Particle size effect in the catalytic hydrogenation of 2,4-dinitrotoluene over Pd/C catalysts

The liquid phase hydrogenation of 2,4-dinitrotoluene (2,3-DNT) to 2,4-diaminotoluene (2,4-DAT) has been studied over palladium supported on carbon. Catalytic activity and selectivity to the intermediate products were found to depend on the metal particle size. The larger metal particles were the most active and selective towards the formation of the 2,3-nitrohydroxyaminotoluene isomers. The catalysts have been characterized by TPR, XRD, TEM and CO chemisorption. TPR analysis has shown that no formation of a palladium beta -hydride phase occurs on these systems irrespectively of the metal particle size. This apparently anomalous behavior has been attributed to the contamination of the Pd metal particles by impurities and/or C atoms migrating from the support. On the basis of the reported results the relationships between the catalytic activity and the metal particle size in the hydrogenation of 2,3-DNT is discussed. (C) 2001 Elsevier science B.V. All rights reserved.