Nano-alloys: The Ultimate promoters for photocatalysis

Introduction

Whereas the current most used photocatalyst, TiO2 has a number of major advantages, like high stability, cheap and abundant availability, one of the major current drawbacks is the limited efficiency and the sensitivity to only UV-light. One of the promising solutions is the use of metal and or alloy co-catalyst nanoparticles. The particles are expected to improve the photocatalytic activity, by improving the separation of holes and electrons, favoring the formation of specific products and most interestingly the particles (specifically Au and Ag) are suspected to show light adsorption properties in the visible light range, which is called Plasmon Resonance.

So, the aim of this project is to evaluate the promoting effect of well-defined metal and alloy nano-particle co-catalysts on Hombicat UV100 TiO2. More specific, both the effect of the particles on the opto-electronic properties and on the surface chemical properties will be investigated. To be able to get well defined particles a rather unique synthesis method is used, called the Spark Generator. This is a gas phase synthesis method, developed in at the Delft University or Technology, which enables the synthesis of particles with uniform sizes and possibly also uniform compositions in the case of alloys. By using this gas phase synthesis method, the photocatalytic surface will not be altered, like is the case for the conventional methods used and therefore a better understanding of the promoting effect of the co-catalyst particles will be possible.

Figure : Particle synthesis setup; DMA = Differential mobility analyzer, used to size select particles, ECP = Electrostatic Precipitator, used to deposit particles, AEM = Aerosol Electrometer

Experimental

For the screening of the photocatalytic samples with the different co-catalyst a 2 ml top-illumination reactor is developed. The advantage of this system that small amount of catalysts can be tested and that the whole reactor volume can be injected into the GC, which will lead to more accurate results about the activity and selectivity towards different products.

Figure : GC Top-illumination reactor setup

The current reaction selected is the gas phase oxidation of propane. The first results confirm that the use of co-catalyst can lead to improved conversion and changes in selectivity. The next step is to investigate in more depth the effects the particle size, the effect of light and the reactions mechanisms for the selective oxidation of propane.

In the further the focus of the reaction will shift from selective oxidation, towards reduction, like for propanol and finally towards the synthesis of hydrocarbons from water and CO2.