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Temperature programmed reduction (t.p.r.) has been used to study the redox behaviour of copper ions in X and Y zeolites. Two distinct CuII to CuI reduction processes are discernible in both X and Y zeolites. These two processes have been attributed to the reduction of CuII ions occupying sodalite and supercage sites ; a small fraction of the CuII ions, assumed to occupy hexagonal prism sites, remain unreduced. At 773 K in nitrogen, autoreduction of both sodalite and supercage CuII occurs in X zeolite, while only supercage CuII ions are autoreduced in Y zeolite. The reductions are reversible in Y zeolite, but some CuO is formed in X which is subsequently reduced by a third process. Activation energies (kJ mol-l) were obtained as follows : CuII to CuI (sodalite cages) 84f 13, CuII to CuI (supercages) 642 10 and CuO to Cuo (X-type zeolite) 494 7.

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The oxidation of hydrogen on platinum has been studied using a microcalorimetric technique. The reaction takes place by two mechanisms depending on whether the surface is in an oxidised or reduced state. On the reduced surface, hydrogen is dissociatively adsorbed and competes with adsorbed molecular oxygen for adsorption sites. The reaction rate is higher on the oxidised surface where hydrogen molecules are weakly adsorbed and react with strongly adsorbed oxygen. * S . Z. Roginsky, Proc. 3rd Int. Congr. Catalysis (Amsterdam) 1964, p. 939.' A. Jones and J. G. Firth, to be published.