“…As shown in Figure S1, clear signal peaks of 884.1, 900, and 916.7 eV were detected in the Ce region of Ce-Cu 2 O, whereas no signal of Ce was observed for pure Cu 2 O, indicating successful introduction of Ce species into the Ce-Cu 2 O catalyst. Six peaks, w 0 (BE ≈ 882.6 eV), w 1 (BE ≈ 889.8 eV), w 2 (BE ≈ 897.6 eV), w′ 0 (BE ≈ 901.7 eV), w′ 1 (BE ≈ 908.3 eV), w′ 2 (BE ≈ 916.8 eV), corresponding to Ce 4+ were observed in Figure B . Additionally, four peaks marked as m 0 , m 1 , m′ 0 , and m′ 1 , with BE around 881.3, 885.6, 898.9, and 905 eV, respectively, were attributed to Ce 3+ .…”