Boosting the C–C Coupling of Bioethanol to Higher Alcohols by Inhibiting Aqueous Phase Reforming Reaction
Xiaoping Wu, Xueying Cai, Yunhong Pi, Bo Chen, Xi‐Yin Li, Qingwei Meng, Qian Zhang, Tiejun Wang
Abstract
A suitable catalyst with an exact match of the acidity/basicity, ingenious geometric structure, and proper electronic environment is vital to the Guerbet reaction for the synthesis of C 6+ higher alcohols. Herein, we synthesized a series of Ni/MgAlO and NiSn/MgAlO catalysts based on hydrotalcite laminate for one-pot upgrading of aqueous bioethanol to C 6+ higher alcohols. Through the introduction of Sn to form NiSn alloys, the Ni–Ni interactions were attenuated and the cleavage of C–C bonds was suppressed with a yield of 21.9% of C 6+ higher alcohols at 250 °C. Meanwhile, by precisely adjusting the ratio of the metal cation Mg 2+ to Al 3+, the acidity and basicity of the catalysts were optimized and Ni/(4-Mg)AlO with an optimal ratio of 4 presented a considerable C 6+ alcohol yield (25.2%) at even 220 °C, as well as an impressive ethanol conversion of 67.7%. Such an excellent activity achieved at lower temperature was attributed to highly dispersed Ni metal with a Ni( Mg )O solid solution structure, leading to the enormously inhibited aqueous ethanol reforming process and significant increased yield of higher alcohols. The results reveal that the electronic structure and coordination environment of metal sites as well as higher moderately basic and strong acid sites were demonstrated to be beneficial for carbon-chain extension of higher alcohols and ethanol selectivity for dehydrogenation/hydrogenation. Moreover, the number of metal, acid, and base sites should be balanced to inhibit side reactions.