CO2 Hydrogenation to Methanol over La2O3-Promoted CuO/ZnO/Al2O3 Catalysts: A Kinetic and Mechanistic Study

Abstract

The hydrogenation of CO2 to methanol has been investigated over CuO/ZnO/Al2O3 (CZA) catalysts, where a part of the Al2O3 (0, 25, 50, 75, or 100%) was substituted by La2O3. Results of catalytic performance tests obtained at atmospheric pressure showed that the addition of La2O3 generally resulted in a decrease of CO2 conversion and in an increase of methanol selectivity. Optimal results were obtained for the CZA-La50 catalyst, which exhibited a 30% higher yield of methanol, compared to the un-promoted sample. This was attributed to the relatively high specific surface area and porosity of this material, the creation of basic sites of moderate strength, which enhance adsorption of CO2 and intermediates that favor hydrogenation steps, and the ability of the catalyst to maintain a large part of the copper in its metallic form under reaction conditions. The reaction mechanism was studied with the use of in situ infrared spectroscopy (DRIFTS). It was found that the reaction proceeded with the intermediate formation of surface formate and methoxy species and that both methanol and CO were mainly produced via a common formate intermediate species. The kinetic behavior of the best performing CZA-La50 catalyst was investigated in the temperature range 190–230 °C as a function of the partial pressures of H2 (0.3–0.9 atm) and CO2 (0.05–0.20 atm), and a kinetic model was developed, which described the measured reaction rates satisfactorily.

An insight of CO 2 hydrogenation to methanol synthesis: Thermodynamics, catalysts, operating parameters, and reaction mechanism

“…Samson et al mentioned that the selection of the catalyst preparation method influences the physico-chemical properties such as the degree of Cu dispersion, electronic state, and polymorphism of ZrO 2 and concluded that the methanol formation rate accelerated by increasing the t-ZrO 2 phase in the Cu/ZrO 2 catalyst. 88 Kourtelesis et al 89 and Guo et al 90 have studied the significance of La 2 O 3 into CuO/ZnO/Al 2 O 3 and Cu/ZrO 2 catalysts. The inclusion of La 2 O 3 increases oxygen vacancies, enhances strong basic sites, and allows the formation of formate and methoxy species, which improve the CO 2 adsorption capacity and methanol yields.…”

Engineering well-defined rare earth oxide-based nanostructures for catalyzing C1 chemical reactions

“…The opposite effect of the different rare earth promotors on activity was mainly due to the enhanced synergistic effect and H 2 adsorption caused by the addition of La and Ce, which were not found in the catalysts with Pr and Nd as additives. Similarly, Kourtelesis et al 105 found that La 2 O 3 could promote 30% of the methanol yield for the CuO/ZnO/Al 2 O 3 catalyst. La 2 O 3 could be facilely introduced by a co-precipitation method, and the enhanced methanol yield could be attributed to enhanced adsorption of CO 2 and active intermediates.…”

“…Some groups used rare earth oxide as promotors to adjust the catalyst structure for CO 2 hydrogenation to methanol and obtained positive results. 104,105 For instance, Ban et al 104 verified that the using of La and Ce as promoters boosted the methanol production of CuZnZr catalyst, especially Ce. However, the introduction of Pr and Nd as additives decreased the activity.…”

Ex-LDH-Based Catalysts for CO2 Conversion to Methanol and Dimethyl Ether

“…Besides the conventional CuO/ZnO/Al 2 O 3 , different Cu-based catalytic systems have been investigated for the methanol synthesis from CO 2 [10][11][12][13]. Among them, the ZrO 2containing catalysts have been recently claimed to be very active and selective due to the versatile properties and weak hydrophilic character of zirconia [12].…”