JPS6241063B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a methanol reforming catalyst. More specifically, as a catalyst for reforming methanol into a gas containing hydrogen and carbon monoxide, alumina is coated with an alkaline earth metal oxide or an alkaline earth metal oxide and zirconia on a carrier coated with platinum, It is characterized by the use of a catalyst that supports one or more metals from the group consisting of palladium, and provides a catalyst that is highly active at low temperatures, has excellent reaction selectivity to hydrogen and carbon monoxide, and has a long life. be. Currently, crude oil and petroleum products refined from it are used as raw materials for producing liquid fuel, gaseous fuel, and reducing gas used in power generation boilers, internal combustion engines, etc., but due to the recent rise in crude oil prices, Methanol, which can be synthesized from fossil fuels other than crude oil, is attracting attention. Furthermore, since methanol is reformed into a gas containing hydrogen and carbon monoxide at a much lower temperature than naphtha, it has the advantage that waste heat can be used as a heat source for reaction heat. At this time, the generated reformed gas has the advantage that the calorific value of the reformed gas increases by the amount equivalent to the endothermic amount of the reforming reaction (approximately 22 kcal/mol). When applied to an internal combustion engine with a high output design, it has the advantage of increasing the compression ratio to improve thermal efficiency, and enables clean combustion without emitting aldehydes, unlike methanol combustion. The main decomposition and reforming reaction of methanol is an endothermic reaction as shown below, and the fuel calorific value due to reforming is approximately 20
%To increase. However, in reality, some side reactions (exothermic reactions)
This produces by-products such as methane (CH ₄ ), carbon dioxide (CO ₂ ), water (H ₂ O), free carbon (C), and dimethyl ether (CH ₃ OCH ₃ ). There is a need for a catalyst with excellent selectivity that suppresses these side reactions and allows only the main reaction to occur. When carrying out a methanol reforming reaction using exhaust gas heat from an internal combustion engine, the exhaust gas temperature varies from 200℃ to about 800℃, so
It can be reformed over a wide temperature range with a small amount of catalyst that can be mounted on an internal combustion engine, and it has excellent selectivity of the main reaction and can be reformed even at high temperatures of about 800°C, as mentioned above. A stable catalyst that does not deteriorate in quality is required. Conventionally, as a catalyst for reforming methanol, a _platinum metal element such as _platinum , copper, nickel, chromium,
Catalysts supporting base metal elements such as zinc and their oxides have been proposed, but these catalysts still have many problems to date, such as poor low-temperature activity and lack of heat resistance. Among the conventional catalysts mentioned above, for example, catalysts in which platinum is supported on γ-Al ₂ O ₃ have low activity at low temperatures;
It is said that it is difficult to improve activity simply by dispersing platinum in γ-Al ₂ O ₃ . Furthermore, if it is used for more than 100 hours at a high temperature of about 800°C, which is the maximum operating temperature in an internal combustion engine, the platinum particles dispersed on the surface of γ-Al ₂ O ₃ will aggregate, and the active surface area of platinum will decrease. There is a problem that the activity decreases. Furthermore, in terms of selectivity, the side reactions mentioned above are likely to occur, and since all of these reactions are exothermic reactions, the calorific value of the cracked gas decreases by the amount equivalent to the calorific value, which is rather a loss in terms of thermal efficiency. There are also problems in terms of selectivity. In order to solve the above-mentioned problem, the present inventors have developed a method of interposing a third substance between alumina and an active metal. By coating with oxide and zirconia, transformation of the crystal form of alumina is difficult to occur, and platinum particles dispersed on the surface of alumina (γ-Al ₂ O ₃ ) are agglomerated at high temperatures. In addition, γ-Al ₂ O ₃ , which normally acts as an acidic catalyst,
By converting to basic properties and causing a dehydrogenation reaction, side reactions are suppressed. In other words, in the case of an acidic catalyst, a dehydration reaction of 2CH ₃ OH → CH ₃ OCH ₃ + H ₂ O occurs, and ether is produced. generate. On the other hand, in the case of basicity, such dehydration reaction does not occur, and CH ₃ OH→
A dehydrogenation reaction of HCHO + H ₂ occurs, and the aldehyde produced in this reaction is subsequently converted into HCHO → H ₂ +
Focusing on the knowledge that CO decomposes through a reaction, we conducted various experiments and found that alumina contains alkaline earth metal oxides or alkaline earth metal oxides and zirconia, which have the ability to suppress side reactions in advance. The catalyst, which has precious metals such as platinum and palladium supported on a carrier coated with , has high activity and excellent heat resistance in methanol reforming reactions, and has excellent selectivity in the main reaction to hydrogen and carbon monoxide. This heading led to the completion of the present invention. In the present invention, as a methanol reforming catalyst, platinum, It is characterized by supporting precious metals such as palladium. To coat alumina with an alkaline earth metal oxide, the alumina is immersed in an aqueous alkaline earth metal nitrate solution and then fired, and the alumina is coated with an alkaline earth metal oxide and zirconia. can be easily obtained by immersing alumina in a mixed solution of an alkaline earth metal nitrate aqueous solution and a zirconia nitrate aqueous solution and then firing it. Next, the method of supporting the noble metal on the carrier obtained in this way can be carried out using conventional methods, such as immersing the carrier in an aqueous solution of noble metal nitrate, calcining it, and then subjecting it to hydrogen reduction treatment. Then, a catalyst on which precious metals are supported can be obtained. The catalyst obtained as described above has excellent selectivity for the main reaction in the reaction of reforming methanol into a gas containing hydrogen and carbon monoxide, and exhibits high activity even at a low temperature of 300°C, and even at a temperature of 800°C. It exhibits high catalytic activity with little deterioration in activity even at high temperatures. Hereinafter, the present invention will be specifically explained based on Examples. [Example 1] Pellets made of γ-Al ₂ O ₃ with a particle size of 2 to 4 mm were immersed in an aqueous solution of magnesium nitrate, calcium nitrate, or barium nitrate, and then dried at 550°C for 30 minutes.
A carrier was prepared in which alumina was coated with 10% by weight of magnesium oxide, calcium oxide, or barium oxide by firing for a period of time. The supports thus obtained were each immersed in an aqueous solution of platinum nitrate, and catalysts 1, 2, and 5 supporting platinum at a concentration of 0.3% by weight were immersed in an aqueous nitrate solution of palladium. Catalysts 3, 4, and 6 were each adjusted to have the following properties. The activity of these catalysts was evaluated under the conditions shown in Table 1, and the results are shown in Table 2.

【table】

[Example 2]

Pellets consisting of γ-Al ₂ O ₃ with a particle size of 2 to 4 mm are immersed in an aqueous solution of magnesium nitrate and zirconium nitrate, or an aqueous solution of calcium nitrate and zirconium nitrate, dried, and calcined at 550°C for 3 hours to form alumina. A carrier coated with 10% by weight each of magnesium oxide and zirconia, or 10% by weight each of calcium oxide and zirconia was prepared. The support obtained in this way was immersed in an aqueous solution of platinum nitrate, and catalysts 1 and 2 were immersed in an aqueous solution of nitrate of palladium.
Catalysts 3 and 4 were each adjusted to have a weight percentage of 1.5% by weight. The activity of these catalysts was evaluated under the conditions shown in Table 1, and the results are shown in Table 3.

[Example 3]

Catalysts with platinum concentrations of 0.1, 0.2, and 0.5% by weight were prepared in the same manner as Catalyst 1 prepared in Example 1, and evaluation tests were conducted on these catalysts under the same conditions as shown in Table 1. 89, 92, 96
% and the percentage of main reactions were 90, 93, and 95%, respectively. [Example 4] Methanol reaction rate was measured for Catalyst 1 prepared in Example 1 and Catalyst 1 prepared in Example 2 under the same conditions as Table 1 except for the reaction temperature, changing the reaction temperature from 100°C to 800°C. The results are shown in Figure 1. [Comparative Example] In addition, when an evaluation test was conducted under the same conditions as in Example 1 for a catalyst in which 0.3% by weight of each of platinum or palladium was supported on a conventional alumina carrier (particle size 2 to 4 mm), the reaction temperature was 300°C. At ℃, the methanol reaction rate is 30% and 38%, respectively, and the main reaction rate is respectively
65% and 62%, indicating that the catalyst of the present invention has higher activity at lower temperatures and higher selectivity for the main reaction than conventional catalysts. Although granular catalysts are described in the examples, the shape of the catalyst is not particularly limited, and it goes without saying that catalyst shapes such as honeycomb shapes and plate shapes may be used. Furthermore, although the examples describe the case where methanol is used alone, the methanol reforming reaction may be carried out in the coexistence of a gas containing water vapor, air, or the like. As shown in the examples above, the catalyst of the present invention is highly active at low temperatures, has high selectivity for the main reaction, and is active even at high temperatures in the reaction of reforming methanol into a gas containing hydrogen and carbon monoxide. It is a catalyst that does not deteriorate.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the performance of the catalyst of the present invention.

Claims (1)

[Scope of Claims] 1. A catalyst for methanol reforming, characterized in that one or more metals from the group consisting of platinum and palladium are supported on a carrier in which alumina is coated in advance with an oxide of an alkaline earth metal. 2. A methanol reforming catalyst characterized in that one or more metals from the group consisting of platinum and palladium are supported on a carrier coated with alumina and an alkaline earth metal oxide and zirconia. 3. The methanol reforming catalyst according to claim 1 or 2, wherein the alkaline earth metal is Mg, Ca, or Ba.