4:00 pm – 5:00 pm
Virtual meeting platform
We are very happy to welcome within the CRC 1333 Colloquium Series:
Prof. Janet Bluemel
Professor of Chemistry
Texas A&M University USA
Thursday, February 03, 2022, 4:00 – 5:00 pm (CEST)
Topic: Immobilized and Adsorbed Catalysts on Silica Surfaces: New Insights by Solid-State NMR Spectroscopy
via Webex video conference
Her research interests span a wide range, from organic and organometallic synthesis, through catalysis and the surface chemistry of amorphous materials, to solid-state NMR spectroscopy. Her research presently concentrates on the following focus areas:
- Immobilized Catalysts
- The Surface Chemistry of Oxide Materials
- Solid-State NMR Spectroscopy
The CRC cordially invites all who are interested to the lecture.
Catalysis is immensely important in industry and academia. Two different directions in the quest for superior catalysts will be presented: (1) Catalysts immobilized on mesoporous oxide supports by chelating phosphine linkers1-3 and (2) metallocenes adsorbed on silica4,5 and other relevant surfaces.6 Solid-state NMR spectroscopy is a powerful method to study these materials and different techniques will be presented.
(1) Wilkinson-type rhodium catalysts (e.g., Fig. 1) have been immobilized covalently via tripodal phosphine linkers with different alkyl chain lengths.1 They have been characterized by HRMAS (High Resolution Magic Angle Spinning) techniques. Tripodal ligands inhibit the formation of nanoparticles and shield the metal centers from neighboring complexes and the reactive surface, and catalysts with unprecedented lifetimes have been obtained.1
Tripodal linker systems can also successfully be employed for other mononuclear and heterobimetallic catalyst systems,2 including the Pd/Cu Sonogashira catalyst.3 HRMAS allows the quantification of dynamic effects.
(2) Metallocenes such as ferrocene (Cp2Fe) and nickelocene (Cp2Ni), a SAC precursor, can be adsorbed on high surface area materials4-6 including silica (Fig. 2),5 carbon nanotubes (Fig. 3) and activated carbon (Fig. 4).6 The adsorption progresses quickly on favorable supports, even without a solvent. The underlying translational mobilities can be visualized, monitored, and quantified on a macroscopic scale when solid substrates migrate into the pores of large silica gel specimens (Fig. 2).5
The mobilities of the metallocene molecules on a surface lead to interesting solid-state NMR phenomena.4-6 The isotropic spiraling movement across the curved walls of the support surfaces (Fig. 3) eliminate line-broadening an-isotropic interactions in the solid state. For example, quadrupolar effects in 2H solid-state NMR spectra (Fig. 4) vanish, and a narrow line is obtained for the adsorbed species.
Importantly, all metallocenes form well-defined monolayers on the surface. Their reduction with hydrogen leads to single atom catalysts.
(1) J. Guenther, J. Reibenspies, J. Blümel, Mol. Catal. 2019, 479, 110629.
(2) K. J. Cluff, N. Bhuvanesh, J. Blümel, Chem. Eur. J. 2015, 21, 10138-10148.
(3) J. C. Pope, T. Posset, N. Bhuvanesh, J. Blümel, Organometallics 2014, 33, 6750-6753.
(4) P. J. Hubbard, J. W. Benzie, V. I. Bakhmutov, J. Blümel, Organometallics 2020, 39, 1080-1091.
(5) K. J. Cluff, J. Blümel, Chem. Eur. J. 2016, 22, 16562-16575.
(6) K. J. Cluff, J. Blümel, Organometallics 2016, 35, 3939-3948.