High-Selective Upgrading of Ethanol to C<sub>4–10</sub> Alcohols over Hydroxyapatite Catalyst with Superior Basicity

The\ncatalytic upgrading of renewable ethanol to C<sub>4–10</sub> alcohols via C–C coupling offers a green and negative-carbon-emission\npathway toward value-added compounds. The manipulation of catalysts’\nsurface basic and acidic properties is the key to achieve high-selectivity\nC<sub>4–10</sub> alcohols. In this study, we present a solvent-free\nmechanochemical approach for the synthesis of hydroxyapatite (HAP)\ncatalysts with enhanced basicity. The selectivity for a total C<sub>4–10</sub> alcohols reaches 97.8% with a yield of 53.9% at\n325 °C and 0.1 MPa, surpassing previously reported catalysts\nin the literature. The mechanochemically synthesized HAP catalysts\nextend along the <i>c</i>-axis and expose the (002) crystal\nplane with enriched strong basic [Ca–O–P] sites. CO<sub>2</sub>-TPD and XPS analyses demonstrated that the hydrogen bonds\nbetween the oxygen atoms of adjoining phosphate groups enhance the\nbasic property of the catalyst surfaces. The kinetic measurements\nhave demonstrated that the abundance of strong basic sites facilitates\nthe adsorption of ethanol molecules and accelerates the rate of C–C\ncoupling reactions, which is responsible for a high yield of C<sub>4–10</sub> alcohols. This work offers a sustainable approach\nfor synthesizing such alcohols and stimulates the advancement of environmentally\nfriendly catalysts.