The Many Applications of Electrostatic Adsorption for the Preparation of Supported Metal Nanoparticles

A simple, scientific method to prepare supported metal nanoparticles was proposed almost 50 years ago, which utilizes the protonation-deprotonation chemistry of the nascent hydroxyl groups that populate typical support surfaces. In aqueous solution, these can be protonated and so positively charged in the pH range below the point of zero charge (PZC) of the support, and deprotonated and negatively charged above the support PZC. An oppositely charged metal complex in the impregnating solution will experience a strong electrostatic attraction to the surface and will be firmly anchored during drying. The metal nanoparticles produced after thermochemical conversion of the dried precursor are typically small (<2 nm) and tightly sized. In this review, the past 50 years of literature reporting this method have been summarized and critiqued. Electrostatic adsorption has been applied for 1) the preparation of single metal nanoparticles on a wide variety of supports, including single-atom catalysts, 2) well alloyed bimetallic and dilute limit nanoparticles, and 3) selective metal deposition over composite supports. The method has been extended to 4) incipient wetness impregnation and, most recently, to 5) formed catalyst supports. The limitations, troubleshooting, and future directions of this method are discussed.