Heterogeneous Mn@CeO₂ Catalyst for α-Alkylation of Ketones with Alcohols via Hydrogen-Borrowing Strategy

Construction of a C-C bond via alkylation of ketones with alcohol as the alkylating source by employing hydrogen-borrowing strategy is attracting significant attention and is highly appealing due to its simplicity, cost-effectiveness, environmental benefits, and the fact that water is the only byproduct. The development of heterogeneous catalysts based on nonprecious base metals is progressing rapidly. Our newly disclosed manganese-doped cerium oxide nanocomposite (10 wt % Mn@CeO₂) stands out as a cost-efficient and air-stable catalyst, synthesized through a straightforward coprecipitation method and employed for α-alkylation of ketones with primary alcohols via the hydrogen-borrowing strategy. X-ray diffraction (XRD) analysis confirms the high crystallinity of CeO₂, while field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) images reveal MnO₂ nanoparticles, measuring 19 nm in size, uniformly decorated on the rod-shaped CeO₂ nanoparticles, which have a size of 33 nm. X-ray photoelectron spectroscopy (XPS) analysis uncovers the presence of Mn⁴⁺ species embedded on the CeO₂ nanorods. Electron paramagnetic resonance (EPR) analysis further indicates that surface defects contribute to the impressive catalytic yield, which ranges from 70 to 98% for the α-alkylated ketones. Thermogravimetric analysis (TGA) demonstrates the remarkable thermal stability of the catalyst, maintaining its stability up to 800 °C. Additionally, inductively coupled plasma mass spectrometry (ICP-MS) confirms no leaching of Mn ions, emphasizing the high heterogeneity of the catalyst. Remarkably, 10 wt % Mn@CeO₂ nanocomposite is recycled for six cycles with no loss of catalytic activity. This study underscores the synergistic effect between the base metal MnO₂ and redox pair of CeO₂, which is key to the exceptional catalytic activity in α-alkylation reactions, making 10 wt % Mn@CeO₂ a highly promising catalyst for sustainable and efficient C-C bond formation.