Rüdiger Ellinghaus

Synthesis and Physicochemical Characterization of Ce1−xGdxO2−δ: A Case Study on the Impact of the Oxygen Storage Capacity on the HCl Oxidation Reaction

This study reports the synthesis of high‐surface‐area Ce1−xGdxO2−δ (CGO) fibers that are used as catalysts for the oxidation of HCl. Special emphasis is put on the role of the oxygen storage capacity (OSC) of the CGO fibers on the catalytic performance. An in‐depth physicochemical characterization of high‐surface‐area CGO was achieved by employing a multitude of dedicated spectroscopic techniques. The increasing OSC with Gd content is traced to the development of a space charge region with increased electron concentration as a result of the nano size of the CGO particles. The activity of CGO in the HCl oxidation reaction is shown to decrease with Gd concentration.

Highly mesoporous CsTaWO6 via hard-templating for photocatalytic hydrogen production

The quaternary photocatalyst CsTaWO6 was for the first time prepared with a high surface area of 115 m2 g−1 via a hard-templating approach. The highly crystalline and phase-pure material was applied in photocatalytic hydrogen production experiments to demonstrate the influence of porosity, surface area and crystallinity on charge carrier transfer.

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

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.

Hierarchically porous monolithic silica with varying porosity using bis(trimethoxysilyl)arenes as precursors

The ortho-, meta- and para-isomers of bis(trimethoxysilyl)benzene and bis((trimethoxysilyl)phenyl)dimethoxysilane were synthesized from their corresponding diarylbromides. Mixtures of these bis(trimethoxysilyl)arenes and tetramethoxysilane (TMOS) were used as organosilica precursors for the preparation of macro-mesoporous silica monoliths using different amounts of the porogen poly(ethylene glycol) to investigate the effect on the porosity of the final materials. The prepared samples were characterized by nitrogen and dibromomethane sorption measurements, mercury intrusion porosimetry and scanning electron microscopy. The analysis of dibromomethane isotherms indicated a significantly lower polarity of the mesopore surface compared to that of pure SiO2 monoliths, proving the presence of arene units at the mesopore surfaces.