BG64476B1 - Oxide catalyst for scrubbing of waste and flue gases and method for the preparation thereof - Google Patents

Abstract

The catalyst comprises metal substrate - profiled stainless steel coated by a thin porous film of zirconium oxide of 3-7 mute and specific surface of 18 to 25 m2/g; intermediate layer of lanthanum oxide and surface layer of copper-cobalt oxide spinel in the following composition, in at.%: from 2 to 15 Zr, 1-4 La, from 4 to 15 Cu and from 6 to 20 Co. The catalyst is highly effective for the reduction of nitrogen oxide in oxidation conditions (oxygen surplus), as well as for the complete oxidation of carbon monoxide (CO) and hydrocarbons (HC). The method for the preparation of the catalyst includes electrochemical deposition of a thin film of zirconium oxide on the surface of a metal substrate, drying and quenching of the coated substrate, impregnation by a solution of easily thermally dissolving lanthanum salt, drying and quenching for the formation of the active carrier, impregnation of the carrier by a mixed solution of thermally easily degradable copper and cobalt salts, subsequent drying and quenching of the coated substrate, The substrate is packed in a integrated structure in the form of a honeycomb or a similar form.

Description

Technical field

The invention relates to an oxide catalyst used for the purification of exhaust and exhaust gases from nitrogen oxides _{χ χ} by reduction with a hydrocarbon, eg methane (CH ₄ ), in the presence of excess oxygen, oxidation of carbon monoxide (CO) and hydrocarbons (HC ) with oxygen to carbon dioxide (CO ₂ ).

BACKGROUND OF THE INVENTION

Catalysts are applied to the exhaust systems of ICE vehicles and to the exhaust gas flue systems of OPGGs (natural gas heating systems) in order to convert the carbon monoxide, hydrocarbons and nitrogen oxides produced by combustion into acceptable gases. When the engine operates with stoichiometric or low rich fuel mixtures, catalysts containing palladium, platinum and rhodium or palladium and rhodium are capable of effectively converting all three gases simultaneously. Hence, such catalysts are called "three-way" catalysts. However, it is desirable to operate with poor fuel mixtures in order to achieve fuel savings and reduce the pollution of the atmosphere by harmful gases. Such conditions are typical of OPGF combustion chambers. Three-way catalysts can convert carbon monoxide and hydrocarbons, but they are not effective in reducing nitrogen oxides under oxidizing conditions (excess oxygen).

One of the first patents for the purification of ICE gases operating with lean mixtures (lit. source 1) describes a low-temperature catalyst, a high-silicon Cu-ion zeolite. However, in the normal operation of the engines, high temperatures are realized at which these catalysts decompose, as the transition metal tends to interact with the zeolite alumina to form an aluminate with a smaller surface area. As a result, the catalytic activity of the system is reduced.

In lit. source 2, a two-phase catalyst system consisting of a phase containing a transition metal zeolite with a high silicon content and a phase containing a transition metal oxide is proposed. The catalyst system may be an intimate mixture or a layered structure with a first layer of Cu-ion-exchanged zeolite and a second layer of Cu-containing zirconium oxide. The transition metal can be one of the groups Cu, Co, Ni, Cr, Fe, Μη, Ag, Zn, Ca or a mixture thereof, and the oxide phase is lanthanum, titanium, silicon or zirconium oxide. The active phases are applied as a slurry on a honeycomb-shaped metal or cordierite substrate. This system is capable of high efficiency purification of both NO * and hydrocarbons in the presence of oxygen-rich car gases.

The disadvantages of the above conventional methods of producing gas cleaning catalysts are that when the active components are applied, the slurry layer is fixed to the substrate by evaporation of moisture during drying and calcination, and therefore the applied catalyst bed is subjected to stresses, which are generated in the layer covering the substrate. As a result, cracks in the coating layer are formed and, due to the inevitable vibrations and abrupt change of thermal regimes, its destruction and displacement from the gas stream can occur over time.

A method for increasing the stability of a catalyst bed deposited on a cordierite or metal substrate is described in lit. source 3, according to which an active coating layer with a thickness <50 µm is applied to the active component layer. However, there is an additional requirement for the slurry from which the protective layer is formed, according to which the particle size therein should be in the range of 3-7 µm. The disadvantage of the catalyst obtained by this method is that it contains the precious precious metal palladium in the first catalytically active layer.

In lit. source 4 proposes a catalyst for the purification of NO _x in the exhaust gases of engines running low fuel mixtures containing at least one of the precious metals Pt, Rh and Pd and perovskite oxide La _lx A * O ₃ such as 0 <x <1; AECa or Ba, deposited on a thermally stable inorganic carrier. Close in action and active components is the catalyst protected in lit. source 5 containing Pd and / or Rh and (La,. 'AD _, BO _b , A being Ba, K and Cs, B is a transition element such as Fe, Co, Ni and / or Μη; ax has a value of 0 -1, a = 0-0.2 and b corresponds to a value at which the double oxide is electroneutral.

Both catalysts contain expensive precious metals as major active components.

There are also mixed oxide spinel catalysts containing one or more metal ions [6-8], but these catalysts are deposited on carriers in the form of: tablets or spheres. This does not allow the catalyst to be packaged in easily manipulated modules, resistant to hydrodynamic and thermal loads.

SUMMARY OF THE INVENTION

The invention relates to an oxide catalyst for the purification of exhaust and exhaust gases, which is a multilayer system consisting of a metal substrate-profiled stainless steel coated with a thin porous zirconium oxide film, with a thickness of 3-7 µm and a specific surface of 18-25 m ² / g; lanthanum oxide intermediate layer and copper-cobalt oxide spinel surface layer at 2-15 at. % Zr, 1-4 at. % La, 4-15 at. % Si and 6-20 at. % Co.

The invention also relates to a process for preparing a catalyst comprising the following steps.

A. Application of the active carrier of zirconium oxide, such as a profiled stainless steel (SS) sheet, type 1.4301, or Sandvik OC404 0.01-0.1 mm thick, is degreased by immersion in a solution containing NaOH, Na ₃ PO ₄ , Na - metasilicate, surfactant heated to 70 ° C for 5 min; washed with hot and copious cold water and dried with hot (150-200 ° C) air; immersed in a bath containing sheet carbon electrode electrodes (anodes) and an electrolyte with a ZrCl ₄ concentration of 10 to 70 g / l and a 0.1-1 ml / 10.2% surfactant solution, followed by electrodeposition of zirconium oxide at a terminal voltage of 1-10 V and a duration of 30-60 min. The resulting thin porous zirconium oxide film has a thickness of 3-7 µm and a specific surface area of 18-25 m ² / g.

B. Application of a lanthanum oxide modifying layer, wherein the active zirconium carrier supported on the metal substrate is modified with a lanthanum oxide layer (La ₂ O ₃ ) to enhance the thermal stability of the carrier and facilitate the formation of the active catalytic layer from Si-Co oxide spinel. The stainless steel profiled sheet bearing the ZrO ₂ carrier was washed extensively with running distilled water, air-dried for 2 hours at 120 ° C, heated for 1 hour at 400-500 ° C, and then cooled to room temperature; immerse in an aqueous solution of (easily decomposable) salt of lanthanum, preferably nitrate at a concentration of 30-60 g / l, which is left to stand for 2 h at 20 ° C or 5-60 min at 60-90 ° C, dried in air for 24 h at room temperature and for 1 h at 120 ° C, and is heated for 1 h in air or oxygen-enriched air at 450 ° C. The resulting intermediate layer covering the film of ZrO ₂ contains 15-22 at.% La, La being in the form of lanthanum oxide (La ₂ O ₃ ).

C. Application of a catalytically active layer of Cu-Co oxide spinel by immersing the profiled sheet bearing the modified carrier in an aqueous solution of readily decomposable copper and cobalt salts, preferably nitrates with a concentration of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) 30-60 g / l and 77-155 g / l for cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O), so that the molar ratio Cu: Co is 1: 2, stand in the solution for 24 h at 20 ° C or 5-60 min at 60-90 ° C, air-dry for 24 h at room temperature and 1 h at 120 ° C, and incubate for 3 h at 550 ° C in air, or oxygen-enriched air. The catalyst system obtained contains 2-15 at. % Zr, 1-4 at. % La, 4-15 at. % Si and 6-20 at. % Co, Cu and Co being preferably in the form of mixed copper-cobalt oxide spinel CuCO _{(3 x)} O ₄ .

The resulting oxide catalyst, a multilayer system deposited on the metal substrate, is highly efficient for gas purification - the reduction of nitric oxide under oxidizing conditions (excess oxygen), as well as for the complete oxidation of carbon monoxide (CO) and hydrocarbons ( NA). In various gas cleaning applications, such as internal combustion engines (ICE) and natural gas heating systems (OSPG), the substrate is packaged in an integrated honeycomb-shaped structure or adjacent thereto.

The ZrO ₂ / SS carrier and the SiCO _(3x) O ^ LajOj / ZrOj / SS catalyst are characterized by XPS (Xray photoelectron spectroscopy), SEM (scanning electron spectroscopy), ICP (ion coupled plasma) and TPD (temperature programmed desorption) methods, and the BET method for a specific surface. The activity with respect to the NO + CO, O ₂ + CO and HC-SCR reactions of NO _x is determined by an integrated reactor at gas flow rates of 800021000 h ¹ .

The catalyst thus described and the process for preparing it have the following advantages:

- the stainless steel metal substrate is a structural material with high mechanical strength and resistance to sudden changes in thermal and corrosion modes of operation; easily molded into modules of suitable shape and size for: embedded in catalytic converters for flue gas cleaning;

- the active carrier is a thin porous zirconium film having a thickness of 3-7 pm and a specific surface area of 18-25 m ² / g and having perfect adhesion to the substrate, in that the integrity of the film and its surface does not change after deposition of the La ₂ O ₃ modifier and the active phase of Cu-Co oxide spinel and air treatment at 550 ° C;

- the catalyst system obtained on the metal substrate contains 2-15 at. % Zr, 1 -4 at. % La, 4-15 at. % Si and 6-20 at. % Co, such as Cu and Co are preferably in the form of mixed copper cobalt oxide spinel Cu _x Co _(3g) O ₄ . The catalyst has high catalytic activity and thermal stability;

- the method enables the controlled and reproducible deposition of 3-7 pm thick zirconium oxide films and a multilayer catalyst system with a defined composition and structure on a metal substrate;

- the method does not require the use of inaccessible and costly raw materials, as well as the use of sophisticated, additional equipment other than conventional chemical reactors.

Examples of carrying out the invention

The catalyst according to the invention can be prepared in the following ways.

Example 1. A profiled stainless steel (SS) sheet Sandvik OC404, 0.05 mm thick and 100 x 500 mm in size, was defatted by immersion in a solution containing 30 g / 1 NaOH, 15 g / 1 Na ₃ PO ₄ , 15 g / 1 Na - metasilicate, 3 g / 1 surfactant and heated to 70 ° C for 5 min; it is washed with hot and copious cold water, then dried with hot (200 ° C) air. Immerse in a bath containing an electrolyte with a concentration of ZrCl ₄ of 10 g / Ι and add 0.1 ml / Ι of 0.2% surfactant solution. Electro deposition of zirconium oxide at terminal voltage 1V and duration 60 min.

The profiled sheet was washed extensively with running distilled water and air-dried at 120 ° C for 2 h. It is heated for one hour at 400 ° C in air, cooled to room temperature and immersed in an aqueous solution of lanthanum nitrate La (NO ₃ ) ₂ .6H ₂ O at a concentration of 30 g / Ι, at a temperature of 20 ° C. . After standing in the solution for 24 h, it was removed, air-dried for 24 h at room temperature and for 1 h at 120 ° C, and heated for 1 h in air at 450 ° C. The profiled sheet is then immersed in an aqueous solution of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) 40 g / l and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O), 103 g / l at temperature. 20 ° C and after standing in the solution for 24 h, it was removed, air-dried for 24 h at room temperature and 1 h at 120 ° C, and heated for 3 h in air at 550 ° C. The catalyst is designated sample A.

Example 2. A stainless steel (SS) profiled sheet of Sandvik OC404 type 0.1 mm thick and 100 x 500 mm in size is oiled by immersion in a solution containing 30 g / 1 NaOH, 15 g /

Na ₃ PO ₄ , 15 g / 1 Na - metasilicate, 3 g / 1 surfactant and heated to 70 ° C for 5 min; it is washed with hot and copious cold water and then dried with hot (150 ° C) air. Immerse in a bath containing an electrolyte with a concentration of ZrCl ₄ of 30 g / Ι and add 0.2 ml / Ι of 0.2% surfactant solution. Electrodeposition of zirconium oxide at a terminal voltage of 5 V and a duration of 30 min. The profiled sheet is washed thoroughly with running distilled water and air-dried at 120 ° C.

h. It is heated for one hour at 450 ° C in air, cooled to room temperature and immersed in an aqueous solution of lanthanum nitrate La (NO ₃ ) ₂ .6H ₂ O at a concentration of 40 g / Ι, at a temperature of 60 ° C. . After standing in the solution for 1 h, it was removed, air-dried for 24 h at room temperature and for 1 h at 120 ° C, and heated for 1 h in air at 450 ° C. The profiled sheet is then immersed in an aqueous solution of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) 60 g / l and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O), 155 g / l at temperature. 60 ° C and after standing in the solution for 1 h, it was removed, air-dried for 24 h at room temperature and 1 h at 120 ° C, and heated for 3 h in air at 550 ° C. The catalyst is designated sample B.

Example 3. The catalyst was prepared as sample B by the method described in example 2, but the deposition of La and then of Cu and Co was carried out at 80 ° C for a duration of 5 min. The catalysis of the fertilizer is referred to as sample C.

EXAMPLE 4 A stainless steel (SS) profiled sheet of Sandvik OC404 0.1 mm thick and 100 x 500 mm in size was degreased by immersion in a solution containing 30 g / 1 NaOH, 5 15 g / 1 Na ₃ PO ₄ , 15 g / 1 Na - metasilicate, 3 g / 1 surfactant and heated to 70 ° C for 5 min; It is washed with hot and copious cold water, then dried with hot (150 ° C) air. Immerse yourself in a bath containing an electrolyte with a concentration of ZrCl ₄ of 50 g / Ι and add 0.5 ml / Ι of 0.2% surfactant solution. The zirconium oxide was deposited at a terminal voltage of 10 V and a duration of 40 minutes. The profiled sheet was washed extensively with running distilled water and air-dried at 120 ° C for 2 h. It is heated for 1 hour at 450 ° C in air, cooled to room temperature and immersed in an aqueous solution of lanthanum nitrate La (NO ₃ ) ₂ .6H ₂ O at a concentration of 60 g / Ι, at a temperature of 80 ° C. . After standing in the solution for 1 h, it was removed, air-dried for 24 h at room temperature and for 1 h at 120 ° C, and heated for 1 h in air at 450 ° C. The profiled sheet was then immersed in an aqueous solution of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) 30 g / l and cobalt nitrate (Co (NOj) ₂ .6H ₂ O), 77.35 g / l at temperature. 80 ° C and after standing in the solution for 1 h, it is removed, air-dried for 24 h at room temperature and 1 h at 120 ° C, and heated for 3 h in air at 550 ° C. The catalyst is referred to as sample D.

Example 5. The catalyst was prepared as sample A by the method described in example 1, but the deposition of La and then of Cu and Co was carried out at 60 ° C for a duration of 60 min. Tempering at 550 ° C after application of Cu and Co is carried out in a stream of O ₂ . The catalyst is designated sample E.

EXAMPLE 6 The catalyst was prepared as sample D by the method described in example 4, but La deposition was carried out at 90 ° C for a duration of 60 min and Cu and Co deposition was carried out with a solution of copper nitrate (Cu ( NO ₃ ) ₂ .3H ₂ O) 50 g / l and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) - 129 g / l at 90 ° C for a duration of 60 min. The calcination at 550 ° C, after application of Cu and Co, is carried out in a stream of O ₂ . The catalyst is designated sample F.

Table 1.

Content of the elements (at%) in the surface layer of the stainless steel film deposited on the profiled sheet, catalytically active film.

Sample Zr 3d La 3ds / 2 Si 2z Co 2ρια Co / Si 'Cr 2.5 1.6 11.2 12.2 1.09 IN 7.1 1.2 13.6 16 1.18 p 4.7 2.7 5.8 19.1 3.29 D 14.5 2.4 4.6 6.4 1.39 • Well 7.9 1.9 6.8 15.5 2.28 ' F 13.3 1.7 8 13 1.63

The concentrations of Zr, La, Cu, Co and O and their chemical state were determined by the XPS method. When La is applied to the surface of electrochemically deposited ZrO ₂ , La ₂ O ₃ is formed. When applied to Cu and Co, the copper is in the Cu ²⁺ state and the cobalt is in the Co ³⁺ state, forming mixed oxide spinels Cu _x Co _{(3 x)} O ₄ with different Co: Cu ratios.

Table 2.

Activity (% conversion of NO to N ₂ ) of the catalysts with respect to the reduction of nitric oxide (NO) with carbon monoxide (CO).

0.12 vol. Gas flow % NO + 0.12% % CO + Ar, volumetric rate 15 000 h ¹ .

Sample / T ° C 150 17.5 200 225 250275 300 350 400 • 450 500 550  A 6 12 18 32 47 69 82 •• -E? '· '13 1 * 19 21 23. 27 31 45 72 82 90 93; F ': 2 ---.......... · -.....- - · : 5 12 22 29 40 -L 59 74 89 99 100 100

Table 3.

Activity (% conversion of CO to CO ₂ ) of catalysts for the oxidation of carbon monoxide (CO) with oxygen (O ₂ ).

Gas flow 0.5 vol. % CO + 1 vol. % O ₂ + Ar, volumetric rate 20 000 h ' ¹

O ^^ azEC / G / C 300] 325 \ 350 \ 375 400 425 450 500 550 31 4 31 63 98 100 100 F 4 12 23 40 56 83 98 100 100

Table 4.

Activity (% conversion of NO to N ₂ ) of the catalysts with respect to the reduction of nitric oxide (NO) with methane (CH ₄ ) in the presence of excess oxygen (O ₂ ).

Gas flow 0.1 vol. % N0 + 0.25 vol. % CH ₄ + 3 vol. % O ₂ + Ar, volumetric rate 8000 h ^_1

200 2 2 280 4 ·· S 2ϋϋ 300 305 Ύ— 315 325 330 350 375 400 410 430 ^ 450 2, 12 39 ί 33 ί 465 ^ 480 .181.16 27 | 21 ______ χ ______ 500515 ₁₄ ty; f 19 and 18 I 520 550 l e · F 5 ^; 12 6 13 9 14 • 11 15 12 22 14 25 16 33 10 42 6 44 4 '· ^; 41 6 17 i 16

Claims (8)

An oxide catalyst for the purification of exhaust and exhaust gases, characterized in that it is a three-layer system consisting of a metal substrate - profiled stainless steel, coated with a thin porous zirconium oxide film 3-7 pm thick and a specific surface 18 -25 m ² / g; lanthanum oxide intermediate layer and copper cobalt oxide spinel surface layer at 2-15 at. % Zr, 1 -4 at. % La, 4-15 at. % Si and 6-20 at. % Co. 2. A process for the preparation of an oxide catalyst for purification of exhaust and exhaust gases, characterized in that the profiled stainless steel sheet 15 with a thickness of less than 0.1 mm is degreased by immersion in a solution containing NaOH, Na ₃ PO ", Na - metasilicate, surfactant and heated to 70 ° C for 5 min; washed with hot and copious cold water, then dried 20 with hot (150-200 ° C) air; Electroplating is made of zirconium oxide in a bath containing sheet carbon charcoal counter electrodes and an electrolyte with a concentration of ZrCl ₄ of 10 to 70 g / Ι and 0.1 -1 ml / 10.2% surfactant solution, at 25 terminal voltage 1-10 V and duration from 30 to 60 min; heated for 1 hour at 400 to 500 ° C in air, cooled to room temperature and immersed in an aqueous solution of 5 lanthanum nitrate La (NO ₃ ) ₂ .6H ₂ O at a concentration of 30 to 60 g / Ι, in which it is left for 24 hours at 20 ° C or 5 to 60 minutes at 60 to 90 ° C, air-dried for 24 hours at room temperature and 1 hour at 120 ° C, and heated for 1 hour in air at 450 ° C; then immersed in aqueous 10 copper nitrate solution (Cu (NO ₃ ) ₂ .3H ₂ O) 30-50 g / l and cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) 77-155 g / l , which is left for 24 hours at 20 ° C or 5-60 minutes at 60 to 90 ° C, air-dried for 24 hours at room temperature and 1 hour at 120 ° C, and heated for 3 hours in air or air enriched with oxygen, at 550 ° C. Literature 1. US4297 328. 2. US 5 155 077. 3. EP1 127 604. 4. JP Appl. 8 / 229,355 / 1997. 5. GB 2 322 309 A. 6. BG 21437. 7. BG 29154. 8. BG 37896.