(587f) Microfibrous Entrapped Catalysts for Low Temperature Carbon Monoxide (CO) Oxidation

Low temperature CO oxidation is characterized by slow surface reaction kinetics and strong CO self-poisoning, which compete with one another. This tradeoff becomes especially problematic at lower temperatures due to the higher activation energy for the surface reaction compared to diffusion. In the case of larger catalyst particles and higher CO concentrations, the increased thermal mass of the large particle and its lower effectiveness factor limit the opportunity for, and potential benefits of, ignition. Conventional packed beds of small particles (ca. < 200 micron) currently pose technological problems due to intrabed flow maldistributions, high pressure drops, and the inability to immobilize/stabilize thin beds toward upsets in orientation and vibration. Monolithic reactors provide low pressure drop for immobilized catalyst washcoats but suffer from low volumetric catalyst loading, high external resistances, and relatively high levels of inert thermal mass.

To circumvent a number of the above noted problems and tradeoffs, a new class of microstructured materials consisting of small sorbent/catalyst particulates entrapped by metal, ceramic, or polymer microfibers (MFES/MFEC) has been developed and optimized for low temperature CO oxidation, among other applications. These materials immobilize active particulates (DP: 10-200μm) by entrapping them within a network of sinter-locked fibers (1.5-12μm dia). The immobilization of small particles from 15 to 40 vol% loading results in higher heterogeneous contacting efficiency, reduced pressure drop, and lower effective thermal mass. Fibers are shown to strongly reduce both microscale interparticle peaking velocities and intrabed flow maldistributions normally associated with small particle intrabed clustering. In comparison with conventional packed beds, MFES provide significant increases in volumetric reactivity and radial dispersion at reduced driving forces normally used for promoting heterogeneous contacting (e.g., reduced pressure drop, temperature, catalyst loading, etc.).

Microfibrous entrapped catalysts provide relatively high heterogeneous contacting efficiency and high volumetric CO oxidation rates at low temperature and low pressure drop. MFEC are useful for performance limiting CO oxidation applications where the driving forces for heterogeneous contacting must be minimized such as in air purification and cathode air protection of PEM fuel cells.