Hydrodeoxygenation of lignin-derived phenolics – a review on the active sites of supported metal catalysts

The development of efficient catalysts is of great importance for hydrogen evolution reaction (HER) of water splitting via electrocatalytic/photocatalytic processes to remediate the current severe environmental and energy problems. By aid of the stabilization effects of uncoordinated groups and inherent pore‐confinement of amine‐functionalized metal–organic frameworks (NH2‐MIL‐125), two forms of Ru species including nanoparticles (NPs) and/or single atoms (SAs) can be firmly embedded in NH2‐MIL‐125 derived N‐doped TiO2/C support (N‐TC), and thus obtain two kinds of samples named Ru‐NPs/SAs@N‐TC and Ru‐SAs@N‐TC, respectively. In the synthetic process, the initial feeding amount of Ru3+ ions not only strongly determines the final size and dispersion states of Ru species but also the morphology and defective structures of N‐TC support. Impressively, Ru‐NPs/SAs@N‐TC exhibit superior catalytic activities to Ru‐SAs@N‐TC for either electrocatalytic or photocatalytic HER. This should be attributed to its larger specific surface area and benefiting from synergistic coupling of Ru NPs and Ru SAs. It is envisioned that the present work can provide a new avenue for development of high‐efficiency and multifunctional hybrid catalysts in sustainable energy conversion.

Ru Species Supported on MOF‐Derived N‐Doped TiO2/C Hybrids as Efficient Electrocatalytic/Photocatalytic Hydrogen Evolution Reaction Catalysts

Nanoparticle/metal–organic frameworks (MOF) based composites have recently attracted significant attention as a new class of catalysts. Such composites possess the unique features of MOFs (including clearly defined crystal structure, high surface area, single site catalyst, special confined nanopore, tunable, and uniform pore structure), but avoid some intrinsic weaknesses (like limited electrical conductivity and lack in the “conventional” catalytically active sites). This review summarizes the developed strategies for the fabrication of nanoparticle/MOF composites for catalyst uses, including the strategy using MOFs as host materials to hold and stabilize the guest nanoparticles, the strategy with subsequent MOF growth/assembly around pre-synthesized nanoparticles and the strategy mixing the precursors of NPs and MOFs together, followed by self-assembly process or post-treatment or post-modification. The applications of nanoparticle/MOF composites for CO oxidation, CO2 conversion, hydrogen production, organic transformations, and degradation of pollutants have been discussed. Superior catalytic performances in these reactions have been demonstrated. Challenges and future developments are finally addressed.

Nanoparticle/Metal-Organic Framework Composites for Catalytic Applications: Current Status and Perspective.

The partial hydrogenation of benzene to cyclohexene is an economically interesting and technically challenging reaction. Over the last four decades, a lot of work has been dedicated to the development of an exploitable process and several approaches have been investigated. However, environmental constraints often represent a limit to their industrial application, making further research in this field necessary. The goal of this review is to highlight the main findings of the different disciplines involved in understanding the governing principles of this reaction from a sustainable chemistry standpoint. Special emphasis is given to ruthenium-catalyzed liquid phase batch hydrogenation of benzene.

Benzene partial hydrogenation: advances and perspectives

The effects of the crystal phases of ZrO 2 in the Pt–WO x /ZrO 2 catalysts on glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO) were comparatively studied. Pt and WO x were sequentially deposited on monoclinic ( m -ZrO 2 ) and tetragonal ( t -ZrO 2 ) ZrO 2 supports with similar surface areas by the wetness impregnation method. On both catalysts, sub-nanosized Pt particles were well dispersed on the supports, and the WO x species were mainly in the monomeric state and partly covered the Pt particles. The Pt–WO x / m -ZrO 2 catalyst had larger Pt particle size and less Bronsted acid sites than the Pt–WO x / t -ZrO 2 catalyst. In glycerol hydrogenolysis, the glycerol conversion and 1,3-PDO selectivity on the Pt–WO x / m -ZrO 2 catalyst were less than one half of those on the Pt–WO x / t -ZrO 2 catalyst. The Pt–WO x / t -ZrO 2 catalyst exhibited a high 1,3-PDO yield of 49.4%, an excellent 1,3-PDO productivity of 5.10 g g Pt −1  h −1 , and good recyclability. The superiority of the Pt–WO x / t -ZrO 2 catalyst in glycerol hydrogenolysis to 1,3-PDO is attributed to the better synergy between smaller Pt particles in affording hydrogen atoms and more Bronsted acid sites in converting glycerol to the intermediate suitable for the formation of 1,3-PDO.

Pt–WOx on monoclinic or tetrahedral ZrO2: Crystal phase effect of zirconia on glycerol hydrogenolysis to 1,3-propanediol

Doping effects of B in ZrO2 on structural and catalytic properties of Ru/B-ZrO2 catalysts for benzene partial hydrogenation

Ru–B nanoparticles on metal–organic frameworks as excellent catalysts for hydrogenation of benzene to cyclohexane under mild reaction conditions

A strategy based on galvanic replacement between metallic Zn and Ru salt followed by acid treatment was developed to fabricate supported Ru–Zn/ZrO2 nanocomposite catalysts with controlled contents of Zn for the benzene partial hydrogenation to cyclohexene. The catalysts were systematically characterized by techniques such as extended X‐ray absorption fine structure, X‐ray photoelectron spectroscopy, and transmission electron microscopy. In benzene partial hydrogenation, with the decrease in the content of Zn, the turnover frequency (TOF) of benzene increased monotonically, whereas the selectivity to cyclohexene evolved in a volcanic trend, passing through a maximum of 72 %. Kinetic analysis indicated that with the depletion of Zn, the rate constant for benzene hydrogenation to cyclohexene and that for cyclohexene hydrogenation to cyclohexane increased simultaneously, but the extents of the increments were at variance. It was identified that the ratios of the rate constants were in parallel with the change in the selectivity to cyclohexene, which is attributed to the electronic effect of metallic Zn that modifies the interactions of Ru with benzene and cyclohexene.

Ru–Zn/ZrO2 Nanocomposite Catalysts Fabricated by Galvanic Replacement for Benzene Partial Hydrogenation

The particle size effect on partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts is reported. Uniform Ru nanoparticles (NPs) with a tunable particle size from 2.4 to 5.4 nm were synthesized by a polyol reduction method and deposited on ZrO2. The catalysts were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), N2 physisorption, H2 chemisorption, temperature-programmed desorption of H2 (H2-TPD), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the type of polyol and the concentration of additive (sodium acetate trihydrate) imposed remarkable effect on the particle size of Ru. A distinct particle size effect occurred in partial hydrogenation of benzene. With the size of the Ru NPs increasing, the hydrogenation activity of benzene increased, and the initial selectivity ( S 0) to cyclohexene showed a volcanic-type variation tendency, which revealed that the optimal Ru size for obtaining the highest S 0 is 4.4 nm. The Ru/ZrO2 catalyst reduced by 1,2-propanediol exhibited the highest S 0 (82%) and the yield of cyclohexene (39%). Based on the characterization results, the size effect of Ru on the activity and selectivity is discussed.

The size effect of the Ru/ZrO 2 catalyst on partial hydrogenation of benzene to cyclohexene

http://www.whxb.pku.edu.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=29472

Effect of the Support on Partial Hydrogenation of Toluene over Ru/Oxide Catalysts

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