Showing papers by "Frank S. Stone published in 1989"

Copper–zinc oxide catalysts. Activity in relation to precursor structure and morphology

Abstract: Cu–Zn hydroxycarbonates have been studied as precursors of Cu–ZnO catalysts, with particular reference to the effect on catalyst activity of ageing the precursor prior to decomposition and reduction. The precursor obtained by precipitation from mixed nitrate solution (Cu/Zn molar ratio 2:1) at 333 K and pH 7.0 consisted of zincian malachite (Cu/Zn ≈ 85:15) and aurichalcite. The precursor was aged in the mother liquor at 333 K for various times. Characterisation by XRD, i.r., DTA, electron microscopy, EDAX and XPS showed that ageing led to loss of the aurichalcite and production of a more finely divided copper-enriched (Cu/Zn = 2:1) malachite phase. The unaged precursor yielded a catalyst of low activity for both methanol synthesis (studied at 50 bar and at 1 bar) and the reverse water-gas shift reaction. The aged precursor gave catalysts of much higher activity for both reactions. Increased ageing did not change the selectivity ratio for methanol synthesis vs. reverse shift in the CO2+ H2 reaction at normal pressure.

Oxygen Reactivity as a Probe for the Surface Composition of Cao-Mno Solid Solutions

Abstract: Oxygen adsorption has been used as a probe for manganese ions in the surface of CaO-MnO. By exploiting adsorption microcalorimetry, the energetics of the oxygen uptake have been determined for the pure solvent matrix CaO and for solid solutions of nominal bulk solute concentrations of 1 mol%, 25 mol% and 50 mol% Mn, designated CM 1, CM 25 and CM 50. Oxygen adsorption on Mn 2+ ions is characterised by a much higher heat than on CaO. In this way it is shown that the uptakes on CM 1, CM 25 and CM 50 are much in excess of those expected on the basis of the nominal (bulk) concentrations of Mn. The conclusion is that the solid solutions exhibit substantial surface enrichment in manganese, and this also affects their reactivity towards water vapour.

Computer Simulation of Hydrocarbons in Zeolites

Abstract: We present preliminary work on the sorption of selected hydrocarbon species in zeolites, using computer simulation techniques. Preferred adsorption sites for methane in zeolite A, methanol and methane in silicalite and methanol in faujasite cages are identified and the interaction energies between hydrocarbons and zeolites are calculated.