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N-doped (NrGO) and non-doped (rGO) graphenic materials are prepared by oxidation and further thermal treatment under ammonia and inert atmospheres, respectively, of natural graphites of different particle sizes. An extensive characterization of graphene materials points out that the physical properties of synthesized materials, as well as the nitrogen species introduced, depend on the particle size of the starting graphite, the reduction atmospheres, and the temperature conditions used during the exfoliation treatment. These findings indicate that it is possible to tailor properties of non-doped and N-doped reduced graphene oxide, such as the number of layers, surface area, and nitrogen content, by using a simple strategy based on selecting adequate graphite sizes and convenient experimental conditions during thermal exfoliation. Additionally, the graphenic materials are successfully applied as electrocatalysts for the demanding oxygen reduction reaction (ORR). Nitrogen doping together with the starting graphite of smaller particle size (NrGO 325 -4) resulted in a more efficient ORR electrocatalyst with more positive onset potentials (E onset = 0.82 V versus RHE), superior diffusion-limiting current density (j L, 0.26V, 1600rpm = −4.05 mA cm −2 ), and selectivity to the direct four-electron pathway. Moreover, all NrGO m -4 show high tolerance to methanol poisoning in comparison with the state-of-the-art ORR electrocatalyst Pt/C and good stability.

Ramos, I. (2019). Ru nanoparticles supported on N-doped reduced graphene oxide as valuable catalyst for the selective aerobic oxidation of benzyl alcohol. Catalysis Today.

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The condensation of ethanol to 1-butanol in the presence of different catalyst systems based on a Pd dehydrogenating/hydrogenating component and magnesium hydroxide-derived materials as basic ingredient was studied in a fixed-bed reactor. The metal was incorporated by wetness impregnation, and the resulting material was then reduced in situ with hydrogen at 573 K for 1 h before reaction. The bifunctional catalysts were tested in a fixed-bed reactor operated in the gas phase at 503 K and 50 bar with a stream of helium and ethanol. A bifunctional catalyst supported on a synthetic composite based on Mg and high surface area graphite (HSAG) was also studied. Improved catalytic performance in terms of selectivity towards 1-butanol and stability was shown by the Pd catalyst supported on the Mg-HSAG composite after thermal treatment in helium at 723 K, presumably due to the compromise between two parameters: adequate size of the Pd nanoparticles and the concentration of strongly basic sites. The results indicate that the optimal density of strongly basic sites is a key aspect in designing superior bifunctional heterogeneous catalyst systems for the condensation of ethanol to 1-butanol.

A number of inorganic carbonaceous materials (activated carbon, high surface area graphite and graphenic materials) have been used as supports of Ru nanoparticles in order to determine their catalytic properties in the base-free aqueous-phase oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). In particular, we have studied in detail reduced graphene oxide (rGO) and nitrogen doped reduced graphene oxide (NrGO), which are the support materials that produce more selective ruthenium catalysts. Also the effects of different metal precursors used in the preparation of the Ru nanocrystallites have been evaluated. Both support materials and Ru catalysts were characterized by elemental analysis, nitrogen physisorption (BET), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The point of zero charge (PZC) for the graphenic materials was also determined. Interestingly the different supports significantly modify the catalytic performances, the graphenic materials being those that under our experimental reaction conditions produce the highest selectivity to FDCA. On these supports (rGO and NrGO) the highest HMF conversion was achieved by using triruthenium dodecacarbonyl as the ruthenium precursor. For the improved catalyst, Ru supported on NrGO, the yield of FDCA becomes close to 80%. This catalyst has been reused several times with neither loss of activity nor modification in selectivity values. Characterization data indicate these catalytic results can be correlated to the basic properties of the NrGO support as well as to the surface properties of Ru nanoparticles. These findings indicated that the metal precursor and the surface functional groups exposed on the support can modulate the catalytic properties, in particular amending the selectivity towards FDCA production.

Amphiphilic hybrid carbon nanotubes (CNTs) containing a hydrophobic undoped section connected to a hydrophilic N-doped segment were synthesized. Their application as basic catalysts in the aldol condensation of furfural and acetone was tested.

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