46 research outputs found
Density functional study of the adsorption and van der Waals binding of aromatic and conjugated compounds on the basal plane of MoS2
Accurate calculations of adsorption energies of cyclic molecules are of key importance in investigations of, e.g., hydrodesulfurization (HDS) catalysis. The present density functional theory (DFT) study of a set of important reactants, products, and inhibitors in HDS catalysis demonstrates that van der Waals interactions are essential for binding energies on MoS2 surfaces and that DFT with a recently developed exchange-correlation functional (vdW-DF) accurately calculates the van der Waals energy. Values are calculated for the adsorption energies of butadiene, thiophene, benzothiophene, pyridine, quinoline, benzene, and naphthalene on the basal plane of MoS2, showing good agreement with available experimental data, and the equilibrium geometry is found as flat at a separation of about 3.5 \uc5 for all studied molecules. This adsorption is found to be due to mainly van der Waals interactions. Furthermore, the manifold of adsorption-energy values allows trend analyses to be made, and they are found to have a linear correlation with the number of main atoms. \ua9 2009 American Institute of Physics
Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces
Topotactic Growth of Edge-Terminated MoS<sub>2</sub> from MoO<sub>2 </sub>Nanocrystals
Layered
transition metal dichalcogenides have distinct physicochemical
properties at their edge-terminations. The production of an abundant
density of edge structures is, however, impeded by the excess surface
energy of edges compared to basal planes and would benefit from insight
into the atomic growth mechanisms. Here, we show that edge-terminated
MoS<sub>2</sub> nanostructures can form during sulfidation of MoO<sub>2</sub> nanocrystals by using <i>in situ</i> transmission
electron microscopy (TEM). Time-resolved TEM image series reveal that
the MoO<sub>2</sub> surface can sulfide by inward progression of MoO<sub>2</sub>(202Ě…):MoS<sub>2</sub>(002) interfaces, resulting in
upright-oriented and edge-exposing MoS<sub>2</sub> sheets. This topotactic
growth is rationalized in the interplay with density functional theory
calculations by successive O–S exchange and Mo sublattice restructuring
steps. The analysis shows that formation of edge-terminated MoS<sub>2</sub> is energetically favorable at MoO<sub>2</sub>(110) surfaces
and provides a necessary requirement for the propensity of a specific
MoO<sub>2</sub> surface termination to form edge-terminated MoS<sub>2</sub>. Thus, the present findings should benefit the rational development
of transition metal dichalcogenide nanomaterials with abundant edge
terminations
A consistent reaction mechanism for the selective catalytic reduction of NO with NH<sub>3</sub>
Renewable Electricity as a Feed Stock for the Chemical Industry
Presented online December 8, 2021 from 3:30 p.m.- 4:30 p.m., Georgia Tech, Atlanta, GA.2011 to present at Haldor Topsoe A/S, Presently head of Solid oxide technology development, previous responsibilities, Exploratory R&D, Project manager for Topsoe’s strategy for a fossil free future, Department manager for atomics scale analysis department (microscopy, spectroscopy, computational chemistry).
Before coming to Topsoe , in 2008 Ph.D Applied Physics, Technical University of Denmark, and 3 years of Post Doc at UCSB Materials department and Stanford Chemical engineering. My research has focused on materials for energy and chemical conversions, with applications in fuels, chemical synthesis, emission control and electrocatalysis.Runtime: 54:03 minutesHeavy industry and long-haul transportation are responsible for a large percentage of humanity's greenhouse-gas emissions. In these sectors, direct electrification is not enough. They need energy-dense green fuels – similar to the fuels used today, but made from renewable sources. In this presentation a set of solutions will be presented. Solutions based on combining proven technologies from the chemical industry with new technology to produce essential chemicals and fuels such as green hydrogen, green ammonia, eMethanol, and other clean fuels from non-fossil feedstocks such as biomass, waste and renewable electricity. The most critical new technology in terms of cost and energy loss is water electrolysis for hydrogen production. A deep dive on the most efficient electrolysis technology, high temperature solid oxide electrolysis will be given ranging from basic thermodynamics to process integration for chemicals production
Modeling the adsorption of sulfur containing molecules and their hydrodesulfurization intermediates on the Co-promoted MoS<sub>2</sub> catalyst by DFT
Modeling the active sites of Co-promoted MoS<sub>2</sub> particles by DFT
The atomic-scale structure of CoMoS and the nature of its active sites for hydrodesulfurization and hydrogen evolution are determined based on DFT simulations.</p
Methanol to Dimethyl Ether over ZSM-22: A Periodic Density Functional Theory Study
Methanol-to-DME
conversion over ZSM-22 Brønsted acid sites
is investigated on the basis of periodic density functional theory
calculations. DME formation has been speculated to take place via
the dissociative or associative pathway. It is shown that the dissociative
pathway is the predominant pathway. We find that water lowers the
activation energies of key reactions but that the lowering of the
activation energies is insufficient to increase the rate because of
the entropy loss associated with water adsorption. The consequence
of acid strength on the methanol-to-DME conversion pathways is investigated
on the basis of Al-, Ga-, or In-induced Brønsted acid sites.
We show that linear correlations between activation energies and acid
strength exist. It is found that weaker acidity leads to higher activation
energies. We find that changes in acidity will not change the conclusion
that the dissociative pathway is the predominant pathway