Industrial Ziegler-Type Hydrogenation Catalysts Made from Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2) and AlEt3: Evidence for Nanoclusters and Sub-Nanocluster or Larger Ziegler-Nanocluster Based Catalysis

Alley, William M.
Hamdemir, Isil K.
Wang, Qi
Frenkel, Anatoly I.
Li, Long
Yang, Judith C.
Menard, Laurent D.
Nuzzo, Ralph G.
Özkar, Saim
Yih, Kuang-Hway
Johnson, Kimberly A.
Finke, Richard G.
Ziegler-type hydrogenation catalysts are important for industrial processes, namely, the large-scale selective hydrogenation of styrenic block copolymers. Ziegler-type hydrogenation catalysts are composed of a group 8-10 transition metal precatalyst plus an alkylaluminum cocatalyst (and they are not the same as Ziegler-Natta polymerization catalysts). However, for similar to 50 years two unsettled issues central to Ziegler-type hydrogenation catalysis are the nature of the metal species present after catalyst synthesis, and whether the species primarily responsible for catalytic hydrogenation activity are homogeneous (e.g., monometallic complexes) or heterogeneous (e.g., Ziegler nanoclusters defined as metal nanoclusters made from combination of Ziegler-type hydrogenation catalyst precursors). A critical review of the existing literature (Alley et al. J. Mot. Catal. A: Chem. 2010, 315, 1-27) and a recently published study using an Ir model system (Alley et al. Inorg. Chem. 2010, 49, 8131-8147) help to guide the present investigation of Ziegler-type hydrogenation catalysts made from the industrially favored precursors Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2), plus AlEt3. The approach and methods used herein parallel those used in the study of the Ir model system. Specifically, a combination of Z-contrast scanning transmission electron microscopy (STEM), matrix assisted laser desorption ionization mass spectrometry (MALDI MS), and X-ray absorption fine structure (XAFS) spectroscopy are used to characterize the transition metal species both before and after hydrogenation. Kinetic studies including Hg(0) poisoning experiments are utilized to test which species are the most active catalysts. The main findings are that, both before and after catalytic cyclohexene hydrogenation, the species present comprise a broad distribution of metal duster sizes from subnanometer to nanometer scale particles, with estimated mean duster diameters of about 1 nm for both Co and Ni. The XAFS results also imply that the catalyst solutions are a mixture of the metal dusters described above, plus unreduced metal ions. The kinetics-based Hg(0) poisoning evidence suggests that Co and Ni Ziegler nanoclusters (i.e., M->= 4) are the most active Ziegler-type hydrogenation catalysts in these industrial systems. Overall, the novelty and primary conclusions of this study are as follows: (i) this study examines Co- and Ni-based catalysts made from the actual industrial precursor materials, catalysts that are notoriously problematic regarding their characterization; (ii) the Z-contrast STEM results reported herein represent, to our knowledge, the best microscopic analysis of the industrial Co and Ni Ziegler-type hydrogenation catalysts; (iii) this study is the first explicit application of an established method, using multiple analytical methods and kinetics-based studies, for distinguishing homogeneous from heterogeneous catalysis in these Ziegler-type systems; and (iv) this study parallels the successful study of an Ir model Ziegler catalyst system, thereby benefiting from a comparison to those previously unavailable findings, although the greater M-M bond energy, and tendency to agglomerate, of Er versus Ni or Co are important differences to be noted.


In Situ Formed "Weakly Ligated/Labile Ligand" Iridium(0) Nanoparticles and Aggregates as Catalysts for the Complete Hydrogenation of Neat Benzene at Room Temperature and Mild Pressures
Bayram, Ercan; Zahmakiran, Mehmet; Özkar, Saim; Finke, Richard G. (American Chemical Society (ACS), 2010-07-20)
"Weakly ligated/labile ligand" nanoparticles, that is nanoparticles where only weakly coordinated ligands plus the desired catalytic reactants are present, are of fundamental interest. Described herein is a catalyst system for benzene hydrogenation to cyclohexane consisting of "weakly ligated/labile ligand" Ir(0) nanoparticles and aggregates plus dry-HCl formed formed in situ from commercially available [(1,5-COD)IrCl](2) plus 40 +/- 1 psig (similar to 2.7 atm) H(2) at 22 +/- 0.1 degrees C. Multiple control...
Dust Effects on Nucleation Kinetics and Nanoparticle Product Size Distributions: Illustrative Case Study of a Prototype Ir(0)(n) Transition-Metal Nanoparticle Formation System
Özkar, Saim (American Chemical Society (ACS), 2017-07-04)
The question is addressed if dust is kinetically important in the nucleation and growth of Ir(0) nanoparticles formed from [Bu4N](5)Na-3(1,5-COD)(IrP2W15Nb3O62)-P-I center dot (hereafter [(COD)Ir center dot POM](8-)), reduced by H-2 in propylene carbonate solvent. Following a concise review of the (often neglected) literature addressing dust in nucleation phenomena dating back to the late 1800s, the nucleation and growth kinetics of the [(COD)Ir center dot POK8- precatalyst system are examined for the effec...
Design Parameters and Principles of Liquid-Crystal-Templated Synthesis of Polymeric Materials via Photolithography
AKDENİZ, BURAK; Büküşoğlu, Emre (American Chemical Society (ACS), 2019-10-08)
The design parameters and principles for the synthesis of polymeric microscopic objects using a method that combines photolithography and liquid crystal (LC) molecular templates have been demonstrated. Specifically, mixtures of a reactive mesogen (RM257) and nonreactive LC (E7) were polymerized using UV light and a photomask. We used photomasks with circular, triangular, rectangular, square, star-shaped, and heart-shaped features to provide initial shapes to the objects. Then, the unreacted parts were extra...
Palladium(0) Nanoparticle Formation, Stabilization, and Mechanistic Studies: Pd(acac)(2) as a Preferred Precursor, [Bu4N](2)HPO4 Stabilizer, plus the Stoichiometry, Kinetics, and Minimal, Four-Step Mechanism of the Palladium Nanoparticle Formation and Subsequent Agglomeration Reactions
Özkar, Saim (American Chemical Society (ACS), 2016-04-19)
Palladium(0) nanoparticles continue to be important in the field of catalysis. However, and despite the many prior reports of Pd(0)(n) nanoparticles,, missing is a study that reports the kinetically controlled formation of Pd(0)(n) nanoparticles with the simple stabilizer [Bu4N](2)HPO4 in an established, balanced formation reaction where the kinetics and mechanism of the nanoparticle-formation reaction are also provided. It is just such studies that are the focus of the present work. Specifically, the prese...
Liposomal Nanoreactors for the Synthesis of Monodisperse Palladium Nanoparticles Using Glycerol
Clergeaud, Gael; Genc, Rukan; Ortiz, Mayreli; O'Sullivan, Ciara K. (American Chemical Society (ACS), 2013-12-10)
The synthesis of highly stable ultrasmall monodisperse populations of palladium nanoparticles in the range of 1-3 nm in size was achieved via polyol reduction within 1,2-dioleoyl-sn-glycero-3-phosphor-rac(1-glycerol) liposomal nanoreactors exploiting glycerol as both reducing and stabilizing agent. The liposome-based green method was compared with synthesis in solution, and the reducing agent concentration and the lipidic composition of the liposomal nanoreactors were demonstrated to have a strong effect on...
Citation Formats
W. M. Alley et al., “Industrial Ziegler-Type Hydrogenation Catalysts Made from Co(neodecanoate)(2) or Ni(2-ethylhexanoate)(2) and AlEt3: Evidence for Nanoclusters and Sub-Nanocluster or Larger Ziegler-Nanocluster Based Catalysis,” LANGMUIR, pp. 6279–6294, 2011, Accessed: 00, 2020. [Online]. Available: