DE2242183A1 - CATALYST AND PROCESS FOR THE REDUCTION OF NITROGEN OXYDE - Google Patents

Description

Standard Oil Company, Chicago, Ill./USA

Catalyst and process for the reduction of nitrogen oxides

The invention relates to a method for reducing nitrogen oxide gases in which the formation of ammonia is minimal is held, and a catalyst for carrying out the process. It is believed that nickel oxide is present in the catalyst is present is responsible for suppressing the formation of ammonia. About 20% by weight, preferably from 20 to 60% by weight, is used. Nickel oxide. The catalyst can also contain other metal oxides such as copper oxide, iron oxide and chromium oxide. These Metal oxides preferably contain a carrier such as inorganic, porous, refractory materials, preferably Aluminum oxide.

A catalytic muffler containing two single catalytic beds has been proposed as a device to prevent the Combat pollution from car exhaust. The first bed contains a catalyst that does the reduction reaction between reducing agents in the exhaust gases such as carbon

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activated monoxide and oxides of nitrogen. At high temperatures nitrogen and carbon dioxide are formed. At low temperatures, especially when tempering, the reaction conditions favor the formation of Ammonia. The second bed contains catalysts that control the oxidation reaction between carbon monoxide and secondary Activate air introduced into the system. If ammonia is present in that second bed, it will become too Oxide of nitrogen is oxidized. Therefore, in order to keep the presence of nitrogen oxide in car exhausts small or to exclude it, it is required, the formation in the first catalytic bed Avoid ammonia or reduce it to the lowest possible level, especially at low temperatures from about 316 to about 704 ° C (600 to 1300 ° F).

It has now been found that nickel oxide prevents ammonia formation during the reduction of nitrogen oxides at low temperatures suppressed. The invention relates to a new process for reducing nitrogen oxides. In the inventive Process, the nitrogen oxides are passed through a zone that is operated under such conditions, in which nitrogen oxides are reduced, the zone containing a catalyst which is at least about 20% by weight nickel contains. Preferably between about 20 and about 60% by weight of nickel oxide, based on the weight of the total catalyst, required to have a remarkable prevention of ammonia formation during the reduction of nitrogen oxides, especially at lower temperatures, from about 316 to about 704 ° C (600 to 1300 ° F).

It is most advantageous to use the method according to the invention to remove the nitrogen oxides that are present in exhaust gases from internal combustion engines occur to reduce. Such exhaust gases also include hydrogen, hydrocarbons and Carbon monoxide. These materials act as reducing agents

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and react with the nitrogen oxides to form nitrogen, water, carbon dioxide and some ammonia. The high content of nickel oxide in the catalyst according to the invention, however, keeps the formation of ammonia low. Generally, the temperature in the reduction zone of between about 260 and about 816 ° C (500 and 1500 ⁰ F) is maintained, and the space velocity of the exhaust gases are passed through this zone, is located in areas between about 15 000 to about 35,000 volume Exhaust gases per hour per volume of catalyst.

The catalyst according to the invention contains inorganic, porous, refractory material which is used as a carrier for the Nickel oxide is used. Alumina is the preferred carrier material, but silica-alumina, bauxite, Zirconium oxide, magnesia-alumina-silicon dioxide, magnesia-aluminum oxide or zinc oxide-aluminum oxide can also be used. These carriers that are physically strong or solid are most preferred, because they can withstand the constant shaking that occurs in catalytic mufflers. The active catalytic Components can be mixed with the carrier materials by impregnation or by coprecipitation will. Some carriers are more easily impregnated than others and this must be done in the preparation of the catalyst note. The ingredients can be mixed together or sequentially.

In addition to the nickel oxide, one or more of the following components can be present in the catalyst: copper oxide (CuO), chromium oxide (Cr ₂ O,), iron oxide (Fe ₂ O ₃ ), barium oxide (BaO) or a metal from the platinum series, ins. special platinum and palladium. In a preferred embodiment of the invention, the catalyst contains nickel oxide and copper oxide on a carrier. The nickel

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22A2183

The oxide is present in an amount between about 20 and about 40 percent by weight and the copper oxide is present in an amount between about 5 and about 15 percent by weight. In another preferred embodiment of the invention, the catalyst contains nickel oxide, copper oxide, iron oxide on the carrier. The nickel oxide is present in an amount between about 20 and about 40 weight percent, the copper oxide in an amount between about 5 and about 15 weight percent, and the iron oxide in an amount between about 1 and about 20 weight percent. The most preferred form of catalyst contains about 23 to 28 weight percent nickel oxide, about 5 to 8 weight percent copper oxide, about 5 to 8 weight percent chromium oxide and about 0.5 to 2 weight percent iron oxide on an alumina support. If desired, this most preferred form can also contain about 0.5 to 2 weight percent barium oxide.

The iron oxide-copper oxide results in a catalytic system that is very effective in reducing the nitrogen oxides activate. The chromium oxide helps this system to maintain its high activity over a wide temperature range. The nickel oxide suppresses the formation of ammonia and gives the catalyst resistance to chemicals Deactivation. The platinum series metals, especially in low concentrations from about 0.02 to about 0.1 wt. 56, give the catalyst the ability to To activate oxidation of carbon monoxide and hydrocarbons at low temperature. When metals the When platinum series are present in the catalyst, the function of the catalyst is twofold. He activates the reduction of nitrogen oxides and the oxidation of hydrocarbons and carbon monoxide. This latter ability is important when starting when the oxidation catalyst in the second bed is not maximally effective.

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It has also been found that the conversion to ammonia by other metal oxide additives, the relative concentrations is influenced by oxygen and carbon monoxide and by the catalyst temperature.

Effect of additional oxides

The addition of certain oxides to the catalyst system of the invention can either activate or further suppress ammonia formation. For example, activate the Oxides of cerium and potassium in a nickel oxide-copper oxide catalyst (25% by weight nickel oxide, 6% by weight copper oxide Aluminum oxide) the formation of ammonia. The oxides of barium, strontium and sodium have no effect and the oxides of magnesium, manganese and calcium suppress the formation of ammonia Further. However, calcium oxide has a tendency to cause the catalyst to become unstable.

Effect of oxygen and carbon monoxide concentrations

Ammonia formation is also a function of the oxygen to carbon monoxide ratio in the exhaust gases. There were carried out experiments in which the concentrations of oxygen and carbon monoxide were varied simultaneously or independently _β The examined regions varied between about 0.5 and about 1.3% for oxygen and between about 0.8 and about 2.5 $ for carbon monoxide In Fig. 1 is a graph showing the conversion of nitrogen oxides and the formation of "ammonia" during the conversion at various ratios of oxygen and carbon monoxide. The catalyst used to produce these results contained 25% % By weight of nickel oxide, 6% by weight of copper oxide and 69% by weight of aluminum oxide. " In Fig. 2 a graph is given which shows the conversion of nitrogen oxides and the formation of ammonia during such a conversion at different acidic

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shows material-carbon monoxide ratios, using a catalyst which did not contain nickel oxide. The catalyst, which was used in the preparation of these results, containing 10 wt.% Iron oxide, 10 wt.% Copper oxide and 80 wt.% Alumina.

The results presented by these drawings are typical and they show that the conversion of nitric oxides to ammonia depends in part on the ratio of oxygen to carbon monoxide. The reduction of nitric oxide remains very high at oxygen-carbon monoxide ratios that are less than 0.6 and takes very sharply at ratios greater than 0.7. The formation of ammonia increases more or less gradually Oxygen-carbon monoxide ratio. The sharp decrease in the conversion of total nitrogen oxides above the ratio of 0.7 presumably results from the ineffectiveness of the reducing agents, which are preferably with Oxygen react at high oxygen concentrations. Measurements have shown that the oxidation of carbon monoxide is almost always complete at ratios above 0.7. On the other hand, reduced ammonia formation can result increased oxygen-carbon monoxide ratio due to the removal of hydrogen through oxidation. It should be noted that the catalyst used in the installation of the values used for Fig. 1 contains approximately 25% by weight nickel oxide. The catalyst that was used to set up of the results of Fig. 2 was used does not contain nickel oxide. Even with a low oxygen-carbon monoxide ratio of about 0.2 was the conversion of nitrogen oxides to ammonia using the catalyst which contained nickel oxide, about 50% less than the catalyst which contained no nickel oxide.

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Effect of temperature

In Fig. 3, the temperature effects of two different catalysts are shown, the oxygen to carbon monoxide ratio being approximately 0.3 and the space velocity of the exhaust gases being approximately 27,000 volumes exhaust gases / h / catalyst volume. Catalyst A contains 25% nickel oxide and catalyst B contains only 10% nickel oxide. At a temperature in the range 549-816 ⁰ C (1020-1500 ⁰ F), the formation of ammonia with increasing temperature decreases. Catalyst A is a more effective catalyst system than Catalyst B because of the larger amount of nickel oxide.

The following. Examples illustrate the invention without, however, restricting it. In the examples are preferred Process for the preparation of the catalyst shown.

example 1

The catalyst of this example is prepared according to a three step process using an alumina sold by American Cyanamid Co. under the designation Aero-100. In step 1, 3974 g nickel (II) nitrate, 1290 g chromium nitrate, 744 g copper nitrate and 413 g iron (III) nitrate are dissolved in warm water up to a volume of 4500 ml. This solution is mixed with 4892 grams of calcined Cyanamid Aero-100 (0.15 cm; 1/16 inch extrudate). The surface water is removed by drying at about 93.3 ° C (200 ⁰ F) for about 16 hours. Thereafter, it is calcined for 5 to 7 hours at 538 ° C (1000 ⁰ F). In stage 2, 3974 g of nickel nitrate, 1290 g of chromium nitrate, 744 g of copper nitrate and 413 g of iron (IIl) nitrate are dissolved in warm water to a volume of 3840 ml. This solution is added to the impregnated calcined intermediate obtained in step 1. The surface water is going through again

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Drying at about 93 ^° C (200 ^° F) for 16 hours is removed and the material is ^{calcined again in air at 538 °} C (1000 ^° F) for 5 to 7 hours. The material obtained from step 2 is impregnated with 278 g of barium nitrate in warm water enough to make a volume of 3840 ml. The material is dried again to remove the surface water and ^{calcined in air at 538 °} C. (1000 ^° F.) for 5 to 7 hours. In this process a basic composition is obtained which contains 25% nickel oxide, 6% copper oxide, 6% chromium oxide, 2% iron oxide and 1% barium oxide.

Example 2

The catalyst of this example is prepared according to the procedure described in Example 1 with the exception that a silica-alumina sold by the American Cyanamid Co. under the designation Aero-105 is distributed. This is a 0.15 cm (1/16 inch) extrusion, which contains approximately 5% silica. Investigations of the catalysts of Examples 1 and 2 showed that both catalysts were highly active, but that the catalyst of Example 1 was somewhat better under the experimental conditions than that of Example 2. In these experiments, these catalysts were auto exhaust from a car on a dynamometer exposed for 50 hours and 80 km / h (50 mph) and to a level of 1.5% carbon monoxide in the exhaust gases.

Example 3

The catalyst of this example is prepared according to a one-step process using an alumina support _{containing 10% Fe 2} O and made by Kaiser Aluminum and Chemical Co. from alumina gel and powdered Fe ₂ O ₅ . This carrier is spherical in shape and the particles have sizes ranging from 0.201 to 0.239 cm (0.079 to 0.094 inches) in diameter

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correspond. The carrier was calcined before use. Copper and nickel were added to this carrier by mixing 2520 g of carrier with 2620 ml of a water solution containing 2801 g of nickel (II) nitrate and 1094 g of copper nitrate. The surface water is removed by drying at about 93.3 ° C (200 ⁰ F) for about 16 hours. It is then calcined in air at 538 ^° C. (1000 ^° F.) for 5 to 7 hours. With this method a basic composition of 20% nickel oxide, 10% copper oxide, 7% iron oxide and 63% aluminum oxide is obtained.

Example 4

The catalyst of this example used a carrier manufactured by Kaiser Aluminum and Chemical Co. _{containing 95% alumina and 5% Fe 2} O-. and made by a two-step process. In the first stage, 2705 g of carrier are mixed with 2870 ml of water solution containing 940 g of copper nitrate and 2410 g of nickel (II) nitrate. After removing the surface water by drying at 93 ⁰ C (200 ⁰ F) for 16 hours, the material is ^{calcined in air at 538 0} C (1000 ⁰ F) for 5 to 7 hours. In the second stage, the impregnated calcined intermediate product from stage 1 is mixed with 2800 ml of water solution containing 4138 g of chloroplatinic acid. Surface water is removed again by drying at 93.3 ⁰ C (200 ⁰ F) for 16 hours and the material is calcined again in air at 538 ⁰ C (1000 ⁰ F) for 5 to 7 hours. In this process, a basic composition of 8.5% copper oxide, 17% nickel oxide, 3.7% Fe ₂ O ^, 0.05% platinum and the remainder of aluminum oxide is obtained. Platinum is incorporated into this catalyst to give the catalyst an improved capability to lend to oxidize carbon monoxide especially at low temperatures. With this catalyst a complete oxidation of the carbon

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monoxide at temperatures as low as 299 ⁰ C (570 ⁰ F). The catalyst does not contain platinum, so the carbon monoxide oxidation is incomplete under otherwise similar conditions at 549 ° C (1020 ⁰ F).

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Claims (18)

- 11 claims MU process for the reduction of nitrogen oxides, thereby
characterized in that the nitrogen oxides through a zone
that is operated under such conditions
which the nitrogen oxides are reduced, and where these
Zone contains a catalyst that is at least approximately
Contains 20% by weight of nickel. 2. The method according to claim 1, characterized in that the nitrogen oxides from exhaust gases from internal combustion engines
originate and also contain hydrocarbons and carbon monoxide. 3. The method according to claim 2, characterized in that the exhaust gases from the combustion zone through the reduction zone at a space velocity in the range between about 15,000 and about 35,000 volumes of exhaust gases per
Hour per volume of catalyst are passed. 4. The method according to claim 3, characterized in that the temperature in the reduction zone is between about 260 and about 816 ° C (500 and 1500 ⁰ F). 5. The method according to claim 1, characterized in that the nickel oxide in an amount in the range between approximately 20 and about 60% by weight is present. 6. The method according to claim 1, characterized in that the catalyst contains one or more of the following components in addition to the nickel oxide: copper oxide,
Chromium oxide, iron oxide, barium oxide or * in metal of the platinum series. 309809/1186 7. The method according to claim 1, characterized in that the catalyst is used as a carrier for the nickel oxide contains inorganic refractory material. 8. The method according to claim 7, characterized in that the carrier material is alurainium oxide, silicon dioxide? Alumina, bauxite, zirconia, magnesia-alumina-silicon dioxide, Magnesia-aluminum oxide or zinc oxide-aluminum oxide used. 9. Catalyst containing an inorganic refractory carrier and at least approximately on the carrier 20% by weight of nickel oxide, calculated on the total weight of the catalyst. 10. Catalyst according to claim 9, additionally containing to the nickel oxide one or more of the following compounds: copper oxide, chromium oxide, iron oxide, barium oxide or a metal of the platinum series. 11. Catalyst according to claim 9, characterized in that the nickel oxide in an amount between about 20 and about 60 weight percent is present. 12. Catalyst according to claim 9, containing between about 20 and about 40 wt.% Nickel oxide and between about 5 and about 15% by weight of copper oxide. 13. Catalyst according to claim 9, containing between about 20 and about 40 wt.% Nickel oxide, between about 5 and about 15% by weight of copper oxide and between about 1 and about 20% by weight of iron oxide. 14. Catalyst according to claim 9, characterized in that the refractory material used is aluminum oxide, silicon 309809/1186 dioxide-aluminum oxide, bauxite, magnesia-aluminum oxide-silicon dioxide, Magnesia-aluminum oxide or zinc oxide-aluminum oxide used. 15 · Catalyst, containing about 23 Ms 28% by weight nickel oxide, about 5 to 8 % by weight copper oxide, about 5 to 8% by weight chromium oxide and about 1 to 5% by weight iron oxide on a carrier. 16. Catalyst according to claim 15 »characterized in that the carrier is an inorganic refractory Material used. 17. Catalyst according to claim 16, characterized in that aluminum oxide is used as the refractory material . 18. Catalyst according to claim 16, characterized in that that it is also about 0.5 to 2% by weight of barium oxide contains. 309809/1 186 Blank page