Damilola A. Daramola

Dissociation Rates of Urea in the Presence of NiOOH Catalyst: A DFT Analysis

Single molecule reactions have been studied between nickel oxyhydroxide, urea, and the hydroxide ion to understand the process of urea dissociation into ammonia, isocyanic acid, cyanate ion, carbon dioxide, and nitrogen. In the absence of hydroxide ions, nickel oxyhydroxide will catalyze urea to form ammonia and isocyanic acid with the rate-limiting step being the formation of ammonia with a rate constant of 1.5 × 10⁻⁶ s⁻¹. In the presence of hydroxide, the evolution of ammonia was also the rate-limiting step with a rate constant of 1.4 × 10⁻²⁶ s⁻¹. In addition, desorption of the cyanate ion presented an energy barrier of 6190 kJ mol⁻¹ suggesting that the cyanate ion cannot be separated from NiOOH unless further reactions occurred. Finally, elementary dissociation reactions with hydroxide ions deprotonating urea to produce nitrogen and carbon dioxide were analyzed. These elementary reactions were investigated along three paths differing in the order that protons were removed and the nitrogen atoms were rotated. The rate-limiting step was found to be the removal of carbon dioxide with a rate constant of 4.3 × 10⁻⁶⁵ s⁻¹. Therefore, the catalyst could be deactivated by the surface blockage caused by carbon dioxide adsorption.

Density Functional Theory Analysis of Raman Frequency Modes of Monoclinic Zirconium Oxide Using Gaussian Basis Sets and Isotopic Substitution

Geometry and vibration properties for monoclinic zirconium oxide were studied using Gaussian basis sets and LDA, GGA, and B3LYP functionals. Bond angles, bond lengths, lattice parameters, and Raman frequencies were calculated and compared to experimental values. Bond angles and lengths were found to agree within experimental standard deviations. The B3LYP gave the best performance of all three functionals with a percent error of 1.35% for the lattice parameters while the average difference between experimental and calculated Raman frequency values was -3 cm(-1). The B3LYP functional was then used to assign the atomic vibrations causing each frequency mode using isotopic substitution of (93.40)Zr for (91.22)Zr and (18.00)O for (16.00)O. This resulted in seven modes assigned to the Zr atom, ten modes to the O atom, and one mode being a mixture of both.

Theoretical study of ammonia oxidation on platinum clusters--adsorption of intermediate nitrogen dimer molecules.

Density Functional Theory calculations with the hybrid B3LYP functional and the LANL2DZ and 6-311++g(**) basis sets were used to calculate the adsorption energies, geometries and vibration modes of N2Hz (z=0-4) molecules on a cluster of 20 platinum atoms. Based on calculated binding energies, the trans conformations of N2H4 and N2H2 were predicted to adsorb with one nitrogen in contact with the cluster; N2H3 and N2H radicals adsorb with both nitrogen atoms in contact with the catalyst; while N2 was not found to adsorb to any appreciable degree. Calculated frequencies showed N-N bond stretching frequency occurs at 913 cm(-1) and 953 cm(-1) for N2H4 and N2H3, respectively and is blueshifted to 1603 cm(-1) and 1631 cm(-1) for N2H and N2H2, respectively. This trend suggests that the formation of this bond could indicate the presence of these species during ammonia oxidation as a shift from 900 to 1600 cm(-1) is expected when the single bond becomes a double bond. Finally, this study combined with earlier studies predicts the following trend for the adsorption energies of species formed: N2

Mathematical model of a parallel plate ammonia electrolyzer for combined wastewater remediation and hydrogen production

A mathematical model was developed for the simulation of a parallel plate ammonia electrolyzer to convert ammonia in wastewater to nitrogen and hydrogen under basic conditions. The model consists of fundamental transport equations, the ammonia oxidation kinetics at the anode, and the hydrogen evolution kinetics at the cathode of the electrochemical reactor. The model shows both qualitative and quantitative agreement with experimental measurements at ammonia concentrations found within wastewater (200-1200 mg L(-1)). The optimum electrolyzer performance is dependent on both the applied voltage and the inlet concentrations. Maximum conversion of ammonia to nitrogen at the rates of 0.569 and 0.766 mg L(-1) min(-1) are achieved at low (0.01 M NH4Cl and 0.1 M KOH) and high (0.07 M NH4Cl and 0.15 M KOH) inlet concentrations, respectively. At high and low concentrations, an initial increase in the cell voltage will cause an increase in the system response - current density generated and ammonia converted. These system responses will approach a peak value before they start to decrease due to surface blockage and/or depletion of solvated species at the electrode surface. Furthermore, the model predicts that by increasing the reactant and electrolyte concentrations at a certain voltage, the peak current density will plateau, showing an asymptotic response.

9.14 Preparative Electrochemistry for Organic Synthesis

This chapter provides an overview of the advances in electrochemistry and electrochemical engineering that have taken place in the last few decades and discusses how these advances could be implemented in the synthesis of organic molecules from conception to the market.

Combined Theoretical and Experimental Investigation and Design of H2S Tolerant Anode for Solid Oxide Fuel Cells

A solid oxide fuel cell (SOFC) is a high temperature fuel cell and it normally operates in the range of 850 to 1000 C. Coal syngas has been considered for use in SOFC systems to produce electric power, due to its high temperature and high hydrogen and carbon monoxide content. However, coal syngas also has contaminants like carbon dioxide (CO{sub 2}) and hydrogen sulfide (H{sub 2}S). Among these contaminants, H{sub 2}S is detrimental to electrode material in SOFC. Commonly used anode material in SOFC system is nickel-yttria stabilized zirconia (Ni-YSZ). The presence of H{sub 2}S in the hydrogen stream will damage the Ni anode and hinder the performance of SOFC. In the present study, an attempt was made to understand the mechanism of anode (Ni-YSZ) deterioration by H{sub 2}S. The study used computation methods such as quantum chemistry calculations and molecular dynamics to predict the model for anode destruction by H{sub 2}S. This was done using binding energies to predict the thermodynamics and Raman spectroscopy to predict molecular vibrations and surface interactions. On the experimental side, a test stand has been built with the ability to analyze button cells at high temperature under syngas conditions.