PdTiCeO2 catalyst with sulfur resistance and preparation method thereof

Abstract

The invention belongs to the technical field of catalyst preparation and thermocatalytic degradation of VOCs (Volatile Organic Compounds), and relates to a Pd / Ti / CeO2 toluene thermocatalytic degradation catalyst with sulfur resistance. According to the catalyst, CeO2 is used as a carrier, noble metal Pd is used as an active component, and the sulfur resistance is improved by doping Ti into the CeO2 carrier. The preparation process is a two-step wet impregnation method and comprises the following steps: 1) adding a certain amount of CeO2 carrier and water into a titanium precursor ethanol solution, carrying out oil bath evaporation at 80 DEG C to obtain white precipitate, drying and roasting to obtain a Ti / CeO2 carrier; and 2) dispersing the Ti / CeO2 carrier into a solution with water, adding a Pd precursor salt solution with a certain concentration, uniformly stirring, evaporating to dryness, drying, and roasting to obtain the Pd / Ti / CeO2 catalyst. The catalyst provided by the invention is simple in preparation method, low in noble metal loading capacity, high in VOCs thermocatalytic degradation efficiency and high in sulfur resistance, and has a huge application prospect in the aspect of treating VOCs waste gas with high sulfur content.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation and thermal catalytic degradation of VOCs, and relates to a method for preparing a toluene thermal catalytic degradation catalyst with sulfur resistance. Background Art

[0002] Volatile organic compounds (VOCs) are important precursors for the formation of ozone (O3) and PM2.5, and the ozone pollution problem they form has attracted widespread attention worldwide. In particular, VOCs emitted from anthropogenic sources will produce secondary organic aerosols (SOA) through photochemical reactions, causing air pollution and adversely affecting the health of sensitive populations. VOCs pollution control technologies can be divided into two categories, one is recovery technology and the other is destruction technology. Among them, thermal catalytic combustion technology effectively reduces the activation energy of the reaction between VOCs molecules and oxygen molecules due to the addition of catalysts, and reduces the ignition energy barrier of VOCs, so that this technology can usually be carried out at a lower temperature (200-500°C). This technology has high economic feasibility, less secondary pollution after treatment, and high degradation efficiency. Therefore, it has always been the focus of VOCs pollution control.

[0003] The design and preparation of highly active and low-cost VOCs catalytic materials are the core of thermal catalytic combustion technology. At present, the catalysts used for VOCs catalytic oxidation are mainly divided into non-precious metal catalysts and precious metal catalysts. Precious metal catalysts have higher activity and selectivity in most catalytic reactions due to their excellent low-temperature catalytic activity and chemical stability, and therefore have attracted more attention. Among them, Pd catalysts have incomparable advantages due to their excellent catalytic performance for alkane VOCs, especially benzene series. However, precious metals are expensive. In order to control costs and improve thermal stability, it is necessary to reasonably select and design the carrier loaded by Pd. Among them, CeO2 has the possibility of becoming an excellent carrier due to its excellent oxygen storage capacity and redox cycle.

[0004] Under actual working conditions, the exhaust gas composition is very complex. In addition to VOCs components, it also contains water, sulfides (SO2, H2S, mercaptans), heavy metal elements, nitrogen oxides and other substances. Among them, sulfides, especially sulfur dioxide (SO2), pose a serious threat to the high efficiency and stability of the catalyst due to its high content in the exhaust gas, and it is very easy to cause the catalyst to be deactivated during actual operation. At present, the sulfur resistance of VOCs thermal catalysts has not received widespread attention. Therefore, the preparation of a catalyst with high low-temperature activity and excellent sulfur resistance is an urgent problem to be solved in the current VOCs thermal catalytic technology. Summary of the invention

[0005] In view of the current problem that VOCs thermal catalysts are deactivated by sulfur components in exhaust gas, the purpose of the present invention is to provide a VOCs thermal catalyst with high degradation activity and sulfur resistance and a preparation method thereof.

[0006] The technical solution adopted by the present invention is as follows: a Pd / Ti / CeO2 catalyst with anti-sulfur performance, characterized in that the catalyst is composed of an active component and a modified carrier; Among them: the active component is the precious metal Pd, and its content, calculated as single metal, is 0.5 wt% - 1wt% of the carrier mass; the modified carrier is Ti-doped CeO2.

[0007] Generally, the content of Ti in the modified carrier is 0.5-6.5 wt% of the carrier mass.

[0008] The present invention also provides a method for preparing a Pd / Ti / CeO2 catalyst having anti-sulfur performance, characterized in that it comprises the following steps: 1) Prepare the carrier: calcine the precursor salt of Ce to obtain CeO2; 2) Preparation of modified carrier: dissolving titanium precursor in solvent, stirring to obtain titanium precursor solution, adding CeO2 and water, evaporating the solvent, drying and calcining the obtained white precipitate to obtain Ti / CeO2 carrier; 3) Loading Pd: Disperse the Ti / CeO2 carrier with water, add the Pd precursor salt solution, evaporate the solvent, dry and calcine to obtain a Pd / Ti / CeO2 catalyst.

[0009] Generally, the precursor salt of Ce used in step 1) to prepare the carrier is Ce(NO3)3·6H2O.

[0010] The methods used in steps 2) and 3) are both two-step wet impregnation methods.

[0011] In the step 2), the titanium precursor is tetrabutyl titanate, and the solvent is ethanol; the volume ratio of tetrabutyl titanate to water is 1:20-80, preferably 1:50, and the molar ratio of Ti to Ce is 0.03-0.2.

[0012] In the step 3), the precursor salt solution of Pd is Pd(NO3)2, and the solution concentration is 0.01 - 0.05 mol / L, preferably 0.03 mol / L.

[0013] The present invention provides a typical preparation method of a Pd / Ti / CeO2 catalyst with sulfur resistance, and the specific steps are as follows: 1) Preparation of carrier: calcining Ce(NO3)3·6H2O at 500°C for 4 hours to obtain CeO2; 2) Preparation of modified carrier by wet impregnation method: tetrabutyl titanate was dissolved in ethanol, stirred in an ice-water bath for 60 minutes to obtain a titanium precursor solution, CeO2 and water were added, and the solvent was evaporated in an oil bath at 100°C. The obtained white precipitate was dried at 120°C for 3h and calcined at 500°C for 4h to obtain a Ti / CeO2 carrier; 3) Loading Pd by wet impregnation method: Disperse the Ti / CeO2 carrier with water, add Pd(NO3)2 solution, evaporate the solvent in an oil bath at 80°C, dry at 110°C for 4h, and calcine at 400°C for 6h to obtain Pd / Ti / CeO2 catalyst.

[0014] The Pd / Ti / CeO2 catalyst with sulfur resistance of the present invention has good degradation efficiency and hydrothermal stability, and is suitable for thermal catalytic treatment of benzene-based VOCs waste gas such as toluene. It also has good sulfur resistance and is suitable for thermal catalytic treatment of VOCs waste gas containing high sulfur components.

[0015] Compared with the prior art, the advantages of the present invention include: (1) The present invention provides a VOCs waste gas catalyst with sulfur resistance, which can achieve efficient thermal catalytic combustion of high-concentration VOCs at low temperature (200°C). It has potential application prospects in VOCs waste gas treatment; (2) The VOCs waste gas catalyst with sulfur resistance provided by the present invention is a supported precious metal catalyst, which has a small amount of precious metal loading, and by modifying the carrier, the loading amount is reduced while maintaining the catalytic activity and improving the hydrothermal stability and sulfur resistance of the catalyst; (3) The sulfur-resistant VOCs exhaust gas catalyst provided by the present invention has excellent sulfur-resistant performance and hydrothermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD spectra of samples prepared for Examples 1-6 and Examples 7-12.

[0017] Figure 2 Infrared spectra of samples prepared for Examples 1-6 and Examples 7-12.

[0018] Figure 3 The toluene conversion rate of Application Example 1 for all catalysts in Examples 1-12.

[0019] Figure 4 For Application Example 2, the 24 h thermal stability and 5 vol.% H2O water resistance test results of Pd / Ti0.10 / CeO2 and Pd / Ti0.10 / CeO2-S in the embodiment were performed. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0021] Examples 1-6 Preparation of Pd / Ti with different Ti / Ce ratios x / CeO2 catalyst, the specific steps are as follows: (1) Ce(NO3)3·6H2O was calcined in a muffle furnace at 500°C for 4 h with a heating rate of 5°C / min to obtain a CeO2 carrier.

[0022] (2) The CeO2 carrier was modified by wet impregnation. A certain amount of tetrabutyl titanate was weighed and dissolved in ethanol. The mixture was magnetically stirred for 60 min in an ice-water bath. Then a certain amount of CeO2 and water were added. The volume ratio of tetrabutyl titanate to water was 1:50. The solvent was completely evaporated in an oil bath at 100 °C, and a white amorphous oxide precipitate appeared. The mixture was placed in an oven and dried at 120 °C for 3 hours. Finally, the dried sample was ground and placed in a muffle furnace. The temperature was raised to 500 °C and maintained for 4 hours at a heating rate of 5 °C min. -1 According to the different molar ratios of Ti / Ce, Ti x / CeO2 carrier ( x =0.03, 0.05, 0.08, 0.10, 0.20).

[0023] (3) Pd was loaded by wet impregnation method. 1.9155 g of different Ti x / CeO2 carrier was placed in a beaker, and 50 mL of water was added to disperse the carrier. During the stirring process, 3 mL of 0.03 mol / L Pd(NO3)2 solution was slowly added drop by drop. After the addition, it was stirred at room temperature for 3 hours. Then it was evaporated in a water bath at 80°C. After the solvent was evaporated, the beaker was placed in an oven at 110°C and dried for 4 h. After drying, the sample was ground into powder and kept at 400°C in a muffle furnace for 6 h. Pd / Ti with different Ti / Ce ratios was obtained. x / CeO2 catalyst, the same method was used to load an equal amount of Pd on CeO2 to prepare the Pd / CeO2 catalyst for comparison.

[0024] Examples 7-12 The Pd / CeO2 catalyst prepared in Example 1 was mixed with Pd / Ti x The CeO2 / CeO2 catalyst is pretreated with SO2 to simulate the catalyst being poisoned and deactivated by SO2 under actual conditions, including the following steps: (1) Pour 0.6 g of the catalyst into a porcelain boat and place it in a tube furnace, and then perform a temperature program from room temperature to 300 °C at a heating rate of 5 °C·min-1 in an air atmosphere, with an air flow rate of 180 mL·min-1; (2) When the temperature rises to 300 °C, another 1% SO2 / N2 gas is quickly introduced and kept at this temperature for 2 h. The flow rate of 1% SO2 / N2 gas is 20 mL min-1. (3) Stop the program and stop introducing SO2 / N2 gas, and wait for the tube furnace to cool down naturally to obtain the sulfation treatment catalysts Pd / CeO2-S and Pd / Ti x / CeO2-S.

[0025] Figure 1 XRD spectra of samples prepared in Examples 1-6 and 7-12 show that all samples show a cubic fluorite structure of CeO2, and no characteristic diffraction peak of Pd is found, indicating that the dispersion of Pd species is high. No diffraction peak of sulfate species is found.

[0026] Figure 2 The infrared spectra of the samples prepared for Examples 1-6 and 7-12 are shown in the range of 3700-3200, 1650-1620 cm -1 The stretching vibration peak and deformation vibration peak attributed to the surface hydroxyl (-OH) appeared at 1040 cm -1 400-700cm -1 After SO2 pretreatment, the stretching vibration peak of Ce-O bond appeared in the range of 1120 cm -1 A new characteristic absorption peak appears at the 2- The characteristic peak of the catalyst indicates that part of the surface sulfide accumulates on the catalyst surface to form sulfate, resulting in sulfur poisoning of the catalyst. This characteristic peak gradually weakens with the increase of the Ti / Ce ratio, which indicates that the sulfate deposition on the sample surface gradually decreases. Application Example 1

[0027] The catalyst prepared in Examples 1-12 was applied to a thermal catalytic toluene oxidation reaction, and the specific steps were as follows: The catalytic activity of toluene was tested on a fixed bed microreactor. Under a constant temperature water bath at 25 °C, 1000 ppm toluene was introduced into the mixing buffer bottle in a steady airflow state by bubbling. The mixed gas was fully mixed in the mixing buffer bottle and then entered the reactor. The air flow rate was 50 mL min -1The tail gas after the reaction is then detected in real time online by gas chromatography to detect and analyze the concentration of gas components after the reaction. 100 mg of the catalyst sieved through a 40-60 mesh sieve is weighed and placed in a quartz tube, and then a temperature program is set to start the programmed temperature reaction from 100 °C.

[0028] Each test point was maintained for 30 minutes, and three parallel samples were collected at each point, and the average value was taken as the activity result. Toluene conversion rate (X toluene ,%) is calculated as follows: X toluene (%) = (C in - C out ) / C in × 100 % Among them, C in and C out are the toluene concentrations at the inlet and outlet of the sample gas, respectively. Figure 3 is the toluene conversion rate of all catalysts in Examples 1-12, and Table 1 is the characteristic temperature of toluene oxidation of all catalysts. Figure 3 From Table 1, we can find that the activity of all catalysts that have not been pretreated with SO2 is not much different in the medium and high temperature range, indicating that changing the Ti / Ce ratio will not significantly affect the activity of Pd. After SO2 pretreatment, the activity of the pure CeO2 carrier decreases most significantly. As the Ti / Ce ratio increases, the catalyst activity gradually recovers with the increase of Ti content, and finally basically recovers to the activity of the fresh sample. This shows that the strategy of improving the sulfur resistance of the sample by Ti modification is effective, among which Pd / Ti 0.10 / CeO2 catalyst has both excellent low-temperature activity and resistance to sulfur poisoning.

[0029] Application Example 2

[0030] For Pd / Ti 0.10 / CeO2 and Pd / Ti 0.10 / CeO2-S was tested for 24 h thermal stability and 5 vol.% H2O water resistance. The test results are shown in Figure 4 Both catalysts maintained good stability under the reaction conditions of 210°C, and their activity did not show a significant decrease after 24 hours of continuous reaction. In addition, the samples still had good stability and adaptability after 600 minutes of continuous on / off water vapor test. This feature makes it have great potential value in future industrial production and applications.

Claims

1. A Pd / Ti / CeO2 catalyst with sulfur resistance, characterized in that: The catalyst is composed of active components and a modified carrier; Among them: the active component is the precious metal Pd, and its content, calculated as single metal, is 0.5 wt% - 1 wt% of the carrier mass; the modified carrier is Ti-doped CeO2.

2. The Pd / Ti / CeO2 catalyst with sulfur resistance as claimed in claim 1, characterized in that: The Ti content in the modified carrier is 0.5 - 6.5 wt% of the carrier mass.

3. The method for preparing the Pd / Ti / CeO2 catalyst with sulfur resistance according to claim 1, characterized in that: The following steps are involved: 1) Prepare the carrier: calcine the Ce precursor salt to obtain CeO2; 2) Preparation of modified carrier: dissolve titanium precursor in solvent, stir to obtain titanium precursor solution, add CeO2 and water, evaporate the solvent, dry and calcine the obtained white precipitate to obtain Ti / CeO2 carrier; 3) Loading Pd: Disperse the Ti / CeO2 carrier with water, add the Pd precursor salt solution, evaporate the solvent, dry and calcine to obtain the Pd / Ti / CeO2 catalyst.

4. The method for preparing the Pd / Ti / CeO2 catalyst having sulfur resistance as claimed in claim 3, characterized in that: Step 1) The precursor salt of Ce used to prepare the carrier is Ce(NO3)3·6H2O.

5. The method for preparing the Pd / Ti / CeO2 catalyst with sulfur resistance as claimed in claim 3, characterized in that: The methods used in steps 2) and 3) are both two-step wet impregnation methods.

6. The method for preparing the Pd / Ti / CeO2 catalyst with sulfur resistance according to claim 3 or 5, characterized in that: In step 2), the titanium precursor is tetrabutyl titanate, and the solvent is ethanol; the volume ratio of tetrabutyl titanate to water is 1:20-80, and the molar ratio of Ti to Ce is 0.03-0.

2.

7. The method for preparing the Pd / Ti / CeO2 catalyst with sulfur resistance as claimed in claim 3 or 5, characterized in that: In step 3), the precursor salt solution of Pd is Pd(NO3)2, and its solution concentration is 0.01 - 0.05 mol / L.

8. The method for preparing the Pd / Ti / CeO2 catalyst with sulfur resistance according to any one of claims 3 to 7, characterized in that: The specific steps are as follows: 1) Preparation of carrier: calcining Ce(NO3)3·6H2O at 500℃ for 4 hours to obtain CeO2; 2) Preparation of modified carrier by wet impregnation method: Tetrabutyl titanate was dissolved in ethanol and stirred in an ice-water bath for 60 minutes to obtain a titanium precursor solution, CeO2 and water were added, and the solvent was evaporated in an oil bath at 100°C. The obtained white precipitate was dried at 120°C for 3h and calcined at 500°C for 4h to obtain a Ti / CeO2 carrier; 3) Loading Pd by wet impregnation method: Disperse the Ti / CeO2 carrier with water, add Pd(NO3)2 solution, evaporate the solvent in an oil bath at 80°C, dry at 110°C for 4h, and calcine at 400°C for 6h to obtain Pd / Ti / CeO2 catalyst.

9. The Pd / Ti / CeO2 catalyst with sulfur resistance as described in claim 1 has good degradation efficiency and hydrothermal stability, and is suitable for thermal catalytic treatment of benzene-based VOCs waste gas.

10. The Pd / Ti / CeO2 catalyst with sulfur resistance as claimed in claim 1 has good sulfur resistance and is suitable for thermal catalytic treatment of VOCs waste gas containing high sulfur components.

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