Hydrogenation by hydrogen bronzes: II. Hydrogenation of ethylene by H xV 2O 5

Abstract

Hydrogen vanadium oxide bronzes have been prepared by spillover of hydrogen from supported Pt particles. The crystallinity of the starting oxide disappears progressively during the insertion of hydrogen so that a bronze with an initial stoichiometry of about H 3.3V 2O 5 is quasi-amorphous. The recovery of the occluded hydrogen, using ethylene as a hydrogen-accepting molecule, depends upon the conditioning temperature, the reaction temperature, and principally on the amount of hydrogen initially inserted in the bronze. Molecular hydrogen and water are released upon outgassing. Upon back-titration with hydrogen, the initial stoichiometry of the bronze can be restored as long as the pretreatment or reaction temperature does not exceed 120 °C. During the reaction with ethylene, CO 2 and H 2O are also formed. There is an inverse relationship between the ethane produced and the amount of oxygen extracted from the oxide lattice. Oxygen treatment results in the formation of crystalline V 2O 4. Back-titration with hydrogen cancels out this phase and the catalytic activity is only partly restored. Pt loadings up to 1% increase markedly the yields of ethane. Comparison is made between the present results and those obtained in a previous study on hydrogen molybdenum bronzes.