The design of efficient photocatalysts is crucial for photocatalytic CO2 reduction. This study developed photocatalysts based on MIL-101(Cr) composited with a facet-engineered Pt/Pd nanoalloy (PPNA). Photocatalytic performance evaluations show that MIL-101(Cr) loaded with PPNA exposing {111} facets, namely M-A(111), exhibits a CO2 to C2H4 conversion rate of 9.5 μmol g-1 h-1 in addition to the CO and CH4, whereas M-A(100) with PPNA exposing {100} facets gives CO2 conversion rates of 33.2 for CO and 9.3 μmol g-1 h-1 for CH4 without C2H4. In situ FT-IR revealed that M-A(111) can readily form C2 intermediates during the reaction. This work offers a strategy for the design of photocatalysts for CO2 reduction to C2H4.