Layered double hydroxide-based core-shells for CO2 adsorption and conversion

Thesis

This thesis discusses the development of novel layered double hydroxide-based (LDH-based) core-shells as CO2 adsorbents and as catalysts for the both the selective hydrogenation of CO2 to methanol and conversion to olefins.

Chapter 1 offers a brief introduction of LDHs as 2D anionic layered materials with versatile composition and wide application, and LDH based core-shell materials which can combine both advantages of inorganic cores and LDHs to display synergy effects. The background literature relating to CO2 adsorption, CO2 hydrogenation to methanol and CO2 conversion to olefins are introduced. The application of LDH and LDH-based core-shell materials in these fields is also presented and discussed.

Chapter 2 describes the synthesis and characterisation a series of zeolite@Mg2Al-LDH core-shell materials and the application of these materials as CO2 adsorbents. It was found that core-shells containing 5 wt% LDH exhibit the highest CO2 sorption capacity (5.75 mmol/g at 1 bar and 35 °C), better than most of the core-shell adsorbents and competing with some MOFs.

Chapter 3 systematically investigates the synthesis of mesoporous SiO2@CuxZnAl-LDH core-shells (mSiO2@CuxZnAl-LDH). The effect of metal solution addition rate, reaction pH, LDH content in the core-shell, copper loading of the LDH, concentration of reaction mixture, pre-treatment (aluminium nitrate wet impregnation) and the roles of the silica on the crystallinity, composition and morphology of core-shells are explored.

Chapter 4 focuses on the application of mSiO2@CuxZnAl-LDH for the selective hydrogenation of CO2 to methanol. The effect of copper loading and the effect of silica core on the catalytic activity was investigated using ES757@CuxZnAl LDH and mSiO2@Cu2ZnAl-LDH, respectively. [email protected] exhibits the best space time yield of methanol due to the highest copper metal nanoparticle surface. It was found that catalysts derived from [email protected] LDH and mSiO2@Cu2ZnAl LDH can outperform current industry standards for methanol production at a lower copper loadings.

Chapter 5 presents the design of [email protected] and their catalytic evaluation for the conversion of CO2 to olefins. Preliminary catalytic results were obtained, it was noted that the sodium in the reaction mixture modified the acidity of zeolite and changed the product selectivity. Alternatives to modify the acidity of catalyst were conducted which includes post-treatment with ammonium salt and sodium-free synthesis.

Authors: Lyu, M

• DOI: 10.5287/ora-vj1rrk91r
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: core-shell materials; layered double hydroxide