BG62687B1 - Gold catalyst for the oxidation of carbon oxide and hydrocarbons, reduction of nitrogen oxides and ozone decomposition - Google Patents

Abstract

The gold catalyst for the oxidation of carbon oxide, in particular C3H6 and C3H8 for the reduction of nitrogen oxides and ozone decomposition shall find application in environmental protection. The catalyst active component is a complex of gold and reduceable oxide of the group of the transition metals. The gold concentration is 0.1-2.5 wt.%, and the total metal concentration in the active component ranges from 0.1 to 10 wt.%. The carrier is cerium and titanium oxides. The catalyst surface is from 80 to 400 m2/g. It operates at temperature range from 0 to 400oC. 3 claims, 4 figures

Description

The invention relates to a gold catalyst for the oxidation of carbon monoxide and hydrocarbons, in particular C ₃ H ₆ and C ₃ H ₈ , reduction of nitrogen oxides and decomposition of ozone, which will be used in environmental protection.

Internal combustion engines contribute significantly to atmospheric air pollution. The global trend towards urbanization of the population will further aggravate the existing situation. Working conditions in many cities, industrial plants and administrative buildings are characterized by air containing an unacceptably high level of a number of harmful gases such as carbon monoxide, nitrogen and sulfur oxides and various organic compounds. A number of commonly used medical devices, instruments such as photocopiers and printing equipment and computers that are used in everyday life, increase the concentration of ozone to a hazardous health level and contribute to further deterioration of air in the work environment.

The protection of the environment and the reduction of harmful emissions from industry, transport and everyday life are some of the major problems that humanity must effectively address. These vital tasks are being addressed in a comprehensive manner: existing technologies are being improved and new more efficient production methods are being introduced, legislation relating to environmental protection and emission limit values for air, water and soil are being systematically changed. they are getting lower, new effective methods of eliminating harmful emissions are being developed.

BACKGROUND OF THE INVENTION

It is known that the reduction of the concentrations of harmful gases released by the operation of gasoline internal combustion engines (ICE) can be achieved by the use of platinum group based metal (PGM) catalysts. The disadvantage of these catalysts, however, is that they have high catalytic activity only at temperatures higher than 3000C. The moisture and sulfur oxides contained in the exhaust gases are catalytic venom and significantly reduce the catalytic activity of PGM-based catalysts, especially at low temperatures. It is well known that 80% of the harmful gases emitted by an ICE occur when a cold engine starts in the first three to five minutes. Due to the low temperature of the gases and the catalyst, conventional catalysts are ineffective during this period of ICE operation.

Purification of flue gases from diesel ICEs is still one of the major unresolved problems in environmental catalysis. Under the conditions of operation of these engines, a number of negative factors arise, such as a lower temperature of the exhaust gases, a large excess of oxygen and a high content of sulfur oxides and soot, which dramatically reduce the catalytic activity and the lifetime of the catalysts used.

The high operating temperature of PGM-based catalysts makes them unsuitable for air purification in buildings, industrial premises, airplanes, ships, submarines, spacecraft and others.

Gold has always been considered to be poorly chemical and catalytic in comparison to SGP. However, publications in the literature show that when gold is finely dispersed on reducing oxides, its catalytic activity at low temperatures in the carbon monoxide oxidation reaction increases sharply. The known catalysts containing gold are either very expensive (with a gold content of up to 12% by weight) or insufficiently active at high flow rates of the passing gases, as a result of which they have not found practical application so far.

A catalyst (DE 3914294) is known in which the gold is coated with iron oxide containing aluminum oxide and / or aluminosilicate. This catalyst has been found to exhibit a low degree of carbon monoxide conversion at high volumetric flow rates. The catalyst is very easily poisoned by moisture and sulfur dioxide.

Also known are gold catalysts deposited on cobalt, titanium and iron oxide (M.Harutaet al., “Mechanistic studies of CO oxidation on highly dispersed gold cataiists: for use in room temperature air purification. Proceeding of the 10 th International Congress of Cataiists , 19-24 July 1992, Budapest, Hungary (2657 - 2660); H. Kageyama et al., "XAFS studies of ultrafine gold cataiists supported on hematite prepared from co-precipitated precursosrs. Physica B 158 (1989) 183 - 184) .

SUMMARY OF THE INVENTION

The catalyst according to the invention exhibits a high activity in the simultaneous flow of oxidation and reduction processes and consists of an active complex deposited on the surface of a porous support.

The active component of the catalyst is a complex of gold and a reducing oxide of the transition metal group. The metal may be copper, cobalt, chromium, iron, manganese or a combination of these metals. The concentration of gold in the catalyst is 0.1 - 2.5% by weight. preferably less than 1.5% by weight, and the total concentration of metals in the active component of the catalyst should not exceed 10 ° ₀ % by weight. from the catalyst. The complex of gold-reducing oxide creates bonds due to chemical and physical interactions between the participating components. The complex is firmly connected to the surface of the carrier.

The catalyst support may consist of single oxides or mixtures of cerium and titanium oxides. The concentration of cerium oxide is from 30 to 95% by weight, and that of titanium oxide is from 5 to 25% by weight. The surface of the catalyst should be 80 m ² / g to 400 m ² / g. It may be in powder form, tableted, extruded or by other known method applied to a suitably preformed base, in the form of a porous sponge, a honeycomb (metal or ceramic) and the like.

The gold complex is treated on a carrier of mixed oxides by known methods - impregnation, precipitation, precipitation or a combination thereof. The active ingredient particles are applied evenly over the entire surface of the carrier. Their size should be less than 40 pt, preferably less than 20 pt. The process for obtaining the gold catalyst is carried out at a pH of between 7.0 and 12.0, preferably between 8.0 and 10.5. The necessary pH is achieved by the addition of basic compounds, for example sodium or potassium carbonate, hydroxides or ammonia. Following the formation of the precursor of the gold-oxide active complex, the catalyst is heated to a temperature of 100 to 500 ° C, whereby fine clusters of the gold complex are formed and firmly fixed to the surface of the support.

The thermal treatment of the catalyst is carried out in an oxidizing medium or air.

The catalyst was operated at a temperature of 0 to 400 ° C. The advantages of the invention are that the catalyst is more effective than similar existing catalysts in oxidizing carbon monoxide and hydrocarbons at low temperatures in the presence of moisture and sulfur dioxide, and the presence of moisture in the reaction mixture promotes the oxidative activity of the catalyst the presence of sulfur dioxide in the reaction mixture does not poison the oxidizing activity of the activator. In addition, the catalyst has a high catalytic activity while reducing gold oxides and oxidizing carbon monoxide and hydrocarbons at low and high temperatures and is highly effective at decomposing ozone at room temperature. The catalyst has a high catalytic activity for the simultaneous oxidation of carbon monoxide and hydrocarbons and the decomposition of ozone at low temperatures in the presence of moisture and sulfur dioxide.

Examples of carrying out the invention

Example 1. Preparation of the catalyst

1.82 g HAuCL ₄ .H ₂ O and 24.7 g Co (NO ₃ ), 6H, O were dissolved in a vessel containing 500 cm ^{3 of} distilled water heated at 60 ° C. To the solution was added 92 g of a carrier consisting of CeO ₂ and TiO ₂ . At this temperature of the mixture, with a continuous stirring, a solution of 50 g of Na ₂ CO ₃ in 500 cm ^{3 of} distilled water was slowly added until the pH of the medium was 8.0 ± 0.1. Under these conditions, the system is maintained for 60 minutes, paying particular attention to the constancy of temperature and pH of the medium. The stirring was then stopped and the precipitate aged for another 60 min. The resulting catalyst was washed with distilled water to the absence of Cl 'and NO ³ ' ions in the wash water and dried at 120 ° C for 4 h and quenched with a slow rise in temperature to 450 ° C. At this temperature, it was heated for 6 hours. 5

Figure 1 shows the existing relationship between gold and the reducing metal of the transition metal Co ₂ O ₃ in the active cluster.

Figure 2 shows the relationship between the cluster and the oxide carrier.

Example 2. Influence of the carrier on the activity of the catalyst

The catalyst obtained by the method in Example 1 on the carrier according to the invention, and the catalyst obtained by the same method on the A1, O ₃ carrier, were tested in a flow reactor containing 1 g of the catalyst at different temperatures, a volumetric rate of 45000 h ' ^1. and gas composition 1% CO, 0.9% O ₂ , 350 ppm C ₃ H ₆ hydrocarbons, 350 ppm C ₃ H ₈ , 15 ppm SO, humidity 95% and balance N ₂ .

The results obtained are presented in Table 1. They illustrate the beneficial effect of the modified carrier on the activity of the gold catalyst in the oxidation reaction of carbon monoxide and hydrocarbons.

Table 1

Temperature (° C) Conversion (%) CO NA A1 _{2 about 3} Mixed oxides A1 _{2 about 3} Mixed oxides 25 45 86 0 60 100 7 96 0 9 200 46 100 13 65 300 100 100 61 79 400 100 100 91 98

Example 3. Positive influence of moisture on the catalytic activity of the gold catalyst in the oxidation reaction of carbon monoxide

The catalyst obtained by the method of Example 1 was tested in a flow reactor containing 1 g of catalyst at a temperature of 250C, a volume velocity of 360000 h ' ¹ and a gas composition of 25 ppm CO, a balance of dry air and 95% humidity. The results obtained are presented in Table 2. The results show the promotional effect of water vapor on the activity of the gold catalyst in the carbon monoxide oxidation reaction.

Table 2

Temperature (° C) CO oxidation (%) Dry air 95% humidity 25 96 100

referred to in Example 1, on a modified carrier, and a PGM-based catalyst was tested in a flow reactor containing 1 g of catalyst at 25 ° C, 60,000 h ^- 'volume velocity and gas composition: 1% Co, 0.9% O ₂ , 350 ppm C ₃ H ₆ , 350 ppm SD, 1000 ppm _{χ χ} , 15 ppm SO ₂ , 95% humidity and N ₂ balance. The results obtained are summarized in Table 3 and show the advantages of the invention, especially at low temperatures of the gases released by the ICE.

Table 3

Temperature (° C) Conversion (%) CO NA N0 X PGM Catalyst- 3 5 0 mash Gold Catalyst- 83 60 87 mash

Example 4. Comparison between the catalytic activity of the gold catalyst according to the invention and the catalytic activity of a PGM-based catalyst in the conversion of gases at cold engine start (first 180 s)

A / The catalyst obtained by the method,

B. A scheme for incorporating the gold catalyst into existing car exhaust systems is given in the attached FIG. 3.

The proposed configuration solves the problem of cold start of internal combustion engines. The gases released from the motor are directed to the gold catalyst via a thermal valve and oxidized to the catalyst surface. The temperature separated from the exothermic chemical reaction is transferred to the platinum catalyst and helps to reach the operating temperature of the conventional catalysts quickly. When the temperature of the platinum catalyst reaches 300 ° C, the thermal valve to the gold catalyst closes and the oxidation and reduction processes for the purification of the harmful gases become on the surface of the catalyst in the platinum group.

A modified scheme of the above single-exhaust configuration is shown in the accompanying FIG. 4.

Example 5. Conversion of waste gases to the surface of the catalyst according to the invention at different temperatures from the cycle of internal combustion engines

The catalyst obtained by the method of Example 1 on a modified carrier was tested in a flow reactor containing 1 g of the catalyst at different temperatures, a volume velocity of 60,000 h ^l and a gas composition of 1% CO, 0.7-0.9% O ₂ , 350 ppm C ₃ H ₆ , 350 ppm C ₃ H ₈ , 1000 ppm _{χ χ} , 15 ppm SO ₂ , 95% humidity and balance N _r

The results obtained are summarized in Table 4. They illustrate the advantages of the invention, in particular at low temperatures of gases emitted by internal combustion engines.

Table 4

Temperature (° C) Conversion (%) CO NA N0 X 25 89 58 91 100 99 9 - 200 100 68 78 300 100 79 95 400 100 98 98

Example 6. Ozone Conversion to the Catalyst Surface of the Invention

The catalyst obtained by the method of Example 1 on a carrier was tested in a flow reactor containing 1 g of the catalyst at different temperatures, a volumetric rate of 120,000 h ' ¹ and a gas composition of 0.01% ozone, air balance.

A 100% conversion rate is observed.

Example 7. Ozone Conversion to the Catalyst Surface

The catalyst obtained by the method of Example 1 on a carrier was tested in a flow reactor containing 1 g of the catalyst at different temperatures, a volumetric rate of 120,000 h ' ¹ and a gas composition of 0.01% ozone, 0.1% CO and balance air.

A 100% conversion rate is observed.

Claims

Claims (3)

A 100% conversion rate is observed. Claims 1. Gold catalyst for the oxidation of carbon monoxide and hydrocarbons, in particular C, H ₆ and C ₃ H ₈ , reduction of nitrogen oxides and decomposition of ozone, including an active complex and a porous carrier, in which the active complex is gold and a reducing oxide of a transition element deposited on a carrier of cerium and titanium oxides, characterized by a precursor of the gold oxide active complex with fine clusters fixed firmly on the surface of the carrier formed after heating the catalyst at temperatures of 100 to 500 ° C, surface in the game itsite from 80 to 400 m ² / g, an operating temperature of 0 to 400 ° C, the content of cerium oxide in the carrier from 30 to 95% by weight. and titanium oxide in the carrier from 5 to 25% by weight, a total concentration of metals in the active complex of the catalyst from 0.1 to 10% by weight. and a gold content of 0.1 - 2.5% by weight. Gold catalyst according to claim 1, characterized in that the reducing oxide may be one or more of the oxides of copper, chromium, cobalt, manganese and iron. Gold catalyst according to claim 1, characterized in that the concentration of gold in the active complex is preferably 0.1 - 1.5% by weight. Attachment: 4 figures