An extensive series of 30 Cu exchanged zeolites and Cu impregnated silicas and aluminas have been tested in their capacities to stabilize the bis(mu-oxo)dicopper core. This core shows a remarkably activity towards methane, as it selectively hydroxylates methane into methanol at the low temperature of 125 degrees C. UV-vis spectroscopy is an easy approach to detect the presence of this bis(mu-oxo)di copper core since it is characterized by an intense charge transfer band at 22 700 cm(-1). In this way it was found that after calcination, only the Cu exchanged zeolites ZSM-5 and MOR are capable of stabilizing this core. In addition, an optimum in the Si/Al ratio and in the calcination temperature were observed, indicating that this core requires a rather specific coordination environment. For ZSM-5, the optimal Si/Al ratio for bis(mu-oxo) dicopper core formation is between 12 and 30 and the amount of this core increases with increasing copper loading above Cu/Al = 0.2. Calcination in O-2 should be done at temperatures higher than 280 degrees C and lower than 700 degrees C. After reaction with methane at low temperature (150 'C), it was found that only Cu-ZSM-5 and Cu-MOR yielded methanol, whereas all the other Cu based materials yielded almost no methanol. At higher temperatures (200 'C) however, Cu-FER and Cu-BEA showed comparable methanol yields as Cu-ZSM-5 and also the methanol yield of Cu-MOR increased at this higher reaction temperature, indicating. that a second not yet identified Cu-oxygen species is activated in the FER, BEA and MOR zeolites at higher temperatures. (c) 2005 Elsevier B.V. All rights reserved.