Year
Publisher
Journal
Institution
1
Institution Country
Publication Type
Field Of Study
Topics
Open Access
Language
Filter 1
Year
Publisher
Journal
Institution
1
Institution Country
Publication Type
Field Of Study
Topics
Open Access
Language
Filter 1
Export
Sort by: Relevance
Atomistic Understanding of the Formation, Structure, and Decomposition of an Fe<sub>4</sub>C Iron Carbide Phase on a Copper Substrate

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.

Read full abstract
Creating and Stabilizing an Oxidized Pd Surface under Reductive Conditions for Photocatalytic Hydrogenation of Aromatic Carbonyls.

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.

Read full abstract
Open Access