The maximum production rate of dimethyl ether (DME) through direct CO2 (or CO) hydrogenations on the bifunctional Cu-ZnO-Al2O3 hybridized with highly crystalline ferrierite (FER) zeolite (CZA/FER) was observed at an optimal Si/Al molar ratio of ∼12 (CZA/FER(12)) due to its larger metallic surface area of Cu nanoparticles and relatively higher hydrophobic surface natures. The smaller size of metallic Cu nanoparticles in the larger Cu-ZnO-Al2O3 matrices decorated with smaller ZnO moiety effectively increased the hydrophobic surfaces of the CZA/FER(12), which further preserved the larger number of acidic sites on the FER surface. The phenomena also caused less aggregations of Cu nanoparticles by their stronger interactions in the Cu-ZnO-Al2O3 matrices. The higher CO2 (and CO) conversion and DME productivity of 4.53 mmol/(gcat h with lower CO formation rate of 0.90 mmol/(gcat h on the CZA/FER(12) were attributed to the stable preservations of the strongly interacted smaller Cu nanoparticles even under water excess environment by easily desorbing water molecules with its suppressed competitive adsorptions on the hydrophobic CZA/FER(12) surfaces.
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