3D-printed flow-mode atmospheric pressure glow discharge reactor for the synthesis of multi-metallic Pt-/Pd-/Os-/Ru-/Re-/W-/Cr-nanocluster catalysts

Abstract

In this study, cold atmospheric pressure plasma (CAPP) was used to synthesise “electron-rich” multi-metallic nanocluster catalysts (NCs) from precursors containing Pt, Pd, Os, Ru, Re, W and Cr, with potential applications in hydrogenation reactions. To this end, direct-current atmospheric pressure glow discharge (dc-APGD) was operated in two configurations: a flowing liquid anode (FLA) and a flowing liquid cathode (FLC). The CAPP system was fabricated using stereolithography. The NCs were characterised by dynamic light scattering and electrophoretic light scattering. Catalytic activity was evaluated using the reduction of 4-nitrophenol (4-NP) to 4-aminophenol. Morphology and surface composition were examined by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The NCs were predominantly smaller than 1 nm forming clustered atoms. The NCs synthesised by FLA- and FLC-dc-APGD with ruthenium as the dominant metal and tungsten as the secondary metal (Ru^WNCs) exhibited zeta potentials of 32.58 ± 0.16 mV and 32.42 ± 0.46 mV, respectively, indicating good colloidal stability. Ru^WNCs synthesised by FLA- and FLC-dc-APGD also showed the highest 4-NP reduction activity, with mass-normalised rate constants (k_1m^b) of 17.81 min⁻¹ mg⁻¹ and 18.09 min⁻¹ mg⁻¹ (75% and 81% conversion), respectively. Os^Pd/CrNCs synthesised by FLA-dc-APGD demonstrated comparable catalytic performance (k_1m^b = 15.87 min⁻¹ mg⁻¹), achieving 86% 4-NP conversion. Notably, this conversion was attained within 1.2 min, whereas all reported values correspond to a reaction time of 8 min.