Preparation of Pt-containing bimetallic and trimetallic catalysts using continuous electroless deposition methods

Electroless deposition (ED) is a highly effective method for synthesis of bimetallic catalysts. However, limitations from ED bath stability often exist with this method using the conventional batch method of preparation. Continuous ED is a synthesis procedure in which the secondary metal salt and reducing agent are added separately at controlled rates such that the rates of electroless deposition and addition to the ED bath are similar. Thus, ED reagent concentrations do not accumulate to a level where spontaneous reduction of the secondary metal salt to nanoparticles occurs. Pt@Au/SiO2 and Pt@Cu/SiO2 bimetallic catalysts have been synthesized by controlled deposition of Cu2+ and AuCl4- salts on a 2% Pt/SiO2 to demonstrate the benefits of continuous deposition. Continuous ED has been extended to deposition of two metal salts onto a third supported metal surface to presumably form a bimetallic shell layer of uniform composition. A series of different Pd@Pt-Cu/C catalysts has been made by simultaneous deposition of Cu2+ and PtCl62- salts on carbon-supported Pd. The transformation of ED from a batch to continuous process has permitted greater control over the ED reaction and solved problems with bath instability of highly reducible metal salts. Formation of trimetallic catalysts is also very straightforward using continuous ED methods.