Adsorption of azomethane on oxides and on silica-supported noble metals

The adsorption and thermal decomposition of azomethane (AM) were investigated on oxides (SiO2, TiO2 and Al2O3) and on silica-supported noble metal (Pt/SiO2, Pd/SiO2 and Rh/SiO2) catalysts by Fourier transform-infrared (FT-IR) spectroscopy with concomitant mass spectroscopic monitoring of the gas phase. AM reacts readily with the surfaces of the catalysts to form chemisorbed species. It was demonstrated that AM chemisorbed in trans-form on SiO2, and Pd/SiO2, while on TiO2, Al2O3, Pt/SiO2 and Rh/SiO2, the chemisorbed cis-AM was dominantly detected. OH groups of the oxides were also involved in binding of AM on the surfaces with the formation of H-bridged bonded species. Chemisorbed cis-AM suffered surface rearrangements, as its tautomerisation into formaldehyde methylhydrazone (CH2=N-NH-CH3) was observed on catalysts adsorbing AM in cis-form. Depending on the forms of chemisorbed AM and their surface rearrangements, different products were detected in the gas phase during thermal annealing. (C) 2002 Elsevier Science B.V. All rights reserved.