FTIR spectroscopy of hydrogen, carbon monoxide, and methane adsorbed and co-adsorbed on zinc oxide

Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H-2/CO, H-2/CH4 and CO/CH4 on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn2+ ions. Adsorption lowers the CH4 symmetry from T-d to C-3v, which is reflected in activation of the v(1) (symmetric stretching) mode and discrete frequency shifts of the upsilon (3) (antisymmetric stretching) and nu (4) (bending) modes, Co-adsorption of the above gases on ZnO having pro-adsorbed hydrogen results, in all cases, in a bathochromic shift of the upsilon (Zn-H) band and a hypsochromic shift of the upsilon (O-H) band, which originally appear at 1710 and 3492 cm(-1), respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas. (C) 2001 Elsevier Science B.V. All rights reserved.