Investigations into the heterogeneous photocatalytic oxidation of methanol to yield formaldehyde in a continuous laboratory plant

This dissertation investigates the heterogeneous photocatalytic conversion of methanol to formaldehyde in a continuous-flow laboratory reactor. Commercial P25 TiO₂ as well as platinum- and palladium-modified P25 catalysts were employed to examine both the aerobic oxidation and the anaerobic dehydrogenation of methanol. The results demonstrate that, in the presence of oxygen, methanol can be continuously oxidized over untreated P25, with formaldehyde being the predominant reaction product. In this context, the effects of key process parameters, including temperature, residence time, and irradiation intensity, were systematically studied. In addition, the underlying reaction network of the aerobic pathway was elucidated. A further focus of this work was the anaerobic dehydrogenation of methanol. It was shown that over Pt/P25 and Pd/P25 catalysts, methanol is converted to formaldehyde with the concomitant formation of hydrogen. Among the modified catalysts, Pd/P25 exhibited superior stability under the investigated reaction conditions. Furthermore, an activation mechanism of the catalysts was identified and characterized. For the anaerobic pathway as well, the influence of temperature, residence time, and irradiation intensity on catalytic performance was systematically determined. This work is among the first studies to address the photocatalytic conversion of methanol to formaldehyde from an engineering perspective under continuous operation and at technologically relevant throughput levels. By providing, for the first time, a comprehensive set of data on methanol conversion and product selectivity, it establishes an important basis for the technical evaluation and future development of photocatalytic formaldehyde synthesis processes.