Electrospinning of CeO2 nanoparticle dispersions into mesoporous fibers: on the interplay of stability and activity in the HCl oxidation reaction

Abstract

CeO₂ nanoparticles with diameters of ca. 6 nm were synthesized using a microwave-based synthetic route, enabling dispersions in various unipolar solvents. From these dispersions, CeO₂ nanofibers were prepared by electrospinning followed by heat treatment at 550 °C in air, possessing mesoporosity with BET surface areas larger than 100 m² g⁻¹. This mesoporosity is due to a nanoscale separation between the nanoparticles and the spinning polymer. The well-defined CeO₂ fibers were used as catalysts in the HCl oxidation reaction (Deacon process), and the catalytic parameters (space-time yield (STY), oxygen storage capacity (OSC), and the so-called complete oxygen storage capacity (OSCc)) were compared with recently reported nanoscopic CeO₂ materials. It is found that the fibers and also the particles themselves show comparably high activity (STY), which correlates with a high OSCc value, in comparison with CeO₂ materials possessing larger particle sizes. This correlation implies that the entire particles, not only the surface, are involved in oxidation reactions. In the HCl oxidation reaction, the fiber morphology is degraded and the surface area is substantially decreased, but the activity is still quite high after 60 h on stream, and no chlorination is detectable by X-ray Diffraction, in contrast to CeO₂ materials with larger particle sizes. These findings demonstrate that the stability and activity of CeO₂-based catalysts can only be scrutinized by a material comprising both a high surface area and well-defined morphology.