JP2009082776A - Method and apparatus for searching catalyst material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently searching a catalyst material easy to advance only objective reaction in a system capable of causing at least two competing reactions. <P>SOLUTION: In a catalyst for more preferentially causing required reaction than another competing reaction in the system capable of causing at least two competing reactions, the difference between the Gibbs energies of a state that the respective reaction seeds/forming seeds of the required reaction and the competing reaction are adsorbed on the catalyst is calculated and a substance having high possibility becoming the catalyst material is selected on the basis of the comparing result of the Gibbs energies. Further, the difference between the Gibbs energies may be calculated by utilizing the adsorption or reaction energy of the molecules related to reaction. The adsorption or reaction energy can be calculated by utilizing first principle calculation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for searching for a catalyst that selectively causes a specific reaction by simulation.

  As a conventional catalyst development method, researchers have repeatedly searched for catalyst materials through trial and error by selecting a catalyst element based on experience and evaluating it through tests. However, the labor and material costs required for this are enormous. Therefore, a method capable of searching for a catalyst more efficiently has been demanded. For example, Japanese Patent Laying-Open No. 2005-270852 (Patent Document 1) discloses that an electron energy is parameterized as an electron distribution state of one catalyst to search for an alternative catalyst.

JP 2005-270852 A

  One of the possibilities of the search method is a computational chemistry method. However, computational chemistry techniques have been used for predicting physical properties of materials, but the reaction prediction problem has not yet reached a practical stage. In particular, in a system in which two or more kinds of competitive reactions can occur, the catalyst is required to have high selectivity.

  In a system in which two or more competitive reactions can occur, a material that is likely to generate only the desired reaction is used as a catalyst. However, the search method is empirical, and no method has been established so far. In such a competitive reaction system, it is very laborious to search for a catalyst with a high selectivity that improves the selectivity of a desired reaction by trial and error. Thus, an object of the present invention is to search for a catalyst that selectively causes a specific reaction or improves the selectivity of a desired reaction in a system (competitive reaction system) in which two or more types of competitive reactions may proceed. It is to provide a technique to do.

  The feature of the present invention that solves the above-described problem is that, in a system in which two or more competitive reactions occur, a catalyst that causes the desired reaction to be preferentially caused over the other competitive reactions, There is a method for calculating and searching by using the Gibbs energy in a state where the generated species are adsorbed on the catalyst. In the present invention, when two or more competitive reactions occur, the competitive reaction inherently including complex elementary processes, the ease of progress of each reaction, the Gibbs energy when the reactant is adsorbed on the catalyst surface, and the catalyst We focused on the difference in Gibbs energy when the product was adsorbed on the surface. Based on the result of comparing these, a substance that is highly likely to be a catalyst material can be selected.

The catalyst search method of the present invention is a method of searching for a catalyst that preferentially generates reaction A by a computer simulation in a system in which a competitive reaction between reaction A and competition reaction X occurs. Gibbs energy G ₁ ^A with the reactive species adsorbed on the catalyst, Gibbs energy G ₂ ^A with the reaction A produced species adsorbed on the catalyst, and Gibbs energy with the reactive species X adsorbed on the catalyst G ₁ ^X a, more and Gibbs energy G ₂ ^X states generating species competing reactions X is adsorbed on the catalyst, G ₂ ^a and G ₁ the difference between the ^{a ΔG a (ΔG a = G} 2 a -G 1 a) And a step of obtaining a difference ΔG ^X (ΔG ^X = G ₂ ^X− G ₁ ^X ) between G ₂ ^X and G ₁ ^X and ΔG ^A and ΔG ^X are compared, and a material in which ΔG ^A is larger than ΔG ^X And selecting a process.

  Also, although the above-mentioned Gibbs energy G may be calculated, it has been found that the above-mentioned Gibbs energy difference can be estimated relatively easily by using the adsorption energy and desorption energy of the molecules involved in the reaction.

Therefore, the present invention calculates each adsorption energy obtained when each reaction species used in the reaction is adsorbed on the surface of the catalyst, calculates ΣE _react by adding the adsorption energies of each reaction species, and generates the reaction. Each adsorption energy obtained when each product species is adsorbed on the surface of the catalyst is calculated, ΣE _product is calculated by adding the adsorption energy of each product species, and the energy difference (reaction energy) ΔE between the reaction species and the product species is calculated. subtracts the? En _pro and Delta] E _gas from? En _{the react} to calculate the _gas to determine the _{ΔG (ΔG = ΣE react -ΣE pro} -ΔE gas) is preferred. In addition, the said adsorption energy and reaction energy can be calculated | required, for example using a first principle calculation.

By selecting a catalyst material having a ΔG ^A larger than ΔG ^X by the above method, it is easy to search for a catalyst in which the reaction A easily proceeds. Further, since the simulation is performed by a computer, it is possible to easily search for a catalyst by constructing a system in advance and setting it as a catalyst search device combined with the computer.

  According to the present invention, a catalyst having a high reaction selectivity can be provided. In addition, costs (labor, time, experimental material costs, etc.) required for developing a catalyst with high selectivity can be reduced.

  In the reaction represented by the following formula (1) and the two competitive reactions represented by the following formula (2), a case will be described in which a catalyst candidate that tends to selectively generate only the reaction in the formula (1) is searched.

A + B → C + D (1)
A + E → F + G (2)
On the other hand, the cases where the reactions in the formulas (1) and (2) occur in the presence of a catalyst are shown in the formulas (3) and (4). For example, in the formula (1), the reactants A and B are adsorbed on the catalyst surface and react on the catalyst surface to become products C and D. In the reaction formulas (3) and (4), the state where the reactive species are adsorbed on the catalyst surface is represented by the symbol (a). The state where the reactants A and B in the reaction formula (1) are adsorbed on the catalyst surface is A (a) + B (a), and the state where the products C and D are adsorbed on the surface is C (a) + D (a ). Further, the state in which the reactants A and E in the reaction formula (2) are adsorbed on the surface is A (a) + E (a), and the state in which the products F and G are adsorbed on the surface is F (a) + G (a ).

A (a) + B (a) → C (a) + D (a) (3)
A (a) + E (a) → F (a) + G (a) (4)
In order to show the thermodynamic stability of the catalyst surface reaction of each of the equations (3) and (4), the Gibbs energy differences ΔG ₃ and ΔG ₄ before and after the reaction are examined. The Gibbs energies in each state of the equations (3) and (4) are represented by G (A, B), G (C, D), G (A, E), and G (F, G). The difference between the Gibbs energy when the reactant is adsorbed on the catalyst surface and the Gibbs energy when the product is adsorbed on the catalyst surface in each reaction is calculated by Equation (5) and Equation (6).

ΔG ₃ = G (C, D) −G (A, B) (5)
ΔG ₄ = G (F, G) −G (A, E) (6)
The smaller the Gibbs energy difference ΔG is, the easier the reaction proceeds. Therefore, in two competitive reactions (Equation (3) and Equation (4)), ΔG (Equation (5)) corresponding to Equation (3), which is the desired reaction, is small, and ΔG of the inhibition reaction (competitive reaction) is large. It is judged that the catalyst material is superior. Therefore, the reaction Gibbs energy can be estimated and the catalyst can be searched.

  FIG. 1 is an energy diagram of a reaction in which a product C and a product D are produced from a reactant A and a reactant B in the presence of a catalyst. ΔG was estimated from the energy difference between the state in which the reactant A and the reactant B were adsorbed on the catalyst surface and the state in which the product C and the product D were adsorbed to facilitate the progress of the catalyst reaction.

  The Gibbs energy of the adsorption state in each reaction can be calculated as the energy of the adsorption state by the first principle calculation. Calculate the adsorption energy of reactants and products in each reaction, approximate the Gibbs energy difference between the reactants on the surface and the products on the surface, compare the magnitude relationship in each competitive reaction, and select the catalyst material I do.

For example, in the case of the reaction formula (3), ΔG ₃ is calculated by the formula (7) as can be seen from FIG.

ΔG ₃ = E _ads (C) + E _ads (D) − (E _ads (A) −E _ads (B)) − ΔE ₁ (7)
ΔE ₁ is the reaction energy of the reaction formula (1). E _ads (A), E _ads (B), E _ads (C), and E _ads (D) are adsorption energies of A, B, C, and D on the catalyst surface, respectively.

  In the following examples, the search for a catalyst that reduces nitrogen oxides to nitrogen gas will be described. In this example, it is assumed that the reaction A is a NOx reduction reaction using CO as a reducing agent, and the competitive reaction X is an oxidation reaction of CO by oxygen.

  Nitrogen oxides from boilers and automobiles are one of the air pollutants, and regulations have been tightened. Currently, nitrogen oxides discharged from boilers are reduced to nitrogen by a denitration catalyst method using ammonia as a reducing agent.

  However, a denitration catalyst using carbon monoxide present in the same exhaust gas as a reducing agent has been developed in order to reduce operating costs necessary for ammonia procurement, storage, and the like. In the reduction reaction of nitrogen oxides by the denitration catalyst in the presence of oxygen (equation (8)), in addition to the reduction of nitrogen oxides, the oxidation reaction of carbon monoxide, which is a reducing agent, also occurs by oxygen (equation (9)). End up.

NO (a) + CO (a) → 1 / 2N ₂ (a) + CO ₂ (a) (8)
CO (a) + 1 / 2O ₂ (a) → CO ₂ (a) (9)
In order to reduce nitrogen oxides with carbon monoxide in the presence of oxygen, it is necessary to use a catalyst that causes a reduction reaction of nitrogen oxides with carbon monoxide over the reaction between carbon monoxide and oxygen. There is. Although such a catalyst that is not affected by oxygen has been studied, no practical catalyst has been found yet. Thus, a system in which two or more types of competitive reactions can occur requires that the catalyst has high selectivity.

  Therefore, assuming various metals as catalyst materials, a catalyst having a high selectivity was searched.

First, the reaction Gibbs energy ΔG _NO of the reaction between carbon monoxide and nitrogen oxide (formula (8)) on the catalyst surface and the reaction Gibbs energy ΔG _O2 of the reaction between carbon monoxide and oxygen (formula (9)) on the catalyst surface. Was calculated. In order to simply estimate the reaction Gibbs energies ΔG _NO and ΔG _O2 , the following means were used. First, the reaction of the gas shown in the equations (10) and (11) was assumed. (G) indicates a gas state.

NO (g) + CO (g) → 1 / 2N ₂ (g) + CO ₂ (g) (10)
CO (g) +1/2 O ₂ (g) → CO ₂ (g) (11)
Next, the reaction energies of the gases shown in Equation (10) and Equation (11) were ΔE _{N2 (g)} and ΔE _{CO2 (g)} , respectively, and were obtained by band calculation. Furthermore, adsorption energy E _ads on the catalyst surface of each gas was determined by band calculation. NO of the adsorption energy of the catalyst surface E _ads (NO), E adsorption energy of CO _ads (CO), E the adsorption energy of N _{2 ads} (N _2), the adsorption energy of the CO ₂ E _ads (CO ₂ ), it shows the adsorption energy of the O ₂ and E _Ads (O _2).

Using the above reaction energy and adsorption energy, the reaction Gibbs energy ΔG _NO (formula (12)) ΔG _O2 (formula (13)) was calculated.

ΔG _NO = 1 / 2E _ads (N ₂ ) + E _ads (CO ₂ ) − (E _ads (NO) + E _ads (CO))
-ΔE _{N2 (g)} (12)
ΔG _O2 = E _ads (CO ₂ ) − (E _ads (CO) + 1 / 2E _ads (O ₂ )) − ΔE _{CO 2 (g)}
(13)
ΔG _NO and ΔG _O2 are compared, and the reaction Gibbs energy having a lower value proceeds more favorably thermodynamically. Therefore, if ΔG _O2 > ΔG _NO holds, the catalyst is judged to be effective. In particular, it is expected that the catalyst performance is higher as-(ΔG _NO -ΔG _O2 ) is larger and positive.

Using this method, the adsorption energies of NO, CO, N ₂ , CO ₂ , and O ₂ were calculated by the band calculation method for platinum, gold, iridium, rhodium, and palladium. The local density approximation of the density functional method was used for the band calculation. The results are shown in FIG.

From these results and ΔE _{N2 (g)} and ΔE _{CO2 (g)} calculated in advance, − (ΔG _NO −ΔG _O2 ) was estimated. The results are shown in FIG. The approximate value of the Gibbs energy of NO and CO on each catalyst surface, the approximate value of the Gibbs energy of reaction of CO and O ₂ , and the difference between them minus the ease of the two competitive reactions. The predicted value is shown.

Subsequently, the actual NO purification rate was measured, and the calculation results were verified. 0.15 mol% of platinum, gold, iridium, rhodium, and palladium were supported on alumina, respectively, to obtain a NO purification catalyst. The NOx purification rate was evaluated for each catalyst. As for the inlet gas composition, NO was 100 ppm, CO was 2000 ppm, O ₂ was 6%, and the remainder was N ₂ . The SV was 15000 (h ⁻¹ ). The reaction temperature was 350 ° C. The NOx purification rate test results are shown in FIG. FIG. 5 shows the result of comparing the actual NOx purification rate test result with-(ΔG _NO -ΔG _O2 ) of each catalyst estimated from the calculation. When-(ΔG _NO -ΔG _O2 ) is greater than zero, the performance is high, and there is a correlation between the calculation result and the actual measurement value. From FIG. 5, it is clear that − (ΔG _NO −ΔG _O2 ) is a value indicating the ease of the selective reduction reaction of NO (NO reduction rate).

  As described above, by selecting and comparing the reaction Gibbs energy at the surface of a plurality of competitive reactions by first-principles calculation before selecting the catalyst material, a superior result can be obtained over a plurality of candidate catalyst material compounds. The one with the highest possibility can be selected.

It is a figure which shows the energy diagram of reaction in which the product C and the product D generate | occur | produce from the reactant A and the reactant B when a catalyst exists. It is a figure which shows the calculation result of the adsorption energy of each combination of various catalysts and various reaction compounds. It is a figure which compares the reaction Gibbs energy of various catalyst surfaces, and the easiness of two competitive reactions to advance. The measurement result of NO reduction rate in 350 degreeC of each catalyst is shown. It is a graph showing the relationship between the value of-(ΔG _NO -ΔG _O2 ) and the NO reduction rate of each catalyst.

Claims (6)

A catalyst search method for searching for a catalyst that preferentially causes reaction A in a reaction system in which at least reaction A and its competitive reaction X occur,
Difference ΔG ^A = G ₂ ^A− G ₁ ^A between Gibbs energy G ₁ ^A in a state where reaction species of reaction A are adsorbed on the catalyst and Gibbs energy G ₂ ^A in a state where species of reaction A are adsorbed on the catalyst To calculate
Difference ΔG ^X = G ₂ ^X −G ₁ ^X between Gibbs energy G ₁ ^X in a state where reaction species of reaction X are adsorbed on the catalyst and Gibbs energy G ₂ ^X in a state where species of reaction X are adsorbed on the catalyst To calculate
^A catalyst search method, wherein a catalyst is selected based on the values of ΔG ^X and ΔGA. A method for searching for a catalyst according to claim 1,
Select a plurality of compounds as candidates for the catalyst, the .DELTA.G ^X and .DELTA.G ^A of the plurality of compounds respectively calculated, said of each compound - calculating the value of (ΔG _A -ΔG _X), the value is large compound The search method of the catalyst characterized by selecting as a catalyst. In the search method of the catalyst according to claim 1 or 2,
ΣE _{react of the} adsorption energies when the reactive species are adsorbed on the catalyst, ΣE _{product of the} adsorption energies when the generated species are adsorbed on the catalyst, and the energy of the reactive species and the generated species, respectively. A search method for a catalyst, wherein a difference ΔE _gas is calculated, and the Gibbs energy difference ΔG is calculated as ΣE _react −ΣE _pro −ΔE _gas . In the search method of the catalyst as described in any one of Claim 1 thru | or 3,
A method for searching for a catalyst, characterized in that an energy difference between a reactive species and a generated species, or an adsorption energy of the reactive species or the generated species to the catalyst is obtained by using a first principle calculation. In the search method of the catalyst as described in any one of Claims 1 thru | or 4,
A method for searching for a catalyst, wherein the reaction A is a NOx reduction reaction using CO as a reducing agent, and the reaction X is a CO oxidation reaction with oxygen. A search device for a catalyst comprising a computer and searching for a catalyst that preferentially causes reaction A in a reaction system in which at least reaction A and its competitive reaction X occur.
Difference ΔG ^A = G ₂ ^A −G ₁ between Gibbs energy G ₁ ^A in a state where reaction species of reaction A are adsorbed on the catalyst and Gibbs energy G ₂ ^A in a state where species of reaction A are adsorbed on the catalyst ^A is calculated, and the difference ΔG ^X = G between the Gibbs energy G ₁ ^X in a state where the reaction species of reaction X is adsorbed on the catalyst and the Gibbs energy G ₂ ^X in the state where the species of reaction X is adsorbed on the catalyst. ΔG calculating means for calculating ₂ ^X −G ₁ ^X ;
Seeker of a catalyst; and a selecting means for selecting a catalyst based on a value of the .DELTA.G ^X and .DELTA.G ^A.

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