Spent Selective Catalytic Reduction Catalyst Research Articles

Deactivation Mechanism of Spent TiO2-Based Selective Catalytic Reduction (SCR) Catalysts and State-of-the-Art Recycling Technologies.

Nitrogen oxides (NOx) make up a group of gases that are mainly formed during the combustion of fossil fuels at high temperatures. NOx contributes to environmental degradation by forming acid rain and enhancing global warming. Exposure to air with a high concentration of NOx can aggravate respiratory diseases, particularly asthma. The elimination of NOx in practical applications mainly proceeds through selective catalytic reduction (SCR) of NOx with NH3 to harmless N2 and H2O. One practical issue of the SCR process is the deactivation of TiO2-based SCR catalysts. In addition, growing numbers of spent SCR catalysts present a serious waste-management challenge for recyclers at end of life. It is therefore crucial to disclose the deactivation mechanism of the spent TiO2-based NH3-SCR catalysts and propose effective recycling technologies for waste valorization. Here we outline the catalyst deactivation pathways for TiO2-based SCR catalysts and critically review methods of improving the direct sustainability of spent catalysts, in areas such as direct regeneration and recovery of spent catalysts. Through this review, the challenges, solutions, and future strategies for handling spent SCR catalysts are clarified for future studies of application on an industrial scale.

The Separation of Vanadium and Tungsten from Spent Selective Catalytic Reduction Catalyst Leach Solution by Alamine 336

The Separation of Vanadium and Tungsten from Spent Selective Catalytic Reduction Catalyst Leach Solution by Alamine 336

TiO2 recovered from spent selective catalytic reduction catalysts as anode material for lithium-ion batteries

Environmental protection and sustainable development are among the most severe problems in the world today. Spent selective catalytic reduction (SCR) catalysts are recognized as hazardous waste. Here, the TiO2, which accounts for nearly 80% of spent SCR catalysts, is recovered by the alkaline leaching method, and performed higher electrochemical performances than commercial TiO2 products for anode materials of Lithium-ion batteries. W, V, Si, and Al leaching rates are 40.04%, 89.59%, 61.64%, and 11.57%, respectively. A combination of density functional theory (DFT)--based calculations and experiments revealed that trace doping of Al is beneficial to the electrochemical performance of the cell, which helps us tune the Al content in the obtained materials. On this basis, the regenerated TiO2 anode materials with graphene (GR) materials are synthesized to improve the electrochemical performance, and the specific capacity of the recycled TiO2 is 188.5 mAh·g−1 after 500 cycles, and that of the regenerated TiO2/GR is the highest at 275.2 mAh·g−1. Finally, an environmental assessment of this recycling process is also carried out, human toxicity potential, CO2 gas emissions, NMVOC gas emissions, and SO2 gas emissions in this work are reduced by nearly 86.9%, 87.0%, 92.5%, and 87.0% compared with commercial sol-gel synthetic method. This work highlights the significance of recovery for preparing new energy storage materials from secondary resources.

Sustainable solution to the recycling of spent SCR catalyst and its prospective gas sensor application

Nitrogen oxides (NOX) are often produced in industrial combustion processes and are among the most harmful air contaminants. Selective catalytic reduction (SCR) is currently the most effective technology for reducing effluents. Due to increasingly strict environmental regulations, the demand for SCR catalysts has increased, and inevitably, the need to dispose of the spent catalysts has increased and produced an environmental burden. The necessity for disposal while finding secondary sources for the vanadium, tungsten and titanium present in the catalyst makes recycling of spent SCR catalysts a pressing issue. During this investigation, two tertiary amines were compared to determine their effectiveness in extracting vanadium and tungsten from a spent SCR catalyst. The enrichment process was optimized, and the loaded organic solution (9-fold increased concentration) was further stripped to prepare a mixed metal oxide (MMO) based active sensing material for use in H2S gas detection. The H2S gas sensing characteristics of the MMO material were studied systematically. The MMO sensor showed an excellent sensing response to H2S gas with a high sensitivity of 12.73 % for 100 ppm and quick response/recovery times (tr = 101 s/tf = 133 s) at a low operating temperature of 130 °C. In addition, the sensor exhibited enhanced selectivity, long-term stability, and a detection limit of ∼47 ppb to H2S gas. The experimental findings of this work suggest that the recycled materials from spent SCR catalysts could have sustainable potential in reproducing the active sensing catalyst materials for the practical applications in the field of environmental protection.

Preparation of adsorptive TiO2/SiO2 core-shell nanospheres by ultrasonic-coupled alkali leaching process: Synergy of adsorption and photocatalysis towards 2,4-dinitrophenol removal

Spent selective catalytic reduction (SCR) catalysts comprise of abundant valuable TiO2. Therefore, recovery of TiO2 from spent SCR catalysts has highly economic benefits. In this study, an ultrasonic-coupled alkali leaching process was developed for environment-friendly preparation of adsorptive TiO2/SiO2 core-shell nanospheres from spent SCR catalysts. The results show that the synergy of ultrasonic and alkali leaching significantly enhances the separation of other ingredients from TiO2/SiO2, and the addition of NaOH, when compared with the traditional roasting-leaching process, decreases by 70%. The as-prepared adsorptive TiO2/SiO2 core-shell nanospheres exhibit superior adsorptive and photocatalytic performance for 2,4-dinitrophenol removal, and 99.9% of degradation rate was achieved within 120 min under the cooperation between adsorption and photocatalytic oxidation. This study provides a potential method for recycling of valuable adsorptive TiO2/SiO2 core-shell nanospheres from spent SCR catalysts.

Extraction of W, V, and As from spent SCR catalyst by alkali pressure leaching and the pressure leaching mechanism

Spent selective catalytic reduction (SCR) catalysts are environmentally hazardous and resource-enriching. In this work, V, W, and As in a spent SCR catalyst was extracted by alkali pressure leaching. Results showed that the V, W, and As were loaded on the anatase TiO2 crystal grains as amorphous oxides. The optimum pressure leaching conditions were NaOH concentration of 20 wt%, reaction temperature of 180 °C, reaction time of 120 min, L/S of 10 mL/g, and stirring speed of 300 rpm. The leaching efficiency of W, V, and As reached 98.83%, 100%, and 100%, respectively. The experiment revealed the preferential leaching of V and As rather than W, and the leaching mechanisms of V, W, and As were studied through experiment and density functional theory (DFT). The leaching kinetics of W conformed to a variant of the shrinking core model and the leaching process of W is controlled by both chemical reactions and diffusion processes. During the leaching process, Na2Ti2O4(OH)2 product powder layer was generated, which affects the mass transfer of W. The destruction of the TiO2 skeleton in the spent SCR catalyst is essential for adequate W extraction, especially for the extraction of W embedded in the TiO2 lattice. The DFT simulation result indicated that the V and As loaded onto the TiO2 support are easier to absorb hydroxide ions rather than W, and the leaching reaction energy of V and As was lower than W, As, and V has leaching priority over the leaching of W. Furthermore, an anatase TiO2 photocatalyst with the {001} crystal surface exposed was successfully prepared from the alkali pressure leaching residue. This work provides theoretical support for the metal leaching and utilization of spent SCR catalysts via alkali pressure leaching.

Reconstruction and recovery of anatase TiO2 from spent selective catalytic reduction catalyst by NaOH hydrothermal method

The improper disposal of spent selective catalytic reduction (SCR) catalysts causes environmental pollution and metal resource waste. A novel process to recover anatase titanium dioxide (TiO2) from spent SCR catalysts was proposed. The process included alkali (NaOH) hydrothermal treatment, sulfuric acid washing, and calcination. Anatase TiO2 in spent SCR catalyst was reconstructed by forming Na2Ti2O4(OH)2 nanosheet during NaOH hydrothermal treatment and H2Ti2O4(OH)2 during sulfuric acid washing. Anatase TiO2 was recovered by decomposing H2Ti2O4(OH)2 during calcination. The surface pore properties of the recovered anatase TiO2 were adequately improved, and its specific surface area (SSA) and pore volume (PV) were 85 m2·g−1 and 0.40 cm3·g−1, respectively. The elements affecting catalytic abilities (arsenic and sodium) were also removed. The SCR catalyst was resynthesized using the recovered TiO2 as raw material, and its catalytic performance in NO selective reduction was comparable with that of commercial SCR catalyst. This study realized the sustainable recycling of anatase TiO2 from spent SCR catalyst.

Recovery of TiO<sub>2</sub> from spent SCR catalyst by acidolysis and additional crystal seeds-hydrolysis method

In this study, a rapid and efficient method of recovering TiO<sub>2</sub> from spent SCR (selective catalytic reduction) catalyst supplied by a coal-fired power plant in Shanghai was developed. The acid leaching and sodium roasting-water leaching residues (titanium slag) from spent SCR catalyst were employed as the raw material. First, titanium slag was dissolved into H2SO4 solution under different conditions. The optimal acidolysis conditions were 85 wt% H<sub>2</sub>SO<sub>4</sub>, 5.0 g/g acid-residues ratio, 90℃ acidolysis temperature and 2.0 h acidolysis time. Simultaneously, the highest acidolysis efficiency can reach 92.02%. The acidolysis solution was collected and concentrated to 200 g/L (measured by TiO<sub>2</sub> concentration). Then, acidolysis solution was adjusted to pH 0.52-9.15, followed by adding 0-40 mL additional crystal seeds and reacting under certain conditions to obtain the hydrolysis product. The optimal hydrolysis conditions were 25 mL additional crystal seeds, pH 7.46, 120℃ hydrolysis temperature and 3.0 h hydrolysis time. Finally, the recovered product was obtained by roasting hydrolysis product at 700℃ for 2.0 h. The results of hydrolysis stability test indicated that this method can make the hydrolysis efficiency of acidolysis solution stabilize at approximately 90% under optimal conditions. The main component of recovered product was anatase TiO<sub>2</sub> with the purity of 86.88%.

G-C3N4 doping TiO2 recovered from spent catalyst for H2 evolution from water

Spent catalysts of selective catalytic reduction (SCR) contain a high content of TiO2 (>70 wt%). The effective recovery of TiO2 from spent SCR catalysts and its reuse in photocatalytic hydrogen production is of great importance for environmental protection. In this study, the recovered TiO2 from the spent SCR catalyst was recovered by the alkali washing method, and the purity of the recovered TiO2 reached 94.7%. g-C3N4 as a co-catalyst and enhanced the separation efficiency of the photogenerated electron-hole pairs of the TiO2 photocatalyst. The composite photocatalyst R–TiO2/g-C3N4 prepared by directly mixing the recovered TiO2 with g-C3N4 significantly improved the photocatalytic activity. The experimental design of the photocatalyst synthesis was optimized using the Design Expert software. The results showed that the recovered TiO2 was 0.334 g when the g-C3N4 was 0.046 g and the ultrasonic time was 163 min. Moreover, the hydrogen production rate reached 443.105 μmol g−1 h−1 within 4 h.

Recovery of tungsten and titanium from spent SCR catalyst by sulfuric acid leaching process

The widespread use of selective catalytic reduction (SCR) catalysts has resulted in a large accumulation of spent SCR catalysts. These spent catalysts present a significant risk of environmental hazards and potential for resource recovery. This paper presents a feasible process, which works using atmospheric pressure leaching, of tungsten and titanium recovery from spent SCR catalysts. In this new method, titanium and tungsten are simultaneously leached with sulfuric acid as the leaching agent. After hydrolysis and calcination, titanium-tungsten powder with low impurity and reconstructed pore properties was obtained. The optimal conditions for the leaching of Ti and W were as follows: temperature, 150 °C; reaction time, 60 min; H2SO4 concentration, 80 %; mass ratio of H2SO4/TiO2, 3:1; and diluted H2SO4 concentration, 20 % after reaction. With these optimum conditions, the leaching efficiency of Ti and W were found to be 95.92 % and 93.83 %, respectively. The ion speciation and reaction mechanism of W were studied by Raman spectroscopy, FTIR, and UV–vis. The formation of heteropolytungstate with a Keggin structure is essential for the synergistic leaching of Ti and W, as the heteropolytungstate can be stably dissolved in the acid solution. During the hydrolysis process, heteropolytungstate gradually decomposed into Ti4+ and WO42− due to the formation of insoluble Ti(OH)4 from Ti4+ in the solution. This study demonstrated an effective method for synergistic recovery of titanium and tungsten from the spent SCR catalyst.

A Review on Resource Utilization of Spent V-W-Ti Based Selective Catalytic Reduction Catalysts.

To address the environmental pollution caused by nitrogen oxides, V2O5-WO3/TiO2 is widely used as a catalyst based on selective catalytic reduction (SCR) technology. However, spent SCR catalysts pose a potential hazard to the environment due to the presence of heavy metals. This problem continues to plague countries with predominantly thermal power generation, and landfills as the dominant disposal method wastes significant metal resources. Previous research into the recovery of these metal resources has received considerable attention. Here, we summarise the methods of recovery and find that research trends are beginning to move towards improving the added value of recovered products. One very promising application is photocatalysts; however, the atomic efficiency of current methods is not satisfactory. Therefore, this review first focuses on the regeneration of spent SCR catalysts and the processes used for elemental extraction to clarify what forms of V, W and Ti can be obtained from existing processes. This is followed by providing directions for the conversion of spent SCR catalysts into photocatalysts with improvements based on such processes. From a different perspective, this also provides a new resource for photocatalysts and is expected to significantly reduce the cost of photocatalyst production.

Recovery of V2O5 from spent SCR catalyst by H2SO4-ascorbic acid leaching and chemical precipitation

Large amounts of spent selective catalytic reduction (SCR) catalysts were produced in industry after losing their activity. This study developed a clean and effective route of leaching and recovery of vanadium (V) from spent SCR catalyst. First, ascorbic acid (C6H8O6) as the adjuvant can enhance vanadium leaching in H2SO4 solution. The effect parameters of acid concentration, leaching temperature, leaching time and liquid-solid (L/S) ratio on the leaching efficiency of vanadium were investigated. Then, the enrichment of vanadium in the leachate to obtain the black cake was carried out through adjusting pH value. The effects of vanadium concentration and pH on the precipitation efficiency of vanadium were studied. Finally, after alkaline dissolution and oxidation of the black cake, ammonium chloride (NH4Cl) was selected and used as the precipitant to obtain the ammonium poly-vanadate (APV). The final product vanadium pentoxide (V2O5) was obtained through roasting APV at 550 ℃ for 1.0 h. The black cake, APV and V2O5 were analyzed by the characterization of XRD or XRF. This study may introduce a new perspective for the effective usage of vanadium from spent SCR catalyst.

Recovery of Tungsten and Vanadium from Spent Selective Catalytic Reduction Catalysts by Soda Roasting: A Mechanistic Study

This research investigated how soda roasting, which alters the roasting temperature and sodium carbonate concentration, recovers tungsten and vanadium from used selective catalytic reduction (SCR) catalysts. The ideal sodium carbonate content and roasting temperature were determined to be 800 °C and 30 wt%, respectively. Under these circumstances, tungsten and vanadium recoveries were 82.63% and 90.07%, respectively. In order to understand the roasting process, the compositions and morphologies of the original catalyst and specimens after roasting were examined by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. In addition, the thermodynamic parameters associated with this process were calculated using the HSC 6.0 program to confirm compositional changes during roasting, the result shows that the chemical reactions among vanadium, tungsten, titanium and sulfur with sodium carbonate have priority in this system, as V2O5= SO3> WO3> TiO2; And the phases formation of vanadium and titanium are different at different temperatures and the amount of sodium carbonate, such as Na2V2O6, NaVO3, Na3VO4, VO2, Na2O* TiO2, Na2O* 3TiO2, 4Na2O* 5TiO2, and so on. Therefore, the recovery of vanadium and tungsten is significantly influenced by the other catalyst components as well as the reaction conditions. Based on this combination of experimental study and theoretical calculations, a technique for recovering tungsten and vanadium from spent SCR catalysts by soda roasting is suggested.

Iron removal and titanium dioxide support recovery from spent V2O5-WO3/TiO2 catalyst

Iron seriously affects the quality of TiO2 support recovered from spent selective catalytic reduction (SCR) catalyst. In this paper, the iron removal and TiO2 support recovery from spent SCR catalyst were studied. The experiment results suggested that iron exists on the surface and bulk structure of a spent SCR catalyst. The iron deposited on the surface of the spent SCR catalyst was removed by ultrasonic cleaning. The iron remaining in the bulk structure of the spent SCR catalyst was primarily Fe(III) and was adequately removed by NaOH activation and acid washing. The NaOH activation process considerably increased the specific surface area of the spent SCR catalyst. Subsequently, iron was efficiently dissolved through the synergistic effect of sulfuric acid and ascorbic acid. Sulfuric acid dissolved iron in the form of Fe3+, and ascorbic acid promoted iron dissolution by reducing Fe3+ to Fe2+. After the recovery process, 97.1% of the iron in the spent SCR catalyst was removed, and anatase TiO2 was recovered from the spent SCR catalyst. The recovered anatase TiO2 can be used as support material to produce fresh SCR catalyst.

Leaching of vanadium and tungsten from spent V2O5-WO3/TiO2 catalyst by ionic liquids

The V2O5-WO3/TiO2 catalyst has been used for selective catalytic reduction (SCR) of NOx for decades and is named as SCR catalyst. Nine ionic liquids (ILs) were screened to directly leach vanadium and tungsten from the spent SCR catalyst in this work. Effects of leaching temperature, time and catalyst pre-oxidation were evaluated and the pregnant leach solution (PLS) was characterized by nuclear magnetic resonance and Fourier transform infrared to investigate the vanadium leaching route. Results indicate that the basic ILs ([MEA]L, [TMG]L, N2222[L-Pro], N2222[Sar]) and the super acidic IL [Hnmp]HSO4 (pH = −0.43) are effective for V2O5 dissolution, while the neutral ILs and the acidic IL [P(C4H9)3C3H6SO3H][Tf2N] (pH = 0.43) do not work. The vanadium oxide V2O3 cannot be dissolved in the above ILs. Oxidation of the catalyst increases the vanadium leaching efficiency while the particle size of catalyst and temperature have little influence on the leaching efficiency. The vanadium leaching efficiency follows the order of N2222[L-Pro] > N2222[Sar] and [Hnmp]HSO4 > [MEA]L and [TMG]L, with a maximum of about 70%. The dissolved vanadium is in the form of [HnV10O28]n-6 for the basic ILs and [VO2]+ or VO(O2)(OH2)3+ for the acidic IL. These five ILs also have a good ability to leach tungsten from the spent catalyst and the maximum leaching efficiency of tungsten is about 77%.

Studying the leaching mechanism of spent SCR catalyst with different leaching agents (NaOH, H2SO4, HCl and HNO3) using DFT calculations

The leaching mechanism of the spent selective catalytic reduction (SCR) catalyst was investigated by density functional theory (DFT) calculations and experiments. Three models, namely V2O5/TiO2, WO3-V2O5/TiO2, and WO3/TiO2, were created to simulate the spent SCR catalyst. Interaction between the surface clusters and the leaching agents of NaOH, H2SO4, HCl and HNO3 was investigated by DFT calculations. The adsorption site was determined through electrostatic potential and adsorption energy. The calculations showed that NaOH tended to be adsorbed on V and W atoms. H2SO4, HCl and HNO3 tended to be adsorbed on specific O atoms. H2SO4 dissociated on all three models, HCl dissociated on V2O5/TiO2 and WO3-V2O5/TiO2, while HNO3 dissociated only on V2O5/TiO2. The order of leaching ability among leaching agents was NaOH > H2SO4 > HCl > HNO3. Experiments showed that the leaching ratios of V and W in NaOH solution were 82.4% and 54.3%. In acid solution, the leaching ratio of V was 69.0% for H2SO4, 52.5% for HCl, and 42.2% for HNO3, while W was hardly leached out. After acid leaching, the change in the TiO2 lattice parameter was greater than that after alkaline leaching. The experimental results were found to be consistent with the calculations.

Environmentally-friendly harvesting TiO2 nanospheres and V2O5 microrods from spent selective catalytic reduction catalysts

Spent selective catalytic reduction (SCR) catalysts are defined as hazardous wastes because of the toxicity of V2O5 to the ecological environment. Recycling of V2O5 and TiO2 from the spent SCR catalysts has strikingly social and environmental benefits as well as economic values. In this work, a “NaOH ​+ ​Na2CO3” system was employed to recycle 99.2% of anatase/rutile TiO2 nanospheres with a nanospherical morphology from the spent SCR catalysts by a simple sintering-leaching process. The observed photocatalytic performance of anatase/rutile TiO2 nanospheres was higher than that of the other TiO2 recovered from the spent SCR catalysts, commercial TiO2, and chemosynthetic TiO2, which can be ascribed to the enhanced separation of photo-excited electron/hole in a direct Z-scheme of anatase/rutile TiO2 homostructures. Additionally, high-purity V2O5 microrods with high H2S removal performance were efficiently prepared by a hydrothermal method in the leaching solution, which is superior to the traditional method including NH4VO3 precipitation and solvent extraction as the present method can recycle vanadate from low-grade filtrate with a 99.6% of recovery rate. This study develops an alternative method for controlling pollution of vanadate to soil and water and recycling of valuable metals.

Optimization of Roasting Parameters for Recovery of Vanadium and Tungsten from Spent SCR Catalyst with Composite Roasting

Every year, large amounts of selective catalytic reduction (SCR) catalysts with losing catalytic activity and failing to be regenerated need to be regenerated, which will result in acute pollution. Recycling valuable metals from spent SCR catalysts can not only solve environmental problems, but also save resources. The process of sodium roasting and water leaching is able to effectively extract vanadium (V) and tungsten (W) from spent SCR catalysts. To improve the efficiencies of V and W, different sodium additives were first investigated in the roasting process. The results revealed that the process of NaCl-NaOH composite roasting and water leaching showed superior leaching efficiencies of V and W, which can reach 91.39% and 98.26%, respectively, and simultaneously, it can be found that adding low melting point NaOH promoted mass transfer as compared with the melting points of different sodium additives. Next, a single-factor experiment was conducted to investigate different roasting conditions, such as roasting temperature, roasting time, mass ratio of sodium additive and catalyst, and mass ratio of NaCl and NaOH, on the leaching efficiencies of V and W. Then, a three-level and four-factor orthogonal experiment and a weight matrix analysis were used to optimize the roasting parameters. The results showed that roasting temperature had the most significant effect on the leaching efficiencies of V and W, and the optimal roasting conditions were as follows: the roasting temperature was 750 °C, the roasting time was 2.5 h, the mass ratio of sodium additive and catalyst was 2.5, and the mass ratio of NaCl and NaOH was 1.5. Under the optimal roasting conditions, the leaching efficiencies of V and W were 93.25% and 99.17%, respectively. The results of XRD analysis inferred that VO2 coming from the decomposition of VOSO4 in spent SCR catalysts may first oxidize into V2O5 and then react with sodium additives to produce NaVO3. The formation of titanium-vanadium oxide ((Ti0.5V0.5)2O3) was a part reason of hindering the leaching of vanadium. With the increase of roasting temperature, TiO2 converted into Na2Ti3O7, which indicated that the main structure of the catalyst was destroyed, and simultaneously, more characteristic peaks of sodium metavanadate and sodium tungstate appeared, thus enhancing the leaching of V and W. Finally, it can be seen that the process of NaCl-NaOH roasting and water leaching remained higher leaching efficiencies of V and W and lower roasting temperature by comparing with leaching efficiencies of V and W in different processes of recycling SCR catalyst. The process of NaCl-NaOH composite roasting and water leaching provided a strategy with a highly efficient and clean route to leach V and W from spent SCR catalyst. The orthogonal experiment and weight matrix analysis in our study can be used as a reference to optimize the reaction conditions of a multiple indexes experiment.

A clean and efficient approach for recovery of vanadium and tungsten from spent SCR catalyst

The widespread use of selective catalytic reduction (SCR) catalysts will provide many waste SCR catalysts. These spent catalysts can be identified as hazardous solid waste because they contain a lot of heavy metals. This work aims to develop a clean, green, and economical way to recover valuable metals and regenerate the catalyst. The effect parameters of hydrogen peroxide and ammonium carbonate concentration, time, and temperature on the V and W leaching efficiencies were investigated. The leaching process can be described by a shrinking core model (SCM). The raw material and the residue were characterized by XRD, SEM-EDS, XPS, and Raman analysis. The crystal structure of the leaching residue was stable through the leaching process and can serve as a carrier for the regenerated catalyst. Ammonium paratungstate (APT) and vanadium pentoxide were obtained. This work may introduce a new perspective for the efficient and comprehensive usage of the spent SCR catalyst.

Environment-Friendly Preparation of Adsorptive TiO <sub>2</sub>/SiO <sub>2</sub> Core-Shell Nanospheres and V2o5 Microrods from Spent SCR Catalysts by Ultrasonic-Coupled Alkali Leaching Process

Spent selective catalytic reduction (SCR) catalysts comprising of valuable V2O5 and TiO2 are usually disposed as hazardous waste because of the toxic V2O5 ingredients. Therefore, recovery of V2O5 and TiO2 from spent SCR catalysts has highly environmental benefits as well as economic value. In this study, an ultrasonic-coupled alkali leaching process was developed for environment-friendly preparation of adsorptive TiO2/SiO2 core-shell nanospheres and V2O5 microrods from spent SCR catalysts. The results show that the synergy of ultrasonic and alkali leaching significantly enhance the separation of V2O5 from spent SCR catalysts, and the addition of NaOH decreases by 70% compared with the traditional roasting-leaching process. The as-prepared adsorptive TiO2/SiO2 core-shell nanospheres exhibit superior adsorptive and photocatalytic performance for 2,4-dinitrophenol removal, and 99.9% of 2,4-dinitrophenol was oxidized within 120 min. In addition, high-purity V2O5 microrods with high H2 S removal rate were efficiently prepared from low-grade filtrate using a hydrothermal precipitation method, which was superior to the traditional NH4VO3 precipitation and solvent extraction process. This study provides a potential method for controlling the environmental pollution of V2O5 and recycling of valuable adsorptive TiO 2 /SiO 2 core-shell nanospheres and V2O5 microrods from spent SCR catalysts.