Liquid-Phase Hydrogenation of 2-Ethylanthraquinone over Pd/Polyaniline Catalysts

Abstract

The conjugated polymer polyaniline (PANI) has been used as the support for palladium catalysts. It was found that the dispersion of Pd in Pd/PANI catalysts depends on the nature of Pd2+–PANI interactions proceeding upon catalyst preparation. The type of interaction (protonation or oxidation–reduction process) was influenced mainly by the acidity of the precursor solution containing PdCl2–H2O–HCl. Under various conditions of acidity, two series of catalysts, A and B (0.8–10 wt% Pd), were prepared. In catalysts of series A, prepared using a strongly acidic solution (2 M HCl), the dispersion of Pd was high. On the other hand, in catalysts of series B, prepared using a weakly acidic PdCl2 solution (0.66×10−3 M HCl), large Pd particles (100–600 nm) were present. They were formed as the result of an oxidation–reduction process proceeding with the participation of PANI chain. The physicochemical properties of catalyst were characterized by XRD and SEM methods. All catalysts exhibited activity in 2-ethylanthraquinone (eAQ) liquid-phase hydrogenation. The catalysts of series A were more active and the selectivity of eAQ hydrogenation in their presence was higher than that seen for catalysts of series B.