Highly active Ir‐La‐S/AC catalyst was successfully prepared by co‐impregnation of an activated carbon（AC） carrier with a sulfuric acid solution of Ir and La species and compared with a tradition‐ally prepared Ir...Highly active Ir‐La‐S/AC catalyst was successfully prepared by co‐impregnation of an activated carbon（AC） carrier with a sulfuric acid solution of Ir and La species and compared with a tradition‐ally prepared Ir‐La/AC catalyst. High angle annular dark‐field‐scanning transmission electron mi‐croscopy（HAADF‐STEM） measurement results show that most of the Ir species on Ir‐La‐S/AC exist as single atomic sites, while those on Ir‐La/AC exist as nanoparticles with an average diameter of 1.5 nm. Evaluation of Ir‐La‐S/AC as a catalyst for heterogeneous carbonylation of methanol to acetyl gave a maximum TOF （turn‐over‐frequency） of 2760 h^–1, which was distinctly higher than that achieved by the Ir‐La/AC catalyst（approximately 1000 h^-1）. Temperature‐programmed desorption of ammonia（NH3‐TPD） result shows that the addition of sulfuric acid during the preparation pro‐cedure results in significantly more acidic sites on Ir‐La‐S/AC than those on Ir‐La/AC, which plays a key role in the enhancement of CO insertion as the rate‐determining step. Tempera‐ture‐programmed reduction（TPR） and in situ X‐ray photoelectron spectroscopy reveal that Ir spe‐cies are more reducible, and that more Ir^＋ might be formed by activation of Ir‐La‐S/AC than those on the Ir‐La/AC catalyst, which is thought to be beneficial for reductive elimination of AcI from Ir^3＋ species as an essential step for CH3I regeneration and acetyl formation.展开更多
We give here an overview of the orbital-flee density functional theory that is used for modeling atoms and molecules. We review typical approximations to the kinetic energy, exchange-correlation corrections to the k...We give here an overview of the orbital-flee density functional theory that is used for modeling atoms and molecules. We review typical approximations to the kinetic energy, exchange-correlation corrections to the kinetic and Hartree energies, and constructions of the pseudopotentials. We discuss numerical discretizations for the orbital-free methods and include several numerical results for illustrations.展开更多
基金supported by the National Key R&D Program of China (2017YFB0602203)~~
文摘Highly active Ir‐La‐S/AC catalyst was successfully prepared by co‐impregnation of an activated carbon（AC） carrier with a sulfuric acid solution of Ir and La species and compared with a tradition‐ally prepared Ir‐La/AC catalyst. High angle annular dark‐field‐scanning transmission electron mi‐croscopy（HAADF‐STEM） measurement results show that most of the Ir species on Ir‐La‐S/AC exist as single atomic sites, while those on Ir‐La/AC exist as nanoparticles with an average diameter of 1.5 nm. Evaluation of Ir‐La‐S/AC as a catalyst for heterogeneous carbonylation of methanol to acetyl gave a maximum TOF （turn‐over‐frequency） of 2760 h^–1, which was distinctly higher than that achieved by the Ir‐La/AC catalyst（approximately 1000 h^-1）. Temperature‐programmed desorption of ammonia（NH3‐TPD） result shows that the addition of sulfuric acid during the preparation pro‐cedure results in significantly more acidic sites on Ir‐La‐S/AC than those on Ir‐La/AC, which plays a key role in the enhancement of CO insertion as the rate‐determining step. Tempera‐ture‐programmed reduction（TPR） and in situ X‐ray photoelectron spectroscopy reveal that Ir spe‐cies are more reducible, and that more Ir^＋ might be formed by activation of Ir‐La‐S/AC than those on the Ir‐La/AC catalyst, which is thought to be beneficial for reductive elimination of AcI from Ir^3＋ species as an essential step for CH3I regeneration and acetyl formation.
基金supported by the National Science Foundation of China under the grant 10425105the National Basic Research Program under the grant 2005CB321704.
文摘We give here an overview of the orbital-flee density functional theory that is used for modeling atoms and molecules. We review typical approximations to the kinetic energy, exchange-correlation corrections to the kinetic and Hartree energies, and constructions of the pseudopotentials. We discuss numerical discretizations for the orbital-free methods and include several numerical results for illustrations.
