Strategy and Technical Progress of Recycling of Spent Vanadium-Titanium-Based Selective Catalytic Reduction Catalysts

Abstract

Selective catalytic reduction denitration technology, abbreviated as SCR, is essential for the removal of nitrogen oxide from the flue gas of coal-fired power stations and has been widely used. Due to the strong demand for energy and the requirements for environmental protection, a large amount of SCR catalyst waste is produced. The spent SCR catalyst contains high-grade valuable metals, and proper disposal or treatment of the SCR catalyst can protect the environment and realize resource recycling. This review focuses on the two main routes of regeneration and recycling of spent vanadium-titanium SCR catalysts that are currently most widely commercially used and summarizes in detail the technologies of recycling, high-efficiency recycling, and recycling of valuable components of spent vanadium-titanium SCR catalysts. This review also discusses in depth the future development direction of recycling spent vanadium-titanium SCR catalysts. It provides a reference for promoting recycling, which is crucial for resource recovery and green and low-carbon development.

Figure 1

(a) Schematic diagram of the NO_x pollution pathway. Reproduced with permission from ref (5). Copyright 2023 Elsevier. (b) NO_x emissions from China, the US, and the EU over the past decade. Reproduced with permission from ref (8). Copyright 2023 Elsevier. (c) SCR technology denitration device structure and production process. Reproduced with permission from ref (9). Copyright 2023 Elsevier.

Figure 2

(a) Catalytic scheme for NO_x removal. (b) Mechanism of the catalytic reduction step of the monomeric VO₃H/TiO₂ (001) model. Reproduced with permission from ref (31). Copyright 2020 Elsevier.

Figure 3

Images of spent SCR catalyst before and after ultrasonic water cleaning. Reproduced with permission from ref (28). Copyright 2022 Elsevier.

Figure 4

(a) Flowchart of the OABL treatment process for spent V₂O₅–WO₃/TiO₂ catalysts and (b) NO conversion of fresh catalyst, spent catalyst, and catalyst regenerated by the OABL process. Reproduced with permission from ref (27). Copyright 2018 Elsevier.

Figure 5

(a) Mechanism of deactivation of As-poisoned V₂O₅–WO₃/TiO₂ catalyst and regeneration by H₂SO₄ scrubbing. Reproduced with permission from ref (72). Copyright 2020 Elsevier. (b) Regeneration with EDTA-2Na in combination with H₂SO₄ solution. Reproduced with permission from ref (71). Copyright 2016 Elsevier. (c) Regeneration of alkali metal-poisoned spent V₂O₅–WO₃/TiO₂ catalyst by acetic acid and sulfuric acid pickling.

Figure 6

Process flow of stepwise alkali-acid leaching. Reproduced with permission from ref (77). Copyright 2019 Elsevier.

Figure 7

(a) Electrochemical detoxification and recovery of As-poisoned V₂O₅–WO₃/TiO₂ catalysts. (b) Comparison of SCR performance of regenerated catalysts recovered by electrochemical detoxification with fresh and spent catalysts. Reproduced with permission from ref (82). Copyright 2017 Elsevier. (c) Schematic diagram of the preparation of electrothermal alloy-embedded V₂O₅–WO₃/TiO₂ catalysts. Reproduced with permission from ref (83). Copyright 2022 Elsevier.

Figure 8

Spent SCR catalyst valuable metal recovery process.

Figure 9

Selective leaching process of V and Fe with oxalic acid. Reproduced with permission from ref (90). Copyright 2018 Elsevier.

Figure 10

(a) Process flow of the simultaneous leaching of W and Ti with H₂SO₄ to reconstruct the pore properties. (b) Effect of acid digestion parameters (time, H₂SO₄ concentration, temperature, H₂SO₄/TiO₂ mass ratio, diluted H₂SO₄ concentration) on leaching efficiency and effect of diluted H₂SO₄ concentration on the leaching concentration of Ti and W. Reproduced with permission from ref (26). Copyright 2023 Elsevier.

Figure 11

W and Ti recovery process using (NH₄)₂CO₃/H₂O₂ leaching. Reproduced with permission from ref (93). Copyright 2021 Elsevier.

Figure 12

NaOH solution roasting leaching process.

Figure 13

(a) Na₂CO₃–NaCl–KCl molten salt roasting-leaching method to recover titanium dioxide and sodium titanate nanowires TiO₂/STNWs from spent V₂O₅–WO₃/TiO₂ catalysts as Cd(II) adsorbent. Reproduced with permission from ref (29). Copyright 2018 Elsevier. (b) Na₂CO₃–NaCl Yungan roasting process to recover TiO₂/STNWs from spent V₂O₅–WO₃/TiO₂ catalysts and extract and separate W and V. Reproduced with permission from ref (102). Copyright 2020 Elsevier.

Figure 14

Recovery of W from spent V₂O₅–WO₃/TiO₂ catalyst by the roasting–HCl decomposition–NaOH leaching–precipitation process for the synthesis of CaWO₄. Reproduced with permission from ref (104). Copyright 2018 Elsevier.

Figure 15

Strong base leaching of spent SCR catalyst followed by W extraction through a strong base anion exchange resin process.

Figure 16

Separation processes of V, Mo, and W in alkaline leachate from spent SCR catalysts using acidified primary amine N1923 as extractant. Reproduced with permission from ref (109). Copyright 2022 Elsevier.

Figure 17

Process flow for the production of sustainable TiO₂ photocatalytic materials using Ti recycled from waste SCR catalysts.

Figure 18

(a) Simultaneous treatment of spent V₂O₅–WO₃/TiO₂ catalysts, Ti-bearing blast furnace slag, and Al alloy scrap to prepare Ti₅Si₃ and Ti₅Si₄–TiAl₃ alloys. Reproduced with permission from ref (116). Copyright 2022 Elsevier. (b) Sustainable recycling of TiO₂ from spent V₂O₅–WO₃/TiO₂ catalysts by molten salt electrolysis. Reproduced with permission from ref (118). Copyright 2021 Elsevier. (c) Preparation of anatase/rutile TiO₂ nanospheres and V₂O₅ microrods from spent V₂O₅–WO₃/TiO₂ catalysts. Reproduced with permission from ref (117). Copyright 2021 Elsevier. (d) Preparation of Ti-FA photocatalysts from spent V₂O₅–WO₃/TiO₂ catalysts. Reproduced with permission from ref (110). Copyright 2022 Elsevier.

Figure 19

(a) Process of Fe removal and TiO carrier recovery from spent V₂O₅–WO₃/TiO₂ catalyst. (b) Mechanism of Fe dissolution in spent V₂O₅–WO₃/TiO₂ catalyst by a combination of H₂SO₄ and ascorbic acid. Reproduced with permission from ref (28). Copyright 2022 Elsevier. (c) Schematic diagram of the acid digestion reaction process of spent V₂O₅–WO₃/TiO₂ catalyst. Reproduced with permission from ref (26). Copyright 2023 Elsevier.

Figure 20

(a) Hydrogen reforming with a catalyst prepared from spent V₂O₅–WO₃/TiO₂. Reproduced with permission from ref (123). Copyright 2020 Elsevier. (b) Schematic diagram of the degradation mechanism of methylene blue (MB) over ZMF@S10. Reproduced with permission from ref (121). Copyright 2022 Elsevier. (c) Solid phase synthesis process of perovskite powder using CaCO₃ and spent SCR catalyst as raw materials. Reproduced with permission from ref (122). Copyright 2022 Elsevier.