title: The effect of sodium species on methanol synthesis and water-gas shift Cu/ZnO catalysts: utilising high purity zincian georgeite.
abstract: The effect of sodium species on the physical and catalytic properties of Cu/ZnO catalysts derived from zincian georgeite has been investigated. Catalysts prepared with <100 ppm to 2.1 wt% Na+, using a supercritical CO2antisolvent technique, were characterised and tested for the low temperature water-gas shift reaction and also CO2hydrogenation to methanol. It was found that zincian georgeite catalyst precursor stability was dependent on the Na+concentration, with the 2.1 wt% Na+-containing sample uncontrollably ageing to malachite and sodium zinc carbonate. Samples with lower Na+contents (<100-2500 ppm) remained as the amorphous zincian georgeite phase, which on calcination and reduction resulted in similar CuO/Cu particle sizes and Cu surface areas. The aged 2.1 wt% Na+containing sample, after calcination and reduction, was found to comprise of larger CuO crystallites and a lower Cu surface area. However, calcination of the high Na+sample immediately after precipitation (before ageing) resulted in a comparable CuO/Cu particle size to the lower (<100-2500 ppm) Na+containing samples, but with a lower Cu surface area, which indicates that Na+species block Cu sites. Activity of the catalysts for the water-gas shift reaction and methanol yields in the methanol synthesis reaction correlated with Na+content, suggesting that Na+directly poisons the catalyst. In situ XRD analysis showed that the ZnO crystallite size and consequently Cu crystallite size increased dramatically in the presence of water in a syn-gas reaction mixture, showing that stabilisation of nanocrystalline ZnO is required. Sodium species have a moderate effect on ZnO and Cu crystallite growth rate, with lower Na+content resulting in slightly reduced rates of growth under reaction conditions.
authors.affiliation: Cardiff Catalysis Institute, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK. KondratSA@Cardiff.ac.uk.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Kondrat
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Smith
authors.forename: James H
authors.initials: JH
authors.lastname: Carter
authors.forename: James S
authors.initials: JS
authors.lastname: Hayward
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Pudge
authors.forename: Greg
authors.initials: G
authors.lastname: Shaw
authors.forename: Michael S
authors.initials: MS
authors.lastname: Spencer
authors.forename: Jonathan K
authors.initials: JK
authors.lastname: Bartley
authors.forename: Stuart H
authors.initials: SH
authors.lastname: Taylor
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Hutchings