(753e) Preparation of Alumina Supported Ir-Ag Bimetallic Catalysts by Electroless Deposition
Bimetallic catalysts have replaced monometallic catalysts over the last several decades in industrial processes due to their superior activity, selectivity and/or stability. Such enhanced performance can be achieved by geometric, electronic or bimetallic effects in the bimetallic system. Often, these supported bimetallic catalysts are prepared either by wet impregnation or by incipient wetness impregnation method, which do not effectively control the distribution or homogeneity of metals on the substrate in many cases. One very promising technique to prepare bimetallic catalysts with uniform composition is electroless deposition (ED). During the ED process, true bimetallic catalysts can be achieved since second metal particles are selectively formed on the pre-existing or primary metal surface sites which are catalytically activated by reducing agent. It has been successfully prepared and demonstrated different transition metals such as Pt-Ag, Pt-Co, Pt-Pd, Pd-Cu, Pd-Ag, Pd-Au catalysts by ED method. However, the use of ED to prepare Ir-based bimetallic catalysts has not received attention. Therefore, in this work, alumina supported Ir-Ag bimetallic catalysts with ultra small particle size have been synthesized via ED method using hydrazine as a reducing agent. Scanning transmission electron microscopy (STEM) study showed the highly dispersed Ir/γ-Al2O3 monometallic catalyst (volume-surface mean diameter of 1.1 nm) with narrow particle size distribution which makes this base catalyst to be a good starting material for Ag deposition. Hydrogen chemisorption was investigated on a series of Ir-Ag bimetallic catalysts with different Ag wt loading to determine the coverage of Ag on Ir metal and revealed that the coverage of Ag increased as increase the Ag wt% (up to 85%). Moreover, in situ transmission Fourier transform infrared spectroscopy (FTIR) of CO adsorption allowed for identification of exposed metal surface area in the bimetallic catalysts.