Palladium Based Catalysts for Hydrogenation of Nitrobenzene

Abstract

Pd-based catalysts are widely used at industrial scale for fine chemical hydrogenation reactions. The reaction is generally carried out in a batch reactor in liquid phase, and the quantity of catalyst is kept at a very low level (a few grams of catalyst to hydrogenate one kilo of substrate). In most cases, the metal is deposited on a C-based carrier, such as carbon black or activated charcoal. Although this type of support exhibits technical advantages, such as easy recovery of the precious metal by burning, its intrinsic properties, especially purity level and surface area, are not easily maintained at a constant level. In the study described in the chapter, a series of catalysts were prepared on activated C—comparatively to Si—and characterized and tested in the well-known hydrogenation of nitrobenzene to aniline. Precipitation deposit of Pd must be preferred to exchange. Two parameters can be responsible for this gap of activity: (1) the metallic distribution and (2) the metallic dispersion.