Study of the deactivation of copper-based catalysts for dehydrogenation of cyclohexanol to cyclohexanone

Catalytic dehydrogenation of cyclohexanol was carried out in the gas phase in a continuous fixed bed reactor under atmospheric pressure. Two commercial catalysts composed by copper chromite and copper zinc oxide were tested. The activity of the catalysts was evaluated at 250 °C, with a weight hourly space velocity of 2.89 h−1 and at times on stream (TOS) higher than 400 h. A slow deactivation of the catalysts was observed during the reaction, obtaining an activity reduction of 50% at TOS = 350 h, but maintaining 30% conversion at these conditions. Yield higher than 97% to cyclohexanone was obtained with both catalysts, in all the range of TOS studied. The main impurity observed was phenol, obtained from dehydrogenation reaction, and cyclohexene, only obtained with the copper chromite catalysts, and derived from cyclohexanol dehydration. The results of stability and selectivity with these catalysts are better than others reported in the literature. The main causes of the activity loss are associated to the coke deposition over the copper active sites and the increase of the copper metallic crystallite size. The copper zinc oxide also presents a slight blockage of the porous structure due to coke deposition, what can also decrease the catalyst activity.

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► Copper–chromite and copper–zinc as catalysts for cyclohexanol dehydrogenation.
► Catalysts show high stability and selectivity to cyclohexanone.
► Partial deactivation due to coke deposition on copper active sites.
► The increase of the copper crystallite size also produces decay on the activity.
► Carbon burn-off produces a temporal regeneration of the catalysts.