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Ordered carbonaceous frameworks (OCFs) are a new class of carbon materials with a three-dimensional ordered structure synthesized by simple carbonization of metalloporphyrin crystals with polymerizable moieties. Carbonization

A promotional effect of surface plasmon resonance (SPR) on direct hydrogen peroxide (H2O2) formation from H2 and O2 over a structure-controlled Pd-Au catalytic system is reported herein. Pd NPs supported on reduced graphene oxide (rGO) layer-coated Au nanorod (NR) nanocomposite catalysts were synthesized, and the structure was confirmed by multiple characterization techniques. H2O2 production is highly enhanced under visible light irradiation in the direct H2O2 formation from H2 and O2. The H2O2 decomposition test and the H2-D2 exchange reaction reveal that the SPR of Au NRs facilitates H2 activation on the Pd NP surface, leading to efficient H2O2 production. Furthermore, the rGO layer not only functions as an electron mediator in the catalytic reaction, but also contributes to the control of Pd NP sizes in the catalyst synthesis.

Graphene mesosponge (GMS) is a new class of mesoporous carbon consisting mainly of single-layer graphene walls. GMS has traditionally been synthesized via chemical vapour deposition (CVD) of methane onto a template of alumina (Al2O3) nanoparticles, which catalyses methane conversion. However, the Al2O3 template needs to be removed using costly and environmentally concerning processes such as hydrofluoric acid or concentrated base. In this work, we examine methane conversion catalysed by magnesium oxide (MgO) and utilized MgO as an alternative catalytic template. In contrast to Al2O3, a solid acid catalyst, MgO is a solid base catalyst that is also active for methane conversion into graphene sheets but dissolves easily in hydrochloric acid. We have investigated the reaction mechanism using in situ weight measurements and gas-emission analysis during CVD complemented by density functional theory calculations. We found that the pure MgO surface is activated via O-elimination with methane above 778 °C. On the activated MgO surface, methane is converted into a graphene sheet with a relatively low activation energy of 134 kJ mol−1. Once the first graphene layer is formed, the methane-to-graphene conversion rate decreases and the activation energy increases to 234 kJ mol−1, which is comparable to that reported in thermal methane-CVD on carbon. As a result of the faster growth rate of the first layer with respect to additional layers, it is easier to obtain single-graphene layers using MgO. The MgO-derived GMS has a unique combination of properties including a high surface area, developed mesopores, high oxidation resistance, significant softness and elasticity, very low bulk modulus (0.05 GPa), and force-driven reversible liquid–gas phase transition. Thus, we expect the MgO-derived GMS can be employed in a variety of applications including high-voltage supercapacitors and as a new type of heat pump based on the force-driven phase transition.

Visible-light boosting chemical reactions by surface plasmon resonance (SPR) have recently received much attention in photocatalysis. Although multiple types of plasmonic catalysts have been develo...

Force-responsive ordered carbonaceous frameworks (OCFs) are synthesized for the first time. Carbonization of Ni porphyrin monomers having eight polymerizable ethynyl groups yields OCFs with atomically dispersed divalent Ni species and developed micropores. The highest specific surface area (673 m2 g−1) among the OCFs has been achieved. The OCFs thus synthesized comprise non-stacked graphene sheets, affording a unique mechanical flexibility that enables force-driven reversible phase transition.

Carbon materials have been extensively studied for several decades as catalytic supports because of their high surface area and porous structures. However, carbon black supports, such as Ketjen black or Vulcan XC-72, have rarely been utilized for organic syntheses, though they have recently been widely studied in electrocatalysts. In this study, we examined Ketjen black with high surface area and high pore volume as a support for Ru nanoparticles (NPs) in the catalytic transfer hydrogenation (CTH) reaction. The performance of the Ru NP catalyst supported on Ketjen black was superior to that on other carbon supports. The catalysts were structurally characterized using X-ray diffraction, X-ray absorption fine structure, transmission electron microscopy, CO chemisorption, and N2 adsorption/desorption measurements. A clear correlation was observed among the micro- and mesopore volume, the adsorption capacity of reactant, and the catalytic activity, and therefore, micro- and mesopores in Ketjen black were foun...

Designing efficient photocatalyst materials for CO2 reduction and utilization has become important to address environmental and energy concerns. A new type of core–shell-structured nanocomposite catalyst is reported herein, in which single-site Co catalytic species are immobilized in graphitic carbon nitride (g-C3N4) layered on Au nanorods (NRs) for surface plasmon resonance (SPR)-enhanced photocatalytic CO2 conversion. Single-site Co species were incorporated into g-C3N4 via a simple pyrolysis process, and core–shell nanocomposites were self-formed via electrostatic interactions between the positively charged surfaces of the Au NRs and negatively charged single-site Co-coordinated g-C3N4 layer. The structure was comprehensively examined by TEM, XRD, UV–vis, Co K-edge XAFS, FT-IR, and zeta potential measurements, which showed that the g-C3N4 layer did not prevent the Au NRs from absorbing visible light. The nanocomposite efficiently catalyzed the reduction of CO2 to CO under visible light irradiation with the assistance of the SPR of the Au NRs. The catalytic activity of the core–shell-structured catalyst was superior to that of the corresponding aggregated catalyst, demonstrating that the formation of a core–shell structure affords efficient electron transport from the Au NRs to the catalytically active Co species.

Pd–Co bimetallic catalysts were prepared by the controlled synthesis of carbon-supported Co catalysts, ranging from single-sites to nanoparticles, via structural transformation of a deposited Co(salen) complex precursor by heat treatment at different temperatures, followed by galvanic replacement with Pd ions. The catalysts were structurally characterized using XRD, TEM, HAADF-STEM, XAFS and XPS. Highly dispersed Pd-rich NPs containing a low concentration of Co species were formed and the original size of the Co NPs was retained. The electronic state of the Pd species was dependent on the size of the bimetallic NPs, and a catalyst with a mean diameter of 10.8 nm was found to be in the most electron-rich state. Not only the particle size, but also the electronic state of Pd play a crucial role in attaining high catalytic activity and selectivity in the selective hydrogenation of phenylacetylene. A Pd–Co catalyst based on a Co catalyst heat-treated at 600 °C showed 92% selectivity at 93% conversion. Furthermore, the Pd–Co catalysts synthesized by the galvanic replacement method showed superior performance to a monometallic Pd catalyst and a Pd–Co alloy catalyst.

A new type of pyrene-thiol derivative-modified Pd nanoparticle (NP) catalyst on a carbon black support for the efficient semihydrogenation of alkynes to alkenes is reported herein. Colloidal Pd NPs surrounded by pyrene-thiol modifiers were prepared using the two-phase Brust method followed by impregnation of carbon black materials. Based on the structural characterization of the prepared catalyst (PyC12S-Pd/VC) by NMR, UV-vis, FT-IR, TEM, HAADF-STEM, Pd K-edge XAFS, XRD, N2 adsorption, and XPS, we show that highly dispersed Pd NPs are immobilized on the catalysts via π-π interaction between pyrene groups bound to the Pd NPs and carbon black supports. PyC12S-Pd/VC efficiently catalyzes the alkyne semihydrogenation reaction while maintaining high alkene selectivity; an alkene selectivity of 94% is attained at 98% conversion after 5 h of reaction, and the selectivity was retained around 80% in 10 h of reaction. This performance is superior to that of a catalyst without pyrene groups and that of a commercial Lindlar catalyst. The steric hindrance of pyrene groups restricts access of the substrates to Pd NP surfaces, suppressing the unfavorable overhydrogenation of alkenes to alkanes, which is revealed by the solvent and substrate dependency on the catalytic performance and a DFT calculation study. Furthermore, the high selectivity and stability of PyC12S-Pd/VC are caused by the strong interaction between pyrene groups and carbon supports, which prevents the separation of pyrene modifiers and the leaching or sintering of Pd NPs during the catalytic reaction. It is demonstrated that the combination of Pd NPs, pyrene-thiol modifiers, and carbon supports offers high activity, alkene selectivity, and stability in the semihydrogenation reaction.

The structure–activity relationship of carbon-supported Co catalysts was investigated in solvent-free aerobic oxidation of ethylbenzene under microwave irradiation. A single-site Co species show specifically high catalytic activity under microwave irradiation compared to conventional heating, while the oxidation is not accelerated by microwave when Co nanoparticle catalysts are used.

Realizing accurate control of catalytically active centers on solid surfaces is one of the most essential goals in the development of functionalized heterogeneous catalysts. Controlled synthesis of carbon-supported Co catalysts from single-site to nanoparticles can be successfully achieved by the structural transformation of the deposited Co(salen) complex precursor under heat treatment. The obtained structures were characterized using techniques such as XRD, in situ XAFS, and TEM. The first decomposition of the Co(salen) complex is initiated by the dissociation of Co–O–C bonds at around 250 °C, which produces isolated single-atom Co species while retaining the Co–N–C bonds even up to 400 °C. When the heat treatment temperature exceeds 450 °C, the second decomposition of the Co–N–C bonds occurs to form Co oxide nanoclusters followed by the growth of Co NPs upon further increase of the heat treatment temperature. The single-site catalyst is highly dispersed and electronically deficient owing to the interaction with the carbon support, and shows activity and selectivity for the oxidation of ethylbenzene, as compared to the inherent Co(salen) complex and nanoparticle catalysts.