Colloidal Cu/ZnO nanocatalysts for CO2 hydrogenation to methanol
File(s)
Author(s)
Weiner, Jonathan
Type
Thesis
Abstract
This thesis centres on the development of colloidal nanoparticles for the hydrogenation of carbon dioxide to methanol. Chapter two focusses on the synthesis of zinc oxide (ZnO) nanoparticles through the hydrolysis of diethylzinc in the presence of sub-stoichiometric quantities of organic ligands. Characterisation of the product, through a range of spectroscopic, diffraction and electron microscopy techniques, reveals small (3-4 nm), equiaxial, mono-disperse ZnO nanoparticles coordinated to alkyl-carboxylate, phosphinate and sulfinate ligands. Detailed investigation of the dioctyl-phosphinate capped-zinc oxide nanoparticles reveals that increasing the loading of ligand into the reaction (from 0.05-0.33 equivalents of ligand to zinc) does not affect the size or morphology of the nanoparticles, rather influencing the ligand density and coverage of the nanoparticle surface.
In chapter three, these partially capped ZnO nanoparticles, mixed with copper nanoparticles, demonstrate catalytic activity for CO2 hydrogenation. Post-reaction analysis showed significant nanoparticle rearrangement, with an interface forming between the copper and the ZnO. In some cases, a self-assembled nanostructure is observed, consisting of a copper nanoparticle sandwiched between two pyramidal zinc oxide nanoparticles. The ligand has a significant effect on the activity of the catalyst; more reductively stable di-alkyl phosphinate ligands show superior activity to carboxylates. Decreasing the ligand loading on the zinc oxide nanoparticles, results in a higher peak activity due to the decreased ligand density exposing more of the catalyst surface, however the stability of the catalyst is also reduced.
In chapter four, the interface between nanoparticles is targeted, with the goal of depositing copper onto the ZnO colloids through reduction and thermolysis reactions to form hybrid Cu/ZnO nanostructures. The most effective route entails the hydrogenolysis of mesitylcopper(I) on to the ZnO nanoparticles, the resulting nanocatalyst displays superior peak activity to both the mixed nanoparticle catalyst described above and a suspension of the commercial catalyst run under the same conditions.
In chapter three, these partially capped ZnO nanoparticles, mixed with copper nanoparticles, demonstrate catalytic activity for CO2 hydrogenation. Post-reaction analysis showed significant nanoparticle rearrangement, with an interface forming between the copper and the ZnO. In some cases, a self-assembled nanostructure is observed, consisting of a copper nanoparticle sandwiched between two pyramidal zinc oxide nanoparticles. The ligand has a significant effect on the activity of the catalyst; more reductively stable di-alkyl phosphinate ligands show superior activity to carboxylates. Decreasing the ligand loading on the zinc oxide nanoparticles, results in a higher peak activity due to the decreased ligand density exposing more of the catalyst surface, however the stability of the catalyst is also reduced.
In chapter four, the interface between nanoparticles is targeted, with the goal of depositing copper onto the ZnO colloids through reduction and thermolysis reactions to form hybrid Cu/ZnO nanostructures. The most effective route entails the hydrogenolysis of mesitylcopper(I) on to the ZnO nanoparticles, the resulting nanocatalyst displays superior peak activity to both the mixed nanoparticle catalyst described above and a suspension of the commercial catalyst run under the same conditions.
Version
Open Access
Date Issued
2015-04
Date Awarded
2016-01
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Williams, Charlotte
Shaffer, Milo
Sponsor
Imperial College London
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)