Researchers in Italy have developed a Pd/Si catalyst for upcycling silicon from waste PV panels. The system showed performance comparable to commercial silicon catalysts and stable recycling over six cycles.
A research team from Italy has proposed a method for upcycling silicon (Si) from PV panels at the end of life (EoL) by developing a Pd/Si catalytic system. In this configuration, palladium (Pd) nanoparticles are supported on recovered silicon, with Pd driving the catalytic activity while the silicon (Si) acts as a stabilizing, reusable support. The system targets cross-coupling reactions commonly used in the pharmaceutical and fine chemicals industries.
“This study presents a strategy for managing the rapidly increasing global waste stream of EoL solar panels, achieving performance comparable to established Pd-based heterogeneous catalysts,” the group said. “This work paves the way for the broader use of silicon derived from EoL photovoltaics as a versatile heterogeneous support for a wide range of metal-based catalytic systems, expanding the possibilities for their application in diverse catalytic processes.”
To prepare the Pd/Si systems, the researchers first removed the front glass from discarded PV modules by heating it to soften the ethylene-vinyl acetate (EVA) encapsulant, leaving EVA, silicon cells, and backing layers intact. The material was cut into small pieces and treated with tetrahydrofuran (THF) at 60 °C to swell the EVA and separate the silicon cells. The recovered cells were then purified via a two-step chemical leaching process: sodium hydroxide (NaOH) was used to dissolve the aluminum back contact, followed by nitric acid (HNO3) to remove silver finger contacts.
After washing and heat treatment at 500°C, the purified silicon was ground in a ball mill into a fine powder with a purity of 86% by weight. For the catalyst preparation, the powder was suspended in diethylene glycol, a palladium precursor (H2PdCl4) was added and the pH was adjusted with NaOH. The mixture was heated to 130 C under argon to reduce palladium and form Pd nanoparticles on the silicon surface, producing the final Pd/Si catalyst. The recovered silicon catalyst, named Pd/Si_EoLPV, was compared with a reference catalyst prepared using commercial metallurgical grade silicon powder, Pd/Si.MP-AES.
“We decided to evaluate the usefulness and efficiency of this catalytic system in a very useful benchmark Mizoroki-Heck reaction. We decided to compare its behavior with that of traditional catalysts, such as Pd/C, with an emphasis on catalytic activity, palladium leaching and recyclability,” the scientists said. “We also evaluated the usefulness of the catalyst by using it to prepare industrially relevant products, natural compounds and intermediates for active pharmaceutical ingredients (APIs), highlighting its potential as a sustainable and promising catalyst for potential applications.”
The analysis showed that Pd/Si_EoLPV showed performance comparable to that of the commercial silicon powder-based catalyst. The recycled material remained stable for six consecutive reaction cycles, with Pd leaching below 3 ppm. These results correspond to a turnover number (TON) of 5,820 and a turnover frequency (TOF) of 582 h⁻¹. TON describes the number of catalytic cycles before deactivation, while TOF indicates the reaction rate per hour.
On a gram scale, the catalyst was used in five recycling cycles, yielding a total of 48.5 mmol of product with an isolated yield of 97% and an E-factor of 9. In addition, the Pd/Si catalyst was applied to the synthesis of 22 substrates from various iodoarenes and olefins, including intermediates relevant to rilpivirine, Lp-PLA2 inhibitors, and methyl-2-ferulates.
The new recycling process was presented in “Upcycling silicon from end-of-life photovoltaic panels into a heterogeneous catalyst for the Mizoroki-Heck cross-coupling”, published in Green Chemistry. Researchers from Italy’s Mediterranea University of Reggio Calabria, the University of Perugia and the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) contributed to the study.
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