Tuning the structure and performance of CuAl2O4 spinel for syngas conversion via hydrophobic modification

Against the backdrop of mounting concerns regarding global energy scarcity and environmental degradation, the design of efficient and stable catalysts for the sustainable conversion of syngas (CO/H 2 ) to dimethyl ether (DME) is of critical importance. While copper-based catalysts demonstrate high selectivity, they are prone to deactivation via sintering and often promote the water-gas shift (WGS) reaction, resulting in undesirable CO 2 byproduct formation. In this work, the surface of CuAl 2 O 4 spinel catalysts was hydrophobically tailored using saturated fatty acids with different carbon chain lengths—stearic acid (C=18), arachidic acid (C=20), and behenic acid (C=22)—to investigate their effects on catalyst structure and catalytic performance. The findings reveal that hydrophobic modification substantially increased the water contact angle (from 18.19° to over 125°), effectively inhibited the WGS side reaction, and lowered CO 2 selectivity to a minimum of 36.87%. Comprehensive characterization verified that fatty acid molecules grafted onto the catalyst surface, forming a stable -COOCu interface structure. This modification enhanced surface roughness and oxygen vacancy concentration while facilitating the generation of finely dispersed, nano-sized Cu species during the reaction. Notably, the CuAl 2 O 4 catalyst modified with arachidic acid (C=20) delivered the optimal balance of high DME selectivity and minimal CO 2 emissions while maintaining robust CO conversion. This study presents a rational and effective strategy for engineering metal oxide catalyst surfaces to selectively suppress competing side reactions in syngas conversion processes.