阅读说明：本技术 一种海绵状天然气发动机尾气催化剂的制备及应用 (Preparation and application of spongy natural gas engine tail gas catalyst ) 是由 孔祥辰 李振国 任晓宁 邵元凯 李凯祥 吴撼明 吕从杰 于 2020-04-28 设计创作，主要内容包括：本发明公开了一种用于天然气发动机尾气催化剂的制备和催化剂氧化处理低级烃的方法,属于发动机尾气排放领域。发动机尾气催化剂以LaCeO<Sub>3</Sub>钙钛矿作为催化载体,通过控制制备工艺参数、前驱体溶液的组分,从而获得具有多孔海绵结构的钙钛矿催化剂,有效的改善了钙钛矿材料比表面积不足的劣势,提升催化剂对尾气气体分子的捕获能力、延长反应时间。同时引入贵金属元素实现钙钛矿B位的掺杂以及表面负载,显著的提升催化剂对天然气尾气反应的活性,且能适应冷启动工况条件的天然气尾气净化系统,且制备工艺简单,便于工业化生产。(The invention discloses a method for preparing a natural gas engine tail gas catalyst and treating lower hydrocarbons by oxidizing the catalyst, and belongs to the field of engine tail gas emission. The engine tail gas catalyst is LaCeO 3 Perovskite is used as a catalytic carrier, and the porous sponge structure is obtained by controlling the preparation process parameters and the components of the precursor solutionThe perovskite catalyst effectively improves the defect of insufficient specific surface area of the perovskite material, improves the capture capacity of the catalyst on tail gas molecules, and prolongs the reaction time. Meanwhile, precious metal elements are introduced to realize doping and surface loading of perovskite B sites, the activity of the catalyst on the reaction of natural gas and tail gas is remarkably improved, the catalyst can adapt to a natural gas and tail gas purification system under a cold start working condition, the preparation process is simple, and the industrial production is facilitated.)

1. A preparation process of a natural gas engine tail gas catalyst is characterized by comprising the following steps: lanthanum nitrate LaNO₃₃6H2O cerium nitrate Ce (NO)₃)₃Rhodium nitrate Rh (NO)₃)₃The solution was dissolved in deionized water, and citric acid CA (C) was added to the solution₆H₈O₇) EDTA (C)₁₀H₁₆N₂O₈) And urea CH₄N₂O and stirring to form a particle suspension, and then dropwise adding ammonia water to adjust and dissolve suspended particles to obtain a clear and transparent precursor solution; quickly freezing and freezing the solution, transferring the solution into a freeze dryer, and obtaining perovskite precursor powder after all liquid phase components are removed; calcining the powder in a muffle furnace under air atmosphere, and cooling to room temperature to obtain LaCe_1-xRh_xO₃Perovskite powder; then adding LaCe_1-xRh_xO₃Placing the mixture in Pd ammonia complex solution for stirring and loading, placing the mixture in a vacuum drying oven for deamination after the stirring is finished, and obtaining Pd_y/LaCe_1-xRh_xO₃A perovskite catalyst.

2. The natural gas engine exhaust catalyst precursor solution as claimed in claim 1, wherein the concentration of La and Ce metal ions in the solution is 0.09-0.11mol/L, and the lanthanum nitrate LaNO is₃₃6H2O cerium nitrate Ce (NO)₃)₃Rhodium nitrate Rh (NO)₃)₃The prepared solution is mixed with citric acid and ethylene diamine tetraacetic acidThe mol ratio of the acid to the urea is (1-1.2) to (1.5-1.8), and the pH value of the precursor solution is 5-6.

3. The natural gas engine exhaust catalyst according to claim 1, wherein the metal ion solution is lanthanum nitrate La (NO)₃)₃6H2O, cerium Ce Nitrate (NO)₃)₃6H2O, rhodium nitrate Rh (NO)₃)₃Pd (NO) palladium nitrate₃)₄The mol/L ratio of the solution concentration is as follows, when no noble metal element is added, the metal element La to Ce is (0.9-1.1) to (0.9-1.1); the noble metal is added in a ratio of x + y being 0.05, when x is 0.01 and y is 0.04 (namely 1% -Rh), the metal element La to Ce is (0.9-1.1) to (0.89-1.11); when x is 0.02 and y is 0.03 (namely 2% -Rh), the metal element La and Ce is (0.9-1.1) and (0.88-1.12); when x is 0.03 and y is 0.02 (namely 3% -Rh), the metal element La: Ce is (0.9-1.1) to (0.87-1.13); when x is 0.04 and y is 0.01 (namely 4% -Rh), the metal element La: Ce is (0.9-1.1): 0.86-1.14).

4. The natural gas engine exhaust gas catalyst according to claim 1, wherein the freeze-drying method comprises the steps of placing the precursor solution in a refrigerator at-5 to-10 ℃ for quick freezing, and then placing the precursor solution in a freeze-dryer for 12 to 18 hours to remove liquid phase components, so as to obtain dry precursor powder.

5. The natural gas engine exhaust gas catalyst according to claim 1, wherein the sintering is performed by placing the freeze-dried powder in a muffle furnace under an air atmosphere for calcination, first raising the temperature to 350 ℃ at a rate of 1-3 ℃/min and preserving the temperature for 3-3.5h, then raising the temperature to 700 ℃ at a rate of 8-10 ℃/min and preserving the temperature for 1.5-2h, and finally naturally air-cooling to a normal temperature of 18-28 ℃.

6. The natural gas engine exhaust catalyst according to claim 1, wherein the noble metal Pd is supported, and the obtained LaCe is_1-xRh_xO₃Putting perovskite powder into tetraamminepalladium nitrate [ Pd (NH) with the concentration of 0.06-0.1mol/L₃)₄](NO₃)₂And stirring the complex solution for 15-30min, wherein the pH value of the solution is 10-12, so that the electrostatic adsorption of the noble metal complex and the perovskite is realized.

7. The natural gas engine exhaust catalyst as claimed in claim 1, wherein the vacuum drying is carried out by centrifugally drying Pd-loaded perovskite powder, placing the perovskite powder in a vacuum drying box with the vacuum degree of less than 0.01Mpa, and drying the perovskite powder for 1-2h at the temperature of 150-180 ℃.

8. The natural gas engine exhaust catalyst of claim 1, wherein the cold start airspeed is 60000h under cold start conditions^-1The concentration of tail gas is CH₄5000ppm，NO_x500ppm，O₂10000ppm。

Technical Field

The invention relates to a preparation method of a natural gas engine tail gas catalyst and a method for oxidation treatment of lower hydrocarbons by using the catalyst.

Background

With the steady improvement of the national economic level, the production scale and the holding amount of fuel oil motor vehicles are continuously increased, so the problem of automobile exhaust pollution caused by the rapid consumption of fuel oil seriously threatens the living health of human beings. In particular NO in motor vehicle exhaust gases_xThe emissions of HC, CO, PM and the like and secondary air pollution caused by these harmful components are attracting global attention. The natural gas engine is widely applied to production life and energy supply by virtue of the advantages of abundant raw material reserves, high efficiency, convenience and high convenience in use, pure tail gas emission and the like. Especially compared with the traditional motor vehicle exhaust emission, NMHC and NO in the natural gas engine combustion system_xThe emission of CO is obviously reduced, and the harm to human bodies caused by carcinogenic substances such as benzene, aromatic hydrocarbon and the like is basically avoided; and the octane number of the natural gas is as high as 130, so that the knocking probability of the engine is reduced, meanwhile, the natural gas fuel has less carbon deposit and high combustion efficiency, and the maintenance cost of the engine is saved. However, methane, the major component of natural gas, has a Global Warming Potential (GWP) that is 76 times higher than that of carbon dioxide, measured for 20 years, and must be strictly controlled; meanwhile, the natural gas engine has the technical problems that the durability of the tail gas catalyst is low, the catalyst is easy to be poisoned and the activity of the catalyst is reduced, and the like, and the natural gas engine is limitedPopularization and application of the gas engine.

Perovskite is a stable bimetallic oxide (basic structure ABO)₃) Rich resources, low cost, good chemical stability and catalytic oxidation capability. The A-site metal ions play a role in supporting a perovskite crystal structure, are mostly rare earth elements or alkali metal elements with larger ionic radius, and form a close-packed cubic structure with 12 lattice oxygens; the B-site metal ion forms 6 sets of oxygen coordination with the oxygen ion occupying the center of the octahedron in the cubic packing structure, which is often the main component determining many properties of perovskite-type materials due to its multiplicity of valency. Compared to simple oxides, perovskite structures can allow some elements to exist in unusual valence states, have non-stoichiometric ratios of oxygen, or allow reactive metals to exist in mixed valence states, giving the solid certain special properties. Because the nature of the solid is closely related to the catalytic activity of the solid, the specificity of the perovskite structure enables the solid to be widely applied to catalysis.

Disclosure of Invention

The invention mainly aims to provide preparation and application of a spongy natural gas engine exhaust catalyst, which is used for synthesizing novel spongy Pd based on better thermal stability, denitration performance and HC oxidation performance of perovskite_y/LaCe_xRh_1-xO₃Perovskite catalyst materials are used in tail gas purification technology for natural gas engines (NG). The pure perovskite catalyst is difficult to be practically applied due to various reasons such as small specific surface, difficult molding, low strength and the like. The preparation of the catalyst powder with high surface area and high surface activity is realized by introducing various solution components, changing the sedimentation state of precursor powder and regulating and controlling the synthesis process parameters of the catalyst. Experiments show that the B site in the perovskite structure still keeps the original lattice structure after being substituted by a small amount of the precious metal Rh, and the structural stability of the precious metal under the high-temperature condition is ensured. Meanwhile, the doping of heterogeneous atoms changes the lattice parameters of the perovskite space lattice to a certain degree, so that a large number of high-energy active centers (vacant sites, unsaturated stoichiometric B-O structures and low-valence metal ion groups) are formed, and the pairs of CO and CH are obviously improved₄Oxidation catalytic ability (see fig. 2). The characteristic of palladium-ammonia complex micromolecule groups is utilized to realize the dispersed loading of the noble metal nanocluster, and the overall activity of the perovskite catalyst is obviously improved.

The perovskite is a stable bimetallic oxide (with the basic structure of ABO3), is rich in resources and low in cost, and has good chemical stability and catalytic oxidation capability. The A-site metal ions play a role in supporting a perovskite crystal structure, are mostly rare earth elements or alkali metal elements with larger ionic radius, and form a close-packed cubic structure with 12 lattice oxygens; the B-site metal ion forms 6 sets of oxygen coordination with the oxygen ion occupying the center of the octahedron in the cubic packing structure, which is often the main component determining many properties of perovskite-type materials due to its multiplicity of valency. Compared to simple oxides, perovskite structures can allow some elements to exist in unusual valence states, have non-stoichiometric ratios of oxygen, or allow reactive metals to exist in mixed valence states, giving the solid certain special properties. Because the nature of the solid is closely related to the catalytic activity of the solid, the specificity of the perovskite structure enables the solid to be widely applied to catalysis.

In order to accomplish the above objects, according to one aspect of the present invention, there is provided a natural gas engine exhaust catalyst and a process for preparing the same, comprising mixing lanthanum nitrate (La (NO) with lanthanum nitrate₃)₃·6H₂O), cerium nitrate (Ce (NO)₃)₃) Noble metal rhodium nitrate (Rh (NO)₃)₃) The solution was dissolved in deionized water and citric acid CA (C6H) was added to the solution₈O₇) EDTA (C10H 16N)₂O₈) And urea (CH)₄N₂O) and stirring to form a particle suspension, and then dropwise adding ammonia water to adjust and dissolve suspended particles to obtain a clear and transparent precursor solution; quickly freezing and freezing the solution, transferring the solution into a freeze dryer, and obtaining perovskite precursor powder after all liquid phase components are removed; calcining the powder in a muffle furnace under air atmosphere, and cooling to room temperature to obtain LaCe₁-xRhxO₃Perovskite powder; then adding LaCe₁-xRhxO₃Placing the mixture in Pd ammonia complex solution to be stirred and loaded, placing the mixture in a vacuum drying oven to be deaminated after the stirring is finished, and obtaining Pdy/LaCe₁-xRhxO₃A perovskite catalyst.

Furthermore, the concentration of La and Ce metal ions in the precursor solution of the natural gas engine exhaust catalyst is 0.09-0.11mol/L, the molar ratio of the added citric acid, the ethylene diamine tetraacetic acid and the urea is (1-1.2): (1-1.2): (1.5-1.8), and the pH value of the precursor solution is 5-6.

Further, the natural gas engine tail gas catalyst is metal ion solution of natural gas engine tail gas catalyst, wherein lanthanum nitrate (La (NO3)₃·6H₂O), cerium nitrate (Ce (NO)₃)₃·6H₂O), rhodium nitrate (Rh (NO)₃)₃) Palladium nitrate (Pd (NO)₃)₄) The solution concentration (mol/L) is in the following proportion, when no noble metal element is added, the metal elements La to Ce are (0.9-1.1) to (0.9-1.1); the noble metal is added in a ratio of x + y being 0.05, when x is 0.01 and y is 0.04 (namely 1% -Rh), the metal element La to Ce is (0.9-1.1) to (0.89-1.11); when x is 0.02 and y is 0.03 (namely 2% -Rh), the metal element La and Ce is (0.9-1.1) and (0.88-1.12); when x is 0.03 and y is 0.02 (namely 3% -Rh), the metal element La: Ce is (0.9-1.1) to (0.87-1.13); when x is 0.04 and y is 0.01 (namely 4% -Rh), the metal element La: Ce is (0.9-1.1): 0.86-1.14).

Further, freeze-drying the natural gas engine tail gas catalyst, putting the precursor solution into a refrigerator at the temperature of between 5 ℃ below zero and 10 ℃ below zero to quickly freeze, and then putting the precursor solution into a freeze dryer to remove liquid phase components for 12 to 18 hours to obtain dry precursor powder.

Further, sintering the natural gas engine tail gas catalyst, placing the freeze-dried powder in a muffle furnace under an air atmosphere for calcining, firstly heating to 350 ℃ at the speed of 1-3 ℃/min, preserving heat for 3-3.5h, then heating to 700 ℃ at the speed of 8-10 ℃/min, preserving heat for 1.5-2h, and finally naturally air-cooling to the normal temperature of 18-28 ℃.

Further, the noble metal Pd element of the natural gas engine tail gas catalyst is loaded, and the obtained LaCe is₁-xRhxO₃Adding tetraamine nitrate with concentration of 0.06-0.1mol/L into perovskite powderPalladium [ Pd (NH) ]₃)₄](NO₃)₂And stirring the complex solution for 15-30min, wherein the pH value of the solution is 10-12, so that the electrostatic adsorption of the noble metal complex and the perovskite is realized.

Further, in the vacuum drying of the natural gas engine exhaust catalyst, the Pd element-loaded perovskite powder is centrifugally dried and placed in a vacuum drying box with the vacuum degree of less than 0.01Mpa and dried for 1-2h at the temperature of 150-.

Further, the tail gas concentration of the natural gas engine tail gas catalyst under the working condition of cold start is 60000h-1, and the gas concentrations are CH respectively₄5000ppm，NO_x500ppm，O₂10000ppm。

By applying the technical scheme of the invention, the NOx conversion efficiency in unit time can be improved, and the problem of the over-limit of the engine cold machine emission can be effectively solved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is an SEM micrograph and elemental surface distribution plot of a spongy perovskite material (Rh-3%);

FIG. 2 is an XRD diffractogram of a spongy perovskite material;

FIG. 3 is H2-TPR for a sponge-like perovskite material;

FIG. 4 is a surface area test result for a sponge-like perovskite material;

FIG. 5 is a result of a test of methane catalytic ability of a sponge-like perovskite catalyst.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

However, the present invention is not limited to the following examples, and in particular, the noble metal species (Pt, Ru, Ir) and the perovskite precursor synthetic salt species (sulfate, acetate, halide, and molecular ligand) may be replaced, and the present invention is applicable to all combustion systems of natural gas combustion engines.