Electrochemical ammonia synthesis is being actively studied as a low temperature, low pressure alternative to the Haber-Bosch process. This work studied pure iridium as the catalyst for ammonia synthesis, following promising experimental results of Pt-Ir alloys. The characteristics studied include bond energies, bond lengths, spin densities, and free and adsorbed vibrational frequencies for the molecules N 2 , N, NH, NH 2 , and NH 3. Overall, these descriptive characteristics explore the use of dispersioncorrected density functional theory methods that can model N 2 adsorption-the key reactant for electrochemical ammonia synthesis via transition metal catalysis. Specifically, three methods were tested: hybrid B3LYP, a dispersion-corrected form B3LYP-D3, and semi-empirical B97-D3. The latter semiempirical method was explored to increase the accuracy obtained in vibrational analysis as well as reduce computational time. Two lattice surfaces, (111) and (100), were compared. The adsorption energies are stronger on (100) and follow the trend E B3LYP > E B3LYP-D3 > E B97-D3 on both surfaces.
Electrochemical ammonia synthesis is being actively studied as a low temperature, low pressure alternative to the Haber-Bosch process. This work studied iridium as the electrochemical catalyst, following a previous study of adsorption characteristics on platinum. The characteristics studied include bond energies, bond lengths, spin densities, and free and adsorbed vibrational frequencies for the molecules N2, N, NH, NH2, and NH3. Overall, these descriptive characteristics explore the use of dispersioncorrected Density Functional Theory methods that can model N2 adsorption-the key reactant for electrochemical ammonia synthesis via transition metal catalysis. Specifically, three methods were tested: hybrid B3LYP, a dispersion-corrected form B3LYP-D3, and semi-empirical B97-D3. The latter semi-empirical method was explored to increase the accuracy obtained in vibrational analysis as well as reduce computational time. Two lattice surfaces, (111) and (100), were compared. The adsorption energies are stronger on (100) and follow the trend EB3LYP > EB3LYP-D3 > EB97-D3 on both surfaces.
Reducing the volume of hazardous waste may not provide relief from the toxic nature of the compound, but it does provide a significant benefit in reducing transportation, treatment, and disposal costs. The Environmental Protection Agency's Hazardous Waste Engineering Research Laboratory supports extramural studies in waste detoxification, concentration and recovery, and minimization. Three concentration and recovery projects are discussed.
A phosphate precipitation process is effective in selectively removing metals from metal finishing sludge materials. Research also indicates that sodium smectite clay, an abundant natural material, can be modified in structure so that it has excellent adsorptive properties for removing compounds like benzene, trichlorophenol, and pentachlorophenol from aqueous solutions. The separation of dilute hazardous organics using thin-film, composite, aromatic polyamide membranes also appears to be advantageous in terms of high solute separation at low pressures (1 to 2 MPa) and broad pH operating ranges (pH 2 to 12).
The Cover Feature shows the (111) surface of iridium. Density functional theory was used to calculate the electronic structure of iridium and adsorption of nitrogenous compounds using three methods: B3LYP, B3LYP‐D3, and B97‐D3. Among these methods, we found trends in surface bonding geometry and vibrational spectra. The semi‐empirical B97‐D3 provided results much closer to experimental benchmarks with greater computational efficiency, warranting its future use in low‐cost computations. Additionally, we explored the key differences between adsorption on platinum and iridium, illustrating why Pt‐Ir alloys show promise in electrochemical ammonia synthesis. More information can be found in the Full Paper Esther F. Grossman et al.
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