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 traditionally prepared Ir-La/AC catalyst. High angle annular dark-field-scanning transmission electron microscopy (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 (NH 3 -TPD) result shows that the addition of sulfuric acid during the preparation procedure 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. Temperature-programmed reduction (TPR) and in situ X-ray photoelectron spectroscopy reveal that Ir species 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 CH 3 I regeneration and acetyl formation.
Xianjie Meng,Heqin Guo,Qiang Wang,Yong Xiao,Congbiao Chen,Bo Hou,Debao Li
In this study, a series of copper/titania–silica mixed oxide (Cu/TS) catalysts with different copper contents were prepared by a sol–gel method. The catalytic activity was evaluated by halide-free methanol carbonylation to methyl acetate (MA). The properties of the catalysts were mainly characterized by N2 adsorption–desorption, X-ray diffraction, dissociative N2O chemisorption, X-ray photoelectron spectroscopy, temperature-programmed desorption of ammonia and in situ Fourier transform infrared. The results show that the crystal size and aggregation degree of Cu increase with increasing Cu content. In addition, the amount of surface Cu+ firstly increases and then decreases, and the maximum is 1.560 mmol g−1 for the 10.24 Cu/TS catalyst. Both the amounts of adsorbed CO and surface Lewis acid sites are found to be proportional to the amount of surface Cu+ species. The catalytic performance shows that the space time yield (STY) of MA is also strongly related to the amount of surface Cu+ species, and the 10.24 Cu/TS catalyst has a maximum of 1.770 mol h−1 kgcat−1. It is found that the surface Cu+ species act not only as metal sites which adsorb CO but also as Lewis acid sites which promote the adsorption of methanol (methoxy). Furthermore, the activation of CO is the major factor for the MA synthesis.
危险品化学品经营许可证（带存储）