Apparatus for driving photo-thermal catalytic oxidation of vocs by solar energy and application thereof

Abstract

The application discloses a device for catalytically oxidizing VOCs by using daily solar light and heat and application thereof. The light and heat device comprises a micro light and heat reactor, a light source for simulating sunlight, a Fresnel lens and a light and heat material. The device is applied to the catalytically oxidizing VOCs driven by solar light. In the application, daily sunlight (light intensity 50-70 mW / cm 2 ) is converged by the Fresnel lens, and the light intensity can be increased by tens of times. The sunlight absorbed and focused by the defect type three-dimensional macroporous lanthanum manganate is converted into heat energy and chemical energy. The application has the beneficial effects that under the irradiation of daily sunlight, the toluene degradation rate is up to 100% by the light-converging catalytic system, and the mineralization efficiency can reach more than 90%.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photocatalysis, and particularly relates to a device for photocatalytic oxidation of VOCs by using daily solar light and heat and application thereof. BACKGROUND

[0002] Volatile organic compounds (VOCs) are important precursors of PM2.5 and ozone pollution, and some of them are toxic and malodorous substances, which can cause harm to human health after long-term exposure.

[0003] Thermal catalytic oxidation has been commercialized for various industrial VOCs treatment, which needs fossil fuel combustion to provide heat energy as driving force. However, high-temperature operation caused by fossil fuel combustion will increase energy consumption and bring new pollution. It is an ideal way to realize VOCs purification by using clean, pollution-free and renewable solar energy to drive VOCs oxidation reaction. For full-spectrum sunlight, semiconductor photocatalysts can usually only absorb ultraviolet light or part of visible light, and the energy in the infrared region is not enough to excite VOCs to react. Part of the visible light and all the infrared light in the solar spectrum are not effectively utilized.

[0004] Photo-thermal conversion is a new type of solar energy utilization scheme. Some metal oxide catalysts have wide spectrum high absorption, good thermal stability, structure modulation and redox ability, and are favored. Wang Wenzhong et al. reported the catalytic performance of two-dimensional porous Co3O4 materials under sunlight irradiation for propylene and propane. Li Yuanzhi's team studied a series of bimetallic oxide photo-thermal catalysts CeO2 / TiO2, Co3O4 / TiO2, MnO x / TiO2, CeMn x O y / TiO2, etc. Although metal oxide photo-thermal catalysts have made some achievements in VOCs treatment, there are still many problems to be solved, such as the need for high-intensity light (500 mW / cm 2 above) to drive VOCs catalytic reaction, and easy to be affected by intermediate product deposition.

[0005] The current solar energy conversion efficiency is low, and one of the important reasons is that the solar energy density is low, the dispersion is strong, and it is discontinuous, so we still lack effective means for efficient, low-cost and large-scale utilization. Therefore, how to utilize the advantages of structural diversity, controllability and designability of metal oxides, reasonably design and prepare efficient, stable and economic photo-thermal catalysts, and how to use concentrating equipment to achieve excellent VOCs purification capacity under daily sunlight irradiation still need more innovative research work. SUMMARY

[0006] The application aims to provide a device for utilizing daily sunlight, which can fully utilize the divergent daily sunlight, the ultraviolet, visible and infrared spectrum parts in the full sunlight spectrum and the focused divergent sunlight, and solves the problem of insufficient utilization of sunlight in the prior art.

[0007] The application is realized by the following technical scheme:

[0008] A solar-driven photo-thermal catalytic VOCs device, comprising a micro photo-thermal reactor, a light source simulating sunlight, a Fresnel lens and a photo-thermal material.

[0009] The photo-thermal reactor is a micro reactor, the light source is located directly above the light window of the micro reactor, and the Fresnel lens is interposed between the two, the lens diameter is adjustable, the size of the focused light spot is adjustable, and the light intensity can be increased by tens of times.

[0010] The photo-thermal material is a defective 3DOM LaMn 1.2 O3, which is prepared by using polymethyl methacrylate (PMMA) as a hard template. 1.2 O3. The manganese metal oxide MnO x O3 is precipitated in situ on the LaMnO3 three-dimensional ordered framework, which can realize the uniform distribution of the highly dispersed metal oxide, and the multiple scattering and reflection effect can enhance light absorption and thus maximize the utilization of sunlight. 1.2 O3 to manufacture surface oxygen defects and increase active sites.

[0011] According to the embodiment of the application, the defective LaMn 1.2 O3 material has a three-dimensional ordered macroporous structure and oxygen defects.

[0012] According to the embodiment of the application, the defective LaMn 1.2 O3 material has a photo-thermal synergistic enhancement effect.

[0013] The application also provides an application of the above-mentioned three-dimensional ordered macroporous material LaMn 1.2 O3 as a catalyst. Preferably, the application in photo-thermal synergistic catalytic purification of VOCs. More preferably, the application in driving the catalyst to catalytically purify VOCs under the photo-thermal synergistic effect with sunlight as the energy source (instead of traditional fossil fuels).

[0014] Illustratively, the application in photo-thermal synergistic catalytic oxidation of toluene.

[0015] Advantages

[0016] (1) The full-spectrum solar light utilization device provided by the application can maximize the use of daily sunlight, converges daily sunlight into a circular light spot by means of a linear focusing Fresnel lens, the size of the light spot is adjustable, the light intensity can be focused and enhanced by tens of times, and is used for a catalytic reaction system. 1.2 O3, the full-waveband solar spectrum can be maximized, ultraviolet-visible light provides high-energy photons and excites the catalyst to generate electron-hole pairs to occur photocatalytic reaction, most of the visible light-infrared light is absorbed and converted into heat energy, and the catalytic reaction is synergistically enhanced, and the utilization range of sunlight is effectively expanded. 1.2 O3, compared with pure 3DOM LaMn 1.2 O3, the defect type 3DOM LaMn -2 O3 has a synergistic light-heat enhancement effect, can effectively realize the degradation of volatile organic compounds under lower sunlight irradiation (60 mW·cm 1.2 O3, the defect type 3DOM LaMn -1 O3 is used in an amount of 30 mg, and the mass space velocity is 25600 mL·h -1 Under the condition, the conversion rate of toluene is 100%, and the mineralization rate is 90%. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The structure schematic diagram of the embodiment of the application.

[0018] Figure 2 The scanning electron microscope graph of the defect type 3DOM LaMn 1.2 O3 prepared in Example 1 (the scales from left to right are 5 mu m, 1 mu m, 500 nm).

[0019] Figure 3 The electron paramagnetic resonance graph of the catalyst prepared in Example 1 and Comparative Example 1.

[0020] Figure 4 The X-ray powder diffraction graph of the catalyst prepared in Example 1 and Comparative Example 1.

[0021] Figure 5 The conversion rate and mineralization rate of toluene change with time when the light intensity of the sunlight of the catalyst prepared in Example 1 and Comparative Example 1 is 60 mW·cm -2 .

[0022] Figure 6 The scanning electron microscope graph of the defect type 3DOM LaMn 1.2When O3 is used as a catalyst, under sunlight intensity of 60 mW·cm -2 Water resistance stability diagram under concentrated light irradiation.

[0023] Figure 7 The catalysts prepared in Example 1 and Comparative Example 1, as well as the commercially available catalyst in Comparative Example 2, were tested under a solar radiation intensity of 60 mW·cm⁻¹. -2 The graph shows the change in catalyst surface temperature over time during photooxidation of toluene under certain conditions. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0025] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0026] Example 1

[0027] Defective 3DOM LaMn 1.2 The method for preparing O3 includes the following steps:

[0028] (1) 3DOM LaMn was prepared by PMMA gel crystal template method 1.2 O3. The specific steps are as follows: At room temperature, measure 10 mL of deionized water into a beaker, and add 3.976 g of La(NO3)3·6H2O, 2.535 mL of 50 wt% Mn(NO3)2 aqueous solution, and 3.84 g of citric acid to the beaker sequentially. Stir magnetically for 1 h to obtain a transparent precursor solution. Then, completely immerse 2.0 g of PMMA template in the precursor solution for 4.0 h, filter to remove excess solution, and place the obtained solid sample in a vacuum drying oven at 60 °C overnight for vacuum drying. Then transfer the sample to a small porcelain boat and place it in a tube furnace for calcination. First, in a nitrogen atmosphere (flow rate 350 mL / min), the temperature was increased from room temperature to 300°C at a rate of 1°C / min and maintained at this temperature for 3 hours, then cooled to room temperature. Next, in an air atmosphere (flow rate 350 mL / min), the temperature was increased from room temperature to 300°C at a rate of 1°C / min and maintained at this temperature for 1 hour. Then, the temperature was increased from 300°C to 750°C at a rate of 1°C / min and maintained at this temperature for 5 hours. Finally, the temperature was cooled to room temperature to obtain 3DOM LaMn. 1.2 O3.

[0029] (2) The above 3DOM LaMn 1.2O3 was reduced to obtain a defective 3DOM LaMn 1.2 O3.

[0030] Comparative Example 1

[0031] Comparative Example 1 except that the catalyst 3DOM LaMn 1.2 O3 obtained in Example 1 was not treated and directly used as Comparative Example 1.

[0032] Comparative Example 2

[0033] Commercial DeSart P25 was directly used as Comparative Example 2.

[0034] Figure 1 is a structural schematic diagram of the embodiment of the present application. It mainly consists of three parts: light source module, light collection module and catalytic module.

[0035] Figure 2 (a), (b) and (c) are scanning electron microscope images of the defective 3DOM LaMn 1.2 O3 prepared in Example 1. It can be seen from the images that the three-dimensional macroporous structure of the defective 3DOM LaMn 1.2 O3 is very regular and ordered, and the pore size is about 150 nm.

[0036] Figure 3 is an electron paramagnetic resonance spectrum of the catalyst prepared in Example 1 and Comparative Example 1. It can be seen from the image that the defective 3DOM LaMn 1.2 O3 prepared in Example 1 has a larger oxygen defect peak at 2.01, while the comparative example has no oxygen defect peak.

[0037] Figure 4 is an X-ray powder diffraction spectrum of the catalyst prepared in Example 1 and Comparative Example 1. It can be seen from the image that the defective 3DOM LaMn 1.2 O3 prepared in Example 1 has a LaMnO 3.08 phase, and no MnO x related components are detected. The crystal phase of the 3DOM LaMn 1.2 O3 prepared in Comparative Example 1 is LaMnO3, and no MnO x related components are detected.

[0038] Test Example 1

[0039] The defective 3DOM LaMn 1.2 O3 prepared in Example 1, the 3DOM LaMn 1.2O3 and commercially available P25 of Comparative Example 2 were used as catalysts to catalytically oxidize toluene under daily sunlight irradiation. The specific implementation steps were as follows: a certain amount of catalyst was weighed and loaded into a quartz reactor, and a small amount of quartz wool was plugged into the inlet and outlet of the reactor. The gaseous toluene was introduced into the reactor through a self-built gas circuit, the initial toluene reaction concentration was 230 ppm, and the flow rate was 12.8 mL / min. The light source used during the reaction was a PLS-SXE300 xenon lamp (Beijing Po Fei Le), and the concentrations of toluene and CO2 during the reaction were detected online by a gas chromatograph.

[0040] The conversion rate of toluene % = 100% x ([toluene] 进口浓度 - [toluene] 出口浓度 ) / [toluene] 进口浓度

[0041] The mineralization rate of toluene % = 100% x [CO2] 产生浓度 / [CO2] 理论浓度 = 100% x [CO2] 产生浓度 / ([toluene] 进口浓度 x 7).

[0042] The catalytic activity of different catalysts under sunlight irradiation is shown in Figure 5 From the figure, it can be seen that the 3DOM LaMn 1.2 O3 catalyst has a toluene conversion rate of 100% and a mineralization rate of 50% under sunlight irradiation with a light intensity of 60 mW·cm -2 -2. When the 3DOM LaMn 1.2 O3 is introduced with certain defects, the catalytic activity is significantly improved. Specifically, the toluene conversion rate is 100%, and the mineralization rate is 90%. Therefore, the defect type 3DOM LaMn 1.2 O3 used as a catalyst has excellent catalytic activity, and the reason is that the defects provide reactive sites, which ultimately improve the catalytic activity.

[0043] Further, the present application also studies the effect of water vapor on the defect type 3DOM LaMn 1.2Effect of the catalytic activity of O3catalyst. The experimental method is as follows: the concentration of toluene is 230 ppm, the reaction space velocity is 25600 mL / (gh), the total flow rate of air is 12.8 mL / min, in which the toluene sweeping gas is 0.2 mL / min, and the balance gas is 12.6 mL / min, the balance gas is passed through a steam generator containing water, and the relative volume content of water in the reaction gas is ensured by adjusting the temperature of water in the generator. When the temperature of water is 25℃, the corresponding saturated steam pressure is 3619 Pa. According to the formula: relative humidity = actual air water vapor pressure / saturated water vapor pressure at the same temperature. By calculation, when the water is at 4℃, 16℃ and 28℃, the relative humidity of water in the total gas flow is 25%, 50% and 100% respectively.

[0044] Figure 6 Defective 3DOM LaMn 1.2 O3used as a catalyst has good water resistance under the condition of sunlight intensity of 60 mW·cm -2 The figure of the water stability of O3used as a catalyst under the condition of sunlight intensity of 60 mW·cm -2 The conversion rate of toluene is 100%, and the yield of CO2 is 88%. When the relative humidity is 50%, the conversion rate of toluene is still 100% and does not change within 25 hours, but the yield of CO2 gradually decreases from 88% to 72%. When the relative humidity increases to 100%, the yield of CO2 further decreases from 72% to 68% and can be maintained for 25h. When the relative humidity decreases to zero (i.e. dry air), the yield of CO2 can be restored to 88% within 20 hours. The above experimental results show that although water vapor and toluene molecules can form competitive adsorption on the surface of the catalyst to a certain extent, and inhibit the catalytic activity of toluene, the catalytic performance of defective 3DOM LaMn 1.2 O3can still be restored after switching the water vapor to dry air. This shows that the defective 3DOM LaMn 1.2 O3used as a catalyst has good water resistance.

[0045] Test Example 2

[0046] Defective 3DOM LaMn 1.2 O3, 3DOM LaMn 1.2 O3of Comparative Example 1 and P25 commercial catalyst of Comparative Example 2 under the condition of sunlight intensity of 60 mW·cm -2 The figure of the change of the surface temperature of the catalyst with time when toluene is photooxidized under the condition of sunlight intensity of 60 mW·cm Figure 7 The results are shown in Figure 7It can be seen that in the presence of commercial P25 (only absorbing UV light, no contribution to light-to-heat conversion) catalyst of Comparative Example 2, the temperature of the reaction bed is only 138℃ under the concentrated light irradiation condition of 60 mW·cm -2 of solar light intensity; while when using the defective 3DOM LaMn 1.2 O3 and 3DOM LaMn 1.2 O3 prepared in Example 1 and Comparative Example 1 as catalyst, the temperature of the reaction bed is increased to 218℃ under the concentrated light irradiation of 60 mW·cm -2 of solar light intensity. Thus it is shown that the defective 3DOM LaMn 1.2 O3 and 3DOM LaMn 1.2 O3 prepared in the present application can quickly and effectively convert the absorbed solar light into heat energy to provide the required temperature of the reaction system.

Claims

1. A device for solar driven photo-thermal catalytic oxidation of VOCs comprising a micro photo-thermal reactor, a light source to mimic sunlight, a Fresnel lens, a photo-thermal material, characterized in that, (1) In the device, the light source is located above the photothermal reactor light window, the Fresnel lens is located between the light source and the light window, the lens diameter is adjustable, and the light intensity can be focused by 50-70 mW / cm 2 The daily sunlight is converged into a circular light spot, the size of the light spot is adjustable, and the light intensity is focused by more than dozens of times;(2) In the device, the photothermal material is a defective three-dimensional large-pore LaMn 1.2 O3, which can make the sunlight in the perovskite multiple refraction and scattering, realize efficient capture, absorption and energy conversion of ultraviolet-visible-infrared full-spectrum sunlight, and provide more active sites; (3) In the device, a thermocouple is arranged in the reaction chamber of the micro photothermal reactor.

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