Propane Dehydrogenation Using Transition Metal Cluster Catalysts

Our research seeks to determine the propane dehydrogenation (PDH) reaction pathways using various transition-metal cluster catalysts. We are studying the first step of the reaction, in which a C-H bond is broken. This has been previously shown to be the rate-limiting step of the PDH reaction. We are calculating the PDH activation energy (Ea) using the Vienna Ab-Initio Simulation Package (VASP) in conjunction with the nudged elastic band algorithm. Thus far, we have studied Pt, Ta, and Ni clusters ranging in size from 2-10 atoms. Our goal is to better understand the dependence of Ea on metal type and cluster size

Propane Dehydrogenation Using Transition Metal Cluster Catalysts

Our research seeks to determine the propane dehydrogenation (PDH) reaction pathways using various transition-metal cluster catalysts. We are studying the first step of the reaction, in which a C-H bond is broken. This has been previously shown to be the rate-limiting step of the PDH reaction. We are calculating the PDH activation energy (Ea) using the Vienna Ab-Initio Simulation Package (VASP) in conjunction with the nudged elastic band algorithm. Thus far, we have studied Pt, Ta, and Ni clusters ranging in size from 2-10 atoms. Our goal is to better understand the dependence of Ea on metal type and cluster size

SPECIATION OF PLUTONIUM IN WATER

Author Institution: Department of Chemistry, The Ohio State University; Chemical Technology Division/Materials Science Division, Argonne National Laboratory; Department of Chemistry, The Ohio State UniversityThe speciation of plutonium in water was modeled using both ab initio quantum chemistry and density functional theory (DFT) methods. Aqueous plutonium exists in four oxidation states: $+3, +4, +5$, and $+6$. The first two forms exist as the bare ions, but the $+5$ and $+6$ states exist as $(PuO_{2})^{+}$ and $(PuO_{2})^{2+}$ species, respectively. The coordination number for the number of water molecules around each of these species is determined and compared to experiment - which uses XANES (X-ray Absorption Near-Edge Spectroscpy) and eXAFS (extended X-ray Absorption Fine Structure) spectroscopy. The DFT calculations include generalized gradient corrections and the quantum chemistry calculations are at the spin-orbit configuration interaction level

SPECIATION OF PLUTONIUM IN WATER

Author Institution: Department of Chemistry, The Ohio State University; Chemical Technology Division/Materials Science Division, Argonne National Laboratory; Department of Chemistry, The Ohio State UniversityThe speciation of plutonium in water was modeled using density functional theory (DFT) methods. Aqueous plutonium exists in four oxidation states: $+3, +4, +5$, and $+6$. The first two forms exist as the bare ions, but the $+5$ and $+6$ states exist as $(PuO_{2})^{+}$ and $(PuO_{2})^{2+}$ species, respectively. The coordination number for the number of water molecules around each of these species is determined and compared to experiment - which uses XANES (X-ray Absorption Near-Edge Spectroscopy) and cXAFS (extended X-ray Absorption Fine Structure) spectroscopy. The DFT calculations include generalized gradient corrections

Structure-Specific Reactivity of Alumina-Supported Monomeric Vanadium Oxide Species

Oxidative dehydrogenation (ODH) catalysts based on vanadium oxide are active for the production of alkenes, chemicals of great commercial importance. The current industrial practice for alkene production is based on energy-intensive, dehydrogenation reactions. UV resonance and visible Raman measurements, combined with density functional studies, are used to study for the first time the structure–reactivity relationships for alumina-supported monomeric vanadium oxide species. The relationship between the structure of three vanadium oxide monomeric surface species on a θ-alumina surface, and their reducibility by H₂ was determined by following changes in the vanadia’s UV Raman and resonance Raman spectra after reaction with H₂ at temperatures from 450 to 650 °C. The H₂ reducibility sequence for the three monomeric species is bidentate > “molecular”> tridentate. The reaction pathways for H₂ reduction on the three vanadium oxide monomeric structures on a θ-alumina surface were investigated using density functional theory. Reduction by H₂ begins with reaction at the VO bond in all three species. However, the activation energy, Gibbs free energy change under reaction conditions, and the final V oxidation state are species-dependent. The calculated ordering of reactivity is consistent with the observed experimental ordering and provides an explanation for the ordering. The results suggest that synthesis strategies can be devised to obtain vanadium oxide structures with greatly enhanced activity for ODH resulting in more efficient catalysts