Nano-size ZrO2 derived from metal organic frameworks and their catalytic performance for aromatic synthesis from syngas
Oxide-zeolite bi-functional catalyst has shown promising potential in syngas aromatization. As the hydrogenation phase, the size effect of metal oxide needs to be researched. Herein, a series of tetragonal ZrO2 with crystal size ranged 4.0~11.3nm is successfully prepared by using UiO-66 as precursors, the CO conversion and the methanol selectivity over ZrO2 decrease with its crystal size increasing. After thoroughly characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption, pyridine-adsorbed infrared spectroscopy, temperature programmed desorption of NH3/CO/H2, X-ray photoelectron spectroscopy and electron paramagnetic resonance, we find oxygen vacancy exists on nano-size ZrO2 surface which shows Lewis acidity, inducing the acid amount and the acid strength increase over nano-size ZrO2 surface: The acid amount reaches 345.62 umol/g with 9.26% strong acid sites over the minimum size ZrO2. Density functional theory calculations are also carried out and demonstrate that oxygen vacancy is beneficial for the CO adsorption and activation, therefore the minimum size ZrO2 shows the best CO conversion with numerous methanol produced. After mixed with H-ZSM-5 physically, such bi-functional catalyst exhibits 11.67% CO conversion with the aromatics selectivity as high as 94.89% in C5+. Furthermore, no obvious deactivation is observed during the 120h stability test.