(461e) Electrostatic “Nano-Engineering” of Promoted and Bimetallic Catalysts

Metal coordination complexes such as chloroplatinic acid, [PtCl6]-2 and copper tetraammine, [(NH3)4Cu]+2 appear to adsorb onto common oxide supports such as alumina and silica via an electrostatic mechanism [1-3]. The charged complexes are attracted to an oppositely charged surface, which is created by either the protonation or deprotonation of hydroxyl groups that populate the oxide surface.

In many cases there appears to be a correlation of strong electrostatic adsorption of precursors and high dispersion of the reduced metal. Using the method of ?strong electrostatic adsorption? (SEA) [4], well dispersed metal particles can be prepared over pure oxide and carbon supports simply and with cheap, common precursors.

In this paper we demonstrate that electrostatic control of metal complex adsorption can be achieved at the nanoscale over surfaces containing two oxides: the SEA method can be extended to provide a simple, scientific method to prepare a wide range of bimetallic catalysts and promoted catalysts. Over promoter/support surfaces, pH has been used to achieve selective adsorption of the metal complex onto the promoter phase and not the support. Bimetallics such as Pt/Co for fuel cell electrocatalysts might be effectively synthesized by adsorbing a second metal complex selectively onto a precursor oxide phase of the first metal and then reducing the intimately contacted metals.

[1] Spieker, W. A., and Regalbuto, J. R., Chem. Eng. Sci. 56, (2001) 214. [2] Schreier, M., and Regalbuto, J.R., J. Catal. 225, 2004, 190. [3] Schreier, M., et al., Nanotech. 16, 2005, S582-S591. [4] Regalbuto, J. R., Surface and Nanomolecular Catalysis, Chapter 6: A Scientific Method to Prepare Supported Metal Catalysts, Richards, R. editor, Taylor and Francis/CRC Press, 2006.