Considering that the cationic copper species, bearing an extra-lattice oxygen [Cu-O-Cu]2+, are more easily reduced than isolated Cu2+,10 the shoulder which appears at around 180 ºC in the H2-TPR profile of |Cu0.38Ca0.086|[ Si12Al]-MFI, might be attributed to the reduction of [Cu-O-Cu]2+ to Cu2O. The higher intensity of the peaks attributed to [Cu-O-Cu]2+ and Cu2O reduction in |Cu0.38Ca0.086|[ Si12Al]-MFI in comparison with |Cu0.49|[Si12Al ]-MFI shows that the ion exchange of Cu2+ by Ca2+ in a solution with a pH slightly higher than seven (see Table 1) favours the formation of Cu(OH)+ cations.11 These cations, which are compensate the negative charge of the zeolite, generate [Cu-O-Cu]2+ species after activation, probably by the mechanism illustrated in Figure 3.