Guozhu Chen

Institut national de la recherche scientifique, Québec, Quebec, Canada

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Publications (6)28.46 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: To enhance the catalytic activity of gold nanoparticles (AuNPs) for the hydrogenation of nitro-aromatic chemicals, Pt was introduced into AuNPs to form "bare" PtAu alloy NPs using a physical approach, pulsed laser ablation in liquid (PLAL), on single metal-mixture targets. These PLAL-NPs are deemed to favor catalysis due to the absence of any surfactant molecules on their unique "bare and clean" surface. The PLAL-NPs were facilely assembled onto CeO2 nanotubes (NTs) by simply mixing them without conducting any surface functionalization, representing another advantage of these NPs. Their catalytic activity was assessed in 4-nitrophenol (4-NP) hydrogenation. The reaction catalyzed by alloy-NP/CeO2-NT catalysts demonstrates a remarkably higher reaction rate in comparison with that catalyzed by pure Au and Pt NPs, and other similar Au and Pt containing catalysts reported recently. A "volcano-like" catalytic activity dependence of the alloy NPs on their chemical composition suggests a strong synergistic effect between Au and Pt in the 4-NP reduction, far beyond the simple sum of their individual contributions. It leads to the significantly enhanced catalytic activity of Pt30Au70 and Pt50Au50 alloy NPs, outperforming not only each single constituent, but also their physical mixtures and most recently reported AuNP based nanocatalysts. The favorable d-band center shift of Pt after alloying, and co-operative actions between Pt clusters and nearby Au (or mixed PtAu) sites were proposed as possible mechanisms to explain such a strong synergistic effect on catalysis.
    Nanoscale 11/2013; · 6.23 Impact Factor
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    ABSTRACT: Ligand-free Ru nanoclusters supported on carbon black have been synthesized in situ for the first time from the reduction of RuCl3 by ammonia-borane concomitantly with its hydrolysis process at room temperature, and their catalytic activity has been investigated. Well dispersed Ru nanoclusters (∼1.7 nm) are stabilized and immobilized by carbon black. Due to the small size and the absence of ligands on the surface, the Ru catalysts exhibit high catalytic activity, which is partly retained after 5 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia-borane is first order with respect to Ru catalyst concentration; the turnover frequency is 429.5 mol H2 min−1 mol−1 Ru. The activation energy for the hydrolysis of ammonia-borane in the presence of Ru/C catalysts has been measured to be 34.81 ± 0.12 kJ mol−1, which is smaller than most of the values reported for other catalysts, including those based on Ru, for the same reaction.
    International Journal of Hydrogen Energy 12/2012; 37(23):17921–17927. · 3.55 Impact Factor
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    ABSTRACT: Hollow Ru nanoparticles with ~14 nm diameter and ~2 nm shell thickness are reported for the first time, by removal of Ni from the delicately designed Ni@Ru core@shell NPs. Such hollow Ru NPs exhibit enhanced catalytic activity in the dehydrogenation of ammonia borane with respect to solid ones.
    Chemical Communications 07/2012; 48(64):8009-11. · 6.38 Impact Factor
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    ABSTRACT: We report the synthesis and characterization of new Ni(x)Ru(1-x) (x = 0.56-0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet-chemistry method using a rapid lithium triethylborohydride reduction of Ni(2+) and Ru(3+) precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We found that the as-prepared Ni-Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni-Ru alloy NPs, and in particular the Ni(0.74)Ru(0.26) sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core-shell NPs. The hydrolysis activation energy for the Ni(0.74)Ru(0.26) alloy catalyst was measured to be approximately 37 kJ mol(-1). This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol(-1)) and Ru NPs (≈49 kJ mol(-1)), and for Ni@Ru (≈44 kJ mol(-1)), and is also lower than the values of most noble-metal-containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.
    Chemistry 04/2012; 18(25):7925-30. · 5.93 Impact Factor
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    ABSTRACT: Core-shell structured Ni@Ru bimetallic nanoparticles are demonstrated as a bifunctional nanoplatform system for the hydrolysis reaction of ammonia-borane and also for magnetic separation.
    Chemical Communications 06/2011; 47(22):6308-10. · 6.38 Impact Factor
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    ABSTRACT: We report the preparation and catalytic properties of a new nanostructured catalyst, made of small (∼5 nm in diameter) and uniform gold nanoparticles (AuNPs) and ceria nanotubes (CeO2 NTs). “Surfactant-free” AuNPs fabricated by pulsed laser ablation in liquid (PLAL) on a bulk Au target are efficiently assembled onto the surface of CeO2 NTs without performing any surface functionalization of either component to promote their coupling, thanks to the presence of OH on the PLAL-AuNPs. The reduction reaction of 4-nitrophenol into 4-aminophenol catalyzed by our PLAL-AuNP/CeO2-NT catalyst exhibits remarkably higher reaction rate in comparison to that catalyzed by similar catalysts composed of chemically prepared AuNPs (Chem-AuNPs) as an active phase and/or commercially available CeO2 powder as support. Their superior catalytic activity is found to be due to the unique, relatively “bare” surface of the PLAL-AuNPs as well as oxidized Au species induced by the strong interaction between the “barrier-free” surface of PLAL-AuNPs and surface defects (oxygen vacancies) of CeO2 NTs. The important role of unique surface chemistry of PLAL-AuNPs in catalysis was further demonstrated in CO oxidation reaction in gas phase. Our results suggest that the use of PLAL-AuNPs enables easy and efficient attachment of AuNPs onto the surface of the CeO2 NTs and their unique combination leads to the development of highly efficient catalysts. Our design and fabrication of the nanocatalysts take full advantage of the unique features of the PLAL-AuNPs and potentially constitute a general and efficient route to prepare other metal-NP/metal-oxide-support catalysts, which can therefore largely expand the applications of PLAL-noble metal NPs in catalysis.
    Applied Catalysis B: Environmental. s 132–133:107–115.