Perturbed angular correlation study of the ion exchange of indium into silicalite zeolites

Two indium-containing silicalite zeolites (In/H–ZSM5) catalysts prepared by wet impregnation and ionic exchange were characterized by the Perturbed Angular Correlation (PAC) technique using ¹¹¹In as probe to determine the nature of the indium species. Some of these species take part in the catalytic reaction of the selective reduction (SCR) of NO_x with methane. PAC experiments were performed at 500oC in air before and after reduction–reoxidation treatments on the catalysts in order to determine the origin of the different hyperfine interactions and then the degree of ionic exchange. Complementary catalytic activity characterizations were also performed. PAC experiments performed on the catalyst obtained by wet impregnation showed that all In-atoms form In₂O₃ crystallites while almost 70% of In-atoms form In₂O₃ in the catalyst obtained by ionic exchange. The PAC experiments of both catalysts performed after the reduction–reoxidation treatment revealed the presence of two hyperfine interactions, different from those corresponding to indium in In₂O₃. These hyperfine interactions should be associated to disperse In species responsible of the catalytic activity located in the ionic exchange-sites of the zeolites. This revised version was published online in August 2006 with corrections to the Cover Date.