Supported Palladium Catalysts: A Facile Preparation Method and Implications to Reductive Catalysis Technology for Water Treatment

Abstract

Supported palladium (Pd) catalysts have been extensively studied for water purification applications. However, this technology is primarily challenged by the high cost of Pd and the lack of optimization of catalyst formulations. In this report, we demonstrate a convenient approach to prepare and optimize Pd catalysts for the reduction of toxic oxyanions (bromate, chlorate, and perchlorate). Water-dissolved Na2PdCl4 was quickly adsorbed in the suspension of activated carbon within 5 min and reduced into Pd0 nanoparticles in situ within another 5 min under 1 atm H2 at 20 °C. In terms of both material characterizations and reaction kinetics, the Pd catalysts prepared with the new method show no significant difference from those prepared by the conventional method (involving multiple-step high-temperature procedures) and from benchmark commercial Pd catalysts. With the very simple approach to control, evaluate, and optimize Pd content in the catalyst, we elucidate the relationships among the Pd content, Pd0 particle size, and catalytic activity. We further showcase that the precious metals in previously reported Re–Pd/C and Mo–Pd/C catalysts can be saved up to 80% without sacrificing the activity. The new and convenient catalyst preparation method will significantly enhance the cost-effectiveness of reductive catalysis technologies for water purification.

Ultrasound-mediated synthesis of nanoporous fluorite-structured high-entropy oxides toward noble metal stabilization

“…Judging from the asymmetric peak shape and positions, it appears as though Pd exits as a combination of Pd 0 and Pd +2 . The peaks at 340 and 335 eV are attributed to 3d 3/2 and 3d 5/2 spin-orbits of metallic Pd 0 while those at 342 and 337 eV are ascribed to 3d 3/2 and 3d 5/2 spin-orbits of ionic Pd 2+ in accordance with the literature ( Gao et al., 2021 ; Mandapaka and Madras, 2016 ; Pillo et al., 1997 ; Priolkar et al., 2002 ; Ren et al., 2020 ). This submission is collaborated by the Pd CO adsorption behavior in the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectra displayed in Figure 4 B.…”

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

“…Although an exact molecular structure for the active Mo sites remains elusive, the above findings have collectively confirmed the heterogeneous nature of the catalyst. The critical role of the carbon support may be to provide a large surface area (>900 m 2 g –1 ) , to disperse the insoluble [(NH 2 ) 2 bpy ]­MoO x structure for up to 5 wt % Mo (Figure g), or to stabilize the specific coordination structure that is reactive with ClO 4 – . In addition, since (NH 2 ) 2 bpy is strongly prone to pyridyl protonation, the [(NH 2 ) 2 bpy ]­MoO x coordination structure is less likely to remain intact upon dissolution in the aqueous phase.…”

“…Still, this product dissolved poorly in water and did not reduce aqueous ClO 4 − (Figure S16a). In comparison, the use of activated carbon (without Pd 0 nanoparticles) 36 together with Na 2 MoO 4 , (NH 2 ) 2 bpy, and TPPTS resulted in a slow but significant ClO 4 − reduction at pH 3.0 (Figure S16b and c). Although an exact molecular structure for the active Mo sites remains elusive, the above findings have collectively confirmed the heterogeneous nature of the catalyst.…”

Molybdenum-Catalyzed Perchlorate Reduction: Robustness, Challenges, and Solutions

“…The first step followed our previously developed in situ method to prepare Pd/C. 27 The amounts of carbon and Pd are adjustable based on the specific catalyst powder loading in water (0.2−2.0 g/L) and the specific Pd content in the catalyst (0.1−5.0 wt %). In a 50 mL flask, activated carbon powder was added to 50 mL of DI water.…”

“…Stirring for another 5 min was sufficient for Pd II immobilization onto carbon support. 27 H 2 gas was supplied through a 16gauge stainless steel needle. Another needle was used as the gas outlet so that the H 2 pressure in the flask was maintained at 1 atm.…”