PNNL

Abstract

Homogenous catalysts utilize discrete molecular species which imparts high selectivity and facilitates mechanistic understanding, but encounter separation and stability problems. Since they are more stable and easily separated, heterogeneous catalysts are more widely used in industry, but normally contain a multiplicity of sites leading to reduced selectivity and difficult mechanistic interpretations. Attaining molecular (single site) behavior similar to homogenous catalysts on heterogeneous surfaces has been an enduring goal. Here we show that when Ir and La halides are deposited on carbon, exposure to CO spontaneously generates a discrete molecular heterobimetallic species containing an Ir-La covalent bond, likely IrLa(CO)2Cl4. The generation of these discrete species on the surface leads to a highly active and selective heterogeneous catalyst for the carbonylation of methanol to produce acetic acid, in which enhanced activity may be mechanistically rationalized based on the chemistry of lanthanide-transition metal complexes and earlier studies on the Ir catalyzed methanol carbonylations. Acknowledgements: This research was supported by Eastman Chemical Company and by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle under contract number DE-AC05-76RL01830. The electron microscopy work carried out at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.