The properties of platinum or palladium supported on β-aluminium trifluoride or magnesium difluoride: catalysts for the hydrodechlorination of 1,1-dichlorotetrafluoroethane

Abstract

Palladium or platinum supported on β-aluminium(III) fluoride or magnesium fluoride are effective catalysts for the conversion of the ozone-depleting compound, CCl₂FCF₃, to the environmentally acceptable refrigerant, CH₂FCF₃ (HFC-134a). The gas phase hydrodechlorination reaction has been studied in the temperature range 373–773 K under steady flow conditions, under which the fluorides were shown not to catalyse any isomerization or dismutation reaction that would lead to unwanted by-products. Increased catalytic activity was found for both metals with increasing metal content of the catalysts. The temperature dependencies revealed higher yields with increased temperature. The selectivity to the desired product, CH₂FCF₃, is significantly higher in the case of Pd on both supports and is slightly higher for β-AlF₃ than for MgF₂. The results of temperature programmed reduction (TPR) of the catalyst precursors and hydrogen chemisorption and transmission electron microscopy (TEM) studies on the catalysts are discussed in relation to the surface hydrolysis of the support materials, for which evidence has been obtained from [³⁶Cl] measurements. It is proposed that water desorbed from the hexagonal channels of β-AlF₃ has an influence on the metal dispersions of the catalysts.