Solid Lewis acid-base pair catalysts constructed by regulations on defects of UiO-66 for the catalytic hydrogenation of cinnamaldehyde

A series of highly-defective UiO-66 were synthesized and utilized as catalyst in the hydrogenation of cinna-maldehyde (CALD) to cinnamylalcohol (CALH) in isopropanol. The physico-chemical properties of the catalysts were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis and N2 adsorption-desorption. It was found that there are two kinds of atomic Lewis acid-base pairs existing in the defective UiO-66, exactly Zr4+-O2-and Zr4+-OH-, which are active sites for CALD hydrogenation to form CALH. UiO-66-0.3 with the most defects shows a much higher reaction rate constant, which is 5.5 times that of UiO-66-2.0, and gives the best CALD conversion of 85.5% and CALH selectivity of 94.0% at 140 celcius after 3 h. The acid-base synergistic catalysis mechanism was proposed. Moreover, the defective UiO-66 showed good recyclability for up to 7 cycles with retention of catalytic activity as well as structural stability.