Palladium supported on sulfonated polystyrene resins as catalyst for the direct flow synthesis of H2O2

Hydrogen peroxide (H2O2) has a wide application range in industry. It is a strong oxidant used e.g. for bleaching, water treatment, semiconductor wafer cleaning and propylene oxide synthesis. It is produced on large scale by the anthraquinone process to yield highly concentrated (50–70 wt%) product in a routine fashion. Nevertheless, this process is very energy consuming, generates a lot of waste and requires transport of hazardous quantities of H2O2. Therefore, direct H2O2 synthesis (starting from gaseous H2 and O2; Figure) has recently emerged as a viable alternative.[1] Flow chemistry using microreactor technology has made its entry into this field, offering opportunities for safer and efficient process operation.[2]
Metal catalysts supported on strongly acidic macroreticular polystyrene resins have also been applied for this transformation.[3] In this work, we describe a transfer of this type of catalysis into flow technology. The preparation and characterization of the catalysts are described, followed by a presentation of their catalytic performances. Having found the optimal values for gas and liquid flow rates, gas ratio and catalyst mass, we further focused onto the importance of the immobilization solvent, reductive treatment and %Pd (and/or other metals) loaded. Our results (~1% wt. H2O2, ~60 % selectivity vs. H2O) are superior to most current literature results.

References
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[2] T. Inoue et al, Chem. Eng. J. 2010, 160, 909; T. Inoue et al, Catal. Today 2015, 248, 169; T. Inoue et al, Fuel Process. Technol. 2013, 108, 8.
[3] G. Blanco-Brieva et al, Chem. Commun. 2004, 1184; C. Burato et al, Appl. Catal., A 2009, 358, 224; J. Kim et al, ACS Catal. 2012, 2, 1042; S. Sterchele et al, Appl. Catal., A 2013, 468, 160.