Hollow Spherical Al2O3 for Enhanced Transesterification of Dimethyl Oxalate to Diethyl Oxalate

This study prepared and evaluated hollow spherical (B-Al 2 O 3 ) and needle-like (N-Al 2 O 3 ) alumina catalysts in a fixed-bed reactor for the transesterification of dimethyl oxalate (DMO) with ethanol (EtOH) to produce diethyl oxalate (DEO), using commercial alumina (C-Al 2 O 3 ) as a reference. Experimental results indicated that catalytic activity followed the order B-Al 2 O 3  > N-Al 2 O 3  > C-Al 2 O 3 . At 140 °C and a space velocity of 0.2 h –1 , B-Al 2 O 3 achieved a DMO conversion of 100%, with a DEO selectivity of 84.9% and an ethyl methyl oxalate (EMO) selectivity of 15.1%. The superior performance of B‑Al 2 O 3 originated from its largest specific surface area (202.52 m 2 /g), abundant weak acid‑base sites, and high oxygen vacancies that served as Lewis acid sites, providing more accessible active sites and promoting reactant activation. In situ DRIFTS results suggested a possible nucleophilic substitution pathway for the reaction, involving the replacement of CH 3 O − in DMO by C 2 H 5 O− from EtOH to form DEO. Deactivation studies revealed that coke deposition primarily caused catalyst deactivation; however, catalytic activity could be fully restored after regeneration. This study highlighted the morphological advantages of hollow spherical alumina and elucidated its structure–activity relationship, offering a design strategy for developing efficient catalysts for the green synthesis of DEO. Graphical