Liquid-phase hydrogenation of 2-ethylanthraquinone over Pd/Polyaniline catalysts

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 x 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. (C) 1999 Academic Press.