Boosting Photothermal Synergistic Catalysis of Amine Carbonylation with CO 2 over K-Promoted Spinel Co 2 AlO 4 Nanosheets from Hydrotalcite

The catalytic synthesis of N, N ′-dialkylureas from CO 2 and amines offers a sustainable route for carbon utilization yet remains constrained by inefficient catalysis. Herein, a K + -doped CoAl-layered double oxide (K(0.3)-CoAl-LDO) is presented, which addresses this challenge through a pronounced photothermal effect. K + doping triggers a charge compensation mechanism (2K + → 2M 3+ + O v ), generating abundant oxygen vacancies within an expanded lattice. These vacancies serve as Lewis bases for CO 2 activation, while adjacent Co 3+ cations function as Lewis acids for amine adsorption, establishing synergistic active sites that collectively lower the reaction energy barrier. Simultaneously, K + doping narrows the bandgap to 1.73 eV and enhances charge separation, improving light absorption and electron transfer. As a result, K(0.3)-CoAl-LDO achieves a 68.81% yield of N, N ′-dibutylurea under mild conditions (110 °C, 1.0 MPa)─a 2.4-fold increase over the undoped analogue. By using PEG 400 as a reaction-promoting medium, the urea yield can be further increased to 98.41%. The catalyst also demonstrates broad substrate generality and retains a high stability over five cycles. This work establishes a generalizable doping strategy for precisely engineering defect sites and acid–base pairs in layered oxides, providing a powerful blueprint for the rational design of advanced photothermal catalysts for efficient CO 2 conversion under mild conditions.