Application of in-situ IR spectroscopy for the evaluation of new palladium based catalysts for the hydrogenation of anthraquinone

Abstract

The anthraquinone process is the most important method in the manufacture of hydrogen peroxide. The hydrogenation of anthraquinone is the key reaction in this method. Because of the instability of the product in this reaction, and the lack of anthraquinone measuring method during the reaction, the mechanism study on this reaction was exclusively based on the hydrogen consumption and the stoichiometry relationship between hydrogen and anthraquinone. Hence we introduce IR in situ detection, which is a powerful technique that has the ability to directly study the mechanism by monitoring not only the anthraquinone consumption but also the product formation in the hydrogenation of anthraquinone. It is worth to notice that this is the first time that the unstable product anthrahydroquinone be detected by the researchers. By using in situ IR and hydrogen consumption measurement orthogonality, a great advantage had been shown not only in the study of the kinetic of the primary hydrogenation of anthraquinone, but also in studying the degradation of the primary product anthrahydroquinone when comparing to the conventional methods. In situ IR shows it’s potential to be a powerful technique in the mechanism study of reactions that involve intermediate detection. Different supports for palladium loading had be studied for the hydrogenation of anthraquinone. Among these supports, the dealuminated Y zeolite supported Pd catalyst shows a 38% improve in the activity to γ-alumina supported Pd catalyst, the latter is widely used as a commercial catalyst in the hydrogen peroxide manufacture. Besides this, water promotes both the primary hydrogenation rate and degradation rate in the hydrogenation of anthraquinone. Phenyl grafted MCM41 support suppresses the water effect in the degradation, showing a 42% less degradation rate and 15% more selectivity to active quinone when compared to commercial catalyst. The possible explanation is that its hydrophobic property hinder the contact between catalyst and primary product.