Catalytic exchange of benzene with deuterium and allied reactions on X-type molecular sieves containing nickel ions

Abstract

The exchange of benzene and deuterium has been studied in a static system using as catalysts molecular sieves of the X type with different extents of replacement of sodium ions by nickel ions. The rate of reaction at 170°C rose by a factor of more than 10⁵ as the nickel content was increased to one ion per 8 cages but remained constant with further ion-exchange. The catalytic activity of sieves, particularly those of low nickel content, outgassed at 420°C was reduced by addition of a small quantity of water (one molecule per three cages) at room temperature. The exchange of the three xylenes and toluene with deuterium was studied on NiX (1), a sieve containing 2.95 nickel ions per cage. In all cases, the side-group hydrogen atoms were replaced more rapidly than the ring atoms but with the xylenes all the ring atoms reacted at similar rates independent of molecule or position and no steric effects were observed. With toluene, three ring atoms reacted more rapidly than those of the xylenes and two more slowly. Hydrogen-deuterium exchange occurred rapidly on NiX (1) at 85°C but the exchange of benzene with sorbed deuterium oxide was slow at 300°C. NiX (1) treated for 30 min at 300°C with hydrogen developed reversible colour changes, an e.s.r. signal and enhanced catalytic activity for the exchange of benzene but reverted to normal behaviour on evacuation for 30 min at 300°C.