Utilisation of CO2 for the preparation of inorganic solids

Bennett, Matthew John

March 2019

Thesis or dissertation

© 2019 Matthew John Bennett. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The work in this project reports: (1) the preparation of the mixed oxide carbonates; Sr₂CuO₂(CO₃), Sr₁:₈Ba₀:₂CuO₂(CO₃) and Sr₁:₇₅Ca₀:₂₅CuO₂(CO₃) via direct reaction of the parent oxides with CO₂, (2) the extraction of CO₂ to re-form the original oxides and (3) a Density Functional Theory (DFT) model for understanding the thermodynamics and structural changes of Sr₂CuO₃ reacting with CO₂, forming Sr₂CuO₂(CO₃).

The one-dimensional structured series of Sr₂₋ₓAₓCuO₃ (A = Ca, Ba and x = 0 – 2) was directly reacted with CO₂, forming oxide carbonates. An alternating gaseous approach was used so CO₂ would react within the anion vacancies of these compounds at specific temperatures. Identical reaction parameters were used for barium and strontium compounds, however calcium compounds required a longer residence time. This has been attributed to the smaller anion vacancies and lower CO₂ reaction affinity. In all cases CO₂ could be removed from the oxide carbonates to re-form the original oxides for consequent reactions. The structural changes as well as carbonate formation were studied using a DFT model. This showed how atomic positioning changes when forming Sr₂CuO₂(CO₃) from the original oxide. An ∆Hᵣₓₙ value was calculated which included the enthalpy of structural rearrangement, ∆Hstructure, and formation of the carbonates, ∆Hcarbonate. This provides an insight into the thermodynamics involved when forming mixed oxide carbonates from an oxide.

Ce₂MnN₃ and the Sr₂₋ₓBaₓPdO₃ (x = 0 – 2) series are both isostructural to Sr₂CuO₃ and were also investigated. Sr₂₋ₓBaₓPdO₃ compounds indicated only surface carbonates whilst Ba₂PdO₃ resulted in Ba₁₁Pd₁₁O₂₀(CO₃)₂, BaCO₃ and Pd metal. CO₂ splitting has been proposed to occur with Ce₂MnN₃, resulting in reactions with O₂ forming CeO₂ and MnO₂.

Department of Chemistry, The University of Hull
Francesconi, M. Grazia; Benoit, David M., 1973-
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