Graphene oxide: preparation, functionalization, and electrochemical applications.

Graphene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reaction, water splitting and CO2 activation, and have been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals). We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and the development of industrial applications.

Catalysis with two-dimensional materials and their heterostructures

Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy

Nanocarbons for the Development of Advanced Catalysts

excellent thermal conductivity, [ 2 ] and a high optical transparency. [ 3 ] These properties lead to very promising applications of graphene in electronic devices, [ 4 ] transparent electrodes, [ 5 ] and energy-storage devices. [ 6 , 7 ] Recently, it was found that graphene has an extraordinary catalytic activity. [ 8–14 ] For example, N-doped graphene has a high catalytic activity toward the oxygen-reduction reaction (ORR). [ 8 ] Furthermore, graphene oxide (GO), an important derivative of graphene, is an effi cient catalyst for oxidation and hydration reactions of various alcohols, [ 9 ] whereas reduced GO can be used for catalyzing the hydrogenation of nitrobenzene. [ 10 ] Studies have shown that the heteroatoms in graphene derivatives, such as N and O, play a critical role in their catalytic activities. [ 10 , 15 , 16 ] Thus, the introduction of dopants into the graphene lattice has been the focus of much research in order to achieve a high catalytic activity toward target reactions. Among various doped graphenes, nitrogen-doped graphene (NG) has attracted much attention because of its high catalytic activity toward the ORR – the electrode reaction that often limits the performance of the cathode in a fuel cell or a metalair battery. Conventional Pt-based catalysts have a high intrinsic catalytic activity toward the ORR, but suffer from the drawbacks of high cost, poor long-term stability, and susceptibility to the crossover effect, which hinder the commercial viability of Ptloaded fuel cells. [ 17 ] Thus the search for an alternative catalyst, such as NG, is of great importance in replacing these expensive Pt-based catalysts. To prepare NG, chemical-vapor deposition in the presence of N-containing precursors is the most-common method; [ 18 ] arc discharge of graphite electrodes in a H 2 /pyridine or H 2 /NH 3 atmosphere can also produce NG. [ 19 ] However, the extremely low yield and high cost of these methods limit their application only to fundamental studies. Later, it was found that GO can be

Facile Synthesis of Nitrogen-Doped Graphene via Pyrolysis of Graphene Oxide and Urea, and its Electrocatalytic Activity toward the Oxygen-Reduction Reaction

In the time period 2010 2015, the worldwide annual production
of plastics is very likely to surpass 300 million tons,1,2 requiring
multiple amounts of petroleum and leading to hundreds
of millions of tons ofCO2 in addition to health risks for the public
due to the release of other types of emissions.1,3 A large amount
of plastics (at least 40% of the total consumption) is used in
short-term applications, and the resulting waste can quickly
lead to additional environmental damage unless adequate
waste management systems are in place. For example, conventional
petrochemical plastics are harmful for terrestrial and
sea animals as well as birds that tend to eat plastic residues;4
these impacts could be reduced by plastics that are biodegradable
by microorganisms. In short, petrochemical plastics are
not sustainable and bio-based sustainable plastics should be
developed to avoid problems caused by the petrochemical
plastics.

Plastics derived from biological sources: present and future: a technical and environmental review.

Reduced graphene oxide as a catalyst for hydrogenation of nitrobenzene at room temperature

A theoretical study combining first-principles and Monte Carlo simulations has been carried out to investigate the interactions of H2 and CO molecules with carbon nanotube (CNT) surfaces. The results show that there are stronger interactions of both H2 and CO with the interior nanotube surface than with the exterior surface. In addition, CO interacts more strongly with CNT surfaces than H2. This can be explained by the nature of the molecules and the different electronic properties of the concave and convex surfaces of CNTs formed by graphene layers. As a result, syngas molecules are enriched inside CNTs and the enrichment generally becomes greater in smaller nanotubes. Furthermore, the ratio of CO/H2 inside CNTs increases with respect to the composition of syngas in the exterior gas phase. The enriched reactants and altered CO/H2 ratio inside nanotubes could be beneficial for the reaction rate and lead to modification of the product selectivity.

Syngas Segregation Induced by Confinement in Carbon Nanotubes: A Combined First-Principles and Monte Carlo Study

A combination of state-of-the art in situ one- and two-dimensional NMR spectroscopy and density functional theory (DFT) calculations have been employed for the first time to investigate the role of amines in the synthesis of aluminophosphate molecular sieves in ionic liquids (ILs). In situ rotating-frame nuclear Overhauser effect spectroscopy (ROESY) was used to demonstrate that the hybrid of imidazolium ionic liquids with organic amines, such as morpholine, connected through a hydrogen bond can be formed in the gel during the crystallization of molecular sieves. By combining the characterizations of the final solid products obtained by using XRD analyses, solid-state NMR spectroscopy, thermogravimetric analysis, and DFT calculation results, it was verified that the hybrid between morpholine and the imidazolium cation in the initial preparation stage can act as the structure-directing agent (SDA) for the synthesis of AFI-structured aluminophosphate molecular sieves. Our findings may suggest a synthesis mechanism of molecular sieves in ionic liquids in which the IL-organic amine hybrid is required in the nucleation step, whereas the crystal growth occurs through the occlusion of ionic liquids in the zeolite channels.

New Insights into the Role of Amines in the Synthesis of Molecular Sieves in Ionic Liquids

Density functional theory (DFT) calculations were performed to study the detailed reaction mechanism of the cross-metathesis of ethylene and 2-butylene over heterogeneous Mo/HBeta catalysts. The whole process is divided into two stages: the initiation of Mo-carbene species from Mo-oxo precursors and the propagating process by these active sites to yield propylene. The formation of initial Mo-carbene takes place via the endothermic addition and the subsequent decomposition of the oxametallacyclobutane intermediate. In the propagating stage to yield the final products, Mo=CHCH3 firstly reacts with ethylene to form Mo=CH2, which would further react with 2-butylene to give another propylene molecule. The oxidation states of the Mo species have great influences on the reactivities associated with these two stages. It is unfavorable for Mo-IV-oxo precursors to produce Mo-alkylidene species compared with Mo-VI and Mo-V sites. The energy barriers indicate that the Mo-VI and Mo-V-alkylidene species could catalyze the olefin metathesis reaction, but Mo-V ones are more preferred to be the active sites. The calculation results are consistent with our previous XPS results. (C) 2010 Elsevier B.V. All rights reserved.

DFT studies on the reaction mechanism of cross-metathesis of ethylene and 2-butylene to propylene over heterogeneous Mo/HBeta catalyst

Formation of Mo-carbene active sites in Mo/Beta zeolite catalysts with different olefins: Theoretical exploration of possible reaction pathways and substituent effects

Jing Guan

Papers

Reduced graphene oxide as a catalyst for hydrogenation of nitrobenzene at room temperature

Syngas Segregation Induced by Confinement in Carbon Nanotubes: A Combined First-Principles and Monte Carlo Study

New Insights into the Role of Amines in the Synthesis of Molecular Sieves in Ionic Liquids

DFT studies on the reaction mechanism of cross-metathesis of ethylene and 2-butylene to propylene over heterogeneous Mo/HBeta catalyst

Formation of Mo-carbene active sites in Mo/Beta zeolite catalysts with different olefins: Theoretical exploration of possible reaction pathways and substituent effects