Jingjie Luo

One‐Pot Synthesis of a Nitrogen‐Doped Carbon Composite by Electrospinning as a Metal‐Free Catalyst for Oxidation of H2S to Sulfur

A macroscopic composite consisting of nitrogen‐doped carbon fibers (N@CFs) was synthesized by electrospinning. The as‐prepared N@CF material was further applied as a metal‐free catalyst in the catalytic oxidation of H2S to sulfur, which is one of the most important purification processes for raw chemical resources (that is, biogas, natural gas, and petrochemical compounds). The catalyst, after a carbonization step at T=800 °C, exhibits a high and stable desulfurization activity for more than 100 h of testing with 57 % H2S conversion and 95 % sulfur selectivity at T=230 °C, which is two times higher than that of the most active metal‐based catalyst (Fe2O3/SiC). The desulfurization performance could also be improved by changing the reactant velocity. Moreover, the macroscopic shaping with an inner hierarchical structure network allows the avoidance of problems linked with the transport and handling of nanoscopic carbon‐based materials and also enhances the mass diffusion during the oxidation reaction.

Sampling the structure and chemical order in assemblies of ferromagnetic nanoparticles by nuclear magnetic resonance

Assemblies of nanoparticles are studied in many research fields from physics to medicine. However, as it is often difficult to produce mono-dispersed particles, investigating the key parameters enhancing their efficiency is blurred by wide size distributions. Indeed, near-field methods analyse a part of the sample that might not be representative of the full size distribution and macroscopic methods give average information including all particle sizes. Here, we introduce temperature differential ferromagnetic nuclear resonance spectra that allow sampling the crystallographic structure, the chemical composition and the chemical order of non-interacting ferromagnetic nanoparticles for specific size ranges within their size distribution. The method is applied to cobalt nanoparticles for catalysis and allows extracting the size effect from the crystallographic structure effect on their catalytic activity. It also allows sampling of the chemical composition and chemical order within the size distribution of alloyed nanoparticles and can thus be useful in many research fields.

Hierarchical porous carbon fibers/carbon nanofibers monolith from electrospinning/CVD processes as a high effective surface area support platform

Nanocarbons with unique physicochemical properties have been considered typical sustainable materials for use as catalyst supports and directly as catalysts. Unfortunately, the powder form of nanocarbons renders them difficult to use in industrial processes due to the high pressure drop, their difficulty of handling as well as health injuries caused to human beings. Herein, hierarchical carbon fibers/carbon nanofibers (CF/CNF) composites, with high effective surface areas and controlled macroscopic shapes, were successfully synthesized through a combination of electrospinning (ES) and chemical vapour deposition (CVD). A web of poly(acrylonitrile)/poly(vinyl pyrrolidone) (PAN/PVP) composite fibers embedding a nickel salt was firstly produced by electrospinning. After a carbonization step, the polymeric material was converted into porous carbon embedding nickel nanoparticles, available on the fiber surface. Then, the catalytic growth of the CNFs was carried out from the nickel nanoparticles by CVD leading finally to the formation of a hierarchical carbon web of hairy fibers with a high effective surface area. The density, diameters and lengths of the CNFs attached on the surface of the CFs could be finely tuned by adjusting the CVD conditions. The specific surface area of the CF/CNF monolith amounted to more than 200 m2 g−1 along with high accessibility due to the small dimensions. The hierarchical CF/CNF composite has been used as a metal-free catalyst for the steam- and oxygen-free catalytic dehydrogenation of ethylbenzene to styrene. The catalytic results have pointed out that such a monolith can be efficiently used as a material platform for different applications , going from catalysis to wastewater treatment, thanks to the high effective surface area and reactivity of the CNF with prismatic planes.

Anchoring and promotion effects of metal oxides on silica supported catalytic gold nanoparticles.

The understanding of the interactions between the different components of supported metal doped gold catalysts is of crucial importance for selecting and designing efficient gold catalysts for reactions such as CO oxidation. To progress in this direction, a unique supported nano gold catalyst Au/SS was prepared, and three doped samples (Au/SS@M) were elaborated. The samples before and after test were characterized by Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). It is found that the doping metal species prefer to be located on the surface of gold nanoparticles and that a small amount of additional reductive metal leads to more efficient reaction. During the catalytic test, the nano-structure of the metal species transforms depending on its chemical nature. This study allows one to identify and address the contribution of each metal on the CO reaction in regard to oxidative species of gold, silica and dopants. Metal doping leads to different exposure of interface sites between Au and metal oxide, which is one of the key factors for the change of the catalytic activity. The metal oxides help the activation of oxygen by two actions: mobility inside the metal bulk and transfer of water species onto of gold nanoparticles.

A green and economical vapor-assisted ozone treatment process for surface functionalization of carbon nanotubes

We report herein a green and economical strategy for oxidative modification of carbon nanotubes (CNT) by a facile ozone treatment in the presence of solvent vapor (H2O, 30% H2O2 solution and ethanol). This procedure is able to introduce a considerable level of oxygen groups with a dominant population of carboxyl groups at near ambient temperature. The optimization study of the process provides the reaction temperature and time, as well as the source and partial pressure of the vapor, key parameters determining the oxidation efficiency. The process efficiency and sustainability are assessed to compare with conventional oxidative treatment (e.g., nitric acid oxidation). Ozone treatment assisted by water or H2O2/H2O vapor can introduce abundant oxygenated groups on the sidewalls of CNT, and the process with H2O2/H2O vapor can deliver a much higher selectivity towards carboxyl species on the sidewalls of CNT. With the appropriate functionalization temperature (40 °C) and incremental partial pressure of vapor, the surface defect and oxygen content on the CNT could be dramatically increased. The ozone treated CNT can be used for diverse applications such as metal-free catalyst and support; the modified CNT display higher activity for the ring-opening reaction of styrene oxide than HNO3 treated CNT and develop strong interaction for anchoring iron oxide nanoparticles even up to 350 °C. This ozone treatment in the presence of vapor could also be accomplished by using compressed air as the carrier gas, which can be considered an efficient and eco-friendly functionalization process.

Correlation between Microstructure Evolution of a Well-Defined Cubic Palladium Catalyst and Selectivity during Acetylene Hydrogenation

The varied surface structures of a Pd catalyst showed different catalytic performances in the partial hydrogenation of acetylene. The exposed Pd (1 0 0) facet is considered to be the most selective of all other facets for the formation of ethylene, but it is unstable and the fine structure needs to be revealed during the reaction. Herein, the evolution of the surface structure of cubic Pd nanoparticles, which are all bound with (1 0 0) facets, was studied by transmission electron microscopy in the partial hydrogenation of acetylene. Furthermore, the relation between the varying surface structure and the activity/selectivity was correlated. The (1 0 0) facets of Pd were transformed into stepped facets during the reaction, derived by adsorption/desorption of the reactants and energy compensation, which was the main reason for the decrease in the selectivity towards ethylene.