Monitoring cation-site occupancy of nickel-exchanged zeolite Y catalysts by high-temperature in situ X-ray powder diffractometry

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Abstract
Procedures based on the Rietveld method of refinement of X-ray powder profiles have been used to determine the sites and occupancies of extra-framework cationic nickel, potassium and sodium in typical zeolitic catalysts at temperatures in the range 400–500 °C. The siting of Ni2+ and other ions at high temperature differs from that at room temperature previously reported. There are also significant differences in the location of cations and in the reducibility of Ni2+ which depend upon the nature of the treatment (e.g. steam treatment, treatment with an alkaline solution) to which the as-prepared zeolite is subjected prior to dehydration and/or reduction.