2 research outputs found
Electronic Properties and Reactivity of Simulated Fe<sup>3+</sup> and Cr<sup>3+</sup> Substituted α‑Al<sub>2</sub>O<sub>3</sub> (0001) Surface
Metal oxide-based minerals naturally contain transition
metal impurities
isomorphically substituted into the structure that can alter the structural
and electronic properties as well as the reactivity of these metal
oxides. Natural α-Al<sub>2</sub>O<sub>3</sub> (corundum) can
contain up to 9.17% (w/w) Fe<sub>2</sub>O<sub>3</sub> and 1.81% (w/w)
of Cr<sub>2</sub>O<sub>3.</sub> Here we report on changes in the structural
and electronic properties of undoped and doped α-Al<sub>2</sub>O<sub>3</sub> (0001) surfaces using periodic density functional theory
(DFT) methods with spin unrestricted B3LYP functional and a local
atomic basis set. Both structural and electronic properties are altered
upon doping. Implications for doping effects on photochemical processes
are discussed. As metal oxides are major components of the environment,
including atmospheric mineral aerosol, DFT was also used to study
the effect of transition metal impurities on gas/surface interactions
of a model acidic atmospheric gas molecule, carbon monoxide (CO).
The theoretical results indicated that the presence of Fe<sup>3+</sup> and Cr<sup>3+</sup> impurities substituted on the outer layer of
natural corundum surfaces reduces the propensity toward CO adsorption
relative to the undoped surface. However, CO–surface interactions
resemble that of bulk α-Al<sub>2</sub>O<sub>3</sub> when the
impurity is substituted below the first surface layer. The presence
and location of the mineral dopant were found to significantly alter
the structural and electronic properties and gas/surface interactions
studied here
Computational Studies of CO<sub>2</sub> Activation via Photochemical Reactions with Reduced Sulfur Compounds
Reactions between CO<sub>2</sub> and reduced sulfur compounds
(RSC),
H<sub>2</sub>S and CH<sub>3</sub>SH, were investigated using ground
and excited state density functional theory (DFT) and coupled cluster
(CC) methods to explore possible RSC oxidation mechanisms and CO<sub>2</sub> activation mechanisms in the atmospheric environment. Ground
electronic state calculations at the CR-CCÂ(2,3)/6-311+GÂ(2df,2p)//CAM-B3LYP/6-311+GÂ(2df,2p)
level show proton transfer as a limiting step in the reduction of
CO<sub>2</sub> with activation energies of 49.64 and 47.70 kcal/mol,
respectively, for H<sub>2</sub>S and CH<sub>3</sub>SH. On the first
excited state surface, CR-EOMCCÂ(2,3)/6-311+GÂ(2df,2p)//CAM-B3LYP/6-311+GÂ(2df,2p)
calculations reveal that energies of <250 nm are needed to form
H<sub>2</sub>S–CO<sub>2</sub> and CH<sub>3</sub>SH–CO<sub>2</sub> complexes allowing facile hydrogen atom transfer. Once excited,
all reaction intermediates and transition states are downhill energetically
showing either C–H or C–S bond formation in the excited
state whereas only C–S bond formation was found in the ground
state. Environmental implications of these data are discussed with
a focus on tropospheric reactions between CO<sub>2</sub> and RSC,
as well as potential for carbon sequestration using photocatalysis