A series of copper-based catalysts prepared by dispersing the CuO phase on a titanium silicate (ETS-10) crystalline matrix were studied towards their de-NOx activity. The copper concentration ranged from 0.7 to 70 atom(Cu) nm(-2), corresponding to 3-18 wt%. The activity of NO reduction with ethylene was related to morphological and chemical properties of the catalysts. The crystalline character of the catalysts possessing high internal surface and microporosity was preserved up to ca. 3 atom(Cu) nm(-2). At higher copper concentration, structure collapse was observed with formation of large aggregates of CuOx. Temperature-programmed reduction experiments showed two reduction peaks with maximum temperatures at ca. 470 and 560 K, for catalysts with copper concentration up to 3.5 atom(Cu) nm(-2). The two peaks corresponded to the reduction of highly dispersed and non-interacting CuOx species (470 K) and of crystalline CuOx species (560 K). Catalysts containing copper at higher concentration had only the high-temperature reduction peak, indicating the presence of large aggregates of CuOx. All the results collected seem basically consistent with a value of about 2.5-3 atom(Cu) nm(-2) for the maximum dispersion capacity of CuO on the ETS-10 matrix. The amount of copper deposited on ETS-10 affects the activity of catalysts towards NO reduction. The turnover frequencies per copper site calculated as a function of copper concentration showed a clear decreasing trend starting from 0.7 to 3.5 atom(Cu) nm(-2). Catalysts with higher copper concentration were completely inactive towards NO reduction.