Abstract:
Copper-chromia catalysts in 3,5 and 10 weight % of Cu on chromia have been prepared and characterized by surface area measurements, scanning electron microscopic, and x-ray diffraction studies after treatment in various conditions. It was found that physical characteristics as well as catalytic activity is affected by conditions of the pre-treatment. Controlling the rate of rise in temperature to reach the calcinate ion temperature resulted in the formation of high surface area catalysts with well dispersed copper particles on chromia. Catalyst formed where the rate of rise in temperature was not controlled had low surface area as well as the dispersion of copper on chromia was not uniform, large aggregates of copper particles are visible on chromia surface. Three model reactions, (i) cyclohexane conversion benzene, (ii) isopropanol conversion to acetone and to (iii) cyclohexanol conversion to cyclohexanone were tested. It was found that reaction (i), for which detailed studies in comparison to (ii) and (iii) were performed, could be catalysed efficiently in oxygenated atmosphere. Isopropanol conversion to acetone was efficiently catalysed in non-oxygenated atmosphere. These catalysts were not very effective for catalysing reaction, (iii) even when (10% Cu/Cr203)/Zr02 was used as catalyst both in oxygenated and non-oxygenated atmosphere. However, conversion in oxygenated atmosphere was better than non-oxygenated atmosphere. 10% copper chromia catalyst was found to be more effective than 3 and 5 % catalysts.
Regeneration of these catalysts was achieved by simple treatment of keeping the catalysts in N2 flow for 90 minutes at 473 K. Catalysts have long life with a little loss of activity over a long period of time.
Cyclohexane conversion was found to be a kinetically controlled reaction, whereas the Langmuir-Hinshelwood/Eley-Rideal type reaction mechanism could be involved.
