Understanding the effects of nanostructuring on gold catalysis [electronic resource] : a study of morphology, electronic structure, and electrocatalytic activity
- Benjamin N. Reinecke.
- Physical description
- 1 online resource.
- Reinecke, Benjamin N.
- Jaramillo, Thomas Francisco, primary advisor.
- Nilsson, Anders, 1956- advisor.
- Noerskov, Jens, advisor.
- Stanford University. Department of Chemical Engineering.
- The main objective of this thesis is to disentangle the myriad of factors that can potentially explain the origins of catalysis on gold nanostructures. Our approach to sort out these effects is to synthesize supported and unsupported gold nanostructures within a suitable nano-scale size range and measure their morphologies, electronic structures with and without reactants present, and electrocatalytic activities for several oxidation reactions. Using this approach, we can best attempt to relate the geometric and electronic nature of gold to its electrocatalytic activity, thereby lending insights into the origins of gold catalysis in general. The work delineated in this thesis provides evidence that surface structure is a key determining factor in gold catalysis, particularly for gold nanocatalysts with feature sizes 3.4 nm or greater. Undercoordinated atoms at the surface of Au nanostructures as well as surface strain are the likely contributors to significant, measurable changes in the electronic structure for Au nanoparticles, as evidenced by measuring their valence band using hard X-ray photoemission spectroscopy (HAXPES), though size dependent band structure changes may also play a role as well. At smaller sizes such as 1.6 nm, additional factors may come into play, as shown through ambient pressure photoemission spectroscopy (APPES) measurements. This thesis also details the sintering behavior of Au nanoparticles in electrochemical environments, and in particular differences observed in acid versus base. Recognizing and understanding these effects is critical to elucidating the intrinsic catalytic activity of nanoparticulate gold samples, highlighting the importance of accurately measuring gold surface area before/during/after electrochemical measurements. It was found that sintering is more prominent for gold samples with smaller feature sizes, particularly in basic environments, and higher oxidative potentials. Finally, unsupported, nanostructured Au thin films were synthesized and examined for the electro-oxidation of methanol in acid. The high activity of these nanostructures confirms the importance of surface structure in dictating the catalytic activity of Au at nano-scale dimensions.
- Publication date
- Submitted to the Department of Chemical Engineering.
- Thesis (Ph.D.)--Stanford University, 2013.