Kinetic Promotion Effect of Hydrogen and Dimethyl Disulfide Addition on Propane Dehydrogenation over the Pt-Sn-K/AlO Catalyst.

The kinetic effects of co-feeding of dimethyl disulfide (DMDS) and hydrogen on propane dehydrogenation (PDH) over the Pt-Sn-K/AlO catalyst were investigated by the response surface method. The 3-level Box-Behnken design for 4 factors (reaction temperature, propene, hydrogen, and DMDS flow rate) was used to design the experiment. The initial propane conversion, propene selectivity, and coking amount were chosen as responses and the results were fitted by quadratic models.

Surface phase diagrams of La-based perovskites towards the O-rich limit from first principles.

The exposed termination of transition-metal oxide surfaces plays a major role in determining the catalyst performance in redox reactions. In this contribution, the surface phase diagrams of LaMO(001) (M = Sc-Fe) and LaMO(110) (M = Co-Cu) are constructed by using the DFT+U method. The stabilities of six terminations derived from the stoichiometric MO and LaO surfaces are determined over a wide range of temperatures and oxygen partial pressures.

Insights into Hydrogen Transport Behavior on Perovskite Surfaces: Transition from the Grotthuss Mechanism to the Vehicle Mechanism.

Hydrogen transport on transition-metal oxides is a shared process in many important physical and chemical changes of interest. In this work, DFT + U calculations have been carried out to explore the mechanism for hydrogen migration on the defect-free and oxygen-deficient LaMO(001) (M = Cr, Mn, and Fe) surfaces. The calculated results indicate that hydrogen is preferentially adsorbed at the oxygen sites on all surfaces other than the defective LaCrO(001), where the occupation of vacancies is energetically most favorable.

BEEF-vdW+U method applied to perovskites: thermodynamic, structural, electronic, and magnetic properties.

The recently developed BEEF-vdW exchange-correlation method provides a reasonably reliable description of both long-range van der Waals interactions and short-range covalent bonding between molecules and surfaces. However, this method still suffers from the excessive electron delocalization that is connected with the self-interaction error and, consequently, the calculated chemical and physical properties such as formation energy and band gap deviate markedly from the experimental values, especially when strongly correlated systems are under investigation. In this contribution, BEEF-vdW+U calculations have been performed to study the thermodynamic, structural, electronic, and magnetic properties of La-based perovskites.

Decoding structural complexity in conical carbon nanofibers.

Conical carbon nanofibers (CNFs) exist primarily as graphitic ribbons that fold into a cylindrical structure with the formation of a hollow core. Structural analysis aided by molecular modeling proves useful for obtaining a full picture of how the size of the central channel varies from fiber to fiber. From a geometrical perspective, conical CNFs possibly have cone tips that are nearly closed.

DFT study of propane dehydrogenation on Pt catalyst: effects of step sites.

Self-consistent periodic slab calculations based on gradient-corrected density functional theory (DFT-GGA) have been conducted to examine the reaction network of propane dehydrogenation over close-packed Pt(111) and stepped Pt(211) surfaces. Selective C-H or C-C bond cleaving is investigated to gain a better understanding of the catalyst site requirements for propane dehydrogenation. The energy barriers for the dehydrogenation of propane to form propylene are calculated to be in the region of 0.