Electrospun Fibers in Catalysis

Transcription

1 Electrospun Fibers in Catalysis Polymer based Composite Nanofibers by Co-Electrospinning Martin Graeser Philipps-University, Marburg

2 Outline Methods: - Introduction to Electrospinning - Co-Electrospinning - TUFT Tubes by Fiber Templates Aim of this work Experiments - preparation of catalytic system - reactions Results Outlook

3 Electrospinning wide range of polymers wide range of solvents long polymer fibers diameter: few nm to several μm adjustable fiber structure incorporation of nonpolymer materials like salts or particles

4 Co-Electrospinning core-shell fibers inner material can be of low molecular weight many fiber topologies possible Complex fiber topologies

5 TUFT Tubes by Fiber Templates: - preparation of core / shell fibers by subsequent coating - hollow fibers by removal of the template fiber

6 Coating Material PPX (Polyparaxylylene): - almost insoluble - highly temperature stable Metals: Al, Pd, Bi, Cr

7 Aim: Fibers in Catalysis Advantages of electrospun fibers as support: - high surface to volume ratio - no negative effect on the catalytic behaviour - different polymers allow adjustment to many reaction conditions - gaseous and fluid flow through nonwoven fiber mesh is possible - continuous reaction process possible

8 Selection of Catalyst For testing of the new catalyst support material the Platinum group metals were chosen - in particular: Pd, Rh and Pt mono- and bimetallic nanoparticles should be incorporated in electrospun fibers - reactions were carried out with Pd/Rh nanoparticles

9 Preparation of Metal Nanoparticles two ways of incorporation of metal particles: 1. previous wet chemical synthesis followed by dispersion in polymer solution problem: nanoparticles tend to aggregate and precipitate in solutions 2. in situ reduction of salts inside the fiber spun from polymer/metal salt solution depending on metal salt / polymer, either thermal degradation or hydrogen reduction was used

10 Preparation of Bimetallic Particles Pd/Rh system - thermal degradation and hydrogen reduction revealed metal nanoparticles - in either way the size of the particles was about 5 nm

11 EDX - Analysis STEM-EDX analysis on single particles: - hydrogen reduction lead to 1:1 composition - expected from salt mixture

12 Phase Diagram in bulk systems the 1:1 mixture is not possible due to miscibility gap nano dimensions: Miscibility gap Atom percent Rh - different bulk- and high surface energies

13 Electrospinning polylactic acid (PDLLA) and polyethylen oxide (PEO) were chosen as fiber polymers fiber diameters were about 80 to 200 nm and 300 to 500 nm salt content was 1/3 of polymer mass

14 Core / Shell Fibers the fibers were PPX coated for stabilisation prior to hydrogen reduction of salts

15 Catalytic Reactions two hydrogenation reactions were chosen as test reactions: 1. hydrogenation of cyclopentadiene 2. hydrogenation of a nitroarene

16 Hydrogenation 1 [Pd/Rh] / 1 eq H 2 [Pd/Rh] / 1 eq H 2 carried out at RT the reaction was followed by mesuring the hydrogen uptake - both double bonds were reduced

17 Hydrogenation 2 O O N + [Pd/Rh] / 3 eq H 2 H 2 N O O O O carried out at RT only the nitro group was reduced GPC showed complete conversion

18 Results reactions with this system were carried out 8 times without loss of activity holder with fibers can easily be removed and reused, no filtration step needed reaction time in same range as Pd/C But: - PPX coating rather expensive

19 Outlook spun PAN fibers with metal nanoparticles - insoluble after oxidation - temperature stable spun PVDF fibers with metal nanoparticles - insoluble in most standard solvents incorporation of other transition metals like Ag, Co and Ni

20 Acknowledgement Dr. E. Pippel, MPI Halle, STEM-EDX Measurements C. Greyling, University of Stellenbosch, Spinning of PAN Fibers Prof. J.H. Wendorff, Interesting PhD Thesis VW Stiftung, Funding