The effect of nanocrystalline TiO2 on structure and catalytic activity of CuO–ZnO in combined methanol reforming

Abstract

CuO–ZnO (CZ) and CuO–ZnO/TiO2 (CZT) catalysts have been prepared by co-precipitation, characterized by X-ray diffraction, surface area measurements and chemical analysis and tested in the combined methanol reforming reaction. Catalytic tests have been performed in the temperature range 200–400 °C with a GHSV = 55.000 h−1, after H2 reducing pretreatment at 250 °C or 450 °C. It is shown that nanocrystalline TiO2 influences the CuO–ZnO nanosized structure, reducibility and reactivity. TiO2 slightly increases ZnO crystallite size of the fresh catalyst. Moreover, it causes the CuO chemical reduction to nanosized Cu2O on exhaust catalyst pretreated in hydrogen at 250 °C, this improves the reaction with higher methanol conversion and hydrogen production. On the contrary, TiO2 reduces CuO to submicron Cu0 and greatly increases ZnO crystallite size on the exhaust catalyst pretreated in hydrogen at 450 °C, this treatment weakens the reaction, with lower methanol conversion and hydrogen production. In both cases, nanocrystalline TiO2 presence is able to decrease the CO formation: independently of the hydrogen pretreatment temperature. This ability of the nanocrystalline TiO2 is ascribed to the presence of the oxygen vacancies, which act as electron donors that contribute to hinder CO2 and H2 surface adsorption for steric, electrostatic and probabilistic factors.