Coordinatively unsaturated ferrous (CUF) sites confined in nanosized matrices are active centers in a wide range of enzyme and homogeneous catalytic reactions. Preparation of the analogous active sites at supported catalysts is of great importance in heterogeneous catalysis but remains a challenge. On the basis of surface science measurements and density functional calculations, we show that the interface confinement effect can be used to stabilize the CUF sites by taking advantage of strong adhesion between ferrous oxides and metal substrates. The interface-confined CUF sites together with the metal supports are active for dioxygen activation, producing reactive dissociated oxygen atoms. We show that the structural ensemble was highly efficient for carbon monoxide oxidation at low temperature under typical operating conditions of a proton-exchange membrane fuel cell.

Polymer electrolyte membrane fuel cells (PEMFCs) running on hydrogen are attractive alternative power supplies for a range of applications, with in situ release of the required hydrogen from a stable liquid offering one way of ensuring its safe storage and transportation before use. The use of methanol is particularly interesting in this regard, because it is inexpensive and can reform itself with water to release hydrogen with a high gravimetric density of 18.8 per cent by weight. But traditional reforming of methanol steam operates at relatively high temperatures (200-350 degrees Celsius), so the focus for vehicle and portable PEMFC applications has been on aqueous-phase reforming of methanol (APRM). This method requires less energy, and the simpler and more compact device design allows direct integration into PEMFC stacks. There remains, however, the need for an efficient APRM catalyst. Here we report that platinum (Pt) atomically dispersed on α-molybdenum carbide (α-MoC) enables low-temperature (150-190 degrees Celsius), base-free hydrogen production through APRM, with an average turnover frequency reaching 18,046 moles of hydrogen per mole of platinum per hour. We attribute this exceptional hydrogen production-which far exceeds that of previously reported low-temperature APRM catalysts-to the outstanding ability of α-MoC to induce water dissociation, and to the fact that platinum and α-MoC act in synergy to activate methanol and then to reform it.

The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.

Iron carbide nanoparticles have long been considered to have great potential in new energy conversion, nanomagnets, and nanomedicines. However, the conventional relatively harsh synthetic conditions of iron carbide hindered its wide applications. In this article, we present a facile wet-chemical route for the synthesis of Hägg iron carbide (Fe(5)C(2)) nanoparticles, in which bromide was found to be the key inducing agent for the conversion of Fe(CO)(5) to Fe(5)C(2) in the synthetic process. Furthermore, the as-synthesized Fe(5)C(2) nanoparticles were applied in the Fischer-Tropsch synthesis (FTS) and exhibited intrinsic catalytic activity in FTS, demonstrating that Fe(5)C(2) is an active phase for FTS. Compared with a conventional reduced-hematite catalyst, the Fe(5)C(2) nanoparticles showed enhanced catalytic performance in terms of CO conversion and product selectivity.

The conversion of methane to more valuable chemicals is one of the most intensively studied topics in catalysis. The direct conversion of methane is attractive because the process is simple, but unfortunately its products are chemicals that are more reactive than methane. The current status of this research field is discussed with an emphasis on C-H bond activation and future challenges.

Methane activation at moderate conditions and with good selectivity for value-added chemicals still remains a huge challenge. Here, we present a highly selective catalyst for the transformation of methane to methanol composed of highly dispersed iron species on TiO2. The catalyst operates under moderate light irradiation (close to one sun) and at ambient conditions. The optimised sample shows a 15% conversion rate for CH4 with an alcohol selectivity of over 97% (methanol selectivity over 90%) and a yield of 18 moles of alcohol per mole of iron active site in just three hours. XPS measurements with and without Xenon lamp irradiation, light intensity-modulated spectroscopies, photoelectrochemical measurements, XANES and EXAFS spectra, as well as isotopic analysis confirm the function of the major ironcontaining species, namely FeOOH and Fe2O3, which enhance charge transfer and separation, decrease the overpotential of the reduction reaction and improves selectivity towards methanol over CO2 production.

Current approaches for efficient C À H bond activation are usually mediated by heterogeneous [1] or homogeneous [2] catalysts. The basis is the employment of transition metals or organometallic centers, which is pivotal for the successful attack on the targeted C À H bonds. [3] However, we have reported that it is feasible to use carbon-based nanomaterials to activate short-chain alkanes in catalytic dehydrogenation reactions [4] although relatively high reaction temperatures are required. It is of particular interest to know whether it is possible to activate CÀH bonds to get high value-added products at a moderate reaction temperatures by using cheap metal-free catalysts. To this end, an elegant approach using metal-or boron-doped carbon nitrides as catalysts [5] has been developed for the selective oxidation of allylic and benzylic hydrocarbons in organic solvents with moderate conversion. Attempts to achieve higher activity also include the application of N-alkoxysulfonyloxaziridines for the activation of C(sp 3 ) À H bonds, [6] although a complicated catalytic system for efficient reaction circulation was required.Layered carbon, that is, highly exfoliated graphitic structures containing one or a few graphene layers, [7] has an unconventional electronic structure, [8] which was speculated to have a high chemical reactivity. [9] Indeed, researchers observed that layered carbon can catalyze hydrogenation, [10] ring-opening polymerization, [11] and CÀH oxidation reaction, [12] and that it could serve as a support for metal oxide catalysts. [13] Herein we describe nitrogen-doped graphene materials that can activate the benzylic C À H bond with exceptionally high activity. The nitrogen atoms introduced are preferentially bound at graphitic sites in the carbon framework. This induces high charge and spin density at the adjacent ortho carbon, which promotes the formation of reactive oxygen species and the materials display exceptional catalytic activity even at room temperature.Firstly, we examined the oxidation of ethylbenzene in aqueous phase with tert-butyl hydroperoxide (TBHP) as the oxidant and without using catalyst. However, no obvious activity was observed by GC after a reaction time of 24 h (Table 1, entry 1). Then we used a graphene sample prepared by the arc-discharge method (referred to as Arc-C) [14] as the catalyst for this reaction. Surprisingly, Arc-C activated ethylbenzene at 353 K to generate acetophenone in 20.7 % yield (Table 1, entry 2). As Arc-C had been prepared by a directcurrent arc-discharge method with a pure graphite rod as the electrode in an NH 3 /He atmosphere, besides trace nitrogen (0.7 %), no element other than carbon was detected by elemental analysis (EA) (oxygen cannot be detected by this method). The full X-ray photoelectron spectrum showed a C content of 97.9 % and low amounts of nitrogen and oxygen of 0.9 % and 1.1 %, respectively. This promising observation suggests that it is layered carbon material itself that catalyzed the oxyfunctionalization of the hydrocarbon. As Arc-C...

We investigate Second Harmonic Generation (SHG) in monolayer WS2 both deposited on a SiO2/Si substrate or suspended using transmission electron microscopy grids. We find unusually large second order nonlinear susceptibility, with an estimated value of deff ~ 4.5 nm/V nearly three orders of magnitude larger than other common nonlinear crystals. In order to quantitatively characterize the nonlinear susceptibility of two-dimensional (2D) materials, we have developed a formalism to model SHG based on the Green's function with a 2D nonlinear sheet source. In addition, polarized SHG is demonstrated as a useful method to probe the structural symmetry and crystal orientation of 2D materials. To understand the large second order nonlinear susceptibility of monolayer WS2, density functional theory based calculation is performed. Our analysis suggests the origin of the large nonlinear susceptibility in resonance enhancement and a large joint density of states, and yields an estimate of the nonlinear susceptibility value deff = 0.77 nm/V for monolayer WS2, which shows good order-of-magnitude agreement with the experimental result.