Heterogeneous catalyst of cobalt phthalocyanine tetrasulfonamide loaded on Ca–Al hydrotalcites for oxidative desulfurization of spent sulfidic caustic

Background Spent sulfidic caustic (SSC) from petrochemical and other chemical industries usually contains high concentrations of sulfur ion (S 2− ) and caustic soda (NaOH), which requires effective treatment. Here a CoPcSA/CaAl-LDHs catalyst was successfully synthesized by using a facile one-pot approach for loading cobalt phthalocyanine tetrasulfonamide (CoPcSA) on Ca–Al hydrotalcites (CaAl-LDHs). The material characterization included powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. Results The effect of various parameters such as reaction temperature, catalyst dosage and aeration rate on the catalytic activity was investigated and optimized to be 75 °C, 1.5 mmol L −1 and 2.5 L min −1 , respectively. CoPcSA/CaAl-LDHs shows very high catalytic efficiency for S 2− removal: a 95.0% S 2− removal can be achieved at extremely high concentration of S 2− (24 000 mg L −1 ). In addition, the catalyst exhibits high stability and reusability even after 8 cycles of reuse. Conclusion CoPcSA/CaAl-LDHs exhibits outstanding catalytic activity and stability, showing impressive potential in practical application. © 2025 Society of Chemical Industry (SCI).