JP4672540B2 - Nitrous oxide decomposition catalyst and purification method of nitrous oxide-containing gas - Google Patents

Description

  The present invention relates to a nitrous oxide decomposition catalyst and a method for purifying a nitrous oxide-containing gas using the catalyst.

Nitrous oxide (N ₂ O) contained in various industrial exhaust gas discharged from combustion exhaust gas and chemical plants decomposes in the stratosphere to produce nitric oxide and shows high greenhouse effect. Decomposition and removal are desired. Therefore, as a method for decomposing and removing nitrous oxide by contacting it with a catalyst, a method using a catalyst in which palladium, nickel, cobalt or the like is supported on a carrier such as aluminum oxide or zirconium oxide (Patent Document 1), or hydrophobic alumina. A method using a catalyst supporting ruthenium and / or rhodium and zirconium oxide or the like (Patent Document 2), or a catalyst containing rhodium oxide or cobalt oxide, a manganese compound, and an alkali or alkaline earth metal compound. A method (Patent Document 3) and the like have been proposed.

JP-A-63-7826 JP-A-6-142517 JP-A-6-106027

  An object of the present invention is to provide a novel nitrous oxide decomposition catalyst capable of efficiently decomposing and removing nitrous oxide, and nitrous oxide for efficiently decomposing and removing nitrous oxide by contacting the catalyst with a gas containing nitrous oxide. The object is to provide a method for purifying nitrogen-containing gas.

According to the studies by the present inventors, it has been found that the above object can be achieved by the following invention.
(1) (A) at least one element or compound selected from alkali metals, alkaline earth metals and rare earth metals, and (B) nickel, cobalt, copper, iron, manganese, silver, ruthenium, rhodium, platinum, gold And a catalyst for nitrous oxide decomposition, comprising at least one element or compound selected from palladium and iridium and having a pore volume in the range of 0.1 to 0.6 ml / g.
(2) containing (A) a compound of at least one element selected from alkaline earth metals and (B) at least one element or compound selected from nickel, cobalt, copper, ruthenium, rhodium and platinum. A catalyst for nitrous oxide decomposition, wherein the pore volume is in the range of 0.1 to 0.6 ml / g.
(3) The nitrous oxide decomposition catalyst according to (1) or (2), further comprising (C) an oxide of at least one element selected from titanium, aluminum, silicon and zirconium.
(4) A method for purifying a nitrous oxide-containing gas, wherein a gas containing nitrous oxide is brought into contact with the catalyst of (1), (2) or (3) to decompose and remove nitrous oxide.

  The nitrous oxide decomposition catalyst of the present invention has high performance and can decompose and remove nitrous oxide with a high removal rate. Therefore, the nitrous oxide-containing gas can be efficiently purified by using the nitrous oxide decomposition catalyst of the present invention.

  The nitrous oxide decomposition catalyst of the present invention (hereinafter sometimes simply referred to as “catalyst”) includes (A) at least one element selected from alkali metals, alkaline earth metals, and rare earth metals, or a compound thereof, (B) At least one element or compound selected from nickel, cobalt, copper, iron, manganese, silver, ruthenium, rhodium, platinum, gold, palladium and iridium is contained as an essential component. Needless to say, each of component A and component B may be composed of two or more different elements or compounds.

  Examples of the alkali metal of component A include lithium, sodium, potassium, rubidium, and cesium. Examples of the alkaline earth metal include magnesium, calcium, strontium, and barium. Examples of the rare earth metal include scandium, yttrium, lanthanum, Cerium and the like can be exemplified. Of these, alkaline earth metals, particularly calcium, are preferably used. Among the components (B), at least one selected from nickel, cobalt, copper, ruthenium, rhodium and platinum is preferably used.

  Accordingly, among the catalysts of the present invention, (A) a compound of at least one element selected from alkaline earth metals and (B) at least one selected from nickel, cobalt, copper, ruthenium, rhodium and platinum. What contains an element or a compound as an essential component is used suitably.

  The proportion of component A and component B in the catalyst of the present invention is not particularly limited, but is usually as follows (based on the total mass of the catalyst). That is, when component B is nickel, cobalt, copper, iron, manganese and silver, component A (oxide conversion) is 1 to 99% by mass, preferably 5 to 95% by mass, and component B (oxide conversion) ) Is 1 to 99% by mass, preferably 5 to 95% by mass (total 100% by mass). When component B is ruthenium, rhodium, platinum, gold, palladium and iridium, component A (as oxide) is 1 to 99.99% by mass, preferably 5 to 99.95% by mass. (Metal conversion) is 0.01 to 10% by mass, preferably 0.05 to 5% by mass (total 100% by mass). By including the component A and the component B in the ratio as described above, the nitrous oxide decomposition performance of the catalyst is sufficiently exhibited.

  The catalyst of the present invention may contain an oxide of at least one element selected from titanium, aluminum, silicon and zirconium as component C in addition to component A and component B. Component C is generally used as a catalyst carrier such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide or a mixture of two or more thereof, or a composite oxide of titanium and at least one selected from aluminum, silicon and zirconium. The metal oxide used can be illustrated. These are all known to contribute to the strength of the catalyst, and in the present invention, the use of component C is expected to improve the strength of the catalyst.

  The proportions of component A, component B, and component C in the catalyst of the present invention are not particularly limited, but are usually as follows (based on the total mass of the catalyst). That is, when component B is nickel, cobalt, copper, iron, manganese, and silver, component A (as oxide) is 1 to 98% by mass, preferably 5 to 94% by mass, and component B (as oxide) ) Is 1 to 98% by mass, preferably 5 to 94% by mass, and component C (oxide) is 1 to 50% by mass, preferably 1 to 40% by mass (total 100% by mass). When component B is ruthenium, rhodium, platinum, gold, palladium and iridium, component A (as oxide) is 1 to 99.99% by mass, preferably 5 to 98.95% by mass. (Metal conversion) is 0.01 to 10% by mass, preferably 0.05 to 5% by mass, and component C (oxide) is 1 to 50% by mass, preferably 1 to 40% by mass (total) 100% by mass). By including component A, component B, and component C in the proportions described above, the nitrous oxide decomposition performance of the catalyst is sufficiently exhibited.

The pore volume of the catalyst of the present invention is 0.1 to 0.6 ml / g, preferably 0.1 to 0.5 ml / g, more preferably 0.1 to 0.4 ml / g. When the pore volume is smaller than 0.1 ml / g, the catalyst performance (N ₂ O removal rate) is greatly reduced. On the other hand, when the pore volume exceeds 0.6 ml / g, the catalyst becomes brittle and has a catalyst strength that can withstand use. It cannot be maintained. The pore volume was measured by mercury porosimetry.

  The catalyst of the present invention containing component A and component B, or component A, component B and component C and having a pore volume in the range of 0.1 to 0.6 ml / g is, for example, as follows. can get.

  The catalyst containing the component A and the component B is formed into a desired shape by sufficiently mixing, for example, a raw material compound containing the element A and a raw material compound containing the element B with an appropriate amount of water and a molding aid. Then, it can be prepared by drying and baking in the range of 300 to 600 ° C, preferably 350 to 550 ° C. Similarly to the above, the catalyst containing component A, component B and component C comprises a raw material compound containing the element of component A, a raw material compound containing the element of component B, and a metal oxide of component C with an appropriate amount of water. It can be prepared by thoroughly mixing with a molding aid or the like, molding into a desired shape, drying, and firing at 300 to 600 ° C., preferably 350 to 550 ° C. In addition, for example, the raw material compound of component A is dissolved in water, mixed with the powders of component B and component C, molded into a desired shape, dried, and then dried at 300 to 600 ° C., preferably 350 to 550 ° C. It can also be prepared by firing within a range. The present invention is not limited to the above method, and the pore volume is in the range of 0.1 to 0.6 ml / g, and can be prepared according to various methods as long as sufficient nitrous oxide decomposition performance is obtained. it can.

  Examples of the raw material compound include oxides, hydroxides, carbonates, ammonium salts, nitrates, sulfates, phosphates, acetates, oxalates, and halogen compounds containing each element.

The form of component A and component B is not particularly limited, but is present in the catalyst in the form of a metal or a compound such as an oxide, carbonate, sulfate, phosphate or the like. In the case of the alkaline earth metal of component A, it exists in the form of an oxide or carbonate of an alkaline earth metal, for example, calcium oxide (CaO) or calcium carbonate (CaCO ₃ ). In the case of component B nickel, cobalt and copper, their oxides, such as nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ) and copper oxide (CuO), and in the case of ruthenium, rhodium and platinum Are each present as a metal. Component C is present as it is in the form of a metal oxide.

  The shape of the catalyst of the present invention is not particularly limited, and may be appropriately selected from a columnar shape, a cylindrical shape (pellet shape), a spherical shape, a plate shape, a honeycomb shape, and other integrally molded ones. The catalyst can be molded by a general molding method such as a tableting molding method or an extrusion molding method. In the case of a spherical catalyst, the average particle diameter is usually 1 to 10 mm. In the case of a honeycomb-shaped catalyst, it is the same as a so-called monolithic carrier, and is manufactured by an extrusion molding method or a method of winding and solidifying a sheet-like element. The shape of the gas passage port (cell shape) may be hexagonal, quadrangular, triangular or corrugated. The cell density (number of cells / unit cross section) is usually 25 to 800 cells / in 2 (x2.5 cm).

According to the method for purifying a nitrous oxide-containing gas of the present invention, the nitrous oxide-containing gas is brought into contact with the catalyst to oxidatively decompose nitrous oxide in the exhaust gas. The method of the present invention is suitably used for purification of exhaust gas having a nitrous oxide concentration of 1 to 500,000 ppm, preferably 10 to 100,000 ppm, more preferably 10 to 10,000 ppm. There are no particular limitations on the reaction temperature and gas space velocity when the nitrous oxide-containing gas is brought into contact with the catalyst of the present invention to decompose and remove the nitrous oxide, so that the decomposition of nitrous oxide proceeds efficiently. It can be determined as appropriate. Specifically, for example, the reaction temperature is 100 to 600 ° C., preferably 200 to 600 ° C., and the gas space velocity (SV) is 1,000 to 50,000 hr ⁻¹ , preferably 2,000 to 2,000. 20,000 hr ⁻¹ .

The invention is further illustrated by the following examples, which illustrate advantageous embodiments of the invention.
Example 1
After adding an appropriate amount of water and a molding aid to 800 g of calcium carbonate and 200 g of nickel oxide (NiO), the mixture was mixed well with a kneader, and then molded into a pellet having a diameter of 5 mm and a length of 5 mm with an extruder. The pellet was dried at 100 ° C. for 10 hours and then calcined at 500 ° C. for 5 hours in an air atmosphere to obtain a pellet-shaped catalyst (1). The composition of this catalyst was Ca: Ni (as CaO: NiO) = 69.1: 30.9 (mass%), and its pore volume was 0.25 ml / g.
(Examples 2 to 4)
Catalysts (2) to (2) to (1) of the compositions and pore volumes shown in Table 1 were used in the same manner as in Example 1 except that basic magnesium carbonate, strontium carbonate, or barium carbonate was used instead of calcium carbonate in Example 1. 4) was obtained.
(Examples 5 and 6)
Catalysts (5) and (6) having the compositions and pore volumes shown in Table 1 were obtained in the same manner as in Example 1 except that tricalcium phosphate or calcium sulfate was used instead of calcium carbonate in Example 1. It was.
(Examples 7 and 8)
In the same manner as in Example 1 except that cobalt oxide (Co ₃ O ₄ ) or copper oxide (CuO) was used instead of nickel oxide (NiO) in Example 1, the compositions and pore volumes shown in Table 1 were used. Catalysts (7) and (8) were obtained.
Example 9
After mixing 995g of calcium carbonate and 5g of ruthenium oxide (made by Tanaka Kikinzoku Co., Ltd., containing 65% by mass of ruthenium) with a suitable amount of water and a molding aid and mixing well with a kneader, the diameter is 5mm and long with an extruder. It was molded into a 5 mm pellet. The pellet was dried at 100 ° C. for 10 hours and then calcined at 500 ° C. for 5 hours in an air atmosphere to obtain a pellet-shaped catalyst (9). The composition of this catalyst was Ca: Ru (as CaO: Ru) = 99.4: 0.6 (mass%), and the pore volume was 0.22 ml / g.
(Examples 10 and 11)
Catalysts (10) and (11) having the compositions and pore volumes shown in Table 1 were obtained in the same manner as in Example 9, except that rhodium oxide or platinum oxide was used instead of ruthenium oxide in Example 9.
(Examples 12 and 13)
Catalysts (12) and (13) having the compositions and pore volumes shown in Table 1 were obtained in the same manner as in Example 9, except that tricalcium phosphate or calcium sulfate was used instead of calcium carbonate in Example 9. It was.
(Example 14)
A mixture of 600 g of calcium carbonate, 200 g of nickel oxide (NiO), and 200 g of aluminum oxide (α-Al ₂ O ₃ ) was mixed well with a kneader while adding an appropriate amount of water and a molding aid, and then 5 mm in diameter and long in an extruder. It was molded into a 5 mm pellet. The pellet was dried at 100 ° C. for 10 hours and then calcined at 500 ° C. for 5 hours in an air atmosphere to obtain a pellet-shaped catalyst (14). The composition of this catalyst is Ca: Ni: Al (as CaO: NiO: Al ₂ O ₃ ) = 45.7: 30.8: 23.5 (mass%), and the pore volume is 0.17 ml / g.
(Examples 15 and 16)
In the same manner as in Example 14 except that titanium oxide (TiO ₂ ) or silicon oxide (SiO ₂ ) was used instead of aluminum oxide (α-Al ₂ O ₃ ) in Example 14, the compositions shown in Table 1 were obtained. Pore volume catalysts (15) and (16) were obtained.
(Comparative Example 1)
A catalyst (comparative 1) having the composition and pore volume shown in Table 1 was obtained in the same manner as in Example 1 except that aluminum oxide (α-Al ₂ O ₃ ) was used instead of calcium carbonate in Example 1. It was.
(Comparative Example 2)
A catalyst (comparative 2) having the composition and pore volume shown in Table 1 was obtained in the same manner as in Example 1 except that aluminum oxide (α-Al ₂ O ₃ ) was used instead of nickel oxide in Example 1. It was.
(Comparative Example 3)
A catalyst having the composition and pore volume shown in Table 1 (Comparative 3) was obtained in the same manner as in Example 9, except that aluminum oxide (α-Al ₂ O ₃ ) was used instead of calcium carbonate in Example 9. It was.
(Comparative Example 4)
In the same manner as in Example 1 except that calcium sulfate was used instead of calcium carbonate in Example 1 and the degree of vacuum in the extruder was further increased, a catalyst having a composition and pore volume shown in Table 1 (Comparative 4) was used. Obtained.
(Comparative Example 5)
In the same manner as in Example 9 except that calcium sulfate was used instead of calcium carbonate in Example 9 and the degree of vacuum in the extruder was further increased, a catalyst having a composition and pore volume shown in Table 1 (Comparative 5) was used. Obtained.
(Example 17)
The nitrous oxide resolution of the catalysts (1) to (16) and the comparative catalysts (Comparative 1) to (Comparative 5) was evaluated by the following method.
(Evaluation methods)
120 ml of catalyst was filled in a glass reaction tube having an inner diameter of 30 mm. A synthesis gas having the following composition was introduced into the catalyst layer under the following conditions.
<Syngas composition>
Nitrous oxide (N ₂ O): 500 ppm, oxygen (O ₂ ): 5% by volume, H ₂ O: 10% by volume, remaining: nitrogen (N ₂ )
<Processing conditions>
Gas amount: 10 NL / min, treatment temperature: 450 ° C., space velocity (SV): 5,000 hr ⁻¹ (STP)
10 hours after the synthesis gas was introduced, the concentration of nitrous oxide (N ₂ O) in the synthesis gas at the inlet and outlet of the catalyst layer was measured using a non-dispersive infrared N ₂ O meter (manufactured by Nippon Thermo Electron Co. , Model 46C-HL), and the N ₂ O removal rate was calculated according to the following formula. The results are shown in Table 1.

Claims (7)

The compound of at least one element as the catalyst component A is selected from A alkaline earth metal, nickel, cobalt, copper, Le ruthenium, at least one element or compound selected rhodium and platinum or found as a catalyst component B The catalyst A component compound is in the form of an alkaline earth metal oxide, carbonate, sulfate or phosphate, and has a pore volume of 0.1 to 0.6 ml / g A nitrous oxide decomposition catalyst characterized by being in the range. The catalyst B component is at least one element or compound selected from nickel, cobalt and copper, the catalyst A component is 1 to 99% by mass in terms of oxide, and the catalyst B component is 1 to 99% by mass in terms of oxide. The nitrous oxide decomposition catalyst according to claim 1, which is contained in a ratio of (total 100 mass%). The catalyst B component is at least one element or compound selected from ruthenium, rhodium and platinum, the catalyst A component is 90 to 99.99% by mass in terms of oxide, and the catalyst B component is 0.01 to in terms of metal. The nitrous oxide decomposition catalyst according to claim 1, which is contained at a ratio of 10% by mass (total of 100% by mass). Furthermore, the catalyst for nitrous oxide decomposition | disassembly of 1-50 mass% (total 100 mass%) of the oxide of the at least 1 sort (s) of element chosen from titanium, aluminum, a silicon, and a zirconium as a catalyst C component . After mixing the raw material compounds of the catalyst A component and the catalyst B component or the catalyst A component, the catalyst B component and the catalyst C component, integrally forming into a cylindrical shape, a cylindrical shape, a spherical shape, a plate shape or a honeycomb shape, and drying, The method for producing a nitrous oxide decomposition catalyst according to claim 1 or 2, obtained by calcination at 300 to 600 ° C. 6. The method for producing a nitrous oxide decomposition catalyst according to claim 5, wherein the raw material compound of the catalyst A component is any one of an alkaline earth metal carbonate, basic carbonate, sulfate or phosphate. A method for purifying a nitrous oxide-containing gas, comprising bringing a gas containing nitrous oxide into contact with the nitrous oxide decomposition catalyst according to any one of claims 1 to 4 to decompose and remove the nitrous oxide.