Study Of Catalysts' Controlled Synthesis And Performance Through Area Selective Atomic Layer Deposition

Catalysis is an important method to accelerate and direct various chemical reactions. It is a key to realizing environmentally benign, conversion of fossil based feeds, energy yielding etc. Catalysts are the basic means for industrially converting carbonaceous feeds to useful products. Nearly 95% of chemicals have come through one or more catalytic steps and nearly every major industry is directly enabled by catalytic technology. Upon catalysts research, the final catalytic performance is closely related with their structure, particle size and composition. To design the optimal catalytic structure and synthesize at atomic scale would greatly enhance our knowledge about the structure-function relationship and improve final catalyst performance. In this thesis, we will focus on precisely controllable synthesis of catalysts with area-selective atomic layer deposition (ALD). Two kinds of catalysts structure are discussed, which include metal-metal core shell catalysts and metal oxide coated metal catalysts.First, we develop a surface modification method with alkylsilane self-assembled monolayers which enable control of active sites on the surface. Then Pd nanoparticles are synthesized on modified surface with ALD and a linearly particles'size control are obtained by varying ALD cycles. It is demonstrated that Pd nanoparticles are selectively nucleate on the defect sites (pinholes structure) on self-assembled monolayers. And with the separation of self-assembled monolayers, a narrower particles size distribution is achieved.By introducing the second metal on the process, we apply this developed area-selective ALD method to fabricate core shell nanoparticles. The second metal is selectively deposit on exsit metal nuclei and is blocked on well packed self-assembled monolayers coated area. Based on this method, Pd/Pt core shell nanoparticles are synthesized with size, composition control. It is found that the shell thickness is linearly related with ALD cycles. We fabricate Pd/Pt core shell nanoparticles with single atomic layer of Pt shell, and demonstrate this structure has best activity and selectivity upon CO oxidation in the excess of hydrogen. Density functional theory simulation is applied and demonstrates that CO oxidation on single atomic Pt shell layer has the lowest reactive barrier.In the following research we develop a cerium oxide coated Pt catalysts, the purpose is to enhance the thermal stability of Pt nanoparticles by oxide layer coating. It is found that cerium oxide is primarily prefer to deposit on Pt (111) facets rather than Pt (200) facets and the cerium oxide coating layer is discontinuous. The composite catalysts demonstrate enhanced activity towards CO oxidation as well as thermal stability.For cobalt oxide/Pt catalysts, we apply ALD method to encapsulate cobalt oxide layer on Pt nanoparticles, as a result the activity towards CO oxidation and thermal stability is enhanced. However the chemical state of cobalt oxide is sensitive to catalytic environment. Under oxidative environment, the content of Co2+ increase which leads to a better activity. It is demonstrated that Co2+ composition is key to the synergistic performance improvement of cobalt oxide/Pt catalysts.This thesis provide a precisely controlled synthesis method and strategy of metal-metal and metal-metal oxide core shell structure catalysts based on area selective atomic layer deposition.