EPR investigations on radiation induced chemical transformations in Pd(ClO₄)₂/i-PrOH/HClO₄ system from 77 to 300 k

Abstract

The EPR studies have been carried out on gamma irradiated samples of Pd(ClO₄)₂ in 9 M/4 M HClO₄ in the presence and absence of isopropanol [i-PrOH (5%, v/v)], in the temperature range of 77-300 K. The EPR studies revealed the formation of Pd+ complex, Pd3+ complex and several radicals such as H·, OH·, ClO₃·₃;, ClO₄· and O₃^- on radiolysis of these systems. Reduction of Pd²⁺ to Pd clusters could not be observed in the absence of i-PrOH and warming of the irradiated sample finally resulted in recovery of Pd²⁺ complex. However, in the presence of 5% i-PrOH, strongly oxidizing radicals like OH·, ClO₃· and ClO₄· are suppressed and (CH₃)₂C·OH radical was produced along with reducing species like H· EPR spectra in these strongly reducing conditions showed formation of Pd⁺ complex, which on heating above 230 K, disproportionated into Pd⁰ and Pd²⁺ complex and finally lead to formation of Pd metal aggregates. Simultaneously, pulse radiolysis technique has been employed as an alternative method to verify the EPR observations.