Synthesis of Highly Porous 3D Cerium Oxide Networks Designed for Catalytic Applications

Metal oxide nanostructures play an important role in the field of catalysis. However, for practical relevant catalysis setups, it is essential to transfer their nanoscale properties to the macroscopic, three-dimensional scale, such as in the form of aerogels or framework structures. Here, we introduce a new method for the wet-chemical synthesis of a three-dimensional and highly porous framework structure, so-called Aero-Ce1–xZnxO2−δ, composed of a network of interconnected and hollow microtubes with nanoscopic wall thickness. The synthesis is based on the growth of zinc-doped cerium oxide (Ce1–xZnxO2−δ) thin films on a sacrificial template consisting of tetrapodal zinc oxide (t-ZnO) microparticles. By adjusting the reaction parameters, the thin film thickness can be controlled from ∼100 nm to ∼1 μm. The reaction mechanism of the room-temperature synthesis introduced here, with an almost linear growth speed of the cerium oxide film, relies on a self-leveling of the pH value. By the removal of the t-ZnO template, free-standing Aero-Ce1–xZnxO2−δ structures with densities between ∼10 mg cm–3 and ∼460 mg cm–3 and a surface area of up to ∼12 m2 g–1 are obtained. The aeromaterials shown here are characterized in terms of crystal structure, composition, oxidation state, particle size, and pressure drop. Thereby, the Aero-Ce1–xZnxO2−δ enables gas flow velocities that are several orders of magnitude higher than those achievable with conventional cerium oxide aerogels. This characteristic positions Aero-Ce1–xZnxO2−δ as a well-suited structure for flow-through setups characterized by a combination of high gas flow velocities and significant surface interaction. The demonstrated synthesis approach is highly versatile, enabling the fabrication of highly porous metal oxide framework structures that can be tailored on the nano-, micro-, and macroscopic scale, making them a promising material system for applications in (photo)catalysis, gas sensing, solid oxide fuel cells, as well as energy storage.