To study the influence of steam on the solid state reaction between MeO (Me = Ni, Co, Cu or Fe) and Al2O3, MeO/alpha-Al2O3 and MeO/gamma-Al2O3 model catalysts were kept in either N-2/20% O-2 or N-2/O-2/30% H2O at 500-1000 degrees C. The samples were subsequently analyzed with RES and FTIR. Surprisingly, nickel, cobalt and copper volatilized when MeO/alpha-Al2O3 or MeAl(2)O(4)/alpha-Al2O3 samples were annealed in the presence of 0.3 atm steam at 1000 degrees C. Especially copper was found to volatilize very rapidly in the presence of steam, even at a temperature as low as 800 degrees C. FTIR spectra of steam-treated NiO/alpha-Al2O3 samples showed the incorporation of hydroxyl groups in the nickel oxide layer. This observation and an excellent agreement with thermochemical calculations support our conclusion that the volatile species are metal hydroxides. The solid state reaction of MeO with gamma-Al2O3 was found to proceed at a much higher rate in the presence of 0.3 atm steam at 500-800 degrees C, presumably as a result of an enhanced surface mobility of Me and Al ions along the grain boundaries and the surfaces of the internal pores of the gamma-Al2O3 support, when steam is present.