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Industrial catalysts are typically made of nanosized metal particles, carried by a solid support. The extremely small size of the particles maximizes the surface area exposed to the reactant, leading to higher reactivity. Moreover, the higher the number of metal atoms in contact with the support, the better the catalyst performance. In addition, peculiar properties have been observed for some metal/metal oxide particles of critical sizes. However, thermal stability of these nanostructures is limited by their size; smaller the particle size, the lower the thermal stability. The ability to fabricate and control the structure of nanoparticles allows to influence the resulting properties and, ultimately, to design stable catalysts with the desired characteristics. Tuning particle sizes provides the possibility to modulate the catalytic activity. Unique and unexpected properties have been observed by confining/embedding metal nanoparticles in inorganic channels or cavities, which indeed offers new opportunities for the design of advanced catalytic sytems. Innovation in catalyst design is a powerful tool in realizing the goals of more green, efficient and sustainable industrial processes. The present Review focuses on the catalytic performance of noble metal‐ and non precious metal‐based embedded catalysts with respect to traditional impregnated systems. Emphasis is dedicated to the improved thermal stability of these nanostructures compared to conventional systems.

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“…[54] Alkoxide precursors of the support were hydrolyzed in the presence of alkylammonium-protected Pd particles to encapsulate them in the gel.…”

Section: Palladiummentioning

confidence: 99%

Embedded Phases: A Way to Active and Stable Catalysts

et al. 2010

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“…The metal nanoclusters stabilized with glycol and OH ) were first captured on the colloidal particles of metal oxides by the electrostatic interaction between the different nanoparticles, then the obtained mixture were gelated through adjusting its pH or heating [34]. This assembling process using two kinds of nanoparticles stabilized with solvent and simple ions as building blocks is different from those based on an in situ hydration process of M(OR) n compounds in the presence of ligand-protected metal nanoclusters reported previously [21,24,25]. The as-resulted catalysts become more regulable in structure, i.e., it becomes convenient to control both the size and composition of metal and support nanoparticles in the resulted catalysts and to modulate the catalytic properties by the interaction between the different nanoparticles as well as the external circumstances surrounding the catalytic sites.…”

Section: Fabrication Of Heterogeneous Catalystsmentioning

confidence: 99%

“…The support-entrapment method characterized by building a framework of inorganic supports via stacking metal oxide nanoparticles around preformed metal nanoclusters protected with organic ligand or polymer have been intensively studied in several groups. In this method, to obtain a close contact of the metal nanoparticles with inorganic supports, organic stabilizers originally adsorbed on the metal nanoclusters usually have to be removed by extraction [21,22] or pyrolysis [23][24][25][26][27] at the end of the catalyst preparation. However, these processes are not necessary in the preparation of heterogeneous catalysts using ''unprotected'' metal nanoclusters, which are favorable nanoscopic building blocks in assembling structuredesignable catalysts and other functional materials.…”

Section: Introductionmentioning

confidence: 99%

Metal Nanoclusters Stabilized with Simple Ions and Solvents—Promising Building Blocks for Future Catalysts

et al. 2005

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This work discusses the preparation of small metal nanoclusters stabilized with glycol and OH )1 , which are attractable building blocks for the fabrication of new heterogeneous catalyst. New Os and Pt/Rh bimetallic nanoclusters with small particle size and narrow size distribution have been prepared by the polyol synthesis method and characterized by TEM, EDX, XRD and XPS. Superior catalytic properties for the selective hydrogenation of chloronitrobenzene over the nanocomposite catalysts composed of metal nanocluters and inorganic semiconductor nanoparticles have been discussed.

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“…[61][62][63] Sol-gel has also been shown as an effective technique to embed nanoscale mono-and bimetallic noble metals. [64][65][66] Yu et al reported [67] that metal particles of tailored size (3-5 nm) and composition prepared by means of inverse microemulsion were encapsulated by ultrathin coatings (< 2.5 nm) of inorganic porous SiO 2 aerogels covered with surface OH groups.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

Pârvulescu

Endruschat

et al. 2006

Chemistry A European J

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Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au Mössbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.

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Cited by 40 publications

References 12 publications

Embedded Phases: A Way to Active and Stable Catalysts

Embedded Phases: A Way to Active and Stable Catalysts

Metal Nanoclusters Stabilized with Simple Ions and Solvents—Promising Building Blocks for Future Catalysts

Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

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Untitled

Cited by 40 publications

References 12 publications

Embedded Phases: A Way to Active and Stable Catalysts

Embedded Phases: A Way to Active and Stable Catalysts

Metal Nanoclusters Stabilized with Simple Ions and Solvents—Promising Building Blocks for Future Catalysts

Characterization and Catalytic‐Hydrogenation Behavior of SiO2‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

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Product

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Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids