Hydrogenolysis of carbon–halogen and carbon–carbon bonds over Pd/Nb2O5–Al2O3 catalysts

Pd/Nb2O5–Al2O3 catalysts exhibited interesting properties in the hydrodechlorination of dichlorodifluoromethane. Introduction of niobia to alumina increases the selectivity for CH2F2, from ∼40% (for Pd/ Al2O3) up to ∼75%, for similar metal dispersions. High-temperature reduction (773 K, HTR) of Pd/Nb2O5–Al2O3 generates the SMSI state, understood as blocking the Pd surface by (partly) reduced niobia. The extent of SMSI effect is judged from a direct comparison between the performance of differently pretreated Pd/Nb2O5–Al2O3 catalysts tested in n-hexane conversion (hydrogenolysis/isomerisation). After HTR of the niobia-containing Pd catalysts, the hydrodechlorination activity disappeared, however the SMSI state became reversed during hydrodechlorination. It is speculated that CCl2F2 and liberated HCl, interact with NbOx decorants, converting them into volatile niobium oxychloride species.