The rebirth of black gold and solar light

Professor Polshettiwar’s group at the Tata Institute of Fundamental Research (TIFR), Mumbai, has developed a novel ‘air-stable plasmonic reduction catalyst’, challenging the common instability of reduction catalysts in the presence of air. The catalyst fuses platinum-doped ruthenium clusters with “plasmonic black gold.” This black gold effectively captures visible light and generates numerous hot spots thanks to plasmonic coupling, thus improving its catalytic performance.

The team describes their work in an article published in the journal Natural communications.

What sets this catalyst apart is its remarkable performance in the semi-hydrogenation of acetylene, an important industrial process. In the presence of excess ethylene and using only visible light illumination without any external heating, the catalyst achieved an ethylene production rate of 320 mmol g.⁻¹ h⁻¹ with a selectivity of approximately 90%. This efficiency surpasses all known plasmonic and traditional thermal catalysts.

Surprisingly, this catalyst only exhibits its best performance when air is introduced alongside the reactants. This unique requirement leads to unprecedented stability for at least 100 hours. The researchers attribute this to simultaneous plasmon-mediated reduction and oxidation processes at the active sites during the reaction.

Further improving our understanding of this catalyst, finite difference time domain (FDTD) simulations revealed a five-fold increase in electric field compared to pristine DPC. This field enhancement, due to near-field coupling between RuPt nanoparticles and DPC, plays a crucial role in activating chemical bonds. The effectiveness of the catalyst is also evident in its kinetic isotope effect (KIE), which is greater in light than in darkness, at all temperatures.

This indicates the important role of non-thermal effects alongside photothermal activation of reactants. Extensive in situ DRIFTS and DFT studies have provided insight into the reaction mechanism at the oxide surface, particularly highlighting the role of intermediates in selectivity. The partially oxidized surface of the RuPt catalyst generates di-σ-linked acetylene, which then transforms in several steps to produce ethene.

This research marks the first report of a highly efficient, air-stabilized, plasmonically activated catalyst for the semi-hydrogenation of acetylene, with potential applications in various other reduction reactions. The results offer significant contributions to the understanding of plasmonic catalysis and pave the way for the development of sustainable and energy-efficient catalytic systems.