Microwave‐Assisted Hydrothermal Synthesis of CuO–ZnO–ZrO₂ as Catalyst for Direct Synthesis of Methanol by Carbon Dioxide Hydrogenation

Abstract

A series of CuO–ZnO–ZrO2 catalysts was prepared by a facile microwave‐assisted hydrothermal synthesis method and used for the direct synthesis of methanol by CO2 hydrogenation in a fixed‐bed reactor at 240 °C, 3.0 MPa, CO2/H2=1:3 (v/v), and space velocity of 2400 mL gcat−1 h−1. The effects of the hydrothermal synthesis temperature (80–150 °C) on the physicochemical properties and catalytic activity of the CuO–ZnO–ZrO2 catalysts were investigated by using several techniques, including XRD, N2 adsorption, reactive N2O adsorption, SEM with energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy, temperature‐programmed reduction by H2, and the temperature‐programmed desorption of adsorbed CO2 and H2. The catalyst prepared at 120 °C possessed a high surface area, a high dispersion of Cu species, a high adsorption capacity for CO2 and H2, and thus exhibited a high CO2 conversion and methanol selectivity. The surface area of metallic Cu (SCu) is the critical factor in determining the activity of the CuO–ZnO–ZrO2 catalyst.

CO2 Hydrogenation to Methanol via In‐situ Reduced Cu/ZnO Catalyst Prepared by Formic acid Assisted Grinding

“…Reports on ways to increase the activity and stability of this Cu/ZnO catalyst have been proposed and different oxide additives like Al 2 O 3 , Ga 2 O 3 , TiO 2 , ZrO 2 , have been used for modification. . Raudaskoski et al.…”

Microwave, Ultrasound, and Mechanochemistry: Unconventional Tools that Are Used to Obtain “Smart” Catalysts for CO2 Hydrogenation

“…On the contrary, XPS analysis did not show significant differences in the type of surface Cu species in catalysts obtained at different temperatures. As a whole, an optimum temperature existed for the synthesis of CuO-ZnO-ZrO 2 catalysts [39]: Cu particle size, surface area, and basicity exhibited a volcano trend with a maximum at 120 • C. The catalyst obtained at 120 °C (CZZ120) showed the best catalytic properties in terms of both CO2 conversion and selectivity to CH3OH, becoming rather stable after 100 h reaction. XRD analysis allowed the calculation of the size of both CuO and Cu crystallites: the CZZ120 catalyst showed the smallest CuO and Cu crystallites before and after reduction, respectively, though Cu crystallites (ca.…”

“…On the contrary, XPS analysis did not show significant differences in the type of surface Cu species in catalysts obtained at different temperatures. As a whole, an optimum temperature existed for the synthesis of CuO-ZnO-ZrO2 catalysts [39]: Cu particle size, surface area, and basicity exhibited a volcano trend with a maximum at 120 °C. CO2 methanation (Equation (2)) is a process that allows transformation of CO2 in a fuel through an exothermic reaction (∆H 0 = −165 kJ mol −1 ), for which Ni/Al2O3 is the commercial catalyst [40]:…”

“…Huang et al [39] studied the effect of MW heating during HT synthesis of CuO-ZnO-ZrO 2 catalysts for CO 2 hydrogenation to CH 3 OH (Equation (1)), for which CuO-ZnO is usually considered the best catalyst and where ZrO 2 has the role of imparting high thermal and chemical stability under redox conditions. This type of catalyst is usually prepared by HT method, requiring long reaction times: the (expected) effect of MW irradiation was indeed the shortening of preparation time.…”

“…This type of catalyst is usually prepared by HT method, requiring long reaction times: the (expected) effect of MW irradiation was indeed the shortening of preparation time. Different temperatures (i.e., 80, 100, 120, and 150 • C) were adopted during the MW-assisted HT method to obtain the catalysts named CZZ80, CZZ100, CZZ120, and CZZ150 [39].…”