The influence of ZnO on the differential heat of adsorption of CO on Cu catalysts: a microcalorimetric study

This shows that the KIE and the nature of the RDS of CO2 hydrogenation to methanol are not affected by different supports or different active metals within the range of tested materials despite very different performance in methanol synthesis.This observation provides support for the view that the widely observed promotional effect of ZnO on Cu-based catalysts affects the activity of methanol synthesis, but does not change its mechanism.We have recently shown that this promotion effect can be successfully modeled by assuming the active site to be a fully Zn-decorated surface step of Cu

R Naumann d'Alnoncourt

2003

Scholarcy highlights

  • Copper catalysts are widely used for methanol synthesis and the water gas shift reaction
  • The differential heat of adsorption of carbon monoxide on carefully reduced copper catalysts employed in methanol synthesis was measured by means of a Tian–Calvet calorimeter to probe the influence of ZnO
  • The Cu surface area was derived from the amount of Cu surface atoms) determined by N2O-reactive frontal chromatography assuming that 1 m2 of Cu surface area equals 24.41 μmol Cu atoms
  • It was possible to measure the differential heat of adsorption and adsorption isotherms for small coverages on metallic Cu
  • Freshly reduced samples exhibited the same initial heats of CO adsorption, the number of sites interacting strongly with CO were decreased in the case of the Pt/SiO2 but remained constant on the Pt/K(Ba)-L during n-hexane conversion.The presence of strong adsorption sites during the reaction was reported to contribute to the higher dehydrocyclization activity over the Pt/K(Ba)-L. d'Alnoncourt et al correlated the initial heats of CO adsorption with activities during methanol synthesis over various Cu-based catalysts.As shown in Fig. 8, the highest CO adsorption heat of 81 kJ/mol was obtained from Cu/Al2O3, even though this material had the lowest activity during methanol synthesis
  • An ethylene glycol selectivity of higher than 95% was obtained after 150 h of reaction
  • In the case of a Cu-Zn-Al oxide catalyst, a linear relationship was obtained between copper surface area and activity, but the linearity is not valid when the preparation method differs, meaning that the water-gas shift is structure-sensitive.Zinc and aluminum oxides are used as the support of catalyst where zinc addition increases the specific rate through decrease of heat of CO adsorption and increases dispersion of Cu while aluminum addition only disperses the Cu phase. numerous efforts have been made for increasing activity and stability, the Cu-based catalysts have drawbacks of easy sintering and pyrophoricity
  • In the presence of ZnO a decrease in the initial heat of adsorption of about 10 kJ mol−1

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