominantly tetravalent. UV-vis spectra revealed that both the direct and indirect band gap energies of the as-prepared ceria nanocrystals showed a pronounced blue-shifting due to the quantum confinement effect compared to bulk ceria. And the dielectric confinement effect on the band gap energies was also discussed. The as-prepared ceria nanocrystals supported on γ-Al 2 O 3 exhibited a rather lower conversion temperature (559 K) for CO oxidation to CO 2 than that of bulk catalysts prepared by the coprecipitation method. Finally, a hydrolytic alcohothermal mechanism for the preparation of ceria nanocrystals was forwarded.

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