Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para‐Hydrogen‐Enhanced Polarization

Zhao, Evan Wenbo; Zheng, Haibing; Zhou, Ronghui; Hagelin‐Weaver, Helena E.; Bowers, Clifford R.

doi:10.1002/ange.201506045

Cited by 26 publications

(7 citation statements)

References 48 publications

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“…A similar trend was reported recently by Bowers and colleagues in propene hydrogenation with parahydrogen when shaped ceria nanocrystals were used as catalysts. 26 There is, however, a clear effect of Pd particle size on the polarization observed in the experiments. The studied catalysts can be contingently grouped into three subgroups according to particle size: smaller than 5 nm (Pd co2.6 /SiO 2 ), 5−15 nm (Pd c10 /SiO 2 , Pd co7 /SiO 2 , Pd/TiO 2 ), and larger than 15 nm (Pd c18 /SiO 2 , Pd oct37 /SiO 2 ).…”

Section: Resultsmentioning

confidence: 83%

Acetylene Oligomerization over Pd Nanoparticles with Controlled Shape: A Parahydrogen-Induced Polarization Study

et al. 2016

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Substantial signal enhancements achieved by using parahydrogen in catalytic hydrogenations are powerful tools for mechanistic studies of chemical reactions involving molecular H2. Potentially, this technique can be extended to other reaction classes, providing new information about reaction mechanisms. Moreover, this can lead to new substances with highly polarized spins. Herein, we report strong signal enhancements of oligomerization reaction products observed during the selective hydrogenation of acetylene over Pd nanoparticles of different shapes and sizes supported on SiO2. C4 oligomeric products (1,3-butadiene, 1-butene, 2-butene) demonstrated a high degree of nuclear spin polarization, with the highest degree observed for 1-butene [more than 1.7% vs (2.4 × 10–3)% at thermal equilibrium], which was an order of magnitude larger than that of the triple CC bond hydrogenation products. No dependence of polarization on the metal surface statistics or, generally, on the nanoparticle morphology (cubic, octahedral, cuboctahedral) could be observed. In contrast, the particle size effect was such that larger particles provided higher signal enhancements. This observation is in line with the increased activity over larger Pd nanoparticles observed during acetylene hydrogenation over the same catalysts.

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Section: Resultsmentioning

confidence: 83%

Acetylene Oligomerization over Pd Nanoparticles with Controlled Shape: A Parahydrogen-Induced Polarization Study

et al. 2016

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“…The equation we used to calculate the theoretical signal enhancement factor was reported previously 24 and is shown in eq S4 2.5. TEM and XRD Characterizaiton.…”

Section: Theoretical Altadena Signal Enhancement Factormentioning

confidence: 99%

Tuning Pd–Au Bimetallic Catalysts for Heterogeneous Parahydrogen-Induced Polarization

Wang

et al. 2018

J. Phys. Chem. C

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The heterogeneous hydrogenation of propene over supported Pd–Au bimetallic nanoparticles was investigated using NMR and the parahydrogen-induced polarization (PHIP) technique. The composition and structure of Pd–Au/TiO2 catalysts were correlated to both catalytic activity and pairwise hydrogen addition. Sol-immobilization, impregnation, and deposition–precipitation methods were used for preparation of the Pd–Au bimetallic catalysts. A strong signal enhancement was observed on the bimetallic catalyst prepared through the sol-immobilization method, up to 24-fold higher than that with the other two methods. The polyvinyl alcohol (PVA) stabilizer bound to the metal surface was responsible for the enhanced PHIP effect. The removal of the PVA ligands by water washing and calcination treatments shows a significant effect on the hydrogen pairwise addition. Increasing the Au content in the bimetallic alloy led to a promotion of the pairwise selectivity due to the ensemble effect. The pairwise selectivity could be tuned by the morphologies of Pd–Au structures; the Au-shell/Pd-core morphology produced a higher pairwise selectivity than that of the Pd-shell/Au-core structure, while the random PdAu alloy showed the best PHIP effect.

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“…18 Quasicubic Fe 2 O 3 nanoparticles exhibited enhanced catalytic CO oxidation activity compared to that of flower-like nanoparticles featuring exclusive exposure of the (110) crystalline planes, 19 and strong facet-dependence of propene hydrogenation activity over ceria catalysts was also reported. 20 The second factor that contributes to the different activities of different morphologies is the extent to which an active facet is exposed, and this is important especially when the active facet is known. The catalytic activity decreased in the order nanobelts > nanoplates > nanosheets in the formaldehyde oxidative decomposition on different morphologies of Co 3 O 4 nanocrystals, and this trend was explained in terms of different specific surface areas and different abundance of active surfacesituated oxygen in these morphologies.…”

Section: Introductionmentioning

confidence: 99%

Integrated Experimental and Theoretical Study of Shape-Controlled Catalytic Oxidative Coupling of Aromatic Amines over CuO Nanostructures

et al. 2016

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We have synthesized CuO nanostructures with flake, dandelion-microsphere, and short-ribbon shapes using solution-phase methods and have evaluated their structure–performance relationship in the heterogeneous catalysis of liquid-phase oxidative coupling reactions. The formation of nanostructures and the morphological evolution were confirmed by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, elemental mapping analysis, and Fourier transform infrared spectroscopy. CuO nanostructures with different morphologies were tested for the catalytic oxidative coupling of aromatic amines to imines under solvent-free conditions. We found that the flake-shaped CuO nanostructures exhibited superior catalytic efficiency compared to that of the dandelion- and short-ribbon-shaped CuO nanostructures. We also performed extensive density functional theory (DFT) calculations to gain atomic-level insight into the intriguing reactivity trends observed for the different CuO nanostructures. Our DFT calculations provided for the first time a detailed and comprehensive view of the oxidative coupling reaction of benzylamine over CuO, which yields N -benzylidene-1-phenylmethanamine as the major product. CuO(111) is identified as the reactive surface; the specific arrangement of coordinatively unsaturated Cu and O sites on the most stable CuO(111) surface allows N–H and C–H bond-activation reactions to proceed with low-energy barriers. The high catalytic activity of the flake-shaped CuO nanostructure can be attributed to the greatest exposure of the active CuO(111) facets. Our finding sheds light on the prospective utility of inexpensive CuO nanostructured catalysts with different morphologies in performing solvent-free oxidative coupling of aromatic amines to obtain biologically and pharmaceutically important imine derivatives with high selectivity.

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Shaped Ceria Nanocrystals Catalyze Efficient and Selective Para‐Hydrogen‐Enhanced Polarization

Cited by 26 publications

References 48 publications

Acetylene Oligomerization over Pd Nanoparticles with Controlled Shape: A Parahydrogen-Induced Polarization Study

Acetylene Oligomerization over Pd Nanoparticles with Controlled Shape: A Parahydrogen-Induced Polarization Study

Tuning Pd–Au Bimetallic Catalysts for Heterogeneous Parahydrogen-Induced Polarization

Integrated Experimental and Theoretical Study of Shape-Controlled Catalytic Oxidative Coupling of Aromatic Amines over CuO Nanostructures

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