Plasma-assisted catalyst desulfurization and storage site thermal regeneration method and application
By combining a non-thermal equilibrium plasma catalytic reactor with high-temperature calcination, the problem of reduced nitrogen oxide storage capacity of PNA catalysts due to sulfur poisoning was solved, achieving low-energy catalyst regeneration and efficient nitrogen oxide storage.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2021-06-08
- Publication Date
- 2026-07-14
Smart Images
Figure BDA0003105975880000041 
Figure BDA0003105975880000042 
Figure BDA0003105975880000051
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nitrogen oxide control technology in environmental protection, specifically relating to a plasma-assisted desulfurization method and application of supported noble metal catalysts and thermal regeneration at storage sites. Background Technology
[0002] In recent years, public awareness of environmental protection has grown significantly. Developed industrialized countries such as the US, Japan, South Korea, and Europe have successively formulated and implemented new emission standards, with increasingly stringent restrictions on NO emissions. Therefore, controlling nitrogen oxides has become a research hotspot both domestically and internationally. (Commercial NO...) x The emission reduction technology is the selective catalytic reduction of NO by NH3. x (NH3-SCR) and NO x Storage reduction (NSR) is an option, but the catalysts in these methods typically operate at temperatures between 250-400°C. Below 200°C, the denitrification system has not yet reached its operating temperature, therefore most NO... x Emissions are generated during the cold start phase. Due to increasingly stringent environmental regulations limiting nitrogen oxide emission concentrations, Passive NOx (PNA) has been introduced during the cold start phase of a vehicle. x Adsorber (low-temperature nitrogen oxide storage catalyst) technology is used to control NOx emissions during the cold start phase of lean-burn engines. x The goal of PNA technology is to store nitrogen oxides during the cold start phase of a vehicle, when NO... x The reduction catalyst releases NO when it reaches its operating temperature. x PNA technology can be used in conjunction with NH3 selective catalytic reduction (SCR) technology.
[0003] The core catalysts in PNA technology are mainly of two categories: Pd ion-exchange zeolite molecular sieves and cerium dioxide-based oxides. However, in practical applications, it has been found that burning sulfur-containing fuels and vehicle lubricating oils inevitably leads to the generation of low concentrations of sulfur oxides in vehicle exhaust. These sulfur oxides can cause storage materials to deactivate due to sulfur poisoning, thus significantly reducing their nitrogen oxide storage capacity. Sulfur oxides and NO... x Competitive adsorption occurs, preferentially occupying NO on the catalyst. x Storage sites to reduce NO in catalysts x The adsorption capacity in NO; x Sulfates formed at storage sites have higher thermal stability than nitrates and nitrites; therefore, the decomposition degree of sulfates is relatively high (generally above 700℃).
[0004] Currently, domestic research focuses on the use of oxide catalysts for low-temperature storage of NO in lean-burn engine exhaust gas during the cold start phase. xTechnical research is still in its early stages, and sulfur poisoning leading to catalyst deactivation is a key problem that needs to be solved in the practical application of this type of catalyst. Currently, the regeneration of sulfur-poisoned catalysts at home and abroad mainly utilizes heating methods. However, the thermal regeneration desulfurization process not only requires higher energy consumption, but may also lead to problems such as catalyst structure deactivation and precious metal sintering, thereby affecting the catalyst's nitrogen oxide storage capacity (Catalysis Today 2015, 258, 378–385; Catalysis Communications, 2013, 5–9). Therefore, there is an urgent need to develop new, low-energy-consumption methods for regenerating sulfur-poisoned catalysts. Summary of the Invention
[0005] The purpose of this invention is to provide a method and application for plasma-assisted catalyst desulfurization and thermal regeneration of storage sites. Applying this method to cold-start reactions can effectively solve the problem of severe degradation of storage performance of existing PNA materials after sulfur poisoning, enabling them to maintain a high nitrogen oxide storage capacity for a long time in practical applications.
[0006] This invention is achieved through the following technical solution:
[0007] A plasma-assisted method for catalyst desulfurization and thermal regeneration of storage sites involves placing a supported noble metal catalyst containing sulfur-poisoned nitrogen oxides in a non-thermal equilibrium plasma catalytic reactor. A mixture containing reducing gases is introduced into the reactor, and the non-thermal equilibrium plasma within the reactor completely decomposes and desorbs the sulfate species adsorbed on the surface of the sulfur-poisoned catalyst, thus completing the desulfurization treatment. Then, by thermally calcining in air, the surface and lattice oxygen species reduced during the desulfurization process are replenished, completing the structural reorganization of oxygen species in the catalyst and restoring its catalytic performance.
[0008] The non-thermal equilibrium plasma catalytic reactor ( Figure 1 The non-thermal equilibrium plasma reactor is used for the adsorption and desorption of SO2 and NO. x The non-thermal equilibrium plasma catalytic reactor comprises a hollow quartz tube (6 mm inner diameter, 8 mm outer diameter), with a discharge region inside the quartz tube. Space is left at both ends of the discharge region and at each end of the quartz tube. The catalyst to be treated is placed inside the discharge region. A ground electrode (copper mesh) is wrapped around the outer wall of the quartz tube at the location of the discharge region. Both ends of the quartz tube are end caps. One end cap has an outlet, and the other end cap is through which a stainless steel electrode (2 mm diameter) passes. The stainless steel electrode remaining on the outside of the quartz tube is connected to the plasma generator, while the stainless steel electrode remaining on the inside of the quartz tube passes through the catalyst to be treated in the discharge region. An inlet is also provided on the end cap connected to the stainless steel electrode.
[0009] Furthermore, the precious metal includes Pt, Pd, or Ag.
[0010] Furthermore, the mixed gas containing reducing gas includes a mixture of reducing gas, H2O, CO2, and inert gas; the reducing gas includes hydrogen.
[0011] Furthermore, the volume ratio of reducing gas, H2O, CO2 and inert gas in the mixed gas is 0.01-0.2:0.02:0.05:0.92-0.73; the total flow rate of the mixed gas is 50-200 mL / min.
[0012] Furthermore, the processing time of the non-thermal equilibrium plasma discharge process is 20-40 minutes, and the temperature is room temperature.
[0013] Furthermore, the discharge mode of the non-thermal equilibrium plasma discharge process is dielectric barrier discharge, with a discharge voltage of 30-35V and an input power of 30-50W.
[0014] Furthermore, the atmosphere for hot roasting is air, the roasting temperature is 500℃-800℃, and the time is 3-25h.
[0015] An application of a plasma-assisted catalyst desulfurization and thermal regeneration method in the desulfurization and regeneration of supported noble metal catalysts stored at low temperatures of nitrogen oxides poisoned by sulfur during automobile cold start reactions. The low temperature is 80-200℃.
[0016] (1) Plasma treatment of catalyst desulfurization process:
[0017] Taking Pd / CeO2 catalyst as an example, sulfur-poisoned catalyst was subjected to room temperature non-thermal equilibrium plasma discharge treatment. The discharge mode was dielectric barrier discharge, the center frequency of the discharge power supply was 30 kHz, the discharge voltage was 30 V, the input power was 48 W, the discharge atmosphere was H2 / H2O / CO2 / Ar, and the total flow rate of the discharge atmosphere was 100 mL / min. After 40 min, the discharge ended and 2Pd / CeO2-nH2 catalyst was obtained.
[0018] (2) Catalyst regeneration and storage process after calcination:
[0019] Furthermore, following the above plasma desulfurization technology scheme, the catalyst storage site regeneration process is as follows: the 2Pd / CeO2-nH2 catalyst is calcined by placing it in a muffle furnace at 500℃ for 3-25h to obtain the 2Pd / CeO2-nH2-nhcalcination catalyst.
[0020] Beneficial effects of the invention
[0021] 1. This invention organically combines plasma desulfurization and calcination regeneration of catalysts, and applies them to the regeneration of sulfur-poisoned PNA materials in the cold start reaction of automobiles.
[0022] 2. The non-thermal equilibrium plasma technology described in this invention can achieve desulfurization of PNA materials at room temperature without the addition of an additional heat source. Compared with high-temperature thermal regeneration, it not only has a higher desulfurization capacity but also a lower desulfurization temperature, thus avoiding the sintering of active center noble metals during the high-temperature desulfurization process.
[0023] 3. This invention can achieve the best desulfurization effect by adjusting the atmosphere and ratio of regeneration. It utilizes the high-energy electrons generated during the non-thermal equilibrium plasma discharge process to dissociate reducing gases such as H2 into atoms or other excited-state species with higher reducing power, so that the sulfate species adsorbed on the catalyst surface are completely converted into H2S and SO2, while ensuring the dispersion of precious metals.
[0024] 4. The present invention mixes H2O and CO2 into the regeneration atmosphere to enhance the rapid desorption of sulfur from the catalyst surface, resulting in a better desulfurization effect on the catalyst.
[0025] 5. The calcination regeneration process of the catalyst storage sites described in this invention is achieved by high-temperature calcination in air to fill the surface and lattice oxygen species reduced during desulfurization, thus reorganizing the catalyst structure. Suitable calcination temperature and extended calcination time are more conducive to completing the regeneration of the catalyst storage sites and the reconstruction of oxygen species. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the non-thermal equilibrium plasma catalytic reactor structure described in this invention.
[0027] In the diagram, 1 is the quartz tube; 2 is the ground electrode; 3 is the stainless steel electrode; 4 is the discharge area; 5 is the air inlet; 6 is the air outlet; and 7 is the plasma generator. Detailed Implementation
[0028] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.
[0029] Example 1: Plasma reducing atmosphere desulfurization experiment
[0030] (1) 130 mg of Pd / CeO2 catalyst was loaded into a fixed-bed reactor. Ar gas was introduced into the reaction tube and the temperature was raised to 300 °C using a non-standard open tubular furnace. After the temperature reached 300 °C, a mixed atmosphere of 20 ppm SO2 and Ar was introduced for 95 min. Then the temperature was lowered to room temperature, thus completing the sulfur addition step. The calculated sulfur addition amount was 0.017 g. SO2 / gcat The catalyst's storage capacity decreased significantly after sulfur poisoning, from 193 μmol / g of fresh catalyst. cat Decreased to 133 μmol / g cat .
[0031] (2) The sulfur-poisoned catalyst was subjected to room temperature non-thermal equilibrium plasma discharge treatment using dielectric barrier discharge. The discharge power supply frequency was 10-30 kHz, the discharge voltage was 30 V, the discharge power was 48 W, and the discharge atmosphere was 1-20% H2 / 2% H2O / 5% CO2 / 92%-73% Ar with a total flow rate of 100 mL / min. During the discharge process, the desorbed SO2 concentration (ppm) was monitored in real time using an SO2 gas analyzer (S710). After 40 minutes, the discharge ended, yielding a 2Pd / CeO2-nH2 catalyst. The desulfurization ratio of the catalyst was then calculated through organic elemental analysis. Experimental results showed that the desulfurization ratio reached 62.3% under the conditions of a discharge power supply frequency of 30 kHz, a discharge voltage of 30 V, and a discharge power of 48 W.
[0032] Table 1 shows the Pd / CeO2-sulfation catalyst NO after sulfur poisoning. x Storage quantity and NO of fresh Pd / CeO2 catalyst x Comparison of storage capacity
[0033]
[0034] Table 2 compares the desulfurization rates under room temperature non-thermal equilibrium plasma conditions in a reducing atmosphere.
[0035]
[0036] Comparative Example 1: Thermal Regeneration Reaction Experiment under Reducing Atmosphere
[0037] (1) 130 mg of Pd / CeO2 catalyst was loaded into a fixed-bed reactor. Ar gas was introduced into the reaction tube and the temperature was raised to 300 °C using a non-standard open tubular furnace. After the temperature reached 300 °C, a mixed atmosphere of 20 ppm SO2 and Ar was introduced for 95 min. Then the temperature was lowered to room temperature, thus completing the sulfur addition step. The calculated sulfur addition amount was 0.017 g. SO2 / g cat .
[0038] (2) Thermal regeneration of the sulfur-poisoned catalyst was carried out according to the designed programmed temperature rise reaction. The experiment was conducted in a fixed-bed reactor with an Ar reaction atmosphere and a total gas flow rate of 100 mL / min. The temperature was increased to 800℃ at a rate of 15℃ / min and held for 2 h. The outlet gas during the desulfurization process was monitored using an S710, and the desulfurization ratio of the catalyst was calculated by organic elemental analysis. The experimental results showed that the desulfurization ratio reached 52.1% under the conditions of thermal regeneration temperature of 800℃ and desulfurization for 2 h, which was lower than the desulfurization ratio of room temperature plasma (62.3%).
[0039] Table 3 shows the SO2 desorption amount under Ar atmosphere under thermal regeneration conditions in Comparative Example 1.
[0040]
[0041] Example 2: Catalyst Calcination Experiment
[0042] (1) The catalyst activity regeneration process is to calcine the 2Pd / CeO2-nH2 catalyst obtained in Example 1 for a long time, and place it in a muffle furnace to calcine at 500-900℃ for 3-25h to obtain the regenerated catalyst.
[0043] (2) The NO content of the regenerated 2wt% Pd / CeO2 catalyst was studied using a fixed-bed microreactor. x Storage performance. The total atmosphere flow rate is 400 mL / min, and the space velocity (GHSV) is 200,000 h⁻¹. -1 The NO concentration (ppm) after desorption was monitored using a NO gas analyzer (S710). First, the catalyst was pretreated at 500℃ for 1 hour with 20% O2 and Ar as the equilibrium gas, and then cooled to 100℃ in an Ar atmosphere for NO removal. x Storage performance testing was conducted under the following atmospheres: 200ppm NO / 500ppm CO / 2% H₂O / 5% CO₂ / 10% O₂ / Ar, with a reaction time of 20 minutes. x The storage capacity (NSC) is normalized to the catalyst mass using the following formula, with units of μmol / g. cat .
[0044]
[0045] Experimental results show that, under the conditions of a discharge power supply frequency of 30 kHz, a discharge voltage of 30 V, a discharge power of 48 W, and a discharge atmosphere of 20% H2 / 5% CO2 / 2% H2O / Ar (100 mL / min), after desulfurization and regeneration by calcination in a muffle furnace at 500 °C for 20 h, the NSC of the catalyst is restored to 171 μmol / g. cat .
[0046] Table 4 shows the NO content of the regenerated Pd / CeO2 catalyst in Example 2. x Storage size comparison
[0047]
Claims
1. A method for plasma-assisted catalyst desulfurization and thermal regeneration at storage sites, characterized in that: The supported noble metal catalyst containing sulfur-poisoned nitrogen oxides is placed in a non-thermal equilibrium plasma catalytic reactor, and a mixture containing reducing gases is introduced into it. The non-thermal equilibrium plasma in the reactor completely decomposes and desorbs the sulfate species adsorbed on the surface of the sulfur-poisoned catalyst, thus completing the desulfurization treatment of the sulfur-poisoned catalyst. Then, by thermal calcination in air, the surface and lattice oxygen species that were reduced during the desulfurization process are replenished, and the oxygen species in the catalyst are restructured, thereby restoring and regenerating the catalytic performance. The aforementioned mixture containing a reducing gas includes a mixture of a reducing gas, H2O, CO2, and an inert gas; the reducing gas is hydrogen. The volume ratio of reducing gas, H2O, CO2, and inert gas in the above mixed gas is 0.1-0.2:0.02:0.05:0.73-0.83; the total flow rate of the mixed gas is 50-200 mL / min. The processing time for the above-mentioned non-thermal equilibrium plasma discharge process is 20-40 minutes, and the temperature is room temperature; The aforementioned plasma-assisted catalyst desulfurization and storage site thermal regeneration method is used for low-temperature nitrogen oxide storage catalyst PNA material; The above-mentioned hot roasting process is carried out in an air atmosphere, with a roasting temperature of 500℃ and a time of 3-25 hours; The support for the noble metal catalyst is CeO2.
2. The method for plasma-assisted catalyst desulfurization and thermal regeneration at storage sites according to claim 1, characterized in that: The precious metals include Pt, Pd, or Ag.
3. The method for plasma-assisted catalyst desulfurization and thermal regeneration at storage sites according to claim 1, characterized in that: The non-thermal equilibrium plasma discharge process is a dielectric barrier discharge with a discharge frequency of 2-30kHz, a discharge voltage of 20-60V, and an input power of 15-80W.
4. The application of the method according to any one of claims 1-3, characterized in that: Application of supported noble metal catalysts in desulfurization and regeneration of sulfur-poisoned low-temperature nitrogen oxides stored in automobile cold start reactions.
5. The application according to claim 4, characterized in that, The low temperature is 80-200℃.