Copper-doped manganese dioxide catalyst rich in oxygen defects as well as preparation method and application of copper-doped manganese dioxide catalyst

Abstract

The invention provides a preparation method of an oxygen-defect-enriched copper-doped manganese dioxide catalyst, which is characterized in that potassium permanganate and copper nitrate are used as precursors, oxalic acid is used as a reducing agent, and an oxygen-defect-enriched copper-doped manganese dioxide material is synthesized through a redox coprecipitation method. A series of characterization proves that the composite material is successfully synthesized and shows excellent low-temperature activity of catalytic oxidative degradation of toluene due to the fact that the specific surface area of the catalyst is increased due to the coralline porous form of the composite material, and more reaction active sites are provided by the synergistic effect of oxygen deficiency and copper species. The catalyst has excellent performance in 12-hour stability and water vapor resistance tests, and has the advantages of stability, high efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental catalytic purification, and specifically relates to an oxygen-defective copper-doped manganese dioxide catalyst, a preparation method and an application thereof. Background Art

[0002] Air pollution is one of the most prominent environmental problems facing my country and one that the public is most concerned about. 2.5 and O 3 The situation of atmospheric complex pollution with characteristic pollutants remains severe. Volatile organic compounds (VOCs) are an important component of my country's atmospheric pollutants. Toluene and other benzene-based volatile organic compounds not only harm the central nervous system and have strong teratogenic, carcinogenic and mutagenic effects, but are also closely related to the formation of atmospheric photochemical smog and aerosols, generating more toxic photochemical smog, which is extremely harmful to human health and the environment. The prevention and control of source VOCs is related to PM 2.5 and O 3 Among various VOCs elimination technologies, catalytic oxidation technology can convert VOCs into non-toxic or environmentally friendly CO at temperatures far below direct combustion. 2 and H 2 O, with the characteristics of high purification efficiency, no secondary pollution, and low energy consumption, has attracted much attention from researchers. Precious metal catalysts are currently the most commonly used high-efficiency thermal oxidation catalysts, but their high economic cost and scarce resources force the research and development of low-cost, easily available, and highly active transition metal catalysts to replace precious metal catalysts.

[0003] MnO 2 Low price, abundant resources, environmental friendliness and unique physical and chemical properties, such as special pore structure, high specific surface area and porosity, multivalent state, and excellent oxygen storage / release capacity, have made MnO an important candidate material for catalytic combustion catalysts. 2 The catalyst still has the problems of poor low temperature activity, poor activity stability and lack of active sites. In order to solve such problems, MnO is mainly modified by regulating surface area and morphology, crystal form, crystal surface and composite system. 2 The catalyst performance is optimized. 2 The modification strategies are often costly, cumbersome and not conducive to large-scale industrial application production. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is to provide an oxygen-defective copper-doped manganese dioxide catalyst and a preparation method and application thereof, so as to overcome the problems that the manganese dioxide prepared by the prior art has poor low-temperature activity, poor activity stability and small active surface, high cost of performance optimization, cumbersome steps and is not suitable for large-scale industrial production.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst comprises the following steps: Step 1: dissolving potassium permanganate and copper nitrate in deionized water and ultrasonically treating the solution to obtain solution A; Step 2: dissolving oxalic acid in deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath and stir to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it, and calcine it in an air atmosphere to obtain a copper-doped manganese dioxide catalyst rich in oxygen defects.

[0007] Preferably, the molar ratio of potassium permanganate to copper nitrate is 1:(0.03-0.2).

[0008] Preferably, potassium permanganate and copper nitrate are dissolved in deionized water and ultrasonically treated for 10 to 30 minutes.

[0009] Preferably, the molar ratio of potassium permanganate to oxalic acid is 1:1.8.

[0010] Preferably, the mixed solution is stirred in a water bath at 50-80 °C for 5-7 h.

[0011] Preferably, the precipitate is washed and centrifuged, then dried at 90-110 °C for 8-12 h, and then calcined at 300-600 °C at a heating rate of 5-10 °C / min for 2-5 h in an air atmosphere.

[0012] Preferably, the oxygen-deficient copper-doped manganese dioxide has oxygen defects and copper species co-modified.

[0013] The present invention also provides an application of an oxygen-defect-rich copper-doped manganese dioxide catalyst. The oxygen-defect-rich copper-doped manganese dioxide catalyst prepared by the above preparation method is used as a thermal catalyst.

[0014] Preferably, the oxygen-defect-rich copper-doped manganese dioxide catalyst is used for catalytic oxidation degradation of toluene.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention improves the preparation method, so that the prepared oxygen-defect-rich copper-doped manganese dioxide has a huge specific surface area. Under the synergistic effect of oxygen defects and Cu species, the adsorption of oxygen and toluene by the catalyst is enhanced, the generation of surface active oxygen species is accelerated, the number of surface active center sites is increased, and the catalytic oxidation degradation performance of volatile organic compounds in the air such as toluene is excellent. Under the reaction condition of 220°C, the degradation of ppb-level toluene in the air is close to 100%, and it has broad application prospects in the field of environmental pollution control.

[0017] 2. With the original MnO 2 In comparison, the oxygen-deficient Cu-doped MnO2 has a higher catalytic activity for toluene oxidation. T 90 (When the toluene conversion rate is 90%, the required reaction temperature) shifts to the low temperature direction by 83 °C; compared with the commercial precious metal catalyst Pt / Al 2 O 3 , oxygen-defect-rich copper-doped manganese dioxide for toluene T 90 Shift towards low temperature by 24 °C.

[0018] 3. The preparation method of the present invention has a simple operation process, mild reaction conditions, low equipment requirements, and the obtained oxygen-defective copper-doped manganese dioxide has excellent catalytic stability and water resistance, and has industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The XRD spectra of the samples obtained in Examples 1 to 5 of the present invention are shown in FIG.

[0020] Figure 2 (ac) transmission electron microscope images, (d) high-angle annular dark field scanning transmission image, and (eh) EDS element mapping images of O, Mn and Cu (the inset is the selected electron diffraction pattern (SAED)) of the sample obtained in Example 4 of the present invention.

[0021] Figure 3 Specific surface area (a) and pore size distribution diagram (b) of the samples obtained in Example 1 and Example 4 of the present invention.

[0022] Figure 4 The EPR spectra of the samples obtained in Examples 1 and 4 of the present invention are shown in FIG.

[0023] Figure 5 XPS spectra of the samples obtained in Examples 1 to 5 of the present invention: (a) Mn 2p, (b) O 1s, and (c) Cu 2p.

[0024] Figure 6 is the H of the samples obtained in Examples 1 and 4 of the present invention 2 -TPR spectrum.

[0025] Figure 7 O of the samples obtained in Example 1 and Example 4 of the present invention 2 -TPD spectrum.

[0026] Figure 8 The samples obtained in Examples 1 to 5 of the present invention and commercial Pt / Al 2 O 3 Catalytic oxidation activity of toluene.

[0027] Fig. 9 The toluene catalytic oxidation stability and water resistance of the sample obtained in Example 4 of the present invention were tested. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Example 1 MnO 2 Catalyst preparation Step 1: Dissolve 3.1606 g potassium permanganate in 40 mL deionized water and ultrasonicate for 15 min to obtain solution A; Step 2: Dissolve 3.2411 g of oxalic acid in 35 mL of deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath at 70 °C with stirring for 6 h to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it at 100 °C for 12 h, and calcine it at 400 °C at a rate of 10 °C / min for 3 h in an air atmosphere to obtain MnO 2 catalyst.

[0030] Figure 1 The MnO obtained in this example is shown 2 The XRD spectrum of the catalyst shows that MnO 2 Catalyst in 2 θ =12.9°, 18.1°, 28.8°, 36.7°, 37.5° and 49.9°, respectively, which are attributed to typical MnO 2 (JCPDS PDF#44-0141) The XRD peaks of the {110}, {200}, {310}, {400}, {211}, {411} and {521} planes of the crystalline phase indicate that the single-component MnO 2 Generation of.

[0031] A fixed bed reactor was filled with 50 mg of the obtained MnO 2 The catalyst was prepared by mixing 1 vol.% toluene with balanced air. The toluene concentration was controlled by adjusting the ratio of the two gas flows to the initial toluene concentration (1000 ppm) entering the fixed bed reactor. The gas flow rate was controlled at 50 mL / min, corresponding to a gas mass space velocity of 60,000 mL·g -1 ·h -1 The toluene content in the mixed air before and after the reaction was detected online by gas chromatography equipped with a FID detector. The toluene degradation rate was calculated by X = (1-C out / C in )*100%, where C in is the initial toluene concentration, C out is the toluene concentration after the reaction.

[0032] Example 2 Cu 0.03 Mn 1 O x Catalyst preparation Step 1: Mix 3.1606 g potassium permanganate and 0.1618 g Cu(NO 3 ) 2 ·3H 2 O was dissolved in 40 mL of deionized water and sonicated for 15 min to obtain solution A; Step 2: Dissolve 3.2411 g of oxalic acid in 35 mL of deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath at 70 °C with stirring for 6 h to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it at 100 °C for 12 h, and calcine it at 400 °C at a rate of 10 °C / min for 3 h in an air atmosphere to obtain Cu 0.03 Mn 1 O x catalyst.

[0033] A fixed bed reactor was filled with 50 mg of the obtained Cu 0.03 Mn 1 O x The catalyst was prepared by mixing 1 vol.% toluene with balanced air. The toluene concentration was controlled by adjusting the ratio of the two gas flows to the initial toluene concentration (1000 ppm) entering the fixed bed reactor. The gas flow rate was controlled at 50 mL / min, corresponding to a gas mass space velocity of 60,000 mL·g -1 ·h -1The toluene content in the mixed air before and after the reaction was detected online by gas chromatography equipped with a FID detector.

[0034] Example 3 Cu 0.05 Mn 1 O x Catalyst preparation Step 1: Mix 3.1606 g potassium permanganate and 0.2416 g Cu(NO 3 ) 2 ·3H 2 O was dissolved in 40 mL of deionized water and sonicated for 15 min to obtain solution A; Step 2: Dissolve 3.2411 g of oxalic acid in 35 mL of deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath at 70 °C with stirring for 6 h to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it at 100 °C for 12 h, and calcine it at 400 °C at a rate of 10 °C / min for 3 h in an air atmosphere to obtain Cu 0.05 Mn 1 O x catalyst.

[0035] A fixed bed reactor was filled with 50 mg of the obtained Cu 0.05 Mn 1 O x The catalyst was prepared by mixing 1 vol.% toluene with balanced air. The toluene concentration was controlled by adjusting the ratio of the two gas flows to the initial toluene concentration (1000 ppm) entering the fixed bed reactor. The gas flow rate was controlled at 50 mL / min, corresponding to a gas mass space velocity of 60,000 mL·g -1 ·h -1 The toluene content in the mixed air before and after the reaction was detected online by gas chromatography equipped with a FID detector.

[0036] Example 4 Cu 0.1 Mn 1 O x Catalyst preparation Step 1: Mix 3.1606 g potassium permanganate and 0.4832 g Cu(NO 3 ) 2 ·3H 2 O was dissolved in 40 mL of deionized water and sonicated for 15 min to obtain solution A; Step 2: Dissolve 3.2411 g of oxalic acid in 35 mL of deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath at 70 °C with stirring for 6 h to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it at 100 °C for 12 h, and calcine it at 400 °C at a rate of 10 °C / min for 3 h in an air atmosphere to obtain Cu 0.1 Mn 1 O x catalyst.

[0037] A fixed bed reactor was filled with 50 mg of the obtained Cu 0.1 Mn 1 O x The catalyst was prepared by mixing 1 vol.% toluene with balanced air. The toluene concentration was controlled by adjusting the ratio of the two gas flows to the initial toluene concentration (1000 ppm) entering the fixed bed reactor. The gas flow rate was controlled at 50 mL / min, corresponding to a gas mass space velocity of 60,000 mL·g -1 ·h -1 The toluene content in the mixed air before and after the reaction was detected online by gas chromatography equipped with a FID detector.

[0038] Example 5 Cu 0.2 Mn 1 O x Catalyst preparation Step 1: Mix 3.1606 g potassium permanganate and 0.9664 g Cu(NO 3 ) 2 ·3H 2 O was dissolved in 40 mL of deionized water and sonicated for 15 min to obtain solution A; Step 2: Dissolve 3.2411 g of oxalic acid in deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath at 70 °C with stirring for 6 h to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it at 100 °C for 12 h, and calcine it at 400 °C at a rate of 10 °C / min for 3 h in an air atmosphere to obtain Cu 0.2 Mn 1 O x catalyst.

[0039] A fixed bed reactor was filled with 50 mg of the obtained Cu 0.2 Mn 1 Ox The catalyst was prepared by mixing 1 vol.% toluene with balanced air. The toluene concentration was controlled by adjusting the ratio of the two gas flows to the initial toluene concentration (1000 ppm) entering the fixed bed reactor. The gas flow rate was controlled at 50 mL / min, corresponding to a gas mass space velocity of 60,000 mL·g -1 ·h -1 The toluene content in the mixed air before and after the reaction was detected online by gas chromatography equipped with a FID detector.

[0040] Figure 1 MnO obtained from Examples 1 to 5 of the present invention 2 , Cu 0.03 Mn 1 O x , Cu 0.05 Mn 1 O x , Cu 0.1 Mn 1 O x and Cu 0.2 Mn 1 O x XRD diagram of the catalyst. It can be seen from the figure that MnO 2 , Cu 0.03 Mn 1 O x , Cu 0.05 Mn 1 O x , Cu 0.1 Mn 1 O x and Cu 0.2 Mn 1 O x The catalyst only contains MnO 2 The XRD peaks of CuO phase were not detected, which confirmed that Cu was doped into MnO. 2 The XRD peak intensity decreases with the addition of Cu, indicating that the crystallinity of the obtained catalyst material decreases, which is conducive to the formation of oxygen defects on its surface.

[0041] Figure 2 TEM image of Example 4 of the present invention ( Figure 2 ac), high-angle annular dark field scanning transmission image (HAADF-STEM Figure 2 d) and EDS element mapping ( Figure 2 eh), by Figure 2 From a and b, we know that Cu 0.1 Mn 1 O x The catalyst surface has a coral-like rough surface morphology. 0.1 Mn1 O x The width of the lattice fringes on the catalyst surface is 0.68 nm ( Figure 2 c), attributed to MnO 2 {110} crystal plane of the crystal phase. This indicates that Cu 0.1 Mn 1 O x The catalyst is MnO 2 The crystal phase further confirmed that Cu 0.1 Mn 1 O x The crystal structure of the catalyst is MnO 2 Phase. Figure 2 As can be seen from the illustration c, Cu 0.1 Mn 1 O x The brightness of the diffraction rings in the catalyst selected area is weak, indicating that its crystallinity is low. Figure 1 The XRD results are consistent with those in Figure 2 eh It can be seen that Cu 0.1 Mn 1 O x The Cu, Mn and O elements in the catalyst selection area are uniformly distributed, which confirms that Cu can be effectively incorporated into MnO according to the preparation method in Example 4. 2 Photo.

[0042] Figure 3 The MnO obtained in Examples 1 and 4 of the present invention 2 and Cu 0.1 Mn 1 O x The specific surface area and pore size analysis of the catalyst showed that the Cu 0.1 Mn 1 O x The specific surface area of ​​the catalyst is 112.6 m 2 / g, and the average pore size is 11.26nm, which is significantly larger than that of MnO obtained in Example 1. 2 The specific surface area and pore size of the catalyst confirm that the preparation method in Example 4 can greatly increase the specific surface area and pore size of the sample, thereby improving the adsorption and mass transfer capacity of the reactants.

[0043] Figure 4 The MnO obtained in Examples 1 and 4 of the present invention 2 and Cu 0.1 Mn 1 O x EPR diagram of the catalyst. It can be seen from the figure that the prepared MnO 2 and Cu 0.1 Mn 1 O xThe catalysts all have obvious signal peaks at g = 2.03, which is due to the formation of oxygen defects on the sample surface; in addition, the Cu 0.1 Mn 1 O x The catalyst peak intensity is significantly stronger than that of MnO obtained in Example 1. 2 , indicating that the incorporation of Cu will increase the number of oxygen defects on the sample surface.

[0044] Figure 5 MnO obtained from Examples 1 to 5 of the present invention 2 , Cu 0.03 Mn 1 O x , Cu 0.05 Mn 1 O x , Cu 0.1 Mn 1 O x and Cu 0.2 Mn 1 O x XPS spectra of the catalysts: (a) Mn 2p, (b) O 1s, and (c) Cu 2p. Figure 5 a shows that the catalysts obtained in Examples 1 to 5 form an asymmetric electron binding energy peak at an electron binding energy of 642.0 eV, which is attributed to Mn 2p 3 / 2 The asymmetric electron binding energy peak can be divided into 642.8 eV and 641.7 eV, which are respectively attributed to Mn 4+ and Mn 3+ The electron binding energy peak. Figure 5 b shows that the catalysts obtained in Examples 1 to 5 form asymmetric XPS peaks at electron binding energies of 533-529 eV. The asymmetric XPS peaks can be divided into 532.5 eV and 529 eV electron binding energy peaks, which are respectively attributed to adsorbed oxygen (O 2 - and O - ) and lattice oxygen (O 2- )’s electron binding energy peak. Figure 5 c shows that the catalysts obtained in Examples 2 to 5 have electron binding peaks at 962.8 eV, 953.5 eV, 942.8 eV and 933.2 eV, which are respectively attributed to Cu 2+ The spin-orbit binding energy peak and satellite peak of the catalyst obtained in Examples 2 to 5 are confirmed to be Cu 2+ According to the quantitative analysis results of the Mn 2p and O 1s electron binding energy peak areas, it is confirmed that the preparation methods in Examples 2 to 5 can significantly increase the Mn content on the sample surface. 3+Therefore, combined with the XRD and EPR analysis results, the preparation methods of Examples 2 to 5 can successfully prepare copper-doped manganese dioxide materials rich in oxygen defects, and the copper-doped manganese dioxide rich in oxygen defects has the characteristics of co-modification of oxygen defects and copper species.

[0045] Figure 6 The MnO obtained in Examples 1 and 4 of the present invention 2 and Cu 0.1 Mn 1 O x The catalyst H 2 -TPR graph. It can be seen from the figure that Cu 0.1 Mn 1 O x The catalyst has a larger hydrogen consumption and a lower initial hydrogen consumption peak temperature, indicating that Cu 0.1 Mn 1 O x The number of reducible oxygen species on the catalyst surface is greater and the activity is better.

[0046] Figure 7 The MnO obtained in Examples 1 and 4 of the present invention 2 and Cu 0.1 Mn 1 O x Catalyst O 2 -TPD graph. It can be seen from the figure that Cu 0.1 Mn 1 O x The larger the amount of oxygen species desorbed by the catalyst and the lower the desorption peak temperature, the higher the desorption rate of the catalyst. 0.1 Mn 1 O x The catalyst has better surface active oxygen species desorption and migration capabilities.

[0047] Figure 8 MnO obtained from Examples 1 to 5 of the present invention 2 , Cu 0.03 Mn 1 O x , Cu 0.05 Mn 1 O x , Cu 0.1 Mn 1 O x and Cu 0.2 Mn 1 O x Catalysts and Commercial Pt / Al 2 O 3 The toluene catalytic oxidation activity of the catalyst. As can be seen from the figure, the Cu 0.03 Mn1 O x , Cu 0.05 Mn 1 O x , Cu 0.1 Mn 1 O x and Cu 0.2 Mn 1 O x The catalytic oxidation activity of toluene is better than that of MnO 2 Catalyst. Prepared Cu 0.1 Mn 1 O x The catalyst has the best catalytic activity for toluene oxidation. T 90 211 °C, compared with the undoped Cu MnO 2 catalyst T 90 The temperature shifted to 83 °C, which is comparable to that of the commercial noble metal catalyst Pt / Al 2 O 3 In comparison, it shifted 24 °C toward lower temperatures.

[0048] Fig. 9 The Cu obtained in Example 4 of the present invention 0.1 Mn 1 O x Catalytic stability and water resistance of the catalyst. As can be seen from the figure, when there is / is no 5 vol% water vapor in the raw material, Cu 0.1 Mn 1 O x The toluene conversion rate of the catalyst was always maintained at a high level (>98%), and no obvious activity reduction was observed after 12 h of reaction. The above results confirm that the Cu prepared by the preparation method of Example 4 0.1 Mn 1 O x The catalyst has excellent catalytic activity stability and water resistance, and has prospects for industrial application.

[0049] The present invention is disclosed above with preferred embodiments, which are not intended to limit the present invention. Any technical solutions obtained by adopting equivalent transformation or equivalent replacement solutions fall within the protection scope of the present invention.

Claims

1. A method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst, characterized in that: The specific steps include: Step 1: dissolving potassium permanganate and copper nitrate in deionized water and ultrasonically treating the solution to obtain solution A; Step 2: dissolving oxalic acid in deionized water to obtain solution B; Step 3: Add solution B dropwise into solution A under stirring to obtain a mixed solution; Step 4: Heat the mixed solution in a water bath and stir to obtain a precipitate; Step 5: Wash the precipitate, centrifuge it, dry it, and calcine it in an air atmosphere to obtain a copper-doped manganese dioxide catalyst rich in oxygen defects; The oxygen-deficient copper-doped manganese dioxide is co-modified with oxygen defects and copper species.

2. The method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst according to claim 1, characterized in that: The molar ratio of potassium permanganate and copper nitrate is 1:(0.03~0.2).

3. The method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst according to claim 1, characterized in that: Potassium permanganate and copper nitrate were dissolved in deionized water and ultrasonically treated for 10 to 30 min.

4. The method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst according to claim 1, characterized in that: The molar ratio of potassium permanganate to oxalic acid is 1:1.

8.

5. The method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst according to claim 1, characterized in that: The mixed solution was stirred in a water bath at 50-80 °C for 5-7 h.

6. The method for preparing an oxygen-defect-rich copper-doped manganese dioxide catalyst according to claim 1, characterized in that: The precipitate is washed and centrifuged and then dried at 90-110 °C for 8-12 h. It is then calcined at 300-600 °C at a heating rate of 5-10 °C / min for 2-5 h in an air atmosphere.

7. An application of an oxygen-defect-rich copper-doped manganese dioxide catalyst, characterized in that: The oxygen-defect-rich copper-doped manganese dioxide catalyst prepared by any preparation method described in claims 1 to 6 is used as a thermal catalyst.

8. The oxygen-deficient copper-doped manganese dioxide catalyst according to claim 7 is used for catalytic oxidation degradation of toluene.

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