JP5002807B2 - Novel nitrogen oxide reduction catalyst and nitrogen oxide reduction removal method - Google Patents

Description

  The present invention relates to a catalyst capable of using toluene as a reducing agent and exhibiting high activity in a nitrogen oxide reduction reaction in the presence of oxygen and water vapor.

Reduction of nitrogen oxides (NO _x ) in the presence of oxygen and water vapor using hydrocarbon as a reducing agent has been widely studied for purification in combustion exhaust. An effective catalyst for selective reduction (SCR) in a lean burn (oxygen-excess) region of an internal combustion engine, which has been difficult, has also been developed.

Toluene is often derived from solvents or the like and contained in exhaust from factories or the like or exhaust from internal combustion engines. Although the results in the case of using Pt / Al ₂ O ₃ or Pt / SiO ₂ as a catalyst and toluene as a reducing agent have been published (for example, Non-Patent Document 1), the performance was not high. Further, when toluene contained in the exhaust gas is used as a reducing agent (for example, Non-Patent Document 2), no catalyst showing sufficient activity at a low temperature of about 523 K (250 ° C.) has been found.

If a catalyst capable of reducing NO _x with toluene at a low temperature is found, it can be widely applied. For example, NO _x reached before the catalyst is completely warmed at the cold start of the internal combustion engine, It is expected that a reduction and removal system will be realized.

Note that Pd / HPW / SiO ₂ used as an element of the catalyst of the present invention in the following examples and the like is a NO reduction catalyst that exhibits a much higher activity than Pt / Al ₂ O ₃ or the like when methane is used as a reducing agent. (Patent Document 1).
JP 2005-230736 A R. Burch, D. Ottery, Appl. Catal. B, 13, 105 (1997) NRBurke, DL Trimm and RFHowe, Appl. Catal. B, 46, 97 (2003)

The present invention has been made in view of the above circumstances, and aims to provide a nitrogen oxide reduction removal method using the catalyst capable, and the catalyst to remove the NO _x toluene at low temperature as a reducing agent To do.

The present invention, as a catalyst capable of removing NO _x toluene at low temperature as a reducing agent, was supported Pd on either or both nitrogen oxide obtained by mixing and the zeolite porous silica supported heteropolyacid The present invention relates to a product reduction catalyst.

First, a porous silica-supported heteropolyacid supporting Pd (hereinafter referred to as “Pd / heteropolyacid / SiO ₂ ”) will be described.

The porous silica contains a heteropolyacid and supports palladium, for example, has a specific surface area of 100 m ² / g or more, preferably 150 m ² / g or more, and a pore volume of 0.5 cm ³ / g or more. Try to use what is. As such porous silica, for example, N-602A (specific surface area of 290 m ² / g, pore volume of 0.8 cm ³ / g) manufactured by JGC Chemical Co., Ltd. is available. The shape of the porous silica may be any shape such as a granular shape, a pellet shape, or a honeycomb shape.

Various heteropolyacids including inorganic oxo acids such as vanadium acid, molybdic acid and tungstic acid can be used. For example, H ₄ SiW ₁₂ O ₄₀ , H ₃ PMo ₁₂ O ₄₀ or H ₃ PW ₁₂ can be used. O ₄₀ is preferred. More preferred is H ₃ PMo ₁₂ O ₄₀ or H ₃ PW ₁₂ O ₄₀ , and most preferred is H ₃ PW ₁₂ O ₄₀ (hereinafter abbreviated as “HPW”).

  The heteropolyacid is contained in the porous silica at a heteropolyacid / (heteropolyacid + porous silica) weight ratio in the range of 0.2 to 0.4.

  The palladium is adjusted to be supported on the heteropolyacid-containing porous silica in a palladium / (palladium + heteropolyacid-containing porous silica) weight ratio of 0.001 to 0.1, preferably 0.002 to 0.02. And use.

Pd / heteropolyacid / SiO ₂ can be produced, for example, by the following method. When used as a heteropoly acid / SiO ₂ is not carrying Pd, it is sufficient to use a heteropoly acid / SiO ₂ prior to the Pd loading step follows.

  The porous silica is immersed in a water or alcohol solution of the heteropolyacid, the pores of the porous silica are impregnated with the heteropolyacid solution, and then heated to volatilize the solvent. Thereby, heteropoly acid is contained in the porous silica. This heteropolyacid-containing porous silica is immersed in a toluene solution of palladium acetate, and the pores of the porous silica are impregnated with the toluene solution of palladium acetate. Subsequently, palladium can be supported on the heteropolyacid-containing porous silica by heating to volatilize toluene and decompose palladium acetate. In addition to palladium acetate, palladium nitrate, palladium chloride, and tetraamine palladium chloride may be used. The amount of palladium supported can be adjusted by changing the amount of palladium acetate, palladium nitrate, palladium chloride or tetraamine palladium.

Next, the zeolite carrying Pd will be described.
Zeolites _are crystalline silicates, denoted in _{M 2 / n · T 2 O} 3 · xSiO 2 generally. Here, T is an element in the zeolite skeleton, and is generally a trivalent metal such as aluminum, iron, or boron, and x is usually an integer of 2 or more. Zeolite is a crystalline compound in which a TO ₄ tetrahedron and a SiO ₄ tetrahedron are regularly and three-dimensionally arranged through oxygen atoms so that the O / (Si + T) ratio is 2. Since T is a trivalent cation, TO ₄ is negatively charged, and therefore M with a positive charge is required to neutralize this negative charge. Therefore, M only needs to be a cationic species in order to maintain the framework structure of the zeolite, and protons, alkali metals, and alkaline earth metals are generally used. n is 1 if M is a monovalent cation, and 2 or 3 if M is a divalent or trivalent cation. Thus, the basic structure of zeolite consists of TO ₄ and SiO ₄ tetrahedrons, and M can be ion-exchanged.

  In the present invention, a zeolite in which M is an alkali metal, preferably lithium, sodium, cesium, more preferably lithium, sodium, most preferably sodium is used. There is no particular limitation on T and x. The crystal structure of the zeolite to be used is not particularly limited, and any of MFI type, MOR type, BEA type, and FAU type may be used, but MFI type, MOR type, BEA type, and FAU type are preferable in this order. Of course, some known as natural zeolites can be synthesized, but it goes without saying that those synthesized can be used. In addition, since zeolite is generally obtained as an alkaline zeolite, in the present invention, it may be used as it is or after ion exchange with a desired alkali cation.

  In particular, an alkali zeolite in which M is an alkali metal, preferably an alkali MFI type zeolite, more preferably an Na or LiMFI type zeolite, and most preferably an NaMFI type zeolite can be suitably used.

  In order to support Pd on the zeolite as described above, a conventionally known method may be used. For example, after impregnating the zeolite with an aqueous solution containing a considerable amount of tetraamminepalladium chloride, drying at room temperature, A method such as an ion exchange method for drying a solid obtained by filtration after stirring in an aqueous solution containing a considerable amount of tetraamminepalladium chloride may be applied.

  The amount of palladium supported can be adjusted in the range of 0.1 to 5% by weight by changing the amount of tetraamminepalladium chloride.

The catalyst of the present invention is formed by mixing porous silica-supported heteropolyacid supporting zeolite on either or both and zeolite. Hereinafter, it may be simply referred to as “mixed catalyst of the present invention”.
For example, Pd / heteropolyacid / SiO ₂ and zeolite may be mixed by simply mixing them and shaking lightly, but it is preferable to carry out moderate mixing. For example, when mixing and pulverizing both using a mortar, it is known that the catalytic activity is lowered when pulverized and mixed for a long time. The same applies to a mixture of Pd / heteropolyacid / SiO ₂ and Pd-supported zeolite, and a mixture of heteropolyacid / SiO ₂ and Pd-supported zeolite.

Mixing of the heteropolyacid / SiO ₂ and zeolite carrying Pd on either or both is sufficient by mixing about 1 (weight ratio) of zeolite to 1 of heteropolyacid / SiO ₂ . Although it is not limited to add more zeolite, the improvement of the catalytic activity cannot be expected to increase the activity commensurate with the addition, and only the volume is increased. As the amount of zeolite added becomes lower than about 1 (weight ratio), the activity becomes lower, so ideally it is about 1: 1 (weight ratio).

“Mixing heteropoly acid / SiO ₂ and zeolite carrying Pd on either or both” means that a predetermined amount of Pd is supported on heteropoly acid / SiO ₂ or zeolite or both before mixing. In other words, it is only necessary to mix the two.

Under mixing conditions such that the mixture is simply shaken without adding pulverization, 50 to 80% by weight of a predetermined amount of Pd is supported on the zeolite side, and Pd / heteropolyacid / SiO 2 on which the remaining Pd is supported. While mixing the ₂ tends to be preferable, for example when taking a pulverizing mixing method such as using a mortar, it is better to leave a certain amount was previously supported on either carrier Pd, conditions such is Not particularly.

Loading amount of Pd, so that the amount of from about 0.5 wt% or more based on the total amount of the mixed catalyst of the present invention obtained by mixing a Pd on either or both of the heteropoly acid / SiO ₂ or zeolites Make it carry. The upper limit is not particularly limited, but the improvement in activity commensurate with the increase is not observed, and Pd is expensive, so the smaller the amount used, the better.

Mixed catalyst of the present invention, as a reducing agent to toluene, as compared with the case of the Pd / heteropolyacid / SiO ₂ alone, showed very high NO _X reduction activity, yet the temperature is about 500~580K showing its activity Low. The activity is higher than that of conventionally known Pt / Al ₂ O ₃ .

(1) Preparation of catalyst HPW was converted to SiO ₂ (manufactured by JGC Chemical; N602-) by an impregnation method so that the weight ratio (HPW / (HPW + SiO ₂ )) of HPW (manufactured by Wako Pure Chemical Industries) in methanol was 30% by weight. After loading on A), the support was dried overnight at 393K.

The obtained support was impregnated with a toluene solution of Pd (AcO) ₂ (manufactured by Wako Pure Chemical Industries, Ltd.) so that the weight ratio (Pd / (Pd + HPW + SiO ₂ ) was 1% by weight, and dried at 393 K overnight. A Pd / HPW / SiO ₂ catalyst was obtained.

The Pd / HPW / SiO ₂ catalyst obtained above was mixed with zeolite (trade name HSZ-820NAA; manufactured by Tosoh Corporation), and pulverized and stirred using an agate mortar.

(2) Measurement of activity Typically, 0.2 g of the obtained catalyst is put into a reaction tube, NO 500 mol ppm (0.05 mol%), toluene 700 mol ppm (0.07 mol%), O ₂ 5 mol%, H _2. A He (remaining) air flow (normal pressure, total flow rate 200 cm ³ min ⁻¹ ) containing 10 mol% of O was circulated, and the composition of the outlet gas was analyzed at a predetermined reaction temperature.

The reason why H ₂ O is introduced is to bring it closer to practical conditions such as combustion exhaust. NO meter (Horiba CLA-510SS) used for the quantification of NO, _toluene, the determination of CO 2, _{N 2} was used TCD (thermal conductivity detector) type gas chromatograph (Hitachi 163). In a normal procedure, gas was circulated without pretreatment, the temperature was raised to a predetermined temperature, and the value at the time when the conversion rate and yield were stabilized after several hours from reaching that temperature was evaluated.

The results are shown as NO conversion rate, N ₂ yield, and toluene conversion rate.
NO conversion rate = 1-outlet NO concentration / inlet NO concentration;
N ₂ yield = outlet N ₂ concentration / inlet NO concentration;
Toluene conversion rate = 1-outlet toluene concentration / inlet toluene concentration

If the target reaction proceeds 100% selectively, the N ₂ yield should be 1/2 of the NO conversion. However, in actuality, there is a slight error in the quantification of N ₂ , so it is a reference value. Further, the higher the selectivity of the target reaction and the slower the side reaction (toluene combustion with oxygen), the lower the toluene conversion / NO conversion, so this number is an index of selectivity. However, since the chemical reaction formula (the maximum number of 7 carbon atoms and 9 hydrogen atoms in the toluene molecule involved in the reduction of NO) has not been established, the selectivity cannot be determined based on the numerical values.

(3) Catalytic activity in the case of Pd / HPW / SiO ₂ catalyst alone Pd / HPW / SiO ₂ (Pd 1 wt%) was put in a 0.1 g reaction tube, and other conditions were described in (2) Measurement of activity above. Measurements were performed in the same manner as the conditions. The results are shown in FIG.

Conversion of NO was observed at 473 or higher, and the reaction rate increased up to 573K. The maximum NO conversion of 34% was obtained at 573 K, and the toluene conversion reached almost 100%. It can be seen that when the temperature further increases, the NO conversion rate decreases while the toluene conversion rate is kept high, and the side reaction in which toluene burns is the main. The N ₂ yield is about half of the NO conversion rate regardless of the reaction temperature, and it can be seen that NO was stoichiometrically converted to N ₂ . Thus, Pd / HPW / SiO ₂ alone exhibits activity.

(4) Catalytic activity in the case of Pt / Al ₂ O ₃ catalyst alone Pt / Al ₂ O ₃ was put in a 0.1 g reaction tube, and other conditions were measured in the same manner as described in (2) Activity measurement above. Went. The results are shown in FIG.
Comparing FIG. 1 and FIG. 2, both Pd / HPW / SiO ₂ and Pt / Al ₂ O _{3 have} the same level of activity at 473-573 K, and higher selectivity at higher temperatures for Pt / Al ₂ O ₃ . showed that. These catalysts contain the same weight of Pt or Pd, and these noble metals account for most of the catalyst cost. Although Pd is cheaper than Pt, it is economically advantageous, but from the above results, it is difficult to say that Pd / HPW / SiO ₂ has higher performance than Pt / Al ₂ O ₃ .

(5) Mixed catalyst activity with Pd / HPW / SiO ₂ and Na-ZSM-5 (effect of mixing time)
FIG. 3 shows the NO conversion rate at 523 and 573 K after adding 0.1 g of Na-ZSM-5 to 0.1 g of Pd / HPW / SiO ₂ (Pd 1 wt%) and grinding and mixing in a mortar. In the figure, the activity of only Pd / HPW / SiO ₂ is indicated by an arrow. When the mixing time is 0, a mortar is not used, and Pd / HPW / SiO ₂ and Na-ZSM-5 powder are put in a reaction tube and lightly mixed. Later results are shown.

Even if lightly mixing Pd / HPW / SiO ₂ and Na-ZSM-5, the activity is slightly improved compared to the case of only Pd / HPW / SiO _2, but the activity is improved when mixed in a mortar for 5 to 60 minutes. Remarkably improved. The activity decreased when the mixing time was too long. This mixing is performed manually, and the time itself has no particular physical meaning, and it is considered that high activity can be obtained when mixing properly.

(6) Pd / HPW / SiO 2 and Na-ZSM-5 Temperature dependence of the mixed catalytic activity of Pd _/ HPW / SiO 2 (Pd1 wt%) 30 added Na-ZSM-5 0.1g to 0.1g FIG. 4 shows the temperature dependence of the conversion rate and yield of the mixed catalyst mixed in the mortar for 5 minutes.

Compared to the case of only 0.1 g of Pd / HPW / SiO ₂ at a low temperature of 523 K (FIG. 1), a very high conversion rate and yield were obtained. The activity was higher than that of conventionally known Pt / Al ₂ O ₃ (FIG. 2). The N ₂ yield was almost half of the NO conversion rate, and it was found that NO was stoichiometrically converted to N ₂ .

(7) Dependence of mixed catalyst activity of Pd / HPW / SiO ₂ and Na-ZSM-5 on the amount of Na-ZSM-5 added Pd / HPW / SiO ₂ (Pd 1 wt%) fixed at 0.1 g Then, the catalytic activity when the amount of Na-ZSM-5 added was changed (523K, 573K) was measured. In this case, the mixing time is 5 minutes. The results are shown in FIG.

As shown in FIG. 5, when the amount of Na-ZSM-5 added was up to 0.1 g, the conversion rate was improved, and there was not much change even when more was added. The reaction rate does not improve even when the amount of Na-ZSM-5 added is 0.1 g or more (in other words, Na-ZSM-5: Pd / HPW / SiO ₂ weight ratio of 1 or more), and Na-ZSM-5 is produced. Therefore, it can be said that Na—ZSM-5: Pd / HPW / SiO ₂ weight ratio of 1 is desirable as the amount of addition.

(8) Mixing ratio dependency of mixed catalyst activity of Pd / HPW / SiO ₂ and Na-ZSM-5 From the viewpoint of evaluating the catalytic activity per volume of the material after mixing, the total weight is constant (0.2 g) Then, the activity was measured by changing the weight ratio of Pd / HPW / SiO ₂ (Pd 1 wt%) and Na-ZSM-5. The results are shown in FIG. The catalyst preparation and mixing time at this time is 30 minutes.

The leftmost point in FIG. 6 shows the NO conversion when 0.2 g of Pd / HPW / SiO ₂ was used, and was higher at 523 K than at 0.1 g (FIG. 1). However, when Na-ZSM-5 is mixed, the activity is improved despite the reduction of Pd, which is a noble metal component, and the maximum activity is shown at a weight ratio of 0.5: 0.5 (equal amount), and then decreases. did. From the above, it is apparent that the catalytic activity is improved when Na—ZSM-5 is mixed with Pd / HPW / SiO ₂ . Also since the Na-ZSM-5 is too much activity decreased, it is clear that high catalytic activity by Na-ZSM-5 and Pd / HPW / SiO ₂ composite effect was expressed.

(9) Time-dependent change of mixed catalyst activity of Pd / HPW / SiO ₂ and Na—ZSM-5 Pd / HPW / SiO ₂ (Pd 1 wt%, 0.1 g) and Na—ZSM-5 (0.1 g) The time-dependent change of the mixed catalyst activity at 523K was evaluated. The results are shown in FIG. The catalyst preparation and mixing time at this time is 30 minutes.

  The activity of the mixed catalyst of the present invention was improved at the beginning of the reaction, and then showed stable activity for at least about 10 hours.

  The results shown in FIG. 1 to FIG. 6 show the time when the conversion rate and yield are almost stable, that is, around 200 minutes.

(10) Influence of zeolite crystal structure on Pd / HPW / SiO ₂ + zeolite mixed catalyst activity Na type zeolite (MFI type, MOR type, Pd / HPW / SiO ₂ (Pd 1 wt%, 0.1 g) and crystal structure different) The catalytic activity at 523K and 573K of the mixed catalyst with BEA type and FAU type (0.1 g) was evaluated. The results are shown in FIG. The catalyst preparation and mixing time at this time is 5 minutes.

  As shown in FIG. 8, when Na type zeolite was added, the activity was higher than when none was added (NO conversion 21% at 523K and 34% at 573K (FIG. 1)).

  It can be seen that, among the Na types, the addition of MFI type (ZSM-5) shows the highest activity, followed by strong activity in the order of MOR, BEA, and FAU.

(11) Pd / HPW / SiO ₂ + zeolite mixed catalyst activity zeolite metal influence (ion exchange rate)
Evaluation of catalytic activity of Pd / HPW / SiO ₂ (Pd 1% by weight, 0.1 g) and zeolite with different Na content (MFI type) (ZSM-5) (0.1 g) at 523K and 573K did. The results are shown in FIG. The catalyst preparation and mixing time at this time is 5 minutes.

  When zeolite in which Na type was ion-exchanged to H type was used, the activity at 523 K was slightly reduced (FIG. 9).

(Alkali metal species)
The catalytic activity at 523K and 573K of a mixed catalyst of Pd / HPW / SiO ₂ (Pd 1 wt%, 0.1 g) and zeolite (MFI type) (ZSM-5) (0.1 g) having different alkali metal species evaluated. The results are shown in FIG. The catalyst preparation and mixing time at this time is 5 minutes.

  When the cation species was changed, LiNa-ZSM-5 in which 10% of Na was ion-exchanged with Li showed almost the same activity as Na-ZSM-5 at low temperatures. Li and Na were found to have almost the same effect. It was also found that there is activity in the order of Cs and H following Na and Li.

From the above, when zeolite is mixed with Pd / HPW / SiO ₂ , the catalytic activity is improved, and the activity of any kind of zeolite to be mixed is improved, but the MFI structure (ZSM-5) is particularly suitable. Furthermore, it was found that Na and Li types are suitable.

The reason why Na-ZSM-5 has higher performance than other Na-type zeolites is presumed to be the ability to adsorb and hold toluene up to about 550 K close to the reaction temperature as shown in FIG. FIG. 14 is a temperature desorption (TPD) spectrum observed by adsorbing toluene on various zeolites and Pd / HPW / SiO ₂ and then raising the temperature.

(12) Mixed catalyst mixed using Pd-supported zeolite Instead of supporting all of Pd on HPW / SiO ₂ in advance and mixing zeolite in the Pd / HPW / SiO ₂ , the total amount of Pd is fixed, and Pd A part or all of this was supported on the zeolite side and then mixed.

That is, (Pd) / HPW / SiO ₂ (0.1 g) and (Pd) / Na—ZSM-5 (0.1 g) were adjusted so that the amount of Pd supported was 0.5% by weight of the total amount of the mixed catalyst. A mixed catalyst was prepared by mixing, and the catalytic activity at 523K was evaluated. The results are shown in FIG. In addition, the catalyst preparation mixing time by the mortar at this time is 5 minutes.

At the same time, without mixing with a mortar, the compressed Pd / HPW / SiO ₂ powder was pulverized and sieved to particles having an apparent diameter of 1/30 to 1/50 inch, as well as compression molding, pulverization, The catalytic activity was also shown when the screened Na-ZSM-5 particles were lightly shaken for about 1 second ("no mixing" in the figure).

As shown in FIG. 11, when mixing with a mortar was not carried out, it was more active when 50-80% of Pd was added after being supported on the Na-ZSM-5 side. Therefore, Pd on Na-ZSM-5 is considered to play some role. Although no experiment was conducted in which Pd was supported on the 100% Na-ZSM-5 side, the catalytic activity was low only with Pd / Na-ZSM-5 (FIG. 12). Therefore, in this reaction, Pd / HPW / SiO _{2 was used.} Is presumed to play a central role. Therefore, Pd / HPW / and SiO ₂ and Pd / Na-ZSM-5 is to share the role each believed to require both coexist.

However, when these samples were mixed in a mortar for 5 minutes, they showed almost equal activity regardless of the ratio of Pd on Na-ZSM-5 before mixing. Therefore, either Pd by mixing is partitioned between HPW / SiO ₂ and Na-ZSM-5, is equivalent role to that previously supported to HPW / SiO ₂ and Na-ZSM-5 particles approach by mixing It is thought that it came to be able to do it.

From the above, when preparing the mixed catalyst of the present invention, whether Pd / HPW / SiO ₂ and Pd / Na-ZSM-5 are mixed after 50 to 80% Pd is supported on the Na-ZSM-5 side. Alternatively, it was found that a predetermined amount of Pd was previously supported on one or both of HPW / SiO ₂ and zeolite, and Pd / HPW / SiO ₂ and Pd / Na-ZSM-5 were mixed in a mortar.

(13) Effect of Pd loading on catalyst activity Pd / HPW / SiO ₂ 0.1 g of Na-ZSM-5 was added to 0.1 g, and pulverized and mixed in a mortar for 30 minutes. The NO conversion rate is shown in FIG.

  It was found that high activity was obtained when the amount of Pd supported was 0.5% by weight or more based on the total amount of the mixed catalyst. Since Pd is expensive, the lower the amount used, the better.

(14) Consideration of the mechanism of high activity As described above, a silica-supported tungstophosphoric acid (H ₃ PW ₁₂ O ₄₀ ) supporting Pd on either side and zeolite (especially Na or Li type ZSM-5) are taken over an appropriate time. Catalysts mixed in a mortar or mixed with some Pd supported on the Na-ZSM-5 side are highly active in the reduction of nitrogen oxides in the presence of oxygen and water vapor using toluene as the reducing agent. It was found that

According to the studies by the inventors, it is considered that HPW activates NO, and Pd on HPW promotes the reaction between the NO-derived active species and the hydrocarbon-derived active species. On the other hand, since zeolite has a property of adsorbing toluene, and it is presumed that Pd on zeolite also has a role as described above, toluene adsorbed on zeolite is activated on Pd / zeolite, Since this reacts on Pd / HPW / SiO ₂ , the NO reduction rate is estimated to have increased. Since the activity became higher when mixed in a mortar, in addition to the possibility that Pd is distributed between HPW / SiO ₂ and zeolite, there are active species having these different roles at a distance that allows molecules to move. This is thought to increase activity.

(15) Consideration of influence of mixing time on activity Add 0.1 g of Na-ZSM-5 to 0.1 g of Pd / HPW / SiO ₂ (Pd 1 wt%), grind and mix in a mortar, mixing with different mixing times The total pore volume of the catalyst was measured by nitrogen adsorption method. The results are shown in FIG.

The total pore volume decreased slowly with increasing mixing time, but the micropore volume did not decrease much. Therefore, it can be said that the volume of the meso macropores derived from the outer surface of the zeolite crystal and the surface of the HPW / SiO ₂ particle is reduced. This is presumably caused by the blockage of HPW / SiO ₂ particles in the meso-macropores, and the HPW / SiO ₂ and zeolite are less likely to contact the reactants on the outer surface and the activity is reduced. Conceivable.

  The catalyst of the present invention can be used for nitrogen oxide reduction using toluene as a reducing agent in the presence of oxygen and water vapor.

Specifically, it can be used as a catalyst for a system for reducing and removing NO _{x of} an internal combustion engine containing toluene as an exhaust gas component.

Graph showing the temperature dependence of the Pd / HPW / SiO ₂ catalyst alone catalytic activity. Graph showing the temperature dependency of Pt / _Al 2 _{O 3} catalyst alone catalytic activity. Graph showing the mixing time influences of the mixed catalyst of Pd / HPW / SiO ₂ and Na-ZSM-5. Graph showing the temperature dependence of the catalytic activity of _{Pd / HPW / SiO 2 + Na} -ZSM-5. _{Pd / HPW / SiO 2 + Na} -ZSM-5 a graph showing the Na-ZSM-5 additive amount dependency of the catalytic activity of. Pd / HPW / SiO ₂ and a graph showing the mixing ratio dependence of the total weight constant of a mixed catalyst activity of Na-ZSM-5. A graph showing changes over time in the catalytic activity of _{Pd / HPW / SiO 2 + Na} -ZSM-5. Graph showing the effect of Pd / HPW / SiO ₂ + zeolite mixed catalyst activity of the zeolite crystal structure. Graph showing the effect of H-Na ion exchange ratio of ZSM-5 zeolite of _{Pd / HPW / SiO 2 + Na} -ZSM-5 catalyst activity. Graph showing the effect of the cationic species in the ZSM-5 zeolite of _{Pd / HPW / SiO 2 + Na} -ZSM-5 catalyst activity. The graph which shows the activity of the mixed catalyst which mixed using Pd carrying | support zeolite. The graph which shows the temperature dependence of the catalyst activity of a Pd / Na-ZSM-5 catalyst single. Graph showing the effect of the amount of Pd supported of the catalytic activity of _{Pd / HPW / SiO 2 + Na} -ZSM-5. Toluene temperature programmed desorption spectra of various carriers. Graph showing the mixing time dependency of the pore volume of the pd _/ HPW / mixed catalyst of SiO 2 + Na-ZSM-5 .

Claims (6)

A nitrogen oxide reduction catalyst using toluene as a reducing agent, which is a mixture of a porous silica-supported heteropolyacid and Na or LiMFI-type zeolite supporting Pd on either or both. The catalyst according to claim 1, wherein the heteropolyacid is H ₃ PW ₁₂ O ₄₀ . Loading amount of Pd is in relative to the total amount of catalyst 0. 5 is the amount of weight% or more, the catalyst according to any of claims 1-2. The catalyst according to any one of claims 1 to 3 , wherein the mixing includes a grinding step. In the method for removing nitrogen oxides in exhaust gas containing at least toluene, oxygen, water vapor and nitrogen oxides as components, the exhaust gas is passed through the catalyst according to any one of claims 1 to 4 to reduce and remove nitrogen oxides. A method for reducing and removing nitrogen oxides. The method for reducing and removing nitrogen oxides according to claim 5 , wherein the reduction temperature of nitrogen oxides is 500 to 580K.

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