ABSTRACT
The present paper addresses the interaction of CO2 with polycrystalline α-Fe2O3 revealing considerable catalytic activity in CO oxidation to yield CO2. The mechanism of adsorption and desorption of CO2 was investigated by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), while the kinetics was examined by temperature-programmed desorption (CO2-TPD). For numeric modeling as well as simulation of the surface coverage, an elementary kinetic mean field model was constructed using Arrhenius-based rate expressions. The kinetic parameters of desorption were taken from fitting calculations (A2 = 3.01 × 10(5) mol (m(2) s)(-1), E2(0) = 112.8 kJ mol(-1), α2 = 70.2 kJ mol(-1)), whereas the adsorption was considered to be non-activated and the pre-exponential factor was estimated from kinetic gas theory (A1 = 0.0192 m s(-1), E1 = 0 kJ mol(-1)). For model validation, predicted and experimental CO2-TPD profiles were compared and thermodynamic consistency was evaluated by using differential scanning calorimetry (ΔadsH(250 °C) = -129 kJ mol(-1)) as well as literature data.
ABSTRACT
Molecular modeling is used to determine low-energy conformational structures and thermodynamic properties of levulinic acid in the gas phase. Structure and IR vibrational frequencies are obtained using density functional and Møller-Plesset perturbation theories. Electronic energies are computed using G3//B3LYP and CBS-QB3 model chemistries. Computed anharmonic frequencies are consistent with reported experimental data. Population analysis shows a boat- and a chainlike structure to be most abundant at 298 K, with increasing proportions of two other conformers at higher temperatures. Population mean distribution values for thermodynamic quantities are derived. At 298 K and 1 atm, the enthalpy of formation, entropy, and heat capacity are -613.1 ± 1.0 kJ·mol(-1), 407.4 J·mol(-1)·K(-1), and 132.3 J·mol(-1)·K(-1), respectively.
