The role of additives in the impregnation of platinum and ruthenium on alumina catalysts

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Abstract
Platinum‐ and ruthenium‐alumina catalysts are prepared in the absence and presence of additives during metal impregnation. In the absence of additives, metal penetration and distribution in the support pellets is poor, whereas in the presence of a proper additive, uniform metal distribution can be achieved. The metal dispersion in the support is found to be a function of its distribution. In Pt/Al2O3, the addition of HCl improve the distribution and dispersion of the metal as its concentration increases. However, the use of monoethanolamine as an additive achieves an abrupt improvement in the distribution and dispersion of platinum, followed by a region of slight improvement (pH range 2.5–6.5). With a further increase in the concentration additive of the platinum distribution and dispersion deteriorates due to excessive metal penetration and accumulation in the centre of the pellet. In ruthenium preparations, citric acid appears to be the best additive. Oxalic acid also improves ruthenium impregnation but needs to be added in larger concentrations than citric acid. The hydrogenation activity of the catalysts reflected the improvement of the Pt and Ru distributions and dispersions in the support pellets.