Activation of platinum‐alumina catalysts for the hydrogenation of aromatic hydrocarbons

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Abstract
A white spirit fraction was hydrogenated in a continuous flow microreactor unit, using 0.35% platinum‐alumina catalysts. These catalysts contained 0.0, 0.40 or 0.87% chlorine. Chlorination of the catalysts was carried out during the process of platinum impregnation. This treatment was found to enhance significantly the hydrogenation activity of the catalysts, and may be attributed to an improvement in the dispersion of platinum in the alumina support. Calcination of the catalysts before their reduction proved to be an important preparation step. Increasing the reduction temperature from 200 to 500°C considerably increased the catalytic activity. The activation energies obtained for hydrogenation of aromatics over catalysts reduced at temperatures between 200 and 500°C were found to range between 10.14 and 6.50 kcal mol−1. These energies were found to decrease, in general, with increasing chlorine content of the catalyst and with its reduction temperature. The variation in activation energy with the Arrhenius pre‐exponential factor, as a function of the catalyst reduction temperature, indicates that catalysts containing 0.40 and 0.87% chlorine follow the equation k0 = exp (‐3.25 + 0.001E), and hence their surface uniformity would be identical. However, unchlorinated catalysts, both calcinated before reduction or uncalcinated, exhibit considerably different surface uniformity.

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