Quantitative studies of gas–solid reactions by powder X-ray diffraction: stoichiometric and catalytic conversion of CO to CO2 over YBa2Cu3O6 +x

Abstract

Using the in situ cell and other analytical facilities described in the preceding paper, we have carried out an in situ study of both the catalytic and stoichiometric conversion of carbon monoxide to carbon dioxide over the triple-layer defective perovskite YBa₂Cu₃O_{6 +x}. Pre-treatment with CO was used to arrive at a well defined value of x. For both the catalytic and stoichiometric reactions a biphasic mixture of the orthorhombic and tetragonal forms of the non-stoichiometric oxide is observed. A ‘biphasic’, Rietveld refinement of the X-ray diffraction patterns was successfully employed: and it proved possible to determine the precise oxygen content of each phase during the course of the gas–solid reaction at elevated temperatures (300–360 °C). The details of the kinetics of the CO to CO₂ transformation and the solid-state compositions associated with the process shed some light on the mechanism of catalytic reaction.