AbstractHeterogeneous catalytic ammoxidation provides an eco‐friendly route for the cyanide‐free synthesis of nitrile compounds, which are important precursors for synthetic chemistry and pharmaceutical applications. However, in general such a process requires high pressures of molecular oxygen at elevated temperatures to accelerate the oxygen reduction and imine dehydrogenation steps, which is highly risky in practical applications. Here, we report an electric field enhanced ammoxidation system using a supported Fe clusters catalyst (Fe/NC), which enables efficient synthesis of nitriles from the corresponding aldehydes under ambient air pressure at room temperature (RT). A synergistic effect between the external electric field and the Fe/NC catalyst promotes the ammonia activation and the dehydrogenation of the generated imine intermediates and avoids the unwanted backwards reaction to aldehydes. This electric field enhanced ammoxidation system presents high efficiency and selectivity for the conversion of a series of aldehydes under mild conditions with high durability, rendering it an attractive process for the green synthesis of nitriles with fragile functional groups.

AbstractHeterogeneous catalytic ammoxidation provides an eco‐friendly route for the cyanide‐free synthesis of nitrile compounds, which are important precursors for synthetic chemistry and pharmaceutical applications. However, in general such a process requires high pressures of molecular oxygen at elevated temperatures to accelerate the oxygen reduction and imine dehydrogenation steps, which is highly risky in practical applications. Here, we report an electric field enhanced ammoxidation system using a supported Fe clusters catalyst (Fe/NC), which enables efficient synthesis of nitriles from the corresponding aldehydes under ambient air pressure at room temperature (RT). A synergistic effect between the external electric field and the Fe/NC catalyst promotes the ammonia activation and the dehydrogenation of the generated imine intermediates and avoids the unwanted backwards reaction to aldehydes. This electric field enhanced ammoxidation system presents high efficiency and selectivity for the conversion of a series of aldehydes under mild conditions with high durability, rendering it an attractive process for the green synthesis of nitriles with fragile functional groups.

Understanding chemical reaction mechanisms could help synthesize sustainable fuels.

Having an atomistic understanding of the formation and structural characteristics of bulk and surface iron carbide phases plays a crucial role in comprehending the mechanisms of phase transformation, microstructure formation, and surface reconstructions in the development of advanced materials with improved magnetic, mechanical, and catalytic properties. This study uses synchrotron (SR) and angle-resolved (AR) XPS, STM, LEED, and theoretical calculations (DFT) with the aim to provide a detailed experimental and theoretical discussion on the formation, stabilization, structure, and decomposition of Fe4C iron carbide. FCC(100) Fe4C iron carbide multilayer films were prepared on Cu(100) by evaporating iron in the presence of an ethylene atmosphere. Angle-resolved XPS measurements reveal that surface and interior carbon can be distinguished due to their appearance at different binding energies and reveal that the surface consists of Fe2C while the bulk has Fe4C stoichiometry. LEED and STM measurements show that the surface exhibits the p4g(2 × 2) clock reconstruction. Theory simulations show that the bulk Fe4C iron carbide has a constrained crystal lattice with alternating Fe and Fe4C2 layers, which grow in a pseudomorphic way on the copper. The carbide phase is stable up to 700 K. Above this temperature, iron diffuses into the copper while carbon remains on the surface, where it forms graphite.

Environmental-friendly halogenation of C-H bonds using abundant, non-toxic halogen salts is in high demand in various chemical industries, yet the efficiency and selectivity of laboratory available protocols are far behind the conventional photolytic halogenation process which uses hazardous halogen sources. Here we report an FeX2 (X = Br, Cl) coupled semiconductor system for efficient, selective, and continuous photocatalytic halogenation using NaX as halogen source under mild conditions. Herein, FeX2 catalyzes the reduction of molecular oxygen and the consumption of generated oxygen radicals, thus boosting the generation of halogen radicals and elemental halogen for direct halogenation and indirect halogenation via the formation of FeX3. Recycling of FeX2 and FeX3 during the photocatalytic process enables the halogenation of a wide range of hydrocarbons in a continuous flow, rendering it a promising method for applications.

AbstractEnvironmental‐friendly halogenation of C−H bonds using abundant, non‐toxic halogen salts is in high demand in various chemical industries, yet the efficiency and selectivity of laboratory available protocols are far behind the conventional photolytic halogenation process which uses hazardous halogen sources. Here we report an FeX2 (X=Br, Cl) coupled semiconductor system for efficient, selective, and continuous photocatalytic halogenation using NaX as halogen source under mild conditions. Herein, FeX2 catalyzes the reduction of molecular oxygen and the consumption of generated oxygen radicals, thus boosting the generation of halogen radicals and elemental halogen for direct halogenation and indirect halogenation via the formation of FeX3. Recycling of FeX2 and FeX3 during the photocatalytic process enables the halogenation of a wide range of hydrocarbons in a continuous flow, rendering it a promising method for applications.

Heterogeneous photocatalysis is effective for the selective synthesis of value-added chemicals at lab-scale, yet falls short of requirements for mass production (low cost and user friendliness). Here we report the design and fabrication of a modular tubular flow system embedded with replaceable photocatalyst membranes for scalable photocatalytic C-C, C-N homocoupling and hydrogenation reactions, which can be operated in either circular and continuous flow mode with high performance. The photocatalyst membranes almost fully occupy the volume of the reactor, thus enabling optimal absorption of the incident light. Additionally, the porous structured photocatalyst membranes facilitate the mass transfer of the reactants to efficiently use the active sites, resulting in 0th-order reaction kinetics and a high space-time yield compared to the batch reaction system at practical application levels and prolonged reaction times.

AbstractHeterogeneous photocatalysis is effective for the selective synthesis of value‐added chemicals at lab‐scale, yet falls short of requirements for mass production (low cost and user friendliness). Here we report the design and fabrication of a modular tubular flow system embedded with replaceable photocatalyst membranes for scalable photocatalytic C−C, C−N homocoupling and hydrogenation reactions, which can be operated in either circular and continuous flow mode with high performance. The photocatalyst membranes almost fully occupy the volume of the reactor, thus enabling optimal absorption of the incident light. Additionally, the porous structured photocatalyst membranes facilitate the mass transfer of the reactants to efficiently use the active sites, resulting in 0th‐order reaction kinetics and a high space‐time yield compared to the batch reaction system at practical application levels and prolonged reaction times.

Thin FCC (100) iron and cobalt carbide films were prepared on Cu(100) to study the connection between their structure, electronic properties and stability. We present the first detailed, real space experimental confirmation of the C-induced clock reconstruction on the FCC(100) surfaces of iron and cobalt. Both Fe and Co surface carbides show p4g (2 × 2) surface reconstruction with tetracoordinated square planar carbon and pure FCC (100) metal layers underneath. Combining tip-sample distance dependent STM imaging with theoretical calculations we present different imaging modes of Fe2C. Using a combination of angle-resolved x-ray photoelectron spectroscopy (AR-XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and theoretical calculations we provide detailed electronic and structural models for Fe2C and Co2C p4g (2 × 2) surface carbides and other 2D Fe2X interstitial compound systems. In various Fe2X (X = B, C, N, O) surface compounds moving to the right in the periodic table with increasing electrons the reconstruction becomes less favorable, while iron carbide shows the highest stability.

Photocatalysis provides an eco-friendly route for the hydrogenation of aromatic carbonyls to O-free aromatics, which is an important refining process in the chemical industry that is generally carried out under high pressure of hydrogen at elevated temperatures. However, aromatic carbonyls are often only partially hydrogenated to alcohols, which readily desorbs and are hardly further deoxygenated under ambient conditions. Here, we show that by constructing an oxide surface over the Pd cocatalyst supported on graphitic carbon nitride, an alternative hydrogenation path of aromatic carbonyls becomes available via a step-wise acetalization and hydrogenation, thus allowing efficient and selective production of O-free aromatics. The PdO surface allows for optimum adsorption of reactants and intermediates and rapid abstraction of hydrogen from the alcohol donor, favoring fast acetalization of the carbonyls and their consecutive hydrogenation to O-free hydrocarbons. The photocatalytic hydrogenation of benzaldehyde into toluene shows a high selectivity of >90% and a quantum efficiency of ∼10.2% under 410 nm irradiation. By adding trace amounts of HCl to the reaction solution, the PdO surface remains stable and active for long-term operation at high concentrations, offering perspective for practical applications.