MedeA Application Notes for Chemical & Petrochemical
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The structure of the Fe₂O₃ (0001) surface as a function of oxygen partial pressure and temperature is computed using first-principles thermodynamics. The results reveal an active four-fold coordinated surface Fe atom which releases oxygen atoms at approximately 850 K at ambient oxygen partial pressure. This property is likely to be related to the catalytic activity of hematite for selective oxidation reactions such as the oxidation from ethylbenzene to styrene. 
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First-principles calculations reveal the atomistic structures of the active phases of CoMoS and NiMoS hydrodesulfurization catalysts. The reliable determination of the catalyst surface is critical, as it represents the starting point for subsequent adsorption and reaction path simulations. The predicted dominant structures are consistent with experimental STM, EXAFS and magnetic susceptibility measurements. 
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First-principles calculations reveal the dominant acid sites on the amorphous silica-alumina (ASA) catalyst surface. Based on the strength of interaction with Lewis base probe molecules, the bridging and pseudo-bridging silanol (PBS) species are determined to be the most acidic and therefore catalytically active groups. Evident in the calculations is the interplay between the Lewis acid and the Brønsted acid sites on the ASA catalyst surface, giving rise to the enhanced acidity of the PBS species. This work provides mechanistic insight to inform efforts at rationally engineering enhanced ASA-based solid acids. 
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First-principles calculations using VASP reveal the lowest energy reaction pathway for the catalyzed skeletal isomerization of 2-pentene by the acidic zeolite H-ZSM. Three potential mechanisms were evaluated: an ethyl-shift pathway, a dimethylcyclopropane (DMCP) intermediate pathway and a pathway involving an edge-protonated DMCP species. The results indicate that the DMCP intermediate pathway is the kinetically preferred pathway with a classical barrier height of 98 kJ/mol. Evident in the calculations is the influence of the transient intermediate stability along the reaction path; with secondary carbenium ions leading to energetically favored mechanisms. 
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MEDEA GIBBS calculates equilibrium properties of fluids either pure or mixed, in a single phase or in multiple phases, using a force field based Gibbs ensemble technique. 
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The energy of adsorption and dissociation of molecules on surfaces plays a critical role in technological processes such as chemical vapor deposition, catalysis, and corrosion. The present case shows the calculation of the energy of the dissociative chemisorption of a silane molecule on a Si (001) surface. 
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Increasingly stringent environmental regulations require a lowering of sulfur in Diesel fuels. This is accomplished by a catalytic process transforming sulfur-containing molecules into H2S, which is removed from the liquid phase. Larger sulfur-organic molecules are more difficult to attack and new catalytic materials are needed. The present screening study demonstrates how the combination of experimental activity data, crystallographic information from structural databases and first- principles computation of binding energies are used to identify potential new candidates. 
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The performance of catalytic materials depends on complex phenomena linked to chemical 
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This application note deals with positioning molecules on surfaces. As an example we will investigate the adsorption of ethyl alcohol (ethanol) on a Cu (111) surface. In doing so we will consider two possible configurations for the adsorbed molecule: 
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