An amine-modified Pd-based catalyst for highly-efficient 2-amylanthraquinone hydrogenation

The development of anthraquinone (AQ) hydrogenation catalysts with high activity and selectivity remains a challenge, but it is critical in industrial applications from both economic and environmental perspectives. In this work, an amine-modified catalyst, i.e., Pd/A/SiO2, was designed and synthesized via grafting 3-aminopropyltri-methoxysilane (APTMS) onto silica support and then loading Pd via the Shiff-base reaction. Multiple techniques were used to thoroughly characterize and analyze the catalysts' structural and electronic properties, such as transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photo-electron spectroscopy (XPS), etc. The Pd particle size (3.86 nm) in Pd/A/SiO2 was found to be very close to the reported optimal value, which balances well between the number of active sites and the required size for AQ adsorption; also, the residual carbon species from APTMS improves the hydrophobic properties of the support, which benefits AQ adsorption and anthrahydroquinone (AQH2) desorption; and furthermore, the electron transferred from N to Pd increases the electron density of the latter, favoring the activation of the C--O bond in AQ. These factors combine to give a very superior performance of Pd/A/SiO2 for AQ hydrogenation, including a hydrogenation efficiency as high as 15.7 g/L with an intriguing selectivity of 96.1 %, and a good reusability merit within a six-run test, all of which are among the best results reported so far. This work, we believe, provides food for thought in the development of a highly efficient catalyst for AQ hydrogenation.