A pure Cu target (purity > 99.9%; 50 mm by 100 mm; Toshima Co. Ltd.) was used to deposit Cu atoms on porous silica pellets CARiACT Q-10. The self-made polygonal rotation SP apparatus is described in fig. S6. After the target was presputtered for 0.5 hours, certain amount of the pretreated SiO2 pellets was loaded into the cavity barrel. Then, the vacuum chamber was evacuated to 9.9 × 10−4 Pa, followed by introducing an Ar (99.995%) flow of 29 ml min−1 into the chamber until the pressure reached 2.0 Pa. The SP experiment started with the input power of 450 W. The hexagonal barrel was rotated at 3.5 rpm and vibrated mechanically to mix the support and deposited metal atoms uniformly. After SP for 3.5 hours, approximately 17 weight % (wt %) of Cu were loaded. Thereafter, a 1.0% O2 (balanced by nitrogen) flow was gradually introduced into the cavity barrel to recover ordinary pressure. Last, the catalyst after SP was pressed and crushed into granules of 20 to 40 mesh before catalytic reaction. The as-prepared catalyst was denoted as SP-Cu/SiO2.

One hundred five milliliters of standard solution (0.3 M) of Cu(NO3)2·3H2O in deionized water was mixed with 10 ml of 25 wt % ammonia aqueous solution and stirred for 30 min to produce uniform copper ammonia complex solution. Subsequently, porous silica pellets CARiACT Q-10 (Fuji Silysia Chemical Ltd.; specific surface area, 283 m2 g−1; mean pore diameter, 10 nm) were slowly added to the copper ammonia complex solution and stirred for 2 hours at room temperature. The suspension was heated in a water bath preheated to 40°C and aged for 4 hours. Afterward, the water bath was continuously heated to 90°C, allowing for the evaporation of ammonia, as well as the consequent deposition of copper species on silica. The evaporation process was terminated as the pH value of the suspension decreased to 6 to 7 (ca. 3 hours). The obtained precipitates were filtrated and washed with deionized water and dried at 120°C for 8 hours. The solid powder was then calcined at 450°C in air for 4 hours. The final catalyst was denoted as AE-Cu/SiO2.

The physically mixed catalysts “PM-Cu/SiO2 and PM-Cu+/SiO2” were prepared by mixing porous silica CARiACT Q-10 and CuO or Cu2O powders with a mortar, respectively. The catalyst was pressed and crushed into granules of 20 to 40 mesh before reduction and catalytic reaction.

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