CN111135827A - Ammonia oxidation catalyst for equivalent-weight-combustion natural gas engine tail gas and preparation method thereof - Google Patents

Ammonia oxidation catalyst for equivalent-weight-combustion natural gas engine tail gas and preparation method thereof Download PDF

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Publication number
CN111135827A
CN111135827A CN202010019300.XA CN202010019300A CN111135827A CN 111135827 A CN111135827 A CN 111135827A CN 202010019300 A CN202010019300 A CN 202010019300A CN 111135827 A CN111135827 A CN 111135827A
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catalytic material
noble metal
slurry
active component
ammoxidation catalyst
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王云
徐海迪
程永香
张艳华
杜洪仪
李阳
淡宜
陈耀强
李云
陈启章
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Sinocat Environmental Technology Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8634—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9436—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

The invention relates to an ammonia oxidation catalyst for equivalent combustion of natural gas engine exhaust and a preparation method thereof3Providing oxygen, thereby significantly increasing NH3The purification efficiency under the anoxic condition ensures that the exhaust emission meets the national standard, and has positive effects on environmental protection and large-scale application of AOC.

Description

Ammonia oxidation catalyst for equivalent-weight-combustion natural gas engine tail gas and preparation method thereof
Technical Field
The invention relates to the field of environmental protection, in particular to the field of automobile exhaust purification, and specifically relates to an ammonia oxidation catalyst suitable for equivalent-weight combustion natural gas engine exhaust and a preparation method thereof.
Background
The product of two reactions in the main reaction of Three Way Catalyst (TWC) for purifying automobile tail gas is H2Are CO and H, respectively2Reaction of O to CO2And H2And HC (Hydro-Carbon) and H2Reaction of O to CO and H2(ii) a On TWC, H2Mainly and O2、NOxReaction to produce H2O but also NOxCO and NOxReaction to form NH3(ii) a Thus, H generated on TWC2And H in the tail gas2All bring new by-product NH3。NH3Is a toxic gas with pungent odor, which affects air quality and human health. GB17691-2018 & lt limit of pollutant emission of heavy-duty diesel vehicle and measurement method (sixth stage of China) & gt (note: the regulation is applicable to heavy-duty diesel vehicles and heavy-duty natural gas vehicles) for separating NH3And HC, NOxCO and PM, among others, as pollutants whose emission needs to be controlled, NH3The emission limit of (2) is 10 ppm.
NH formation on TWC3Has a direct relationship with engine air-fuel ratio control, typically with air-fuel ratio greater than 1, NH, when the engine is operating3The production amount is greatly reduced; conversely, when the air-fuel ratio is less than 1, NH3The amount of production will increase significantly. Reduction of NH formation on TWC3One way is to adjust the air/fuel ratio to a value greater than 1, but at this time, because of O2Increased concentration of NOxThe conversion efficiency is reduced. National sixth stage, NOxRow of (2)The limit value is reduced from 2 g/kwh of the fifth nation to 0.46 g/kwh of the sixth nation by 77 percent. For TWC, it is particularly applied to the exhaust gas of an automobile, NO, in a stoichiometric natural gas engine (stoichiometric combustion, i.e. the ratio of the amount of fuel to the amount of air is theoretically equal to the stoichiometric ratio, the ratio of the two is called the air-fuel ratio, and when the engine is in operation, the air-fuel ratio is controlled to be less than or equal to 1, and the actual air-fuel ratio is switched between more than or less than 1, for example, 1 ± 0.03 fluctuation)xThe emission amount is reduced to below 0.46 g/kwh, and the median value of the optimal air-fuel ratio control is less than or equal to 1. However, when the median air-fuel ratio is 1 or less, NH3The emissions are substantially greater than 10 ppm, typically fluctuating between 10 and 150 ppm. Another method is to add an Ammonia Oxidation Catalyst (AOC) after TWC, and use AOC to react NH generated by TWC3Purifying to the national six-limit.
The existing AOC is made of NH3And O2Reaction to form N2And H2Principle of O to purify NH3Thus, for engine exhaust gases with an air-fuel ratio greater than 1, it is for NH3The purification efficiency is high, and the national emission standard can be reached; however, for an engine with an air-fuel ratio of 1 or less, the exhaust gas is in an oxygen-deficient (rich) state, which not only results in NH being generated at the TWC3The amount is relatively high and, moreover, due to insufficient O on the AOC2And NH3React to purify NH3AOC to NH3Is also very low, resulting in NH in engine exhaust gas having an air-fuel ratio of 1 or less3The emission amount greatly exceeds the standard, and the emission standard of national engine tail gas is seriously violated, so that the air environment is influenced.
Disclosure of Invention
The invention aims to overcome the defect that NH (ammonia to hydrogen) is generated when the air-fuel ratio in tail gas of a natural gas engine with equivalent weight combustion by using the conventional AOC (argon oxygen decarburization) and is particularly less than or equal to 13The defect of low purification efficiency, and provides an ammonia oxidation catalyst and a preparation method thereof; the ammoxidation catalyst significantly improves NH3The purification efficiency under the condition of oxygen deficiency ensures that the tail gas emission of the equivalent natural gas combustion engine meets the national standard,has positive effects on environmental protection and large-scale application of AOC.
In order to achieve the above object, the present invention provides an AOC ammonia oxidation catalyst for equivalent-weight-combustion of exhaust gas of a natural gas engine, the AOC ammonia oxidation catalyst consisting of a carrier and a catalytic material; the catalytic material consists of a noble metal active component and an oxygen storage material; the content of the noble metal active component (calculated by the noble metal simple substance) in the catalytic material is 0.05-0.5% of the mass of the catalytic material; the oxygen storage material is an oxygen storage material containing one or more elements of Ce, Zr, Al, Pr and Nd; the noble metal active component is a composition containing one or more of Pt, Rh and Pb, but not limited to.
The ammonia oxidation catalyst of the invention can utilize the characteristics that the oxygen storage material adsorbs oxygen under the aerobic condition and releases oxygen under the anoxic condition when the equivalent natural gas combustion engine works by loading the noble metal on the oxygen storage material in an active manner, and is NH in anoxic tail gas3To provide oxygen so that the ammonia oxygen catalyst reacts to NH in the oxygen-deficient exhaust gas3Also has high conversion efficiency, thereby obviously improving the total catalytic efficiency of the ammonia oxidation catalyst.
Wherein, the oxygen storage material can automatically adsorb or release oxygen according to the condition of the oxygen in the environment where the oxygen storage material is located; preferably, the oxygen storage materials are oxygen storage materials with different Ce/Zr ratios; most preferably, the oxygen storage material is CeO2、Ce0.1Zr0.9O2、Ce0.35Zr0.65O2、Ce0.5Zr0.5O2、Ce0.1Zr0.2Al0.7O1.65、Ce0.3Zr0.6Pr0.05Nd0.05OxOne or more of (a). The preferable oxygen storage material has high oxygen absorption and release speed and large quantity, and can meet the catalytic requirement of the AOC ammonia oxidation catalyst to the maximum extent.
Wherein, the noble metal active component refers to a compound with NH3Catalytic conversion to N2The noble metal catalyst of (3); the proportion of the noble metal active component is too small,to NH3The catalytic conversion efficiency is low, and the proportion of the noble metal active component is too large, so that the production cost is obviously improved, and the content of the oxygen storage material is reduced, so that the amount of oxygen absorbed and released by the oxygen storage material is insufficient, enough oxygen cannot be provided to meet the catalytic requirement of the ammonia oxidation catalyst, and the catalytic efficiency of the ammonia oxidation catalyst is reduced; in the catalytic material, the ratio of the noble metal active component (calculated by noble metal simple substance) is 0.15-0.3% of the mass of the catalytic material; most preferably, the ratio of the noble metal active component (calculated by the noble metal simple substance) is 0.25 percent of the mass of the catalytic material; the ratio of the noble metal active components is preferably selected, so that the catalytic efficiency of the ammonia oxygen catalyst can be improved to the maximum extent under the condition of reducing the cost.
The loading amount of the catalytic material represents the thickness of a catalyst coating on a carrier, the larger the loading amount is, the thicker the catalyst coating is, the larger the theoretical upper limit value of catalysis is, but the higher the cost is, the utilization rate of the catalyst is reduced due to the increase of the thickness, the smaller the loading amount is, the thinner the catalyst coating is, the smaller the theoretical maximum upper limit value of catalysis is, although the utilization rate of the catalyst is high, the insufficient catalysis degree is possibly caused, and the catalytic effect is reduced; preferably, the loading amount of the catalytic material on the carrier is 50-250 g/L; further preferably, the loading amount of the catalytic material on the carrier is 120-200 g/L; most preferably, the loading of the catalytic material on the carrier is 180 g/L; the preferable catalytic material has the advantages of high loading capacity, high utilization rate of the catalyst, large theoretical catalytic upper limit value and higher catalytic efficiency of the ammonia oxygen catalyst.
On the carrier, the content of the noble metal active component in the catalytic material reflects the catalytic speed of the catalyst coating, the higher the content of the noble metal active component is, the faster the catalytic speed is, but the higher the cost is, and the utilization rate is low, and the lower the content of the noble metal active component is, the slower the catalytic speed is, the catalytic effect is seriously influenced; preferably, on the carrier, the content of the noble metal active component (calculated by the noble metal simple substance) in the catalytic material is 1-10 g/ft3(ii) a Further preferably, the content of the noble metal active component in the catalytic material on the carrier is 3-8 g/ft3(ii) a Optimization ofOptionally, on the carrier, the content of the noble metal active component in the catalytic material is 5 g/ft3(ii) a The content of the optimized noble metal active component is high, the utilization rate of the catalyst is high, and the catalytic efficiency of the ammonia oxygen catalyst is higher.
Wherein the carrier is a conventional carrier used for an automobile exhaust catalyst; preferably, the carrier is a cordierite carrier; the optimized carrier has the advantages of low manufacturing cost, mature technology, wide application range, large load capacity and good stability.
In order to achieve the above object, the present invention further provides a method for preparing an ammonia oxidation catalyst for an oxygen-deficient tail gas, comprising the steps of:
(1) preparation of catalytic material: loading a precursor of the noble metal active component on an oxygen storage material by an equal-volume impregnation method, drying at 60-120 ℃ for 2-6 h, and roasting at 400-550 ℃ for 2-5 h in an air atmosphere to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol, and performing ball milling and pulping to obtain catalytic material slurry;
(3) preparation of an ammoxidation catalyst: coating a catalytic material slurry on a carrier; and drying the carrier coated with the slurry at 60-120 ℃ for 2-6 h, and then roasting at 400-550 ℃ for 2-5 h in an air atmosphere to obtain the AOC ammoxidation catalyst.
In the step (1), the precursor of the noble metal active component is nitrate, tetraamine nitrate or other inorganic salts of noble metal; illustratively, the noble metal active component precursor is one or more of platinum nitrate, palladium nitrate, rhodium nitrate, tetraamine platinum nitrate, tetraamine palladium nitrate, and chloroplatinic acid. The active component precursor solution can be a single active component precursor solution, or a mixed solution of a plurality of active component precursor solutions, or a mixed solution of the precursor solution and an auxiliary agent salt solution.
Wherein, too high temperature or too long time of calcination may destroy or reduce the oxygen storage function of the oxygen storage material, resulting in NH pair of ammonia-oxygen catalyst3The conversion efficiency of (2) is reduced, the temperature or time of calcination is too short, and noble metalsThe precursors of the active components are not completely converted into noble metal active components, which also leads to NH pairs of the ammonia-oxygen catalysts3The conversion efficiency of (2) is lowered; preferably, in the step (1), the roasting temperature is 450-; the optimized roasting temperature and time can better convert the precursor of the noble metal active component into the noble metal active component and better load the noble metal active component on the oxygen storage material, so that the obtained catalytic material can react with NH3The conversion efficiency of (a) is higher.
Compared with the prior art, the invention has the beneficial effects that:
1. the ammonia oxidation catalyst obviously improves NH by loading the noble metal active component on the oxygen storage material and utilizing the characteristics that the oxygen storage material adsorbs oxygen under the oxygen-enriched condition and releases oxygen under the oxygen-deficient condition3The conversion efficiency under the anoxic condition is obviously improved (can reach more than 90 percent) so that the tail gas of the equivalent natural gas combustion engine meets the national emission standard.
2. The ammonia oxidation catalyst can reasonably adjust the addition of the oxygen storage material according to different oxygen concentrations in the engine tail gas, thereby achieving the best tail gas treatment effect, saving the cost of the catalyst, reducing pollutant emission to the greatest extent and being beneficial to environmental protection.
3. The preparation method of the ammoxidation catalyst is simple and reliable, and the prepared ammoxidation catalyst has stable performance, thereby being beneficial to the large-scale production and application of the ammoxidation catalyst.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the following examples and comparative examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
(1) Preparation of catalytic material: loading a platinum nitrate solution (0.25 percent of the mass of the catalytic material calculated by a platinum simple substance) to CeO by an equal-volume impregnation method2Drying at 100 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 80 ℃ for 4h, and roasting at 450 ℃ for 4h to obtain the AOC ammoxidation catalyst.
Example 2
(1) Preparation of catalytic material: a platinum nitrate solution (0.3 percent of the mass of the catalytic material calculated by a platinum simple substance) is loaded on Ce by an equal-volume impregnation method0.1Zr0.9O2Drying at 60 ℃ for 6 h, and roasting at 450 ℃ for 4h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 100 ℃ for 3h, and roasting at 550 ℃ for 2h to obtain the AOC ammoxidation catalyst.
Example 3
(1) Preparation of catalytic material: a platinum nitrate solution (0.15 percent of the mass of the catalytic material calculated by the simple substance of platinum) is loaded on Ce by an equal-volume impregnation method0.35Zr0.65O2Drying at 120 ℃ for 2h, and roasting at 400 ℃ for 5 h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); to be coated with slurryDrying the carrier at 60 ℃ for 6 h, and roasting at 480 ℃ for 3h to obtain the AOC ammoxidation catalyst.
Example 4
(1) Preparation of catalytic material: a platinum nitrate solution (0.05 percent of the mass of the catalytic material calculated by a platinum simple substance) is loaded on Ce by an equal-volume impregnation method0.5Zr0.5O2Drying at 80 ℃ for 4h, and roasting at 550 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 120 ℃ for 2h, and roasting at 450 ℃ for 3h to obtain the ammoxidation catalyst.
Example 5
(1) Preparation of catalytic material: loading a tetramine platinum nitrate solution (0.5 percent of the mass of the catalytic material calculated by platinum simple substance) to Ce by an equal-volume impregnation method0.75Zr0.35O2Drying at 70 ℃ for 5 h, and roasting at 480 ℃ for 3h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 70 ℃ for 5 h, and roasting at 550 ℃ for 2h to obtain the AOC ammoxidation catalyst.
Example 6
(1) Preparation of catalytic material: a platinum nitrate solution (0.25 percent of the mass of the catalytic material calculated by the simple substance of platinum) is loaded on Ce by an equal-volume impregnation method0.9Zr0.1O2Drying at 90 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 90 ℃ for 3h, and roasting at 500 ℃ for 3h to obtain the AOC ammoxidation catalyst.
Example 7
(1) Preparation of catalytic material: a rhodium nitrate solution (0.25 percent of the mass of the catalytic material calculated by rhodium simple substance) is loaded on Ce by an equal-volume impregnation method0.1Zr0.2Al0.7O1.65Drying at 80 ℃ for 6 h, and roasting at 520 ℃ for 3h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparing AOC: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 80 ℃ for 6 h, and roasting at 450 ℃ for 2h to obtain the AOC.
Example 8
(1) Preparation of catalytic material: a palladium nitrate solution (0.25 percent of the mass of the catalytic material calculated by the simple substance of palladium) is loaded on Ce by an equal-volume impregnation method0.3Zr0.6Pr0.05Nd0.05OxDrying at 80 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparing AOC: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 100 ℃ for 4h, and roasting at 450 ℃ for 5 h to obtain the AOC.
Comparative example 1
(1) Preparation of catalytic material: loading a platinum nitrate solution (0.25 percent of the mass of the catalytic material calculated by a platinum simple substance) to La-Al by an equal-volume impregnation method2O3Drying at 100 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 80 ℃ for 4h, and roasting at 450 ℃ for 4h to obtain the AOC ammoxidation catalyst.
Comparative example 2
(1) Preparation of catalytic material: loading a platinum nitrate solution (0.03 percent of the mass of the catalytic material calculated by a platinum simple substance) to CeO by an equal-volume impregnation method2Drying at 100 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: the catalytic material slurry was coated (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 80 ℃ for 4h, and roasting at 450 ℃ for 4h to obtain the AOC ammoxidation catalyst.
Comparative example 3
(1) Preparation of catalytic material: loading a platinum nitrate solution (0.55 percent of the mass of the catalytic material calculated by a platinum simple substance) to CeO by an equal-volume impregnation method2Drying at 100 ℃ for 4h, and roasting at 500 ℃ for 2h to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol (accounting for 5 percent), and performing ball milling for 10 min to prepare slurry, thereby obtaining catalytic material slurry with the solid content of 40 percent;
(3) preparation of AOC ammoxidation catalyst: coating the catalytic material slurryCoating (noble metal content 5 g/ft)3) On cordierite carriers (Φ 25.4 × 101.6/400 cpsi); and drying the carrier coated with the slurry at 80 ℃ for 4h, and roasting at 450 ℃ for 4h to obtain the AOC ammoxidation catalyst.
Experimental example:
1. the catalysts prepared in examples 1 to 8 and comparative examples 1 to 3 described above were subjected to activity evaluation tests under the following test conditions:
simulating the atmosphere: routine 1 (air/fuel ratio greater than 1), 1000 ppm NH3；2000 ppm O2；10%H2O；7%CO2； N2For balance gas, SV =10,0000 h-1. Routine 2 (air/fuel ratio less than 1), 1000 ppm NH3；500 ppm O2；10%H2O；7%CO2；N2For balance gas, SV =10,0000 h-1. During the test, the atmosphere was simulated by switching the program 1 and the program 2 at a frequency of once every 5 s.
The catalyst is programmed to be heated to 550 ℃ under a simulated atmosphere, the temperature is kept for 2h, the temperature is reduced to 25 ℃, and the temperature is raised to 550 ℃ at the speed of 10 ℃/min. Infrared real-time testing of NH in tail gas3And (4) concentration. NH at a certain temperature3The conversion efficiency is calculated by the formula: NH (NH)3Original exhaust (1000 ppm) minus unconverted NH in the tail gas3Concentration is divided by the original row. The temperature at which the conversion efficiency reaches 50% is called the light-off temperature and is recorded asT 50. The temperature at which the conversion efficiency reaches 90% is called the complete conversion temperature and is recorded asT 90. The results are shown in Table 1:
TABLE 1 evaluation test results of activity of ammoxidation catalyst of the present invention
Catalyst and process for preparing same NH3 T 50（℃） NH3 T 90 (℃)
Example 1 317 342
Example 2 236 257
Example 3 248 269
Example 4 275 292
Example 5 281 304
Example 6 302 327
Example 7 312 325
Example 8 325 340
Comparative example 1 249 -
Comparative example 2 331 -
Comparative example 3 312 337
By analyzing the test results of table 1, it can be seen that: in the results of comparative example 1 containing no oxygen storage material, since the catalyst had a high conversion efficiency only in an atmosphere having an air-fuel ratio of more than 1, and a low conversion efficiency in an atmosphere having an air-fuel ratio of less than 1, the maximum average conversion efficiency could not reach 90%, the test results were only T50 (temperature corresponding to 50% conversion) value, but not T90; in comparative example 2, the noble metal content is too small compared to example 1, the limit for conversion efficiency is limited, resulting in a higher temperature required to reach T50 and no T90 value; in comparative example 3, the content of noble metal was too large compared to example 1, and although T50 and T90 effects could be achieved at lower temperatures, the cost was significantly increased. The catalysts of examples 1-8 all contained oxygen storage materials and the conversion efficiency could be 90% or more regardless of whether the air-fuel ratio was greater than 1 or less than 1 as long as the temperature reached the conversion conditions.
2. The catalysts prepared in examples 1-8 and comparative example 1 above were subjected to Oxygen Storage Capacity (OSC) tests under the following test conditions:
the prepared catalyst coating powder (200 mg) was put on a homemade OSC testing device and the sample was put under H at a flow rate of 40ml/min2Heating to 550 deg.C for 60 min, and switching to N2Cooling to 200 deg.C, performing O2Pulse experiment, TCD detection. The test results are shown in table 2:
TABLE 2 oxygen storage test results for ammoxidation catalysts of the present invention
Catalyst and process for preparing same Oxygen storage capacity (mu mol/g)
Example 1 423
Example 2 87
Example 3 251
Example 4 468
Example 5 516
Example 6 483
Example 7 124
Example 8 423
Comparative example 1 0
Comparative example 2 448
Comparative example 3 391
By analyzing the test results of table 2, it can be seen that: the oxygen storage amount in the catalyst is in direct proportion to the content of cerium in the oxygen storage material loaded on the catalyst. However, as the cerium content increases, the ammonia oxidation catalyst reacts to NH3The light-off temperature of the catalyst also increases greatly, so that the content of cerium in the oxygen storage material needs to be selected according to the actual condition of an engine when the ammonia oxidation catalyst is actually applied, so that the relationship between the light-off temperature and the oxygen storage amount is well balanced, and the optimal ammonia oxidation effect is achieved.
3. The ammonia oxygen catalysts of example 1 and comparative examples 1-3 were tested for maximum conversion efficiency under different atmospheric conditions as follows:
simulated atmosphere 1 (air-fuel ratio greater than 1, oxygen-rich), 1000 ppm NH3；2000 ppm O2；10%H2O；7%CO2； N2For balance gas, SV =10,0000 h-1。
Simulated atmosphere 2 (air/fuel ratio less than 1, oxygen deficit), 1000 ppm NH3；500 ppm O2；10%H2O；7%CO2； N2For balance gas, SV =10,0000 h-1。
Simulated atmospheres 3 simulated atmospheres 1 and 2 were switched at a frequency of once every 5 s.
Experiment temperature: 355 c (tested at a temperature at which the theoretical maximum catalytic conversion efficiency was achieved for each group in the experiment).
NH3The conversion efficiency is calculated by the formula: NH (NH)3Original exhaust (1000 ppm) minus unconverted NH in the tail gas3Concentration is divided by the original row.
The test method comprises the following steps: each group was tested in parallel 3 times and the average was taken.
The test results are shown in table 3:
TABLE 3 maximum average conversion efficiency in different simulated atmospheres
Serial number Atmosphere 1 (%) Atmosphere 2 (%) Atmosphere 3 (%)
Example 1 96.9 59.4 96.6
Comparative example 1 98.4 61.4 76.8
Comparative example 2 82.7 48.1 81.5
Comparative example 3 97.2 63.4 95.3
As can be seen from the analysis of the test results in table 3:
ammonia oxide catalyst in atmosphere 1 or 2 in inventive example 1 for NH3The conversion efficiency of (1) was rather slightly lower than that of comparative example, indicating that the addition of the oxygen storage material affected the contact of the noble metal with ammonia gas to a certain extent, resulting in a slight decrease in the conversion efficiency, but the conversion efficiency in atmosphere 3 was significantly higher than that of comparative example 1, to sayThe light oxygen storage material can adsorb oxygen in the oxygen-rich atmosphere of the atmosphere 3 and release oxygen in the oxygen-poor atmosphere, thereby obviously improving NH3The conversion efficiency under the anoxic condition is improved, so that the conversion efficiency in the atmosphere 3 is obviously improved; while comparative example 1 has better conversion efficiency under oxygen-rich conditions, the conversion efficiency is lower under oxygen-poor conditions, and no oxygen storage material is present, and converted oxygen cannot be supplied to the oxygen-poor conditions, so that the conversion efficiency in atmosphere 3 is significantly reduced; in comparative example 2, although containing an oxygen storage material, since the noble metal content is too small, the conversion efficiency is low even if there is sufficient oxygen under anoxic conditions, and thus the conversion efficiency in atmosphere 3 is also low; although comparative example 3 contains higher noble metal and has higher conversion efficiency under the oxygen-rich condition, under the oxygen-poor condition, the oxygen released by the oxygen storage material is limited, and the conversion efficiency under the oxygen-poor condition is rather low, so that the conversion efficiency in the atmosphere 3 is reduced compared with that in example 1, and the method is not suitable for popularization and application under the condition that the cost is remarkably increased.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. An ammonia oxidation catalyst for natural gas engine exhaust, which is characterized by comprising a carrier and a catalytic material; the catalytic material consists of a noble metal active component and an oxygen storage material; the ratio of the noble metal active component is 0.05-0.5% of the mass of the catalytic material; the oxygen storage material is an oxygen storage material containing one or more elements of Ce, Zr, Al, Pr and Nd; the noble metal active component includes, but is not limited to, a composition of Pt.
2. The ammoxidation catalyst according to claim 1, wherein the oxygen storage material is CeO2、Ce0.1Zr0.9O2、Ce0.35Zr0.65O2、Ce0.5Zr0.5O2、Ce0.1Zr0.2Al0.7O1.65、Ce0.3Zr0.6Pr0.05Nd0.05OxOne or more of (a).
3. The ammoxidation catalyst according to claim 1, wherein the proportion of the noble metal active component is 0.15 to 0.3% by mass of the catalyst material.
4. The ammoxidation catalyst according to claim 1, wherein the loading of the catalytic material on the carrier is 50 to 250 g/L.
5. The ammoxidation catalyst according to claim 4, wherein the loading of the catalytic material on the carrier is 200 g/L.
6. The ammoxidation catalyst of claim 1, wherein the amount of the noble metal active component in the catalytic material on the support is in the range of 1 to 10 g/ft3。
7. The ammoxidation catalyst according to claim 1, wherein the natural gas engine is an equivalent combustion engine.
8. A method of preparing the ammonia oxidation catalyst of claim 1, comprising the steps of:
(1) preparation of catalytic material: loading a precursor of the noble metal active component on an oxygen storage material by an equal-volume impregnation method, drying at 60-120 ℃ for 2-6 h, and roasting at 400-550 ℃ for 2-5 h in an air atmosphere to obtain a catalytic material;
(2) preparing coating slurry: mixing a catalytic material with alumina sol, and performing ball milling and pulping to obtain catalytic material slurry;
(3) preparation of an ammoxidation catalyst: coating a catalytic material slurry on a carrier; drying the carrier coated with the slurry at 60-120 ℃ for 2-6 h, and then roasting at 400-550 ℃ for 2-5 h in air atmosphere to obtain the ammoxidation catalyst.
9. The method for preparing an ammoxidation catalyst according to claim 8, wherein the noble metal active component precursor is one or more of platinum nitrate, palladium nitrate, rhodium nitrate, tetraamine platinum nitrate, tetraamine palladium nitrate, and chloroplatinic acid.
10. The method for preparing an ammoxidation catalyst according to claim 8, wherein the calcination temperature in the step (1) is 450 ℃ and 500 ℃ for 3 to 4 hours.
CN202010019300.XA 2020-01-08 2020-01-08 Ammonia oxidation catalyst for equivalent-weight-combustion natural gas engine tail gas and preparation method thereof Pending CN111135827A (en)

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