Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Summary

Presented here is a protocol for the synthesis of silver-palladium (Ag-Pd) alloy nanoparticles (NPs) supported on ZrO₂ (Ag-Pd/ZrO₂). This system allows for harvesting energy from visible light irradiation to accelerate and control molecular transformations. This is illustrated by nitrobenzene reduction under light irradiation catalyzed by Ag-Pd/ZrO₂ NPs.

Abstract

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO₂ (Ag-Pd/ZrO₂) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO₂ support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO₂ support. The Ag-Pd/ZrO₂ NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Introduction

Among the several applications of metal nanoparticles (NPs), catalysis deserves special attention. Catalysis plays a central role in a sustainable future, contributing to less energy consumption, better utilization of raw materials, and enabling cleaner reaction conditions^1,2,3,4. Thus, progress in catalysis can provide tools for enhancing the atomic efficiency of chemical processes, making them cleaner, more economically viable, and more environmentally friendly. Metal NPs encompassing silver (Ag), gold (Au) or copper (Cu) can display inter....

Protocol

1. Synthesis of Ag-Pd/ZrO₂ NPs

NOTE: In this procedure, the Pd mol% in Ag-Pd corresponded to 1%, and the Ag-Pd loading on ZrO₂ corresponded to 3 wt.%.

1. Place 1 g of ZrO₂ powder in a 250 mL beaker.
2. Add 50 mL of an AgNO₃ (aq) (0.0059 mol/L) and 9.71 mL of a K₂PdCl₄ (aq) (0.00031 mol/L) solutions to the beaker under vigorous magnetic stirring (500 rpm) at room temperature.
3. Add 10 mL of lysine (0.53 M) aqueous solution.
4. Keep the mixture under vigorous stirring (500 rpm) for 20 min.
5. After 20 min, use a pipette to....

Results

Figure 1A shows digital photographs of the solid samples containing the pure ZrO₂ oxide (left) and the Ag-Pd/ZrO₂ NPs (right). This change in color from white (in ZrO₂) to brown (Ag-Pd/ZrO₂) provides the initial qualitative evidence on the deposition of Ag-Pd NPs at the ZrO₂ surface. Figure 1B shows the UV-visible absorption spectra from the Ag-Pd/ZrO₂ NPs (blue trace) as well as ZrO₂ (.......

Discussion

The findings described in this method demonstrate that the intrinsic catalytic activity of Pd (or other catalytic but not plasmonic metal) can be significantly enhanced by LSPR excitation via visible-light irradiation in bimetallic alloyed NPs³⁵. In this case, Ag (or another plasmonic metal) is capable of harvesting energy from visible-light irradiation via LSPR excitation. The LSPR excitation leads to the formation of hot charge carriers (hot electrons and holes) and localized heating.......

Materials

Name	Company	Catalog Number	Comments
2-Propanol (anhydrous, 99.5%)	Sigma-Aldrich	278475	CAS Number 67-63-0
Aniline (for synthesis)	Sigma-Aldrich	8.22256	CAS Number 62-53-3
Azobenzene (98%)	Sigma-Aldrich	424633	CAS Number 103-33-3
Ethanol	Honeywell	32221	CAS Number 64-17-5
Hydrochloric acid (37%)	VWR	PRLSMC310066	CAS Number 7647-01-0
L-Lysine (crystallized, ≥98.0% (NT))	Sigma-Aldrich	62840	CAS Number 56-87-1
Nitric acid (65%)	Merck	100456	CAS Number 7697-37-2
Nitrobenzene	Sigma-Aldrich	8.06770	CAS Number 98-95-3
Potassium hydroxide	Fisher	10448990	CAS Number 1310-58-3
Potassium tetrachloropalladate (II) (98%)	Sigma-Aldrich	205796	CAS Number 10025-98-6
Silver nitrate (ACS reagent, ≥99.0%)	Sigma-Aldrich	209139	CAS Number 7761-88-8
Sodium borohydride (fine granular for synthesis)	Sigma-Aldrich	8.06373	CAS Number 16940-66-2
Zirconium (IV) oxide (nanopowder, <100 nm particle size (TEM))	Sigma-Aldrich	544760	CAS Number 1314-23-4