KR100656014B1 - Method for producing platinum catalyst supported on mesoporous molecular sieve for removing rare nitrogen oxides - Google Patents

Abstract

The present invention relates to a method for preparing a mesoporous molecular sieve supported platinum-based catalyst for removing lean nitrogen oxide, and more particularly, to synthesize a mesoporous molecular sieve as a carrier, and to immerse the mesoporous molecular sieve in an aqueous inorganic salt solution and After the reaction was carried out in an oven and then washed, filtered and dried and calcined, platinum was introduced into the mesoporous molecular sieve having excellent hydrothermal stability by introducing platinum (Pt), thereby introducing various metals as active metal components. Compared with the catalyst, a mesoporous molecular sieve supported platinum-based catalyst having a wide activity temperature window and high nitrogen oxide removal activity can be prepared.

Mesoporous, platinum, catalyst

Description

Method for producing platinum based catalysts supported on mesoporous molecular sieves for lean NOx control             

1 shows that MCM-41 subjected to post-treatment was subjected to treatment (a) and post-treatment at 500 ° C. for 10 hours under 10 vol.% H ₂ O conditions (W / F = 0.012 g-catalyst · hour / liter). Treatment of MCM-41 with boiling water at 100 ° C. for 9 hours (b), MCM-48 subjected to post-treatment at 500 ° C., 10 vol.% H ₂ O conditions (W / F = 0.012 g-catalyst, hour / liter X-ray diffraction analysis shows the structure of the mesoporous molecular sieve when MCM-48 treated with c) and post-treatment for 12 h in () was treated for 9 h in 100 ° C. boiling water.

FIG. 2 shows platinum supported on mesoporous molecular sieves (MCM-41 and MCM-48), conventional mesoporous molecular sieves (KIT-1 and SBA-15) and zeolite ZSM-5 subjected to post-treatment in the present invention. It is a graph showing the lean nitrogen oxide removal performance of one catalyst.

3 is a mesoporous molecular sieve [MCM-41 (a), MCM-48 (b)] subjected to post-treatment in the present invention, and a conventional mesoporous molecular sieve [KIT-1 (c), SBA-15 ( d)] is a graph showing the lean nitrogen oxide removal performance of a catalyst in which aluminum is added as platinum and a promoter.

4 is a mesoporous molecular sieve [MCM-41 (a), MCM-48 (b)] subjected to post-treatment in the present invention, and a conventional mesoporous molecular sieve [KIT-1 (c), SBA-15 ( d)] is a graph showing the lean NOx removal performance of a catalyst added with ruthenium as a platinum and a promoter.

5 is a graph showing the lean nitrogen oxide removal performance when using a catalyst carrying platinum and ruthenium in a mesoporous molecular sieve (MCM-48) subjected to post-treatment in the present invention and using dodecane and propylene as a reducing agent. to be.

The present invention relates to a method for preparing a mesoporous molecular sieve supported platinum-based catalyst for removing lean nitrogen oxide, and more particularly, to synthesize a mesoporous molecular sieve as a carrier, and to immerse the mesoporous molecular sieve in an aqueous inorganic salt solution and After the reaction was carried out in an oven and then washed, filtered and dried and calcined, platinum was introduced into the mesoporous molecular sieve having excellent hydrothermal stability by introducing platinum (Pt), thereby introducing various metals as active metal components. Compared to the catalyst, a mesoporous molecular sieve supported platinum-based catalyst having a wide activity temperature window and high nitrogen oxide removal activity can be prepared.

With the recent tightening of exhaust regulations, attention has been focused on the removal of lean NOx from diesel and lean burn gasoline engines. Nitrogen oxides (NOx), which occur in densely populated areas, are mainly emitted from vehicles, cause photochemical smog and acid rain in the atmosphere, and are known to directly harm humans such as bronchitis, pneumonia, cough and dyspnea.

NOx from gasoline engines can be efficiently removed by three-way catalysts, while lean gas from diesel or lean-burn gasoline engines operating under conditions where the air / fuel ratio is higher than the stoichiometric ratio. Nitrogen oxides (Lean NOx) are in a difficult state to remove by conventional techniques. This is because there is an excessive amount of oxygen, a more powerful oxidant than NOx, in diesel and lean burn engine exhaust gases, and this oxygen is more likely to be selectively adsorbed on the catalyst surface than NOx and also difficult to remove NOx by reacting with a reducing agent. Therefore, research to solve these technical problems is concentrated.

As a technique for removing lean NOx generated at the current mobile source, de-NOx technique by engine improvement; Anchorage selective catalytic SCR reduced mobility (mobile) applying the device (Selective Catalytic Reduction, SCR) method and an exhaust gas hydrocarbons using the hydrocarbons as a reducing agent in the use of ammonia, urea, etc. which are commercially available from the (stationary source) with a reducing agent Denitrification techniques using catalysts such as the (HC) -SCR method; Denitrification techniques using adsorbents; Or a denitrification technique using a plasma technique, but a considerable time is still required for commercialization except for the denitrification technique by engine improvement.

In the case of the denitrification technology by improving the engine, the most technical progress has been made, but there is a problem that it is inevitable to install the aftertreatment device because there is a fundamental limitation in removing NOx. The NOx direct decomposition method is a method of decomposing NOx on a catalyst without using a reducing agent, but it is difficult to apply practically since the decomposition efficiency is very low under diesel engine exhaust gas conditions.

The NOx trap is a method of collecting NOx from a lean region and then discharging it into a rich region to remove NOx by a catalyst. NOx traps are considered promising because of the low efficiency of lean NOx catalysts (LNCs). It has the performance of conventional three-way catalyst in the theoretical performance ratio, and absorbs and stores NOx as a NOx trap in the lean region, and purifies the collected NOx when fuel injection or the air-fuel ratio is high, and at the same time restores the NOx trap performance. Ba, K, Sr or the like is used as the NOx trap material. NOx traps have the advantages of high temperature durability but have the problem of being poisoned by sulfur in the fuel.

The method using plasma is advantageous for oxidizing NO to NO ₂ , but it is difficult to practically use it because of very low N ₂ selectivity, by-product treatment, excessive power usage, and maintenance and vehicle mounting space. Therefore, in recent years, the NO ₂ by using the then oxidize NO to NO ₂ catalyst in the plasma of the plasma switch to N ₂ - has been mainly conducted research on the hybrid catalyst system.

Selective reduction method using a reducing agent (SCR) is a commercial application of ammonia denitrification technology in a stationary source, which is currently commercialized, using ammonia as a reducing agent to reduce the NO generated in the diesel engine to N ₂ and O ₂ . Although the removal rate of nitrogen oxides is about 60 to 80% higher than other technologies, it is necessary to solve the problem that a separate ammonia supply device is required and the size of the device is enlarged in order to be practically applied to automobiles. Recently, due to the miniaturization of the device structure and the SCR catalyst using urea as a reducing agent, the practicality has been improved, but the structure is complicated and the price is high, and it is being applied to a large engine.

In recent years, there has been increasing interest in the development of a technology for reducing NOx discharged from a lean burn internal combustion engine by a catalyst using a hydrocarbon as a reducing agent. In general, these catalysts have used as a carrier alumina / silica-zeolites supported with copper or platinum as active metals. Since the selective catalytic reduction of NOx in lean burn conditions has required ammonia, urea, or other expensive or inconvenient reducing agents, the use of hydrocarbons as reducing agents is very important.

The method of selectively reducing NOx by using hydrocarbon as a reducing agent (HC-SCR) is a very practical technique in that residual hydrocarbons or fuel in exhaust gas can be used as a reducing agent. Since the results were reported by the Iwamoto group, extensive research has been conducted as lean nitrogen oxide catalysts (LNCs) which are the most practical to date. Cu-ZSM-5 and Pt-ZSM-5 are known as representative catalysts. Cu-ZSM-5 catalyst has the highest NOx reduction rate at 300 ~ 500 ℃ and shows about 50 ~ 60% removal rate as laboratory value. However, due to the reaction activity temperature higher than the actual diesel exhaust gas discharge temperature (300 ℃), and the activity reduction phenomenon for moisture and sulfur dioxide has shown a problem in practical use. On the other hand, Pt-ZSM-5 catalyst shows the removal efficiency of about 40-50% at 200-300 ° C, but has a disadvantage of high selectivity to N ₂ O, another contaminant, and a narrow window of active temperature.

Thus, various attempts have been made to develop new catalyst systems having low activity temperatures, wide activity window, high N ₂ selectivity and endothelial toxicity.

Metal catalysts supported on zeolites do not solve the deactivation phenomenon until now, so there is a tendency to use non-zeolitic carriers such as alumina. In addition, apart from such a carrier, a single metal catalyst is not practical enough due to problems such as a narrow active temperature window to be applied to a diesel vehicle, and development of a catalyst by various combinations of various metals is essential.

Accordingly, the inventors of the present invention have made efforts to meet the above expectations, using a mesoporous molecular sieve having improved hydrothermal stability by post-treatment using an inorganic salt solution as a carrier and activating various metals such as precious metals and transition metals. The present invention has been completed by incorporating a metal component into a new catalyst exhibiting higher activity than a conventional zeolite catalyst.

Accordingly, the present invention provides a novel mesoporous molecular sieve supported platinum-based catalyst having a wide active temperature window and high NOx removal activity by introducing various metals into the active metal component in the mesoporous molecular sieve carrier having improved hydrothermal stability. The purpose is to provide a manufacturing method.

The present invention comprises the steps of (a) synthesizing mesoporous molecular sieve as a carrier; (b) immersing the mesoporous molecular sieve in an aqueous inorganic salt solution and adjusting the pH to 9.5 to 10.5 and then reacting at 70 to 110 ° C. for 1 day to 20 days; (c) washing the completed mesoporous molecular sieve with distilled water, filtration and drying and calcining at 500 to 650 ° C .; And (d) introducing platinum (Pt) into the calcined mesoporous molecular sieve.

The present invention also provides a mesoporous molecular sieve supported platinum-based catalyst prepared by the above production method.

Hereinafter, the present invention will be described in detail.

The present invention synthesizes a mesoporous molecular sieve as a carrier, immersed in the inorganic salt aqueous solution of the mesoporous molecular sieve, and adjusted the pH, and then reacted in an oven and then washed, filtered and dried and calcined, and platinum (Pt) By introducing a variety of metals into the mesoporous molecular sieve having excellent hydrothermal stability as an active metal component, a mesoporous molecular sieve supported platinum-based catalyst having a broader temperature window and higher nitrogen oxide removal activity than a conventional zeolite catalyst I can manufacture it

Hereinafter, the present invention will be described in detail for each manufacturing step.

First, a step of synthesizing mesoporous molecular sieve as a carrier.

The mesoporous molecular sieve described above is composed of silica and has a pore size of 2 to 50 nm (which is a definition of mesoporous material itself). Specifically, known MCM-41, MCM-48, KIT-1, SBA-15, etc. can be used.

Secondly, the mesoporous molecular sieve is immersed in an aqueous inorganic salt solution, and then adjusted to pH 9.5 to 10.5, followed by reaction at 70 to 110 ° C. for 1 day to 20 days.

The inorganic salt aqueous solution may use NaCl or EDTANa ₄ . The inorganic salt aqueous solution is used in a concentration of 0.32 ~ 13% by weight, the concentration of the inorganic salt aqueous solution may vary depending on the type of mesoporous molecular sieve.

For example, when MCM-41 is used as the mesoporous molecular sieve, the concentration of NaCl aqueous solution is 6.5% by weight, and in the case of MCM-48, the concentration of NaCl aqueous solution is preferably adjusted to 0.32% by weight. If exceeds the above range, the hydrothermal stability of the molecular sieve is reduced.

The hydrothermal stability of the post-treated mesoporous molecular sieve can be optimized according to the concentration and amount of the inorganic salt aqueous solution, and the immersion of the inorganic salt aqueous solution in an amount of 12 to 30 ml per g of molecular sieve is immersed in the mesoporous molecular sieve. It is desirable to.

PH control of the aqueous solution of the inorganic salt containing the mesoporous molecular sieve can be performed using concentrated EDTANa ₄ and the like, to maintain the pH in the range of 9.5 ~ 10.5, preferably to maintain the pH at about 10 The case is good.

The aqueous solution of mesoporous molecular sieve-containing inorganic salt prepared as described above is reacted at 70 to 110 ° C, preferably at about 100 ° C. At this time, if the reaction temperature is less than the above range, the progress of the reaction is difficult, and there is no benefit above the above range. Under these conditions, the reaction is carried out for 1 day to 20 days, preferably for 12 days to 20 days. If the reaction time is less than 1 day, the effect of improving hydrothermal stability does not appear. Most preferably, the reaction is performed in an oven at about 100 ° C. for at least 12 days.

Third, after the reaction is completed, the mesoporous molecular sieve is washed with distilled water, filtered and dried, and then calcined at 500 to 650 ° C.

Firing is important to be carried out at a specific temperature for more than a sufficient time. If the firing temperature is below the above range, the surfactant is not completely removed. If the firing temperature is above the above range, the structure collapses and the surface area and pore volume decrease. The firing time is sufficient to be at least 5 hours so that the surfactant is completely removed.

Fourthly, platinum (Pt) is introduced into the calcined mesoporous molecular sieve.

In this case, the amount of platinum introduced is 0.5 to 5 parts by weight based on 100 parts by weight of the mesoporous molecular sieve. The introduction of the platinum is carried out by the impregnation method, the reaction activity is insignificant if the amount of platinum introduced is less than the above range, there is no profit if the platinum is introduced.

In addition, precious metals selected from ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), and the like as cocatalysts on the mesoporous molecular sieve, vanadium (V), manganese (Mn), and cobalt (Co) , Copper (Cu), tin (Sn), aluminum (Al) and the like may be further used one or two or more selected from a metal selected from, such that the amount of the promoter is 0.5 to 100 parts by weight of the mesoporous powder It is more preferable to use-5 weight part.

The mesoporous molecular sieve supported platinum-based catalyst prepared as described above has a broader activity temperature window and higher nitrogen oxide removal activity than conventional zeolite-based catalysts.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the following Examples.

 Example 1 Synthesis of Mesoporous Molecular Sieves with Improved Hydrothermal Stability

First, the mesoporous molecular sieves MCM-41 and MCM-48 were prepared using conventional methods reported in the academic world, and post-salt treatment was performed to improve hydrothermal stability as described below.

NaCl, an inorganic salt, was dissolved in distilled water to make a salt solution, and the dried mesoporous molecular sieve was added at a rate of 1 g per 25 ml of salt solution. At this time, the concentration of the salt solution was adjusted to 6.5% by weight for the mesoporous molecular sieve MCM-41, 0.32% by weight for the MCM-48. The pH was adjusted to 10 using a concentrated EDTANa ₄ solution and then reacted in an oven at 100 ° C. for 12 days. After completion of the reaction, the mixture was washed with distilled water, filtered and dried, and then calcined at 550 ° C. for 5 hours to prepare a mesoporous molecular sieve carrier.

As shown in FIG. 1, MCM-41 and MCM-48 were subjected to post-treatment when treated at 500 ° C. for 10 hours at 10% by volume H ₂ O conditions (W / F = 0.012 g-catalyst, time / liter). It can be seen that the structure of is maintained better than the case where the post-treatment was not performed. Even after 9 hours in boiling water at 100 ℃, the structure of the MCM-41 and MCM-48 after the post-treatment was maintained relatively well compared to the case without the post-treatment. In the actual NOx removal process, there is a situation where the moisture content and the temperature are kept high, so this improved hydrothermal stability is an essential element of the NOx removal catalyst.

Example 2 Preparation of Mesoporous Molecular Sieve Supported Metal Catalysts

Pt as a single metal component was introduced into the mesoporous molecular sieve prepared in Example 1, and Ru, Pd, Rh, Ag, Sn, V, Cu, and Co were introduced as cocatalysts. The promoter except Al was dried by 100 impregnation and calcined at 550 ° C. after Al impregnation, and in case of Al, AlCl ₃ was dissolved in ethanol and stirred for 30 minutes with the dried mesoporous molecular sieve. It was then filtered, dried at 100 ° C. and calcined at 550 ° C. The Pt content was adjusted to 1 wt%, the cocatalyst content was adjusted to 0.5 to 5 wt%, and in the case of Al cocatalyst, the molar ratio of Si / Al was adjusted to 90 or less.

Example 3 NOx Removal Performance of Mesoporous Molecular Sieve Supported Metal Catalyst

The mesoporous molecular sieve supported platinum catalyst prepared in Example 2 was 0.2g of powder, and the reaction was carried out in a continuous flow type in a quartz tube with temperature control. The concentration of NO was 2,000ppmv and the reaction was carried out by changing the concentration of reducing agent, oxygen and space velocity. The outlet flow was measured by on-line gas chromatography and NOx analyzer.

Mesoporous molecular sieves (MCM-41 and MCM-48) and the conventional mesoporous molecular sieves (KIT-1, SBA-15) and zeolite ZSM-5 supported by platinum were subjected to the post-treatment process. The lean nitrogen oxide removal performance (reaction conditions: 2,000ppmv NO; 2,000ppmv C ₃ H ₆ , 5% by volume O ₂ , W / F = 0.012 g-catalyst / hour / liter) is shown in FIG. 2.

When Pt is introduced as a single metal, it can be seen that the mesoporous molecular sieve-supported metal catalyst of the present invention has a higher NOx removal activity and a wider activation temperature window than the most widely known Pt / ZSM-5.

In the case of a catalyst incorporating a multi-component metal, the reaction activity increased when Al was used as a promoter (see FIG. 3). In addition, when Ru was introduced, the NOx removal activity in the high temperature region was increased (see FIG. 4). Therefore, it can be seen that the active temperature window can be widened through the optimized Ru content. Mesoporous molecular sieves (MCM-41 and MCM-48) and conventional mesoporous molecular sieves (KIT-1 and SBA-15) subjected to post-treatment in the present invention are made of aluminum (or ruthenium) as platinum or a promoter. The lean nitrogen oxide removal performance (reaction conditions: 2,000ppmv NO; 2,000ppmv C ₃ H ₆ , 5% by volume O ₂ , W / F = 0.012g-catalyst, time / liter) of the introduced multicomponent metal supported catalyst 3 and 4 are shown.

When dodecane (C ₁₂ H ₂₆ ) was used as a reducing agent, as shown in FIG. 5 (reaction conditions: 2,000 ppmv NO; 5 vol% O ₂ , W / F = 0.012 g-catalyst, hour / liter) The reaction activity of the mesoporous molecular sieve (MCM-48) -supported metal catalyst of the present invention was lower than that of propylene (C ₃ H ₆ ), but the reaction activity of the conventional Pt / ZSM-5 catalyst using propylene as a reducing agent. Higher. Therefore, the catalyst according to the present invention can be usefully applied even when diesel fuel is directly used as a reducing agent.

As described above, according to the method for preparing a mesoporous molecular sieve supported metal catalyst, various metals are introduced as active metal components into mesoporous molecular sieves having excellent hydrothermal stability, and thus have a wider active temperature window than conventional zeolite catalysts. And a mesoporous molecular sieve supported platinum-based catalyst having high nitrogen oxide removal activity.

Claims (7)

(a) synthesizing mesoporous molecular sieve as a carrier; (b) immersing the mesoporous molecular sieve in an aqueous inorganic salt solution and adjusting the pH to 9.5 to 10.5 and then reacting at 70 to 110 ° C. for 1 day to 20 days; (c) washing the completed mesoporous molecular sieve with distilled water, filtration and drying and calcining at 500 to 650 ° C .; And (d) introducing a platinum (Pt) into the calcined mesoporous molecular sieve. The method of claim 1, wherein the aqueous inorganic salt solution is selected from NaCl or EDTANa ₄ method for producing a mesoporous molecular sieve supported platinum-based catalyst. The method of claim 1, wherein the inorganic salt aqueous solution is 0.32 to 13% by weight concentration of the method for producing a mesoporous molecular sieve supported platinum-based catalyst. The method of claim 1, wherein the mesoporous molecular sieve is made of silica and has a pore size of 2 to 50 nm. The method of claim 1, wherein the platinum (Pt) is used in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the mesoporous molecular sieve. The noble metal selected from ruthenium (Ru), rhodium (Rh), palladium (Pd) and silver (Ag), vanadium (V), manganese (Mn) and cobalt as a promoter in the mesoporous molecular sieve. (Co), copper (Cu), tin (Sn) and aluminum (Al), a method for producing a mesoporous molecular sieve supported platinum-based catalyst, characterized in that further using one or two or more selected from a metal selected from. The method of claim 6, wherein the promoter is used in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the mesoporous molecular sieve.

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