CuO _x Sitting on Titanium Silicate (ETS-10): Influence of Copper Loading on Dispersion and Redox Properties in Relation to de-NO _x Activity

Abstract

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-NO_x 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 CuO_x. 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 CuO_x species (470 K) and of crystalline CuO_x species (560 K). Catalysts containing copper at higher concentration had only the high-temperature reduction peak, indicating the presence of large aggregates of CuO_x. 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.