Completely Inorganic Deep Eutectic Solvents for Efficient and Recyclable Liquid-Liquid Interface Catalysis

Organic acid-based deep eutectic solvents (DESs) as catalysts always suffer from weak stability and low recyclability due to the accumulation of organic oxidative products in the DES phase. Herein, a completely inorganic deep eutectic solvent (IDES) ZnCl2/PA with zinc chloride (ZnCl2) and phosphoric acid (PA) as precursors is constructed to realize liquid-liquid interface catalysis for desulfurization of fuel and product self-separation for the first time. Owing to the inorganic nature, the organic oxidative products are accumulated at the interface between the IDES and fuel rather than the IDES phase. With this unique feature, the IDES can be reused for at least 15 times without any further treatment in oxidative desulfurization process, showing a state-of-the-art cycle-regeneration stability. Moreover, compared with the reported organic DESs, the IDES also reveals more attractive catalytic oxidative desulfurization performance. Experimental and theoretical studies indicate that the strong coordination Zn<middle dot><middle dot><middle dot>O & boxH;P and the strong adsorption energy between IDES and sulfides enhance the activation of H2O2 to reactive oxygen species, leading to the superior catalytic performance in oxidative desulfurization of fuel. A completely inorganic deep eutectic solvent (IDES) is synthesized by ZnCl2 and phosphoric acid through hydrogen bonding (Cl<middle dot><middle dot><middle dot>H & horbar;O) and coordination (Zn<middle dot><middle dot><middle dot>O & boxH;P). Due to the presence of composite catalytic active site (Zn<middle dot><middle dot><middle dot>O & boxH;P), the IDES could convert the oxidant into a triple reactive oxygen species with stronger oxidation ability, leading to rapid and efficient oxidation removal of thiophenes from fuel. image