Some experimental evidences for hydrogen spillover on Pt/Al2O3 catalysts by electrical conductivity transient response

Transient method and temperature-programmed desorption (TPD) measurements b ased on the response of the AC electrical conductance (G) have been used to characterise a H-2-Pt/Al2O3 system. It was shown that if the surface was i nsufficiently cleaned and contained traces of oxygen, the transient respons e H-2 (inc., 0) - G was of the overshoot type. Its characteristics are rela ted with the involvement of some competitive processes controlled by the hi ghly exothermic parasite reaction between hydrogen and oxygen. The "ignitio n" reaction O-2-H-2 produces the sharp increase of the amount of the spillo ver hydrogen, which decreases by back spillover and desorption as much as t he "extinction" is in progress. The G-TPD profiles, registered after H-2 (i nc., 0) - G transient experiments and in conditions simulating the reaction sequence of the proposed mechanism, provide additional support for this st atement. (C) 1999 Elsevier Science B.V. All rights reserved.