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 H2/CO, H2/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 Td to C3v, which is reflected in activation of the v1 (symmetric stretching) mode and discrete frequency shifts of the v3 (antisymmetric stretching) and ν4 (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(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.