Acid-promoted Ir-La-S/AC-catalyzed methanol carbonylation on single atomic active sites

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.