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.

Intermetallic compounds are garnering increasing attention as efficient catalysts for improved selectivity in chemical processes. Here, using a ship-in-a-bottle strategy, we synthesize single-phase platinum-based intermetallic nanoparticles (NPs) protected by a mesoporous silica (mSiO 2 ) shell by heterogeneous reduction and nucleation of Sn, Pb, or Zn in mSiO 2 -encapsulated Pt NPs. For selective hydrogenation of furfural to furfuryl alcohol, a dramatic increase in activity and selectivity is observed when intermetallic NPs catalysts are used in comparison to Pt@mSiO 2 . Among the intermetallic NPs, PtSn@mSiO 2 exhibits the best performance, requiring only one-tenth of the quantity of Pt used in Pt@mSiO 2 for similar activity and near 100% selectivity to furfuryl alcohol. A high-temperature oxidation-reduction treatment easily reverses any carbon deposition-induced catalyst deactivation. X-ray photoelectron spectroscopy shows the importance of surface composition to the activity, whereas density functional theory calculations reveal that the enhanced selectivity on PtSn compared to Pt is due to the different furfural adsorption configurations on the two surfaces. ABSTRACT: Intermetallic compounds are garnering increasing attention as efficient catalysts for improved selectivity in chemical processes. Here, using a ship-in-a-bottle strategy, we synthesize single-phase platinum-based intermetallic nanoparticles (NPs) protected by a mesoporous silica (mSiO 2 ) shell by heterogeneous reduction and nucleation of Sn, Pb, or Zn in mSiO 2 -encapsulated Pt NPs. For selective hydrogenation of furfural to furfuryl alcohol, a dramatic increase in activity and selectivity is observed when intermetallic NPs catalysts are used in comparison to Pt@mSiO 2 . Among the intermetallic NPs, PtSn@mSiO 2 exhibits the best performance, requiring only one-tenth of the quantity of Pt used in Pt@mSiO 2 for similar activity and near 100% selectivity to furfuryl alcohol. A hightemperature oxidation−reduction treatment easily reverses any carbon deposition-induced catalyst deactivation. X-ray photoelectron spectroscopy shows the importance of surface composition to the activity, whereas density functional theory calculations reveal that the enhanced selectivity on PtSn compared to Pt is due to the different furfural adsorption configurations on the two surfaces.

A bifunctional Zr-MOF catalyst containing palladium nanoclusters (NCs) has been developed. The formation of Pd NCs was confirmed by transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS). Combining the oxidation activity of Pd NCs and the acetalization activity of the Lewis acid sites in UiO-66-NH 2 , this catalyst (Pd@UiO-66-NH 2) exhibits excellent catalytic activity and selectivity in a one-pot tandem oxidation-acetalization reaction. This catalyst shows 99.9% selectivity to benzaldehyde ethylene acetal in the tandem reaction of benzyl alcohol and ethylene glycol at 99.9% conversion of benzyl alcohol. We also examined various substituted benzyl alcohols and found that alcohols with electron-donating groups showed better conversion and selectivity compared to those with electron-withdrawing groups. We further proved that there was no leaching of active catalytic species during the reaction and the catalyst can be recycled at least five times without significant deactivation.

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Recently, a facile method for the synthesis of size-monodisperse Pt, Pt Sn, and PtSn intermetallic nanoparticles (iNPs) that are confined within a thermally robust mesoporous silica (mSiO ) shell was introduced. These nanomaterials offer improved selectivity, activity, and stability for large-scale catalytic applications. Here we present the first study of parahydrogen-induced polarization NMR on these Pt-Sn catalysts. A 3000-fold increase in the pairwise selectivity, relative to the monometallic Pt, was observed using the PtSn@mSiO catalyst. The results are explained by the elimination of the three-fold Pt sites on the Pt(111) surface. Furthermore, Pt-Sn iNPs are shown to be a robust catalytic platform for parahydrogen-induced polarization for in vivo magnetic resonance imaging.

Control of heterogeneous catalytic sites through their surrounding chemical environment at an atomic level is crucial to catalyst design. We synthesize Pd nanoclusters (NCs) in an atomically tunable chemical environment using isoreticular metal-organic framework (MOF) supports (Pd@UiO-66-X, X = H, NH 2 , OMe). In an aerobic reaction between benzaldehyde and ethylene glycol, these catalysts show product distributions that are completely altered from the acetal to the ester when we change the functional groups on the MOF linkers from −NH 2 to −H/-OMe. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies, along with density functional theory (DFT) calculations, show that the coordination of the −NH 2 groups to the Pd NCs could weaken their oxidation capability to a greater extent in comparison to that of the −OMe group. Moreover, the limited number of −NH 2 groups per cavity in the MOF change the electronic properties of the Pd NCs while still leaving open sites for catalysis.

Few-layer graphene (FLG) supported ruthenium nanoparticle catalysts were synthesized and used for the hydrogenation of levulinic acid (LA), one of the "top 10" biomass platform molecules derived from carbohydrates. FLG-supported ruthenium catalyst showed 99.7% conversion and 100% selectivity toward γvalerolactone (GVL) at room temperature in a batch reactor under high-pressure hydrogen. This catalyst showed 4 times higher activity and exceptional stability in comparison with traditional activated carbon supported ruthenium catalysts (Ru/C). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies suggest that the superior catalytic properties of Ru nanoparticles supported on FLG in LA hydrogenation could be attributed to the greater metallic Ru content present in the Ru/FLG in comparison to that in Ru/C. ABSTRACT: Few-layer graphene (FLG) supported ruthenium nanoparticle catalysts were synthesized and used for the hydrogenation of levulinic acid (LA), one of the "top 10" biomass platform molecules derived from carbohydrates. FLG-supported ruthenium catalyst showed 99.7% conversion and 100% selectivity toward γ-valerolactone (GVL) at room temperature in a batch reactor under high-pressure hydrogen. This catalyst showed 4 times higher activity and exceptional stability in comparison with traditional activated carbon supported ruthenium catalysts (Ru/C). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies suggest that the superior catalytic properties of Ru nanoparticles supported on FLG in LA hydrogenation could be attributed to the greater metallic Ru content present in the Ru/FLG in comparison to that in Ru/C. NotesThe authors declare no competing financial interest. ■ ACKNOWLEDGMENTSThis work was supported through funding from the Iowa Energy Center. We thank Iowa State University for startup funds. We also thank Gordon J. Miller for use of his XRD instrument and Igor I. Slowing for use of his ICP-AES instrument. The valuable discussion with Young-Jin Lee and Aaron J. Rossini is greatly appreciated.