Incorporation Of Trivalent Ions Research Articles

Synthesis, characterization, and catalytic performance of bifunctional titanium silicalite-1

A series of bifunctional Ti-molecular sieves (M-TS-1, M = Al, B, or Fe) containing different trivalent ions (Al3+, B3+, or Fe3+), with MFI topology, were synthesized using tetrapropylammonium bromide, silica sol, and n-butylamine as a template, base, and Si source, respectively. The simultaneous presence of Ti and trivalent ions in lattice positions provided catalysts with activity in both oxidation and acid-catalyzed reactions. The samples were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, NH3 temperature-programmed desorption, inductively coupled plasma atomic emission spectroscopy, and N2 adsorption-desorption isotherms. The results showed that the numbers and strength of acid sites of TS-1 were enhanced by the incorporation of trivalent ions. Using selective oxidation of ethylene as the probe reaction, the catalytic properties of M-TS-1 were investigated. The results showed that Al-TS-1 and B-TS-1 had better catalytic properties; conversion and utilization of H2O2 reached 95% and 90%, respectively, and the yield of ethylene glycol plus its monomethyl ether was greater than 10%.

Energetics of Aluminum Vacancies and Incorporation of Foreign Trivalent Ions in γ‐Al2O3: An Atomistic Simulation Study

Atomistic simulation methods based on pair‐wise interatomic potentials and energy minimization have been applied to elucidate the energetics of cation vacancies and the incorporation of 13 trivalent M3+ cations (Cr3+, Ga3+, Fe3+, Lu3+, Yb3+, Er3+, Y3+, Tb3+, Gd3+, Eu3+, Sm3+, Nd3+, La3+) in γ‐Al2O3. Calculations have been carried out using Al64O96 defect spinel supercells containing eight aluminum vacancies. The lowest energy configurations correspond to a random distribution of tetrahedral and octahedral vacancies. The energy gain in comparison with exclusive tetrahedral or octahedral vacancies is rather small (0.03 and 0.09 eV/Al2O3, respectively). Unit cell volume, density, and lattice properties of optimized structures are in good agreement with the experimental values or the results of high‐quality density functional theory calculations. The trends observed for the solution energy of the M2O3 oxides in the supercell with minimum energy indicate the preferential incorporation of the foreign ions at the tetrahedral site and an increase of the solubility of M2O3 in the defect spinel in comparison with α‐Al2O3. Configurations with the lowest energy have negative solution energies and, consequently, incorporation of trivalent ions can improve the thermodynamic stability of γ‐Al2O3 in comparison with α‐Al2O3 and increase the γ→α transition temperature.

Aluminum in magnesium silicate perovskite: Formation, structure, and energetics of magnesium‐rich defect solid solutions

MgSiO3‐rich perovskite is expected to dominate Earth's lower mantle (pressures >25 GPa) with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA + SiB = MA + MB and SiB = AlB + 0.5 (vacancy)O. Phase synthesis studies show that both substitutions do occur and the nonstoichiometric or defect substitution is prevalent along the MgSiO3‐MgAlO2.5 join. Lattice parameters associated with the first substitution (stoichiometric) show more rapid increases with increasing Al content than those for the second substitution (nonstoichiometric), consistent with the differences in size of substituting ions. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of −0.8 ± 2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5 ± 4.6 kJ/mol. Configurational T ΔS terms play a role in both substitutions. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite and may significantly affect the elasticity, rheology, and water retention of silicate perovskite in Earth.

Aluminum in Magnesium Silicate Perovskite: Synthesis and Energetics of Defect Solid Solutions

AbstractMgSiO3 - rich perovskite is expected to dominate the Earth's lower mantle (pressures > 25 GPa), with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA+ SiB = MA + MB and SiB = AlB + 0.5 VO. Phase synthesis studies show that both substitutions do occur, and the nonstoichiometric or defect substitution is prevalent along the MgSiO3 - MgAlO2.5 join. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of -0.8±2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5±4.6 kJ/mol. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite, and may significantly affect the elasticity, rheology and water retention of silicate perovskite in the Earth.