Atomic Layer Deposition of Catalytic Materials for Environmental Protection

Abstract

The reduction of toxic pollutants emitted by human activities to ambient air is an important issue nowadays. The technological approach to this problem is the development of different oxidation techniques together with catalytic materials, which can convert toxic emission products to safe compounds. Current methods for the preparation of heterogeneous catalysts which fully control the structure, size and composition are limited. The atomic layer deposition (ALD) technique can create catalytic thin films with precise thickness and structure control even on complex substrates.

The present work describes the development of TiO2, CeO2 and Ag-doped CeO2 catalytic thin films deposited by ALD in order to find their capacity for the decomposition of toluene and soot. TiO2 catalytic films with different thicknesses were grown to investigate their nucleation delay and changes in their polycrystalline structure and the impact of these on their photocatalytic properties. It was shown that porous glass filters coated by TiO2 in combination with a dielectric barrier discharge (DBD) reactor could decompose toluene at a concentration of 2450 ppm with the specific input energy (SIE) of 336 J/l.

In CeO2 studies it was found that a deposition temperature of 300 °C changes the structural properties of the catalytic thin films. The combination of small crystallites, larger clusters and the existence of Ce3+ in CeO2 catalytic films showed 100% soot decomposition at 450°C under loose contact mode. The doping of CeO2 with Ag in the ratio of CeO2:Ag = 10:1 by ALD reduced the soot decomposition temperature to 390°C. It was proposed that Ag+ sites could promote oxygen species and reduce the Ce ions in stoichiometric CeO2 from Ce4+ to Ce3+. Most catalytic thin films prepared by ALD showed good durability after repetitive tests of soot decomposition.