Incorporation of cations into zeolites by a new reaction between Brönsted acid zeolites and metals. I. Zinc into faujasites and mordenites

Abstract

A redox reaction was found to proceed between metallic zinc and zeolitic lattice protons when ground mixtures of zinc dust (<10 μm) and NH 4,Na–Y zeolite, mordenite or varieties of these zeolites prepared by steaming or acid leaching were heated in a vacuum or an inert atmosphere to temperatures above 250°C. This process results in the evolution of molecular hydrogen and in the formation of Zn 2+ cations occupying, as evidenced by XRD and FTIR spectroscopy, lattice cation sites in the zeolite structure. The reported redox reaction can be regarded as the solid-state analogue of the dissolution of metals in aqueous solutions of acids. In the case of NH 4,Na–Y with zinc admixed in an amount equivalent to the ammonium content, the amount of the evolved hydrogen was found to be equivalent to the amount of Brönsted acid sites in the zeolitic component. The hydrogen release proceeded, depending on the type and modification of the applied zeolite, in different temperature ranges. Possibilities of developing a highly sensitive method for the quantification and distinction of hydroxyl groups in zeolites on the basis of the reported reaction are discussed.