CN101015800A - Honeycomb metal wire net carrier catalyst for catalytically reducing nitrogen oxide and preparing method thereof - Google Patents
Honeycomb metal wire net carrier catalyst for catalytically reducing nitrogen oxide and preparing method thereof Download PDFInfo
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- CN101015800A CN101015800A CN 200710010357 CN200710010357A CN101015800A CN 101015800 A CN101015800 A CN 101015800A CN 200710010357 CN200710010357 CN 200710010357 CN 200710010357 A CN200710010357 A CN 200710010357A CN 101015800 A CN101015800 A CN 101015800A
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Abstract
The invention relates to a honeycomb metal network carrier catalyst for catalyzing and reducing nitrogen oxide, and relative preparation, used in vehicle tail gas purification technique. The invention comprises metal carrier and catalyst, characterized in that the catalyst is load-type catalyst, the catalyst carrier is honeycomb metal network carrier carrying gamma-Al2O3 coat, referring coat mass, the content of TiO2 is 14.0-20.0wt% and the content of CeZrO is 3.0-6.0wt%, and referring to catalyst mass, the content of active component palladium is 0.1-1.0wt%, and the preparation comprises that preparing TiO2 gel, preparing TiO2 coat at the face of carrier, loading cerium zirconium oxide on carrier, leading in catalyst active component palladium. The invention has the advantages that the invention can improve mass transfer and heat transfer in catalyst, the catalyst has higher catalysis activity in low-temperature oxygen-abundant condition, wide active temperature window, simple preparation and low cost.
Description
Technical field
The present invention relates to a kind of Cellulated wiremesh Catalysts and its preparation method that is applicable to the Metal Palladium of poor combustion gasoline engine or the processing of diesel engine exhaust catalytic purification as active component, belong to the catalytic cleaning of car tail gas technical field.
Background technology
Vehicle exhaust has become the main source of atmospheric pollution, and it is one of most effectual way of carrying out the tail gas pollution control that catalytic cleaner is installed.At present, the mainstream technology of automobile exhaust gas purifying is to use triple effect catalytic converter, this purification techniques requires engine to work under the stoichiometric proportion condition, under control air-fuel ratio situation, can purify carbon monoxide, unburned main harmful and noxious substance in hydrocarbon and three kinds of tail gas of nitrogen oxide completely simultaneously, and to a certain extent, be to be cost with the economy of sacrificing fuel.Along with to energy-conservation and reduce greenhouse gases CO
2The pay attention to day by day of discharging, the market prospects of fuel-lean type gasoline engine and diesel engine are more and more wide.Fuel-lean type gasoline engine and diesel engine not only can improve the utilization rate of fuel, improve the economy of fuel, and reduce CO
2Discharging Deng pollutant.
But the fuel-lean type engine exhaust is rich in oxygen, and now commercial three-way catalyst can not be with the nitrogen oxide (NO that is wherein contained
x) be catalytically conveted to nitrogen effectively.Round the catalytic purification of exhaust of lean-burn automotive, carried out a large amount of research.At present, remove NO in the exhaust of lean-burn automotive
xMethod mainly be: NO
xDirect decomposition, poor combustion NO
xAbsorption, reduction technique and NO
xThe selection catalytic reduction.Wherein select Reduction of NO
xBe proved to be a kind of very potential NO that is used for removing under the excess oxygen
xMethod.
Utilize in the exhaust tail gas unburned completely hydrocarbon be to select Reduction of NO as reducing agent
xAn important directions.When reducing agent one timing, to NO
xCatalytic reduction ability and reaction temperature position of window and width depend on the prescription and the preparation method of catalyst.At present, as reducing agent, studying more both at home and abroad is as catalytic active component with noble metal with hydrocarbon.Noble metal catalyst is general active high, and low temperature active is good, and sulfur poisoning-resistant ability and steam deactivation are strong.But, when being catalyst with platinum to N
2Selectivity not high, especially when lower temperature, produce a large amount of accessory substance N
2O, and its active temperature scope is less.When precious metal palladium was active component, except possessing the total advantage of noble metal catalyst, it was few also to have an accessory substance, the selectivity advantages of higher.
For being applied in the exhaust tail gas employed exhaust gas purifying catalyst in the cleaning equipment, the general requirement: in this catalyst, the coating of being made by metal oxide loads on the surface of catalyst carrier, and so that bigger specific area to be provided, catalytic active component is dispersed on the coating surface.Because vehicle operational mode is different with load, travel speed and pavement behavior, therefore require catalyst carrier to have: higher heat endurance; Higher mechanical strength comprises wearability, hardness, compression strength and good shock-resistant and vibration performance; Higher specific surface area; Lower specific heat capacity etc.At present, most widely used is the monoblock type ceramic monolith.But, with respect to the mechanical shock that is born, the undercapacity of ceramic monolith.So the carrier that is made of metal has caused people's extensive concern.
Metallic carrier is with respect to ceramic monolith, has higher specific area, littler exhaust resistance and higher mechanical strength, and because the specific heat capacity of metallic carrier is low, for cleaning catalyst for tail gases of automobiles, low specific heat capacity just means the catalyst immersion heater, and this is during for cold-starting automobile, and it is particularly important that catalyst is under the low temperature condition catalyzed conversion to waste gas.But, because metallic carrier and coating material thermal coefficient of expansion is different, cause still imperfection very of its surface coating technology, cause it can not be widely used in practice.Use the more honeycomb ceramic carrier that remains in research and in using, wherein typical example has:
(1) people such as J.R.Gonz á lez-Velasco is at Ind.Eng.Chem.Res.2003, " the Pt/Ce that delivers on the 42:311-317
0.68Zr
0.32O
2Integer catalyzer is used for the control of vehicle exhaust " (Pt/Ce
0.68Zr
0.32O
2Washcoated Monoliths for Automotive Emission Control) in the literary composition, its scheme is: be dispersed in the water with the Ce/Zr mixed oxide, by dip coating, load on the monoblock type ceramic monolith and make catalyst then.With analog gas NO, C
3H
6Come the catalytic activity of evaluate catalysts with CO.Advantage, (1) transformation efficiency is higher, and the light off characteristics of catalyst is better; (2) with Ce/Zr mixed oxide replaced C eO
2/ Al
2O
3, improved the stability and the oxygen storage capacity of catalyst.Shortcoming: the catalytic carrier that uses is the monoblock type ceramic monolith, has influenced the light off characteristics of catalyst.
(2) people such as Li Landong is at Environ.Sci.Technol.2005, in " the Cu-ZSM-5 monoblock type ceramic catalyst that original position is synthetic is used for selecting catalytic reduction exhaust of lean-burn automotive nitrogen oxide " (Selective Catalytic Reduction of Nitrogen Oxides from Exhaust ofLean Burn Engine over In-Situ Synthesized Cu-ZSM-5/Cordierite) literary composition of delivering on the 39:2841-2847, its scheme is: synthesize the Cu-ZSM-5 catalyst with in-situ synthesis on the monoblock type ceramic monolith, and it is applied in NO in the exhaust of lean-burn automotive
xThe selection catalytic reduction handle.Advantage: (1) adopts integral catalyzer to handle exhaust of lean-burn automotive: (2) are used to handle actual automobile exhaust gas, reach treatment effect preferably; (3) behind the interpolation metal La, improved the catalytic performance of catalyst.Shortcoming: the catalytic carrier that adopt (1) is a ceramic monolith; (2) the catalytic reaction temperature is higher; (3) catalyst that uses is molecular sieve carrier, easy inactivation in the presence of steam.
It is catalyst carrier that the present invention adopts the Cellulated wiremesh carrier of adhesion-tight aluminum oxide coating layer.The honeycomb metal carrier is except the plurality of advantages with common metal carrier, because three-dimensional permeable structures makes it have higher mass-and heat-transfer coefficient, moderate degree of pressure is fallen, while wire mesh carrier good ductility, be suitable for the installation of various reactors, reduce the inside reactor dead volume, avoided penetrating of reactant.
Summary of the invention
Purpose of the present invention and task will overcome in the prior art and exist: the heat conductivility of (1) honeycomb ceramic carrier catalyst is relatively poor, influences the light off characteristics of catalyst; (2) low temperature active of catalyst is relatively poor, the deficiency that temperature window is narrower, and provide a kind of low temperature active height that has, the operating temperature window is wide, be applicable to honeycomb metal wire net carrier catalyst of selecting catalyzing and reducing nitrogen oxides under the lean-burn condition and preparation method thereof, special proposition technical solution of the present invention.
Design of the present invention is: in order to improve the intensity of catalyst, improve the heat conductivility of catalyst, to improve the catalytic performance of catalyst, and for the ease of catalyst being processed into the needs that different shape adapts to real catalytic converter, enlarge the Application of Catalyst scope, catalyst cupport is arrived metal carrier surface.
According to above-mentioned design, the present invention proposes a kind of honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides, comprise: honeycomb metal carrier and catalyst, it is characterized in that: catalyst is a loaded catalyst, Cellulated wiremesh carrier is a catalyst carrier, and multiple metal oxide is a coating material, and the small amount of precious metals palladium is the catalyst of catalytic active component, wherein
A) catalyst carrier is for having γ-Al
2O
3The Cellulated wiremesh carrier of coating, carrier framework material are the stainless steel metal silk screen, and carrier inside is three-dimensional permeable structures;
B) weight with carrier is benchmark, TiO
2Content be 14.0～20.0wt.%; The content of CeZrO is 3.0～6.0wt.%;
C) weight with catalyst is benchmark, and the content of catalyst activity component palladium is 0.1～1.0wt.%;
D) γ-Al
2O
3Coating layer thickness is 30～70 μ m;
E) the catalyst expression formula of Huo Deing is Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
The preparation method of the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides proposed by the invention is characterized in that, preparation process is as follows:
The first step, the preparation of TiO 2 sol
With the volume ratio is V
Butyl titanate: V
Absolute ethyl alcohol=1: 2～1: 6 ratio, butyl titanate is added in the absolute ethyl alcohol, then adding its concentration in solution of diethanol amine is 4.8% (volume ratio), magnetic agitation 2h at room temperature, slowly dripping its volume ratio then is V
Ethanol: V
Water=10: 1 the absolute ethyl alcohol and the mixed solution of water, adding molecular weight then and be its concentration in colloidal sol of polyethylene glycol of 2000 is 5～20g/L, ultrasonic again dispersion 10～20min obtains transparent TiO
2Colloidal sol;
Second step, the preparation of Cellulated wiremesh carrier surface titanium dioxide coating
The Cellulated wiremesh carrier of load aluminum oxide coating layer is immersed this TiO
2In the colloidal sol, treat to take out behind 2～10min, at first, dry 6-10h under 100-120 ℃; Subsequently, sample is immersed TiO again
2Colloidal sol repeats 2-5 time repeatedly; Then, the speed with 120 ℃/h in Muffle furnace is warming up to 400-600 ℃, insulation 2-3h; At last, reduce to room temperature;
The 3rd step, the preparation of cerium zirconium colloidal sol
Be M in molar ratio
Ce: M
Zr=67: 33 ratio is with Ce (NO
3)
36H
2O and Zr (NO
3)
45H
2O is mixed with mixed aqueous solution, and adding its concentration of polyethylene glycol then is 1.5～3.0g/L, and mixed solution is stirred in 60～80 ℃ of lower magnetic forces, slowly drips the 0.1mol/L citric acid in the process that stirs, and obtains white emulsus CeZrO colloidal sol;
The 4th step, the load of cerium Zr mixed oxide on the Cellulated wiremesh carrier
The Cellulated wiremesh carrier that will adhere to coating of titanium dioxide immerses in the CeZrO colloidal sol, treats to take out behind 5～15min, then, at 100～120 ℃ of down dry 6～10h; Dried sample places Muffle furnace to rise to 400～600 ℃ with the programming rate of 120 ℃/h, insulation 2～3h; At last, reduce to room temperature;
In the 5th step, introduce the catalytic active component palladium
The Cellulated wiremesh carrier of good titanium dioxide of load and cerium Zr mixed oxide coating is immersed in the PdCl of 100ppm
21～32h in the solution, then, at 100-120 ℃ of down dry 6～10h; Dried sample places Muffle furnace to rise to 400～600 ℃ with the programming rate of 120 ℃/h, insulation 2～3h; At last, reduce to room temperature, obtain Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
So the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides proposed by the invention has γ-Al
2O
3The Cellulated wiremesh carrier of coating is a carrier, and the thickness of aluminum oxide coating layer is decided according to the technology of preparation coating, and the thickness in this scope can both meet the demands.
The preparation method of the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides proposed by the invention when the content of active component palladium is lower than 0.1wt%, can not well bring into play the catalytic performance of catalytic active component; When the content of palladium during, not only reduced the catalytic activity of catalyst, and increased the cost of catalyst owing to the increase of palladium content greater than 1.0wt%.The content of catalytic active component Pd is relevant with dip time, along with the increase of dip time, and Pd content height.The content of titanium dioxide surpasses 20wt% in the catalyst, and promptly coating of titanium dioxide is thicker, through roasting, is easy to form and chaps; When content was lower than 14wt%, coating of titanium dioxide was thinner, can not cover aluminium dioxide fully.The too high levels of cerium Zr mixed oxide surpasses at 6.0% o'clock, and the CeZrO that titanium dioxide surface adheres to is too much, has hindered titanium dioxide and has participated in reaction; When cerium Zr mixed oxide content is lower than 3.0%, can not satisfy the needs of experiment.
Content, coating time, number of times and the roasting condition of the ratio of butyl titanate and absolute ethyl alcohol, polyethylene glycol are relevant among the preparation method of the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides proposed by the invention, coating of titanium dioxide and TiO 2 sol proportioning.When the ratio of butyl titanate and absolute ethyl alcohol is low excessively, the colloidal sol of preparation is thickness relatively, influences adhering to of coating; When its ratio was too high, the viscosity of obtained melten gel can not satisfy the requirement of coating.The excessive meeting of polyethylene glycol causes adhering to of coating insecure.The thickness of coating time and number of times and coating of titanium dioxide, promptly the content of titanium dioxide has direct relation.The overlong time of coating or the number of times of coating are too much, can cause the too high levels of titanium dioxide, and promptly coating of titanium dioxide is blocked up, through roasting, are easy to form and chap; But the coating time is very short or number of times seldom the time, and the coating of titanium dioxide that alumina surface forms is very thin, can not satisfy actual needs.
The firm degree of sintering temperature and coating and the crystalline structure of coating composition are relevant.When sintering temperature is lower than 400 ℃, can not make coating firm attached to alumina surface; When sintering temperature is higher than 600 ℃,, can cause the transformation of titanium dioxide crystalline form although can improve the adhesive ability of coating.
Baking temperature and drying time are as the criterion with the coating bone dry.In the dry run,, the temperature of drying need the dry time oversize when being lower than 100 ℃; Baking temperature is high more, drying time the long more drying that helps coating, still, temperature is higher than 120 ℃ and time and surpasses 8h and then consume the too much energy.
Catalyst of the present invention is carrier with the Cellulated wiremesh, catalytic active component is loaded to the coating of metal carrier surface, have the following advantages: (1) is because the metallic carrier thermal response is fast, make catalyst can be very fast when variations in temperature reach molecular balance, help the operation of automobile tail gas purification system; (2) the three-dimensional permeable structures of Cellulated wiremesh carrier helps catalyst inner radial mass transfer and heat transfer.And, uneven even the porch reactant mixes, can also further mix in catalyst inside, more help the carrying out that reacts; (3) adopt sol-gel process load TiO on the metallic carrier aluminum oxide coating layer
2Coating, TiO
2Evenly be coated in the alumina particle surface, help the high degree of dispersion of active component, improved dispersion degree of active components, thereby improved activity of such catalysts; (4) catalyst of the present invention is introduced the cerium Zr mixed oxide, further improved the decentralization of noble metal catalyst, and has certain storage oxygen function, under excess oxygen, catalyst can be operated in wider temperature range, thereby enlarged the reactivity window, reaction window temperature scope is 100 ℃; (5) catalyst of the present invention is active component with the precious metal palladium, produces synergy with titanium dioxide and cerium Zr mixed oxide, makes this catalyst to the NO in the exhaust of lean-burn automotive
xHave the good low-temperature catalytic activity, reaction temperature still has the conversion ratio near 70% about 100 ℃; (6) the present invention is combined into one Cellulated wiremesh carrier and catalyst, more helps improving its good catalysis characteristics of wide window at low temperatures, has solved the cold start-up problem of motor vehicle exhaust emission to a great extent.
The subordinate list explanation
The present invention is provided with 1 subordinate list altogether
Table 1 is the Pd/CeZrO/TiO of different palladium content
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is to NO
xThe influence of removing
The Pd/CeZrO/TiO that shows different palladium content in the table
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is applied to resulting each parameter of treatment of simulated exhaust of lean-burn automotive.As seen from table, the content of Pd is bigger to the catalytic performance influence of catalyst, and when the content of Pd was lower than 0.2%, catalyst was to NO
xCatalytic capability increase with the increase of palladium content; When Pd content was higher than 0.2%, catalyst was to NO
xCatalytic capability reduce with the increase of palladium content.Experimental result proof Pd content is 0.2% o'clock, catalytic effect the best.
Specific embodiment:
Below by specific embodiment, further specify catalytic cleaning of lean-burn engine tail gas NO
xHoneycomb metal wire net carrier catalyst and preparation method thereof.
Embodiment 1
For the existing narrower problem of operation window that is applicable to exhaust of lean-burn automotive, be equipped with titanium dioxide and cerium Zirconium oxide content is higher in order to the below legal system, and the lower honeycomb metal wire net carrier catalyst of catalytic active component palladium content.
The first step, the preparation of TiO 2 sol
The 28.43ml butyl titanate is dissolved in the 56.87ml absolute ethyl alcohol, the diethanol amine that then adds 4.8ml, after stirring 2h under the room temperature, the water that adds the 9.9ml volume ratio and be 1: 10 is in the mixed solution of ethanol, add the 0.5g molecular weight then and be 2000 polyethylene glycol, ultrasonic again dispersion 10min can obtain yellow transparent colloidal sol;
Second step, the preparation of alumina powder surface titanium dioxide coating
The Cellulated wiremesh carrier that will adhere to aluminum oxide coating layer immerses 2min in the 100ml titanium colloidal sol, dry 6h under 120 ℃; Repeat this step 2 time repeatedly, rise to 600 ℃ at Muffle furnace with the programming rate of 120 ℃/h then, insulation 2h reduces to room temperature, and obtaining area load has the Cellulated wiremesh of coating of titanium dioxide to carry;
The 3rd step, the preparation of cerium zirconium colloidal sol
Cerous nitrate (Ce (NO with 66ml 0.116mol/L
3)
36H
2O) zirconium nitrate (Zr (NO of solution and 80ml 0.0466mol/L
3)
45H
2O) solution mixes, and adding concentration then is the polyethylene glycol 14.5ml of 16.6g/L, and mixed solution is stirred in 80 ℃ of lower magnetic forces, slowly drips 0.1mol/L citric acid 60ml in the process that stirs, and obtains white emulsus CeZrO colloidal sol;
The 4th step, the load of adhering to cerium Zr mixed oxide on the carrier of titanium dioxide
There is the Cellulated wiremesh carrier of coating of titanium dioxide to immerse in the 100ml cerium zirconium colloidal sol load, take out behind the 15min, with 120 ℃ of following dry 6h, rise to 600 ℃ at Muffle furnace with the programming rate of 120 ℃/h at last, insulation 2h, reduce to room temperature, i.e. Zhi the Cellulated wiremesh carrier that contains the cerium Zr mixed oxide.The sample that obtains the wherein content of titanium dioxide is 20.0wt%, and the content of cerium Zr mixed oxide is 6.0wt%;
In the 5th step, introduce the catalytic active component palladium
The Cellulated wiremesh carrier of good titanium dioxide of load and cerium Zr mixed oxide coating is immersed in the PdCl of 100ml 100ppm
21h in the solution, then, dry 6h under 120 ℃; Drying is placed on that the programming rate with 120 ℃/h rises to 600 ℃ in the Muffle furnace, and insulation 2h reduces to room temperature, obtains 0.1%-Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
0.1%-Pd/CeZrO/TiO with preparation
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is applied to simulate the processing of nitrogen oxide in the exhaust of lean-burn automotive.The simulation exhaust of lean-burn automotive consists of: 2000ppmNO
x, 4000ppm C
3H
6, 6%O
2, N
2Be balanced gas.The gas speed of reacting gas is 1.67L/min, and air speed is 4325h
-1
Testing result: this catalyst shows medium catalytic activity in low temperature range, but the operating temperature window broad of catalyst, and 80～170 ℃ of temperature range catalyst conversion ratios change little; When reaction temperature was 140 ℃, the catalytic effect that catalyst behaves oneself best, conversion ratio were 56.93%.
Embodiment 2
For the existing catalyst reaction temperatures problem of higher that is applicable to exhaust of lean-burn automotive, be equipped with titanium dioxide and cerium Zirconium oxide content is lower in order to the below legal system, and the higher honeycomb metal wire net carrier catalyst of catalytic active component palladium content.
The first step, the preparation of TiO 2 sol
The 12.19ml butyl titanate is dissolved in the 73.11ml absolute ethyl alcohol, the diethanol amine that then adds 4.8ml, after stirring 2h under the room temperature, the water that adds the 9.9ml volume ratio and be 1: 10 is in the mixed solution of ethanol, add the 2.0g molecular weight then and be 2000 polyethylene glycol, ultrasonic again dispersion 20min can obtain transparent faint yellow colloidal sol;
Second step, the preparation of alumina powder surface titanium dioxide coating
The Cellulated wiremesh carrier that will adhere to aluminum oxide coating layer immerses 10min in the 100ml titanium colloidal sol, dry 10h under 100 ℃; Repeat this step 5 time repeatedly, rise to 400 ℃ at Muffle furnace with the programming rate of 120 ℃/h then, insulation 3h reduces to room temperature, obtains the Cellulated wiremesh carrier that area load has coating of titanium dioxide;
The 3rd step, the preparation of cerium zirconium colloidal sol
Cerous nitrate (Ce (NO with 66ml 0.116mol/L
3)
36H
2O) zirconium nitrate (Zr (NO of solution and 80ml 0.0466mol/L
3)
45H
2O) solution mixes, and adding concentration then is the polyethylene glycol 32.2ml of 16.6g/L, and mixed solution is stirred in 60 ℃ of lower magnetic forces, slowly drips 0.1mol/L citric acid 60ml in the process that stirs, and obtains white emulsus CeZrO colloidal sol;
The 4th step, the load of adhering to cerium Zr mixed oxide on the carrier of titanium dioxide
There is the Cellulated wiremesh carrier of coating of titanium dioxide to immerse in the 100ml cerium zirconium colloidal sol load, take out behind the 5min, with 100 ℃ of following dry 10h, rise to 400 ℃ at Muffle furnace with the programming rate of 120 ℃/h at last, insulation 3h, reduce to room temperature, i.e. Zhi the Cellulated wiremesh carrier that contains the cerium Zr mixed oxide.The sample that obtains the wherein content of titanium dioxide is 14.0wt%, and the content of cerium Zr mixed oxide is 3.0wt%;
In the 5th step, introduce the catalytic active component palladium
The alumina powder of good titanium dioxide of load and cerium Zr mixed oxide coating is immersed in the PdCl of 100ml 100ppm
232h in the solution, then, dry 10h under 100 ℃; Drying is placed on that the programming rate with 120 ℃/h rises to 400 ℃ in the Muffle furnace, and insulation 3h reduces to room temperature, obtains 1.0%-Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
1.0%-Pd/CeZrO/TiO with preparation
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is applied to simulate the processing of nitrogen oxide in the exhaust of lean-burn automotive.The simulation exhaust of lean-burn automotive consists of: 2000ppmNO
x, 4000ppm C
3H
6, 6%O
2, N
2Be balanced gas.The gas speed of reacting gas is 1.67L/min, and air speed is 4325h
-1
Testing result: this catalyst is relatively poor in the low temperature range catalytic activity, and when reaction temperature was 200 ℃, the conversion ratio of catalyst just was 46.22%.
Embodiment 3
Generally all adopt ceramic monolith for the catalyst that is used for motor-vehicle tail-gas, the catalyst for preparing on Cellulated wiremesh carrier in order to following method has solved and existingly has been applicable to that the reaction temperature of exhaust of lean-burn automotive catalyst is higher, the problem that operation window is narrower can satisfy laboratory and actual needs.
The first step, the preparation of TiO 2 sol
The 17.02ml butyl titanate is dissolved in the 68.28ml absolute ethyl alcohol, the diethanol amine that then adds 4.8ml, after stirring 2h under the room temperature, the water that adds the 9.9ml volume ratio and be 1: 10 is in the mixed solution of ethanol, add the 1.0g molecular weight then and be 2000 polyethylene glycol, ultrasonic again dispersion 15min can obtain transparent faint yellow colloidal sol;
Second step, the preparation of alumina powder surface titanium dioxide coating
The Cellulated wiremesh carrier that will adhere to aluminum oxide coating layer immerses 5min in the 100ml titanium colloidal sol, dry 8h under 110 ℃; Repeat this step 2 time repeatedly, rise to 500 ℃ at Muffle furnace with the programming rate of 120 ℃/h then, insulation 2h reduces to room temperature, obtains the Cellulated wiremesh carrier that area load has coating of titanium dioxide;
The 3rd step, the preparation of cerium zirconium colloidal sol
Cerous nitrate (Ce (NO with 66ml 0.116mol/L
3)
36H
2O) zirconium nitrate (Zr (NO of solution and 80ml 0.0466mol/L
3)
45H
2O) solution mixes, and adding concentration then is the polyethylene glycol 20ml of 16.6g/L, and mixed solution is stirred in 70 ℃ of lower magnetic forces, slowly drips 0.1mol/L citric acid 60ml in the process that stirs, and obtains white emulsus CeZrO colloidal sol;
The 4th step, the load of adhering to cerium Zr mixed oxide on the carrier of titanium dioxide
There is the Cellulated wiremesh carrier of coating of titanium dioxide to immerse in the 100ml cerium zirconium colloidal sol load, takes out behind the 10min,, rise to 500 ℃, insulation 2h at Muffle furnace with the programming rate of 120 ℃/h at last with 110 ℃ of dry 8h down.Reduce to room temperature, i.e. Zhi the Cellulated wiremesh carrier that contains the cerium Zr mixed oxide.The sample that obtains the wherein content of titanium dioxide is 17.02wt%, and the content of cerium Zr mixed oxide is 4.05wt%;
In the 5th step, introduce the catalytic active component palladium
The alumina powder of good titanium dioxide of load and cerium Zr mixed oxide coating is immersed in the PdCl of 100ml 100ppm
23h in the solution, then, dry 8h under 110 ℃; Drying is placed on that the programming rate with 120 ℃/h rises to 500 ℃ in the Muffle furnace, and insulation 2h reduces to room temperature, obtains 0.2%-Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
0.2%-Pd/CeZrO/TiO with preparation
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is applied to simulate the processing of nitrogen oxide in the exhaust of lean-burn automotive.The simulation exhaust of lean-burn automotive consists of: 2000ppmNO
x, 4000ppm C
3H
6, 6%O
2, N
2Be balanced gas.The gas speed of reacting gas is 1.67L/min, and air speed is 4325h
-1
Testing result: this catalyst shows higher catalytic activity in low temperature range, and the operating temperature window of catalyst is higher.The conversion ratio of 80～170 ℃ of temperature range catalyst changes between 65%～74%.
The Pd/CeZrO/TiO of the different palladium content of table 1
2/ Al
2O
3Honeycomb metal wire net carrier catalyst is to NO
xThe influence of removing
| NO xConversion ratio (%) | ||||||||
| Temperature (℃) | 25 | 50 | 80 | 110 | 140 | 170 | 200 | |
| Embodiment 1 | 0.1％-Pd/CeZrO/TiO 2/Al 2O 3The Cellulated wiremesh catalyst | 45.27 | 50.88 | 47.92 | 47.07 | 56.93 | 45.48 | 44.24 |
| Embodiment 2 | 1.0％-Pd/CeZrO/TiO 2/Al 2O 3The Cellulated wiremesh catalyst | 23.62 | 33.64 | 37.28 | 20.54 | 15.84 | 32.61 | 46.22 |
| Embodiment 3 | 0.2％-Pd/CeZrO/TiO 2/Al 2O 3The Cellulated wiremesh catalyst | 46.52 | 75.59 | 65.22 | 68.43 | 74.03 | 72.95 | 55.06 |
Claims (2)
1. the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides, comprise: metallic carrier and catalyst, it is characterized in that: catalyst is a loaded catalyst, with the Cellulated wiremesh carrier is catalyst carrier, multiple metal oxide is a coating material, the small amount of precious metals palladium is the catalyst of catalytic active component, wherein
A) catalyst carrier is for having γ-Al
2O
3The Cellulated wiremesh carrier of coating, carrier framework material are the stainless steel metal silk screen, and carrier inside is three-dimensional permeable structures;
B) weight with carrier is benchmark, TiO
2Content be 14.0～20.0wt.%; The content of CeZrO is 3.0～6.0wt.%;
C) weight with catalyst is benchmark, and the content of catalyst activity component palladium is 0.1～1.0wt.%;
D) γ-Al
2O
3Coating layer thickness is 30～70 μ m;
E) the catalyst expression formula of Huo Deing is Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
2. prepare the method for the honeycomb metal wire net carrier catalyst of catalyzing and reducing nitrogen oxides as claimed in claim 1, it is characterized in that, preparation process is as follows:
The first step, the preparation of TiO 2 sol
With the volume ratio is V
Butyl titanate: V
Absolute ethyl alcohol=1: 2～1: 6 ratio, butyl titanate is added in the absolute ethyl alcohol, then adding its concentration in solution of diethanol amine is 4.8% (volume ratio), magnetic agitation 2h at room temperature, slowly dripping its volume ratio then is V
Ethanol: V
Water=10: 1 the absolute ethyl alcohol and the mixed solution of water, adding molecular weight then and be its concentration in colloidal sol of polyethylene glycol of 2000 is 5～20g/L, ultrasonic again dispersion 10～20min obtains transparent TiO
2Colloidal sol;
Second step, the preparation of Cellulated wiremesh carrier surface titanium dioxide coating
The Cellulated wiremesh carrier of load aluminum oxide coating layer is immersed this TiO
2In the colloidal sol, treat to take out behind 2～10min, at first, dry 6-10h under 100-120 ℃; Subsequently, sample is immersed TiO again
2Colloidal sol repeats 2-5 time repeatedly; Then, the speed with 120 ℃/h in Muffle furnace is warming up to 400-600 ℃, insulation 2-3h; At last, reduce to room temperature;
The 3rd step, the preparation of cerium zirconium colloidal sol
Be M in molar ratio
Ce: M
Zr=67: 33 ratio is with Ce (NO
3)
36H
2O and Zr (NO
3)
45H
2O is mixed with mixed aqueous solution, and adding its concentration of polyethylene glycol then is 1.5～3.0g/L, and mixed solution is stirred in 60～80 ℃ of lower magnetic forces, slowly drips the 0.1mol/L citric acid in the process that stirs, and obtains white emulsus CeZrO colloidal sol;
The 4th step, the load of cerium Zr mixed oxide on the Cellulated wiremesh carrier
The Cellulated wiremesh carrier that will adhere to coating of titanium dioxide immerses in the CeZrO colloidal sol, treats to take out behind 5～15min, then, at 100～120 ℃ of down dry 6～10h; Dried sample places Muffle furnace to rise to 400～600 ℃ with the programming rate of 120 ℃/h, insulation 2～3h; At last, reduce to room temperature;
In the 5th step, introduce the catalytic active component palladium
The Cellulated wiremesh carrier of good titanium dioxide of load and cerium Zr mixed oxide coating is immersed in the PdCl of 100ppm
21～32h in the solution, then, at 100-120 ℃ of down dry 6～10h; Dried sample places Muffle furnace to rise to 400～600 ℃ with the programming rate of 120 ℃/h, insulation 2～3h; At last, reduce to room temperature, obtain Pd/CeZrO/TiO
2/ Al
2O
3Honeycomb metal wire net carrier catalyst.
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