Seawater derived magnesia-copper nanostructured mixed oxide catalyst for oxidant-selective aqueous oxidation of benzyl alcohols

The seawater is directly utilized as an abundant and sustainable source of magnesium for in situ co-precipitation with transition metal salts of Cu, Fe, Mn, Ni, Co, etc., to prepare the marine magnesia-metal nanostructured mixed oxides (Cu-O-Mg, Fe-O-Mg, Mn-O-Mg, Ni-O-Mg, Co-O-Mg, etc.) and demonstrated as cooperative base-redox catalysts. Among all, the catalyst Cu-O-Mg was prepared using 0.5 Eq. CuCl2:1 Eq. Mg in seawater (Cu loading of 16.7%) expedited the highest efficiency for the selective oxidation of benzyl alcohols to benzaldehydes and benzoic acids with broad substrate scope in water as a solvent at reflux conditions for 8 and 10 h. The catalyst governed the oxidant tuning product selectivity, as hydrogen peroxide (H2O2) selectively endorses the partial oxidation of benzyl alcohols to benzaldehydes, while tert-butyl hydroperoxide (TBHP) overoxidizes benzaldehydes to benzoic acid with good to excellent yields. The reaction followed a non-radical pathway unveiled by controlled experiments. Comprehensive characterization of the catalysts by FT-IR, XRD, XPS, SEM, TEM, BET, and TGA, etc., confirmed the structural features of the active phases and revealed the formation of Cu-O-Mg (OH) species during the reaction, suppressing copper leaching, and introduced basic sites essential for alcohol and oxidant activation. This heterogeneous, nanostructured, recyclable catalytic system retains its activity over six consecutive runs, underscoring its potential for a sustainable oxidation protocol.