Structure-property relationships of copper modified mesoporous TiO2 materials on alkyne homocoupling reactions

Three different modification (doping, solvent free, and impregnation) methods were used to obtain a series of mesoporous Cu-TiO2 materials with various copper loading amounts (0-15 mol%). The influence of the modification procedure on the physico-chemical properties was characterized by PXRD, N-2 sorption, SEM, EDX elemental mapping, and XPS techniques. The presence of copper species has been detected either in the TiO2 lattice as Cu+ (via doping methods) or on the surface of TiO2 as CuO species (via solvent free and impregnation methods). With the modification of Cu, the surface area of mesoporous Cu-TiO2 materials can be increased up to 128 m(2)/g. The catalytic activities of Cu-TiO2 materials were investigated using the alkyne-alkyne homocoupling reaction with air as the sole oxidant under mild reaction conditions without any additives. The doped Cu-TiO2 materials show the highest catalytic activity (1,4-diphenyl-1,3-butadiyne yields > 99%). The different catalytic mechanisms, active sites, and structure-property relationships of all the catalysts are discussed. Definitive features affecting the catalytic performance of the obtained Cu-TiO2 materials are the loading amounts and the states of Cu, surface area, and pore size distributions. Reusability tests were conducted on the collected sample without washing, and 74% yield was achieved even after three cycles. (C) 2016 Elsevier Inc. All rights reserved.