Precise tailoring of nickel crystalline phase for efficient low‐temperature aqueous ethanol coupling to higher alcohols

Low‐temperature (≤100°C) aqueous‐phase ethanol coupling over hexagonal close‐packed nickel (hcp‐Ni) exhibits great potential for higher alcohol (HA) synthesis and conversion of crude fermentation broth. Precise control of Ni crystalline phase remains challenging. Herein, we develop a hydrogen‐induced phase‐engineering strategy to synthesize hcp/fcc‐Ni catalysts with tunable hcp‐Ni fractions (0%–100%). Under reaction conditions, ethanol conversion correlates positively with hcp‐Ni content At 100°C, hcp‐Ni delivers 28.2% ethanol conversion, twice the value of mixed‐phase hcp/fcc‐Ni and superior to benchmark noble‐metal catalysts. A cyclic system with HA product separation between batches is demonstrated over six batch cycles, corresponding to 432 h of cumulative reaction time. Characterizations and calculations analyses suggest that the geometric and electronic characteristics of hcp‐Ni(014) favor initial ethanol activation, consistent with its lower OH bond‐cleavage barrier. This work provides insight into the phase–activity relationship between hcp‐Ni phase fraction and ethanol conversion and guides phase engineering of Ni‐based catalysts.