Catalytically sustainable, palladium-decorated graphene oxide monoliths for synthesis in flow

Abstract

Continuous flow synthesis is an essential route towards high throughput manufacturing of fine chemical and pharmaceutical products. The mentioned chemistries are often catalyzed by solid-supported catalysts via packed beds which are characterized by multiple issues such as high pressure-drops, micro channeling through the bed, and leaching of the metallic catalyst into the product stream. These issues lower the overall process efficiency. Three dimensional (3D) structures, known as monoliths, with high porosity and mechanical robustness, offer the ideal properties to be used macroscopic supports for metallic catalyst particles. This approach has shown to alleviate several known issues with catalyst packed beds effectively.Herein centimeter-scale monolithic catalysts of palladium (Pd)-decorated, covalently-bonded graphene oxide (GO) layers have been prepared via a completely aqueous, one-pot system. These monolithic composite structures were designed for Suzuki cross-coupling reactions in flow. As highly engineered materials, monoliths’ properties such as oxygen content and Pd catalyst ionic species were tuned via microwave irradiation and ethanol vapor reduction treatments. The optimal monolithic catalysts showed over 5 h of operational longevity in flow, which was 300% higher than the conventional Pd on GO catalyst packed beds. As a proof of concept, the monolithic catalyst was successfully used as a model structure for nondestructive X-ray CT-scan elemental and porosity mapping in the centimeter scale.