Role of mordenite acid properties in silver cluster stabilization

In the present work, the role of SiO2/Al2O3 molar ratio in silver cluster stabilization inside mordenite pores was studied. It was found that SiO2/Al2O3 molar ratio regulates silver cluster stabilization by means of change of mordenite acid properties. The high concentration and high strength of Bronsted acid sites favor the stabilization of silver in the form of clusters inside the pores. In contrast, low concentration and low strength of Bronsted acid sites and high concentration of Lewis sites inside the channels can hinder stabilization of silver clusters. In this case, large particles on the external surface of zeolite are preferably formed. It was revealed that silver cluster introduction in its turn influences acid properties of mordenites, changing the concentration and structure of acid sites. As a result of silver incorporation, four types of Lewis acid sites presented in H-mordenites disappear and a new type of Lewis acid site appears. For the majority of samples, it is accompanied by enhancement of concentration of Lewis sites so that all Al becomes 'IR visible'. (C) 2000 Elsevier Science S.A. All rights reserved.