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 An gular Correlation (PAC) technique using In-111 as probe to determine the na ture of the indium species. Some of these species take part in the catalyti c reaction of the selective reduction (SCR) of NOx with methane. PAC experi ments were performed at 500 degrees C in air before and after reduction-reo xidation treatments on the catalysts in order to determine the origin of th e different hyperfine interactions and then the degree of ionic exchange. C omplementary catalytic activity characterizations were also performed. PAC experiments performed on the catalyst obtained by wet impregnation show ed that all In-atoms form In2O3 crystallites while almost 70% of In-atoms f orm In2O3 in the catalyst obtained by ionic exchange. The PAC experiments o f both catalysts performed after the reduction-reoxidation treatment reveal ed the presence of two hyperfine interactions, different from those corresp onding to indium in In2O3. These hyperfine interactions should be associate d to disperse In species responsible of the catalytic activity located in t he ionic exchange-sites of the zeolites.