A Clean and Flexible Catalyst Synthesis Method

Abstract

A highly porous fractal-like nanostructured metal oxide catalyst support with characteristic dimensions of a few nanometers is formed by producing metal nanoparticles in the gas phase, oxidizing them and depositing/sintering them on a nanofiber network. By admixing nanoparticles in the aerosol phase, these can evenly be distributed in the fractal-like metal oxide structure. The nanofiber network is a polymer and is produced by electrospinning [77]. It serves as an initial support, while the structure supports itself after forming a certain thickness. Spark discharge is used to produce the active nanoparticles as well as the support [11]. Rapid diffusion limited aggregation governs the deposition process, guaranteeing formation of the fractal-like structure [38]. Due to the flexible nature of the spark discharge process, a virtually unlimited number of combinations of oxide supports, metals, alloys and bi-catalysts can be made. The method proved to work for titanium dioxide, aluminium oxide and magnesium oxide catalystsupports. Combinations of these metal oxides with gold and platinum proved the broad applicability of the method. The process can be called environmentally friendly, since it does not use any solvents or produce any hazardous waste. Initial photocatalytic experiments on titanium dioxide nanostructures were carried out to test the catalytic activity of the material. It was observed that the titanium dioxide nanostructures were amorphous, but still exhibited catalytic properties. Adding gold nanoparticles to the nanostructures lowered the catalytic effect. In-situ annealing of amorphous titanium dioxide nanoparticles, before admixing gold nanoparticles, yielded highly porous fractal-like crystalline titanium dioxide nanostructures with gold nanoparticles on the surface.