Modeling phase formation on catalyst surfaces: Coke formation and suppression in hydrocarbon environments

We develop a simulation toolset employing density functional theory (DFT) in conjunction with grand canonical Monte Carlo (GCMC) to study coke formation on Fe-based catalysts during propane dehydrogenation (PDH). As expected, pure Fe surfaces develop stable graphitic coke structures and rapidly deactivate. We find that coke formation is markedly less favorable on FeC and FeS surfaces. Fe-Al alloys display varying degrees of coke resistance, depending on their composition, suggesting that they can be optimized for coke resistance under PDH conditions. Electronic structure analyses show that both electron-withdrawing effects (on FeC and FeS) and electron-donating effects (on Fe-Al alloys) destabilize adsorbed carbon. On the alloy surfaces, a geometric effect also isolates Fe sites and disrupts the formation of graphitic carbon networks. This work demonstrates the utility of GCMC for studying the formation of disordered phases on catalyst surfaces and provides insights for improving the coke resistance of Fe-based PDH catalysts.

Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

The air annealing induced grain growth from nano to microscale and a transformation sequence from Bi → β-Bi2O3 → γ-Bi2O3 → α-Bi2O3 was evident. All the annealed samples are oxygen-deficient, resulting in the appearance of a strong red emission band.

DFT Study into the Influence of Carbon Material on the Hydrophobicity of a Coal Pyrite Surface

From the macroscopic point of view, the hydrophilicity of symbiotic carbon pyrite is weakened overall compared to that of pure pyrite. It is very important to explain the impact of elemental carbon accreted on a pyrite surface on the surface’s hydrophobicity from the perspective of quantum chemistry. To study the influence of adsorbed carbon atoms on the hydrophilicity of a coal pyrite surface versus a pyrite surface, the adsorption of a single water molecule at an adjacent Fe site of a one-carbon-atom-covered pyrite surface and a carbon atom monolayer were simulated and calculated with the first-principles method of density functional theory (DFT). The water molecules can be stably adsorbed at the adjacent Fe site of the carbon-atom-covered pyrite surface. The hybridization of the O 2p (H2O) and Fe 3d (pyrite surface) orbitals was the main interaction between the water molecule and the pyrite surface, forming a strong Fe–O covalent bond. The water molecule only slightly adsorbs above a C atom on the carbon-atom-covered pyrite and the carbon atom monolayer surfaces. The valence bond between the water molecule and the pyrite surface changed from an Fe–O bond to an Fe–C–O bond, in which the C–O bond is very weak, resulting in a weaker interaction between water and the surface.

Growth mechanism of 3D graphene-carbon nanotube hybrid structure

In this paper, a novel molecular dynamic model is presented to describe the growth mechanism of three-dimensional (3D) graphene-carbon nanotube (G-CNT) hybrid structure synthesized by catalytic chemical vapor deposition. For this purpose, first, the physisorption of a carbon atom on a graphene sheet (GS) is studied. Then the model is formulated by using kinetic theory and the longitudinal phonon oscillation of adsorbed carbon atoms on GS. Results show that the CNT grows on GS up to 0.3 mm. Also, there is an optimum temperature for growth of the 3D G-CNT hybrid structure, which can be calculated by the presented model. Finally, it is shown that increase of partial pressure leads to increase of length of growing CNT on GS.

Adsorbed carbon nanomaterials for surface and interface-engineered stable rubidium multi-cation perovskite solar cells

Adsorbed carbon nanomaterial based dual electron transport layer ensures more efficient and stable perovskite solar cells.