Synthesis of metal oxide-overcoated carbon materials by liquid phase ALD and their applications in catalysis

Coating nano particles and other substrates for efficiency enhancement, protection and obtaining new atomic structures is a widespread research topic in catalysis and material synthesis. Thus far, different approaches of coating, ranging from simplest to sophisticated ones, including spin coating, chemical & physical vapor deposition, atomic layer deposition (ALD) and so on has been developed and introduced. Many of these methods suffer from expensive, complex reaction setup and scaling limitations, liquid phase coating and deposition can be a potential answer particularly with nano and micro-sized powders. Stoichiometrically limited injection liquid phase ALD is a new method developed in our laboratory to simplify the previous gas phase ALD techniques as well as reducing the cost of coating therefore enabling upscaling and processing considerable amount of powders without loss of precious organometallic precursors. The global aim of this doctoral research is to extend the application of this method for coating carbon-based substrates and highlighting the capability of this method as a potential replacement of traditional gas phase ALD procedures and consequently opening the route for ALD to become an affordable approach to be used for industrial advanced powder production. In the first chapter, we present an introduction of gas phase ALD and elucidate the reactions happening during substrate coating especially for the most common example of ALD which is alumina deposition. We also discuss the effect of substrate and different methods of pretreatment for ALD initiation. Next, we covered the reaction setups and conventional equipment used for gas phase ALD and highlighted how this equipment are complicated questioning the upscaling potential of these methods. Then we reviewed liquid phase coating strategies and described the stoichiometrically limited liquid phase ALD and finally a brief summary of the applications of ALD is provided. In the second chapter, which is based on a published paper in the jounral "Advanced Energy Material", we applied stoichiometrically limited liquid phase ALD for activated carbon. Precisely, we deposited alumina layer with the same precursors used in the gas phase ALD on Ni/carbon catalyst and after a successful uniform deposition, we studied the effect of this layer in preventing sintering of Ni particles during lignin hydrogenolysis which is one of the key reactions in obtaining chemicals from plants and woods. In the third chapter, we used the carbon as a hard template and deposit Al2O3 with the previously mentioned liquid phase ALD method. After treatment of the coated carbon at high temperature to achieve the desired crystalline pahse, the template is removed by calcination in air or pure oxygen. Finally, we investigated the properties of the resulting metal oxide including surface area, porosity and phase characteristics. In summary, this thesis concluded the applicability of liquid phase ALD on carbon-based supports and suggest other possible substrates, other types of coating and even single atom synthesis which need to be explored with this method.