BG62723B1 - Gold catalyst and its application in fuel components - Google Patents

Abstract

The gold catalyst for electrochemical oxidation of carbon fuels, methanol and methane shall be used in the manufacture of fuel components. It is suitable for the neutralization of pollutions, basically of carbon oxide, from the carbon fuel. The active component of the catalyst is a complex containing gold from 0.1-2.5 wt.% and reduceable oxide from the group of the transition metals having concentrations of the preceding metals from 0.1 to 5 wt.%. The catalyst carrier consists of oxides of cerium, zirconium and titanium, and its operational temperatures range from 0 to 650 degrees C. 10 claims

Description

Technical field

The invention relates to a gold catalyst for the oxidation of hydrocarbon fuels and its application in the production of fuel cells.

Fuel cells are suitable for replacing internal combustion engines because they are environmentally friendly, do not emit harmful gases and have greater efficiency and stability.

The introduction of mass production of fuel cells is delayed for technical and economic reasons, such as the availability of adequate fuel in sufficient quantities and at an affordable price and the absence of an anode reaction catalyst that is active at low temperatures and affordable. Hydrogen is one of the most suitable fuels, but its extraction is a costly process that requires a considerable amount of energy.

In the last 20 years of the development of the fuel cells, it appears that fuels other than hydrogen that are considered suitable are: hydrocarbons, methanol, hydrazine and ammonia. Once hydrazine has been found to be carcinogenic and ammonia very expensive, natural gas and methanol appear to be the most suitable because they are cheap and in large quantities.

Direct methanol fuel cells (DMGE) are considered to be the most appropriate system because they generate electricity by directly converting the methanol to the anode of the fuel element. DMGEs are preferable to hydrogen fuel cells and especially in transport, where pressure vehicles need to be fitted to hydrogen gas cylinders. A serious impediment to the introduction into the production of these fuel elements is the reaction of the anode, which requires a highly active catalyst with reasonable cost (low cost).

BACKGROUND OF THE INVENTION

It is known that catalysts based on the transition metals used in the fuel cells are deactivated very quickly. Platinum-based catalysts have some advantages, but it is not possible to achieve sufficiently high activity with low platinum content. Platinum catalysts work well at temperatures higher than στ 200 ° C, and 5 moisture is a catalytic poison for them, especially at low temperatures. This requires the fuel cells to operate at high temperatures, which in turn accelerates their deactivation and increases the overall IQ energy consumption of the unit.

Gold has always been considered to be weakly active in chemical and catalytic terms as compared to the metals in the platinum group ι Π GM). However, publications in the literature show 5 watts. that when gold is finely dispersed on reducing oxides, its catalytic activity in the carbon monoxide oxidation reaction at low temperatures increases sharply.

DE 3914294, which describes a catalyst in which gold is deposited on a carrier 20, is known. . iron oxide, which also contains 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 easy to poison $ 2 of moisture and sulfur dioxide.

BG 101 490 describes a gold catalyst for the oxidation of carbon monoxide and hydrocarbons, the reduction of nitrogen oxides and the decomposition of ozone, which is used to reduce the 30 concentrations of harmful gases emitted by the operation of internal combustion engines (ICE). during the decomposition of ozone at low temperatures, etc.

SUMMARY OF THE INVENTION

To date, no catalyst known to have high catalytic activity at low temperatures and a reasonable price is known.

4Q According to the invention, the catalyst for the direct electrochemical oxidation of hydrocarbon fuels, methane and methanol consists of an active complex deposited on the surface of a porous carrier by the oxides of cerium, titanium and zirconium.

The catalyst active complex is a complex of gold and a reducing oxide of the transition metal group. The transition metal can be copper, chromium, cobalt, manganese, iron, or a combination of these metals. The concentration of gold is from 0.1 to 2.5% by weight. in relation to the total mass of the catalyst, preferably less than 1.3% by weight, the concentration of the reducing oxide is 0.1 to 5% by weight. relative to the total mass of the catalyst, and the total mass of the active components should not exceed 6% by weight. relative to the total mass of the catalyst.

The mixed oxide carrier has a surface area of 80 to 400 m ² / g and a cerium oxide concentration of 30 to 70% by weight, of titanium oxide of 5 to 25% by weight. and zirconium oxide from 5 to 25% by weight. relative to the mass of the media.

The gold complex is applied to the carrier by known methods: impregnation, precipitation, co-precipitation or a combination of these methods. The active ingredient particles are applied evenly over the entire surface of the carrier. Their size should be less than 40 nm, preferably 20 nm.

The calcination of the catalyst was carried out in an oxidizing medium at a temperature of 100 to 500 ° C. The catalyst was operated at a temperature of from 0 to 650 ° C.

The catalyst according to the invention is used in the following fields of fuel cell technology: for the direct electrochemical oxidation of methanol; methane reforming; direct electrochemical oxidation of liquid hydrocarbon fuels at temperatures lower than those currently used, which prevents the rapid decline in fuel cell performance due to electrode decontamination due to high temperatures; Purification of pollution (mainly carbon monoxide) by the anode fuel.

The fuel cells convert the energy of the electrochemical reaction into an electrical current. They consist of two electrodes with a catalyst deposited on them and an electrolyte. Gaseous fuel is supplied to the anode and an oxidation process takes place on its catalytic surface. An electron transfer process takes place from the fuel molecule to the anode. In this way, the ionized fuel passes through the electrolyte and on the surface the cathode reacts with oxygen, receives back electrons and forms water. The anode and cathode reactions are as follows:

Anodic reaction 2H ₂ -> 4H ⁺ + 4e

Cathodic reaction O ₂ + 4H ⁺ + 4e -> H ₂ O The migration of ions results from the presence of a concentration gradient between the electrodes and the electrolyte. The oxidation of methane produces hydrogen, which is the fuel for electrochemical oxidation on the anode of the fuel element:

CH, + O = CO, + 2H,

2 2 2

Studies show that this process does not proceed efficiently on known industrial catalysts. Even the best known Pt catalyst deposited on activated carbon does not achieve the required high conversion rate.

Methanol direct conversion fuel elements (DMGE) are considered to be most suitable since electricity is generated by the direct conversion of methanol to the anode of the fuel element. DMGE is more appropriate than the conventional fuel cell using hydrogen for fuel, in particular when used in vehicles.

The direct oxidation of methanol is carried out according to the following reaction:

CH ₃ OH + H ₂ O = co ₂ + 6H ⁺ + was

Mass production of the direct methane fuel element is delayed due to its lower efficiency compared to that of hydrogen-air systems. The main reason for this is the poor catalytic activity of the anode in the methanol oxidation reaction.

Advantages of the invention

The gold catalyst can be used in the direct electrochemical oxidation of hydrocarbons at temperatures lower than their thermal decomposition temperatures.

The gold catalyst oxidizes methanol at temperatures below 100 ° C.

The catalyst is highly effective in oxidation processes. Complete oxidation of methane, and C to C _{| 2} hydrocarbons to hydrogen and carbon dvuokisd is obtained even under conditions suitable for partial oxidation.

The complete oxidation of methane and C ₂ to C ₂ hydrocarbons is obtained at temperatures below 550 ° C and this extends the life of the fuel element.

The presence of moisture improves the oxidation activity of the catalyst, which is important in the conversion of hydrocarbons at low temperatures.

The low content of gold in the catalyst makes it economically viable.

The catalyst according to the invention has an extremely high oxidizing capacity at low temperatures, which makes it suitable for oxidizing the carbon monoxide formed on the anode.

Examples of carrying out the invention

Example 1

Complete oxidation of methane in the composition of the reaction gas 0.25% vol. methane and 99.75% | θ vol. air

8.0 g of Co (NO ₃ ) ₂ .6H ₂ O and 0.23 g of HAuC1 ₄ .H, 0 were dissolved in 300 cm ^{3 of} distilled water heated to 55 ° C. Pre-dried at 120 ° C, 98 g of the mixed carrier oxides were added to the mixture with continuous stirring. A 0.1 M KOH solution was added until pH = 9.0 ± 0.2. The impregnation was continued for 2 h, after which the mixture was filtered and washed with Cl 'and

NO ' ₃ ions. The catalyst was dried at 120 ° C and calcined at 400 ° C for 60 min. The catalyst thus obtained contains 0.5% Ai (sample 1). Samples 2, 3, 4, 5 and 6 are prepared in the same way, but the gold content is increased to 0.6%, 0.7%, 0.8%, 0.9% and 1.0% respectively.

Experiments on the complete oxidation of methane 25 were carried out with the six gold catalyst samples obtained in the above manner in a flow reactor. Samples 1,2 and 3 were tested at a temperature range of 250 to 500 ° C, while samples 4.5 and 6 were tested at a temperature range of 250 to 600 ° C, composition of the reaction gas 0.25% vol. methane and 99.75% vol. air and volume velocity (GHSV) of the reaction mixture 12000 h '

1 g of catalyst is charged into the reactor.

The degrees of conversion of methane as a function of the reaction temperature were determined. The test results are presented in Table 1.

After reaching the maximum temperature, the samples are cooled in a stream of air to room temperature and in order to evaluate the stability of the catalyst and the reproducibility of the results, the test is repeated. The results of the retests are presented in Table 2.

Table 1 shows that a significant conversion of methane was observed at temperatures higher than 400 ° C, with the highest rotation rate shown in sample 6.

Table 2 shows that under the test conditions the catalyst is stable and very good reproducibility of the results is observed. The highest catalytic activity is shown by sample 6. It should be noted that after working at high temperatures, the catalysts exhibit improved catalytic activity after repeated tests.

Table 1.

Full oxidation of methane (0.25 y-methane. 99.75% air)

Temperature (° C) Methane conversion rate (%) sample 1 sample 2 sample 3 sample 4 sample 5 sample 6 250 4 <1 <1 6 5 7 300 5 2 16 7 7 8 350 6 4 20 9 9 10 400 13 12 24 13 12 14 450 28 24 30 31 30 46 500 56 48 58 60 52 71 550 - - - 92 85 99 600 - - - 100 100 100

Table 2.

Reproducibility test: Full oxidation of methane (0.25% methane, 99.75% air)

Temperature (° C) Degree of methane (%) sample 1 sample 2 sample with sample 4 sample 5 sample 6 250 8 <1 2 4 8 14 300 8 4 ] 4 10 18 350 8 4 <4; 4 10 22 400 11 14 * p 6 12 29 450 32 36 37 23 61 500 53 54 59 64 38 88 550 - - 92 71 93 600 - - - 100 100 100

Example 2

Complete oxidation of methane in the reaction gas composition 2.5% vol. methane and 97.5% vol. air

The experiments on complete oxidation of methane were carried out with the six samples of gold catalyst obtained in the manner shown in Example 1 in a flow reactor. Samples 1,2 and 3 were tested in the temperature range from 250 to 500 ° C, while samples 4, 5 and 6 were tested at the temperature range from 250 to 600 ° C, composition of the reaction gas 2.5% vol. methane and 97.5% vol. air and volume velocity (GHSV) of the reaction mixture 12000 h '. 1 g of catalyst is charged into the reactor.

The degrees of conversion of methane as a function of reaction temperatures were determined. The test results are presented in Table 3.

After reaching the maximum temperature, the samples are cooled in a stream of air to room temperature and in order to evaluate

Complete oxidation of methane in the reaction gas composition 2.5. The catalyst stability and reproducibility of the results are repeated. The results of the retests are presented in Table 4.

Table 3 shows that a significant conversion of methane was observed at temperatures higher than 400 ° C, with the highest activity shown in sample 6.

The increase in the concentration of methane 10 10 times from 0.25 (example 1) to 2.5% vol. does not significantly change the degree of conversion of .methane.

Table 4 shows that under the test conditions the catalyst is stable and 15 very good reproducibility of the results is observed. The highest catalytic activity is demonstrated by sample 6. It should be noted that after working at high temperatures, the catalysts exhibit improved catalytic activity after repeated tests.

Table 3.

° ₀ vol. methane and 97.5% vol. air

Temperature (° C) Degree of methane excess (%) sample 1 sample 2 sample 3 sample 4 sample 5 sample 6 250 <1 <1 <1 <1 <1 <1 300 4 3 <1 <1 <1 <1 350 5 4 <1 <1 2 400 7 7 2 10 2 3 450 15 15 8 33 8 12 500 26 32 34 66 49 37 550 60 76 70 90 90 83 600 88 94 95 100 100 100

Table 4.

Sample Reproducibility Test 6: Fully oxidized methane (2.5% vol. Methane and 97.5% vol. Air)

Temperature (° C) Methane conversion rate (%) first attempt second attempt 250 <1 <1 300 <1 2 350 2 3 400 3 4 450 12 10 500 36 36 550 83 86 600 100 100

Example 3

Complete oxidation of methane with methane content in the reaction gas 25% vol.

The experiments on complete oxidation of methane were carried out with sample 4 gold catalyst prepared according to the method described in example 1 in a flow reactor at a temperature range of 250 to 600 ° C and a volume rate (GHSV) of the reaction mixture 12000 h ' ¹ . 1 g of catalyst is charged into the reactor. The following compositions of the reaction mixture were used:

(a) 25% vol. methane, 15.8% vol. O ₂ and nitrogen balance (b) 25% vol. methane, 3.9% vol. O ₂ and nitrogen balance

Are determined the degrees of conversion of methane and selectivity to _CO2 and CO as a function of the reaction temperature. The results of the tests with mixture (a) are shown in Table 5.

After reaching the maximum temperature, the samples are cooled in a stream of air to room temperature and in order to assess the stability of the catalyst and the reproducibility of the results, the test is repeated. The results of the retests are presented in Table 10 5.

From Table 6 it can be seen that almost complete oxidation of methane to CO ₂ occurs on the gold catalyst even at the ratio O ₂ : CH ₄ = 1: 1.06 (reaction mixture (b)), showing 15 that even under conditions, favorable for partial oxidation, a complete oxidation process takes place.

Reaction with reaction mixture (a)

Table 5.

The temperature of the island Degree of conversion: COj selectivity (%) First attempt Second attempt First attempt Second attempt 350 52 - 89 - 400 60 58 90 100 450 62 - 95 - 500 67 64 91 - 550 70 - 92 - 600 73 73 93 97

Reaction with reaction mixture (b)

Table 6.

Temperature C'C) Degree of conversion Yu ι CO 2 selectivity (%) First attempt Second attempt First attempt Second attempt 350 13 97 - 400 14 95 - 450 16 97 - 500 18 98 - 550 19 95 - 600 22 21 93 73

Example 4

Complete oxidation of methanol

The experiments on the complete oxidation of methanol 45 were carried out with samples 2 and 5 of the gold catalyst obtained according to the method described in example 1 in a flow reactor in the temperature range from 50 to 100 ° C, composition of the reaction gas 6.5% vol. methanol and 93.5% vol. air and volume velocity 50 (GHSV) of the reaction mixture 20000 h 1 g of catalyst is charged into the reactor.

The degrees of conversion of methanol as a function of reaction temperature were determined. The test results presented in Table 7 show that sample 5, which contains a higher concentration of gold, outperforms the rest in catalytic activity.

Table 7.

Complete oxidation of methanol

Temperature ( ^and C) Methanol oxidation rate (%) Sample 2 Sample 5 50 20 100 100 69 100

Example 5

Comparison of the catalytic properties of gold and platinum catalysts in the methanol oxidation reaction

Experiments on the complete oxidation of methanol to platinum and gold (sample 1), prepared as described in Example 1, catalysts, were carried out in a flow reactor in the temperature range from 50 to 100 ° C, reaction gas composition 10.5% vol. methanol and 89.5% vol. air and volume velocity (GHSV) of the reaction mixture 10 60000 h ¹ . 1 g of catalyst is charged into the reactor.

Although the platinum catalyst contains 3 ° ₀ wt. Pt or 6 times as much metal as gold, as can be seen from Table 8, the catalytic activity of the gold 15 catalyst at temperatures below 100 ° C is significantly higher.

Table 8.

Comparison of the catalytic activity of Au u Pt catalyst in the methanol oxidation reaction

Temperature (° C) Methanol oxidation rate (%) Gold catalyst Platinum catalyst 30 99 50 50 100 80 100 100 99

Example 6

Comparison of the catalytic properties of gold and platinum catalysts in the oxidation reaction of CO

Attempts to oxidize methanol are platinum (3% by weight) and gold (sample 1) obtained

Table 9.

Comparison of the catalytic activity of Au u Pt catalyst in the oxidation reaction of CO

C's temperature) Degree of conversion of CO (%) Au catalyst Pt catalyst 25 100 2 100 100 I 12

Claims

Claims (10)

1. A gold catalyst for the direct electrochemical oxidation of hydrocarbon fuels at low enough temperatures to avoid thermal destruction of the fuel comprising an active complex and a porous support, characterized in that the active complex of the catalyst is a complex of gold and reducing oxide from the group of the transients as described in Example 1, the catalysts were carried out in a flow reactor in the temperature range from 25 to 100 ° C, reaction gas composition 1% vol. methanol and 89.5% vol. air and volume velocity (GHSV) of the reaction mixture 60000 h ¹ . 1 g of catalyst is charged into the reactor. metals such as the transition metal may be copper, chromium, cobalt, manganese, iron or a combination of 45 such metals that the gold concentration is from 0.1 to 2.5% by weight relative to the total mass of the catalyst. preferably less than 1.3% by weight, that the concentration of the reducing oxide is from 0.1 to 5% by weight. relative to the total mass of the catalyst 50, and the total mass of the active components should not exceed 6% by weight relative to the total mass of the catalyst. Gold catalyst according to claim 1, characterized in that the reducing oxide may be one or more of the oxides of copper, chromium, cobalt, iron and manganese. Gold catalyst according to claim 5 1, characterized in that the concentration of the reducing oxide in the active component is between 0.1 and 5.0% by weight. of the total mass of the catalyst. Gold catalyst according to claim 10 1, characterized in that the catalyst support is separate oxides or mixed oxides of cerium, zirconium and titanium. Gold catalyst according to claims 1 to 4, characterized in that the concentration of cerium oxide is from 30 to 70 ° ₀ % by weight, the concentration of titanium oxide is from 5 to 25% by weight. and the concentration of zirconium is from 5 to 25% by weight. 6. Application of a gold catalyst for the oxidation of hydrocarbon fuels, methanol, methane and carbon monoxide at temperatures from 0 to 65 ° C. Use of a gold catalyst according to claim 6 for methane reforming. Use of a gold catalyst according to claim 6 for the direct electrochemical oxidation of methanol. Use of a gold catalyst according to claim 6 for the direct electrochemical oxidation of hydrocarbon fuels. Use of a gold catalyst according to claim 6 for the selective oxidation of anode fuel CO traces.