Crystal phase engineering emerges as a powerful strategy to enhance photocatalytic activity, yet controlled phase-selective synthesis and phase-dependent performance understanding remain challenging. In this study, we introduce a novel method for synthesizing phase-engineered In2O3 via the pyrolysis of metal–organic frameworks (MOFs). We demonstrate that the functional groups and pyrolysis temperatures of MOFs are critical for phase-selective synthesis. Specifically, pyrolysis of MIL-68(ln)–NH2 at optimal temperatures yields In2O3 with rhombohedral (rh-In2O3), cubic (c-In2O3), and rhombohedral/cubic heterophase (rh/c-In2O3) structures. Our photocatalytic CO2 reduction tests reveal that c-In2O3 outperforms rh-In2O3 and rh/c-In2O3, achieving a CO production rate of 29.19 μmol g-1h−1 with 94.47 % selectivity. Spectroscopic and theoretical analyses show that c-In2O3 has superior charge transfer efficiency and lower reaction energy barriers, particularly for the rate-determining *CO intermediate, which exhibits a lower Gibbs free energy on its surface. This work provides a significant advancement in optimizing photocatalytic CO2 reduction efficiency through precise phase engineering, underscoring the vital role of phase control in enhancing catalytic performance.
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