Reusable Pd nanoparticle catalysts supported on KOH-activated waste coffee grounds for the catalytic reduction of 4-nitrophenol

Waste coffee grounds (CGs) are typically incinerated or sent to landfills, which can pollute the environment. However, after chemical treatments, such as carbonization and KOH-activation, CGs can exhibit macroporous and microporous structures, besides high chemical stability and surface area (2,710 m²/g). Thus, activated CGs (ACGs) may be used as catalyst supports. Herein, Pd nanoparticles (NPs) loaded with ACG catalysts were prepared by two different methods: immobilization of PdNPs on the support and in situ reduction of Pd ions to Pd metal in the support. The catalytic performance of the ACG-supported PdNPs for the reduction of 4-nitrophenol to 4-aminophenol was investigated. In the recycling test, the ACG-supported PdNP catalysts outperformed the unsupported PdNPs in terms of the stability and conversion efficiency. Thus, the as-prepared ACG support was determined to be a suitable candidate for aqueous catalytic reactions.