Comparison of alkene hydrogenation in carbon nanoreactors of different diameters: probing the effects of nanoscale confinement on ruthenium nanoparticle catalysis

Abstract

Exploratory, competitive hydrogenation reactions reveal the optimum level of confinement to control chemical reactions.

Magnetically Recyclable Catalytic Carbon Nanoreactors

“…Carbon nanotubes are mechanically robust, thermally and chemically stable cylinders of sp 2 ‐carbon that can be used to immobilize both molecules and nanoparticles which efficiently adsorb onto the nanotube walls and/or are encapsulated within the internal cavity of the nanotube via noncovalent interactions such as van der Waals forces . Once the catalyst is immobilized in the hollow structure, catalytic chemical reactions which occur within the accessible nanoscale space of the nanoreactor interior can benefit from enhanced rates of reactions and selectivity …”

“…Specifically, metal nanoparticles (NPs) supported in graphitized carbon nanofibers (GNFs) catalysts have recently been used for a variety of different reactions, including platinum nanoparticles (PtNPs) in CC cross coupling reactions, IrNPs in hydrosilylations, and CuNPs in click chemistry . In a recent study, we demonstrated that RuNPs confined in GNFs result in dramatic changes to reactions with the highest observed activity and selectivity in single and competitive hydrogenations of norbornene and benzonorbornadiene compared to unconfined RuNPs supported on single‐walled carbon nanotubes (SWNTs) and commercial carbon black . PtNPs confined within GNF were also investigated in the oxygen reduction reaction (ORR) by Gimenez‐Lopez et al and outstanding electrochemical stability was observed over 50 000 cycles of ORR, with the PtNPs stabilized by the step edges significantly more strongly than commercial PtNPs on carbon black .…”

“…Therefore, carbon nanotubes are of great interest for use as nanoreactors in a variety of different catalytic chemical reactions as they not only template the formation of catalytically active metallic nanoparticles but also influence the subsequent pathway of reactions . However, despite the fact that carbon nanotubes are excellent support materials for heterogeneous catalyst systems, the inherent properties of carbon nanotubes, including their low density and hydrophobisity, make their separation from the reaction solution using conventional separation techniques, such as filtration and centrifugation challenging, meaning that currently expensive equipment and secondary processes are required .…”

“…Furthermore, GNFs have differently structured internal and external surfaces and wide, continuous internal channels, with an average internal diameter of ≈50 nm. Finally, unlike carbon nanotubes, the internal surface has a succession of step edges which can act as anchoring points for guest species making GNF a highly effective nanoreactor for immobilization of catalytic nanoparticles and to perform catalytic reactions at the nanoscale . With this aim, we developed two different procedures for forming magnetically recyclable GNF based carbon nanoreactors: (1) in situ formation of Fe@C n inside the GNF channels and (2) attachment of commercially available Co@C n to GNF through noncovalent interactions.…”

Three dimensional metal/N-doped nanoplate carbon catalysts for oxygen reduction, the reason for using a layered nanoreactor

“…These nanosized containers are either synthetically produced (for instance, nano porous, tubular and hollow nanomaterials with various geometries and diameters) or they are inherently composed of nano pores and channels (for instance, proteins, lipids and zeolites, etc) 16–20 . This confinement offers the control of a chemical reaction to make a particular product such as a new class of nanomaterials and/or gains a new insight into fundamental basics of physics and chemistry of the material 16,19 .…”