Translucent nanoparticle-based aerogel monoliths as 3-dimensional photocatalysts for the selective photoreduction of CO2 to methanol in a continuous flow reactor

Abstract

The selective photoreduction of CO₂ to methanol is an energy efficient way to transform a harmful greenhouse gas into a hydrocarbon of great industrial importance. However, the search for efficient photocatalysts able to reduce CO₂ with water turned out to be extremely challenging. Besides studying new materials compositions and combinations, architectural design involving the structuring of catalysts from the nanometer to the centimetre scale and over three dimensions represents a much less studied, but nevertheless highly promising approach for the development of new photocatalysts. Translucent nanoparticle-based aerogels with their large surface areas, high porosity, well-developed crystallinity, multiscale structural features and their excellent light absorption properties offer all the advantages of a successful photocatalyst. Unfortunately, the mechanical fragility strongly limited their use in monolithic form. Here we present a prototype of a flow reactor, which enables the direct exploitation of cylindrical aerogel monoliths in various gas phase reactions. In particular, we studied the performance of TiO₂–Au nanoparticle based aerogels for the photoreduction of CO₂ with water to methanol, resulting in a conversion rate of 2.58 μmol g⁻¹ h⁻¹ with high selectivity. The assembly of nanoparticles into three-dimensional macroscopic bodies, which can directly be introduced in a flow reactor, opens up unique opportunities for the development of new and efficient photocatalysts beyond powders and films for a wide range of gas phase reactions.