Synthesis and characterization of iridium model, and cobalt and nickel, industrial Ziegler-type hydrogenation catalysts and their precursors
Date
2011
Authors
Alley, William Morgan, author
Finke, Richard G., advisor
Chen, Eugene Y.-X., committee member
Elliott, C. Michael, committee member
Levinger, Nancy E., committee member
Kipper, Matthew J., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Following a comprehensive critical review of the pertinent literature, the research presented herein is focused on the synthesis of an Ir precursor used to model industrial Ziegler-type hydrogenation catalysts, and on catalyst characterization using both the Ir model, and genuine Co and Ni, industrial catalyst materials. The studies include: (i) the synthesis, characterization, and initial catalytic investigation of Ir (and Rh) compounds for use as models for the industrial Co and Ni Ziegler-type hydrogenation catalysts; (ii) characterization of the Ziegler-type hydrogenation catalyst made from the Ir precursor; and (iii) characterization of the authentic industrial Co and Ni Ziegler-type hydrogenation catalysts. The synthesis and definitive characterization of Ir (and Rh) precatalysts designed to facilitate investigation into the homogeneous versus heterogeneous nature of Ziegler-type hydrogenation catalysts is described herein. Additionally, the ability of these Ir (and Rh) precatalysts to form active Ziegler-type hydrogenation catalysts upon combination with AlEt3 is demonstrated. The homogeneous versus heterogeneous nature of the Ir Ziegler-type hydrogenation catalyst is investigated using several complementary analytical methods plus kinetic studies. Initial active catalyst solutions contain a variety of Ir species ranging from mono-Ir compounds to nanometer-scale Irn clusters, but on average are subnanometer, Ir~4-15 species. However, crystalline Ir(0)~40-150 nanoclusters are rapidly formed when the solutions are put under pressurized H2 gas, and these larger, "Ziegler nanoclusters" are shown to be the most active catalysts, an important result in comparison to all the prior, extensive literature of these important industrial catalysts. The homogeneous versus heterogeneous nature of the authentic industrial Co- and Ni-based Ziegler-type hydrogenation catalysts are investigated using an approach parallel to that used for the Ir system, and are compared to the results from the Ir model system. The metal cluster species are essentially the same pre- and posthydrogenation; they comprise a broad distribution of Mn cluster sizes from subnanometer to nanometer in scale, with average diameters of about one nanometer, and with some amount of unreduced mono-metallic complexes also present dependent on the Al/M ratio. These findings support the primary working hypothesis present in the most recent literature, namely that Ziegler-type hydrogenation catalysis is enacted by "Ziegler nanoclusters" (as defined herein), nanoclusters of size M4 in the case of the industrial Co and Ni system.