Catalysts for Water Treatment

Mechanism of Heterogeneous Catalytic Oxidation and Degradation of Pollutants

• Heterogeneous Fenton Catalysis

The Fenton catalytic oxidation reaction chain system is as follows:

Figure 1. The schematic of the heterogeneous Fenton catalytic process.[1]

• Heterogeneous photocatalysis



• Heterogeneous electrocatalysis

Electrocatalysis is a kind of catalysis that accelerates the charge transfer reaction between the electrode and the electrolyte. Electrocatalysis is mainly used for the treatment of organic wastewater, the degradation of chromium-containing wastewater, the desulfurization of flue gas and raw coal, the simultaneous removal of NO_x and SO₂, and the reduction of carbon dioxide and nitrogen.

• Common catalysts for pollutants

The comparison of the degradation of different pollutants by some catalysts is shown below.

Figure 2. Comparison of catalysts for pollutant degradation. [1]

Catalyst for Heterogeneous Catalytic Ozonation

• Heterogeneous catalytic ozonation has potentially higher efficiency in the degradation and mineralization of refractory organic pollutants, and has less negative impact on water quality. Cobalt-based catalysts (such as Co/SiO₂, CoO_x/Al₂O₃, CoMgAl and CoNiAl, etc.) have been used in ozonolysis studies, but their stability is insufficient, and a large amount of Ni²⁺ will remain in the solution. Recent studies have shown that MnO_x, CoO_x or CuO_x can be anchored on the surface of mesoporous ZrO₂ or γ-Al₂O₃ by interacting with the surface hydroxyl groups of the carrier, which improves the catalytic efficiency and stability, and can be used for difficult-to-degrade organic compounds in mineralized water.

Figure 3. The removal of TOC during the degradation of 2,4-D in aqueous dispersions of various catalysts with ozone. [2]

Catalyst for Ultrasonic-Assisted Water Treatment

• Ultrasonic combined catalyst is used in water treatment, which can effectively improve the removal rate of organic pollutants and reduce energy consumption. Among all types of catalysts, iron-based catalysts have the greatest potential due to their low cost, high safety and wide distribution. Zero-valent iron (ZVI), Fe₂(SO₄)₃, FeSO₄, FeCl₃, and FeOOH have long been used in water treatment.

Figure 4. Schematic diagram of the mechanism of sonocatalytic degradation. [3]

References

1. Ting Zhang. (2019). "Heterogeneous Catalytic Process for Wastewater Treatment." Advanced Oxidation Processes - Applications, Trends, and Prospects.
2. Dapeng LI. (2009). "The progress of catalytic technologies in water purification: A review." Journal of Environmental Sciences 21(6): 713-719.
3. Nan Zhang. (2018). "Iron Based Catalysts Used in Water Treatment Assisted by Ultrasound: A Mini Review." Frontiers in Chemistry 6: 12.