Smart Microreactors

An innovative approach has been implemented to fabricate efficient microreactor system for multi-phase (Gas-Liquid-Solid) catalytic chemical reactions by synthesizing structured catalyst support layer based on carbon nanofibers (CNFs). A well-attached and well-defined CNF layer was synthesized on flat fused silica substrate (representing microreactor channel walls) via thermal catalytic vapor deposition of ethylene using thin-film nickel catalyst.

Decorating this CNF layer with uniformly distributed catalyst nanoparticles would eventually results into the efficient multi-phase microreactor system.

CNF used in Microreactor

The objective of the ‘Smart Microreactors’ project is to fabricate the microreactor module with innovative features for carrying out appropriate multi-phase catalytic chemical reactions.

Different steps in process Recently the application of micro chemical reaction systems (i.e. the reactors with three-dimensional structures having the inner dimensions between ten and a hundred micrometers [1]) for carrying out multi-phase (gas-liquid-solid) chemical reactions has gained significant importance. Various reactions that are of particular interest to the fine chemical and pharmaceutical industry, e.g. hydrogenation and/or oxidation, can be efficiently carried out using these systems owing to the virtues obtained essentially from their very small dimensions [2].

Fabrication of such multi-phase microreactor particularly with gas–liquid reactants reacting over solid phase catalyst desires special consideration regarding the synthesis of stable structured catalyst support layer on microreactor channel walls with highly open structure. The catalytic support layer based on Carbon nanofibers (CNFs), which can be produced via catalytic decomposition of a carbon containing gas over transition metal catalyst (e.g. nickel), poses as a novel option to facilitate this task [3, 4]. With their inherent high surface area-to-volume ratio CNFs provide more catalytic surface area, obtaining sufficient activity per unit of volume of catalyst. Additionally the bulk density, diameter and length of the fibers can be manipulated to achieve high porosity (comprising mainly meso or macro- pores) with minimized tortuosity in order to optimize the accessibility of the active phase deposited on the CNFs which helps to diminish the internal diffusion limitations by preventing any concentration gradients inside the CNF layer.

We have successfully synthesized a well-defined CNF layer on flat substrates (e.g. fused silica) which represents the walls of typical microreactor channel (Fig.1a). Using the clean room technology, deposition of stable nickel thin layer was achieved on these substrates. Thermal catalytic vapor deposition (TCVD) of ethylene, with carefully optimized operating conditions, was utilized to synthesize CNF from the deposited nickel layer. The detail investigation about thermal stability of the various adhesion layer materials (viz. Ti, TiW and Ta) revealed the suitability of TiW and Ta for obtaining well-attached layer of entangled CNF on fused silica substrates (Fig.1b and 1c) against Ti which lead to formation of CNF carpet. The thickness of this well-adhered CNF layer can be tuned by varying the duration of their synthesis as well as by adding hydrogen to the reaction gas mixture. High resolution transmission electron microscopy has clearly indicated tip-type growth mode of CNF (Fig.1d) with numerous interstitial defects in the synthesized fibers (Fig. 1e) which particularly has also been confirmed from Raman spectroscopic analysis (Fig.1f).

Digital photograph fused silica and attached CNF Further study about influence of growth parameters on CNF morphology is in progress. Additionally, exploration of various methods for the decoration of these CNF layers with well-defined Pd and/or Ru nanoparticles, to test the final microreactor module for appropriate reactions (e.g. nitrite reduction to N₂), is also underway.

In general, use of microstructured reactors should enhance activity and selectivity of the multiphase reactions being carried out and hence facilitate significant size reduction of equipments and obtain reduced loss of waste products, achieving profitability for the fine chemicals and pharmaceutical industry in addition to the environmental benefits.

The financial support from MicroNed 2-G-2 project is greatly acknowledged.

References

[1] Jahnisch K, Hessel V, Lowe H, Baerns M. Chemistry in microstructured reactors. Angewandte Chemie-International Edition. 2004;43(4):406-46.

[2] Losey MW, Jackman RJ, Firebaugh SL, Schmidt MA, Jensen KF. Design and fabrication of microfluidic devices for multiphase mixing and reaction. Journal of Microelectromechanical Systems. 2002 Dec;11(6):709-17.

[3] Serp P, Corrias M, Kalck P. Carbon nanotubes and nanofibers in catalysis. Applied Catalysis a-General. 2003 Oct 28;253(2):337-58.

[4] Thakur D.B., Tiggelaar R.M., Seshan K., Gardeniers J.G.E. and Lefferts L. Synthesis of Carbon Nanofibers as Support Layer for Metal Catalyst in a Microreactor for Three-phase Reactions. Advances in Science and Technology Vol. 54 (2008) pp 231-236.

	Home-CPM > Research > Smart Microreactors
Home News Contact Mission People Publications Research Research Themes Group Seminars Inside CPM Teaching Vacancies IRTG workshop Sitemap Search	Smart Microreactors An innovative approach has been implemented to fabricate efficient microreactor system for multi-phase (Gas-Liquid-Solid) catalytic chemical reactions by synthesizing structured catalyst support layer based on carbon nanofibers (CNFs). A well-attached and well-defined CNF layer was synthesized on flat fused silica substrate (representing microreactor channel walls) via thermal catalytic vapor deposition of ethylene using thin-film nickel catalyst. Decorating this CNF layer with uniformly distributed catalyst nanoparticles would eventually results into the efficient multi-phase microreactor system. The objective of the ‘Smart Microreactors’ project is to fabricate the microreactor module with innovative features for carrying out appropriate multi-phase catalytic chemical reactions. Recently the application of micro chemical reaction systems (i.e. the reactors with three-dimensional structures having the inner dimensions between ten and a hundred micrometers [1]) for carrying out multi-phase (gas-liquid-solid) chemical reactions has gained significant importance. Various reactions that are of particular interest to the fine chemical and pharmaceutical industry, e.g. hydrogenation and/or oxidation, can be efficiently carried out using these systems owing to the virtues obtained essentially from their very small dimensions [2]. Fabrication of such multi-phase microreactor particularly with gas–liquid reactants reacting over solid phase catalyst desires special consideration regarding the synthesis of stable structured catalyst support layer on microreactor channel walls with highly open structure. The catalytic support layer based on Carbon nanofibers (CNFs), which can be produced via catalytic decomposition of a carbon containing gas over transition metal catalyst (e.g. nickel), poses as a novel option to facilitate this task [3, 4]. With their inherent high surface area-to-volume ratio CNFs provide more catalytic surface area, obtaining sufficient activity per unit of volume of catalyst. Additionally the bulk density, diameter and length of the fibers can be manipulated to achieve high porosity (comprising mainly meso or macro- pores) with minimized tortuosity in order to optimize the accessibility of the active phase deposited on the CNFs which helps to diminish the internal diffusion limitations by preventing any concentration gradients inside the CNF layer. We have successfully synthesized a well-defined CNF layer on flat substrates (e.g. fused silica) which represents the walls of typical microreactor channel (Fig.1a). Using the clean room technology, deposition of stable nickel thin layer was achieved on these substrates. Thermal catalytic vapor deposition (TCVD) of ethylene, with carefully optimized operating conditions, was utilized to synthesize CNF from the deposited nickel layer. The detail investigation about thermal stability of the various adhesion layer materials (viz. Ti, TiW and Ta) revealed the suitability of TiW and Ta for obtaining well-attached layer of entangled CNF on fused silica substrates (Fig.1b and 1c) against Ti which lead to formation of CNF carpet. The thickness of this well-adhered CNF layer can be tuned by varying the duration of their synthesis as well as by adding hydrogen to the reaction gas mixture. High resolution transmission electron microscopy has clearly indicated tip-type growth mode of CNF (Fig.1d) with numerous interstitial defects in the synthesized fibers (Fig. 1e) which particularly has also been confirmed from Raman spectroscopic analysis (Fig.1f). Further study about influence of growth parameters on CNF morphology is in progress. Additionally, exploration of various methods for the decoration of these CNF layers with well-defined Pd and/or Ru nanoparticles, to test the final microreactor module for appropriate reactions (e.g. nitrite reduction to N₂), is also underway. In general, use of microstructured reactors should enhance activity and selectivity of the multiphase reactions being carried out and hence facilitate significant size reduction of equipments and obtain reduced loss of waste products, achieving profitability for the fine chemicals and pharmaceutical industry in addition to the environmental benefits. The financial support from MicroNed 2-G-2 project is greatly acknowledged. References [1] Jahnisch K, Hessel V, Lowe H, Baerns M. Chemistry in microstructured reactors. Angewandte Chemie-International Edition. 2004;43(4):406-46. [2] Losey MW, Jackman RJ, Firebaugh SL, Schmidt MA, Jensen KF. Design and fabrication of microfluidic devices for multiphase mixing and reaction. Journal of Microelectromechanical Systems. 2002 Dec;11(6):709-17. [3] Serp P, Corrias M, Kalck P. Carbon nanotubes and nanofibers in catalysis. Applied Catalysis a-General. 2003 Oct 28;253(2):337-58. [4] Thakur D.B., Tiggelaar R.M., Seshan K., Gardeniers J.G.E. and Lefferts L. Synthesis of Carbon Nanofibers as Support Layer for Metal Catalyst in a Microreactor for Three-phase Reactions. Advances in Science and Technology Vol. 54 (2008) pp 231-236.