Supported Pd–Cu catalysts in the water phase reduction of nitrates: Functional resin versus alumina

Pd–Cu bimetallic catalysts supported on the cationic resin Dowex 1 × 4 (gel type poly(styrene-co-divinylbenzene) with −N(CH3)3+Cl− groups) and basic γ-Al2O3 were prepared by ion exchange and the incipient wetness impregnation method, respectively, and tested in the liquid-phase hydrogenation of nitrates in water. Various methods of the reduction of metal precursors were used. The effect of the preparation method, the temperature, the reduction conditions and the support on the properties of palladium–copper composites was investigated by means of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and temperature programmed reduction (TPR). The Pd–Cu catalysts prepared by liquid-phase reduction of anionic chloro-complexes of palladium(II) and copper(II) immobilised in a resin, mainly isolated domains of metallic palladium and copper, if any, contained. The reduction using hydrogen joined with calcination of palladium and copper salts supported on γ-alumina led to well formed crystallites of a palladium–copper alloy. The Pd–Cu catalysts supported on γ-Al2O3 exhibited higher activity of nitrate removal under given reaction conditions in a batch reactor. However, with the Pd–Cu resin-based catalysts a better final selectivity (selectivity to products other than nitrites and ammonia) at a comparable conversion of nitrates has been obtained in comparison with alumina based catalysts. The catalysts exhibited different stability with respect to the leaching of metals.

A performance of bimetallic Pd–Cu catalysts supported on functional gel type resin and gamma-alumina in the liquid-phase hydrogenation of nitrates has been compared. Pd–Cu alloys (alumina support) or isolated domains of metallic palladium and copper, if any, were found by means of TEM and XRPD. The Pd–Cu catalysts supported on alumina were more active, but less selective to nitrogen than their resin type counterparts. In spite of smaller metal particles generated inside the polymer framework, this type of catalyst proved to be more stable than that supported on γ-alumina. Figure optionsDownload as PowerPoint slide