JPH04265156A - Catalyst for steam reforming of hydrocarbon - Google Patents

Abstract

PURPOSE:To provide a high activity catalyst for steam reforming of hydrocarbon on which carbon deposits hardly. CONSTITUTION:A Pt family metal is supported on ceria contg. 0.2-20wt.% (expressed in terms of metal oxides) one or more kinds of metals selected among alkali metals and alkaline earth metals or ceria-based oxides of rare earth elements to obtain a catalyst for steam reforming of hydrocarbon. Even when a steam reforming reaction is carried out with the catalyst under conditions of a relatively low pressure and a low ratio of steam to carbon, carbon deposits hardly and the catalyst has high activity and long service life.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a catalyst for steam reforming of hydrocarbons, and in particular, it has low carbon deposition, high activity, and long catalyst life even under conditions of relatively low pressure and low steam/carbon ratio. This invention relates to a steam reforming catalyst having the following characteristics.

0002

[Prior Art] Conventionally, catalysts used in the so-called steam reforming of hydrocarbons to produce hydrogen, carbon monoxide, carbon dioxide, and methane by reacting hydrocarbons with steam are Ni containing alkali metals or alkaline earth metals. catalysts have been used. Normal steam reforming reactions of hydrocarbons are operated at relatively high pressures (20 kgf/cm2 or higher) and high steam/carbon ratios (3.0 or higher), but the gas obtained by steam reforming naphtha or kerosene In the case of a fuel cell system using fuel as fuel, it is preferable that the reaction pressure be as low as possible from the viewpoint of ease of handling the device. Further, from the viewpoint of power generation efficiency of the fuel cell, the lower the steam/carbon ratio in steam reforming, the more preferable. Conventional Ni is used in steam reforming for fuel cells, which requires such low pressure and low steam/carbon ratio.
When a system catalyst is used, carbon deposition on the reforming catalyst becomes a serious problem. Significant carbon deposition on the catalyst can lead to closure of the catalyst bed, resulting in an increase in differential pressure and the inability to continue operation of the device unless the catalyst is replaced. Moreover, frequent replacement of the catalyst significantly deteriorates the economic efficiency of the fuel cell system. Therefore, as a steam reforming catalyst for fuel cells, it is desirable to use a catalyst that deposits as little carbon as possible.

[0003] It is known that precious metal catalysts, especially rhodium and ruthenium catalysts, are effective as catalysts that cause less carbon deposition (for example, JP-A-2-439).
50, JP-A-2-2878, JP-A-61-
28451, JP-A-57-4232, etc.). However, even these catalysts still cannot sufficiently suppress carbon deposition when used at low pressure and low steam/carbon ratio.

0004

[Problems to be Solved by the Invention] An object of the present invention is to provide a catalyst suitable for steam reforming reactions of hydrocarbons.
The purpose of the present invention is to provide a catalyst with high activity and long catalyst life, which exhibits little carbon deposition even at low pressure and low steam/carbon ratio.

[0005]

[Means for Solving the Problems] As a result of intensive research focused on suppressing carbon precipitation in the steam reforming reaction of hydrocarbons, the present inventors discovered that carbon precipitation can be suppressed by using a specific catalyst. Based on this knowledge, we were able to achieve the present invention.

That is, the present invention provides ceria containing 0.2 to 20 wt% of one or more metals selected from alkali metals and alkaline earth metals as a metal oxide, or a rare earth element mainly composed of ceria. The present invention relates to a catalyst for steam reforming of hydrocarbons, characterized in that a platinum group metal is supported on an oxide.

In the present invention, ceria, rare earth element oxides containing ceria as a main component, alkali metals, and alkaline earth metals are used as catalyst carriers.

The method for preparing ceria used in the present invention is not particularly limited, but for example, cerium nitrate (Ce(NO3)
3 ・6H2 O), cerium chloride (CeCl3 ・7
H2 O), cerium hydroxide (CeO2 ・nH2 O
), cerium carbonate (Ce2 (CO3)3 ・8H2
Those prepared from O) etc. by a conventional method can be used.

[0009] It may also be prepared from a mixed rare earth element salt containing cerium as a main component. Rare earth element oxides other than ceria include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr),
Neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd)
), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (T
m), ytterbium (Yb), and lutetium (Lu), among which oxides of yttrium, lanthanum, and neodymium are preferably used, and lanthanum oxides are particularly preferred. .

[0010] The rare earth element oxide containing ceria as a main component has a ceria content of 50 wt% or more, preferably 50 to 9
5 wt%, more preferably 70 to 90 wt%.

[0011] Examples of the alkali metals used in ceria in the present invention include Li, Na, K, Rb, Cs, and Fr. As an alkaline earth metal, B
Examples include e, Mg, Sr, Ba, and Ra. These metals may be used alone or in combination. As the alkali metal, Cs and K are preferable, and Cs is more preferable. Alkaline earth metals include Mg, Ba, Ca
is preferred, and Ba is more preferred.

These metals may be used in any form such as oxides, hydroxides, carbonates or nitrates.

[0013] These metals may be added to ceria during the preparation of ceria, or may be impregnated into molded ceria afterwards.

The content of the alkali metal or alkaline earth metal is determined by the weight of the catalyst carrier as a metal oxide (the total amount of ceria or rare earth element oxide containing ceria as a main component and the alkali metal or alkaline earth metal oxide). 0.
The content is 2 to 20 wt%, preferably 0.5 to 5 wt%.

[0015] If the content of the alkali metal or alkaline earth metal is less than 0.2 wt%, it is not possible to enhance the activity of the catalyst and suppress carbon precipitation. 20wt
%, the catalyst activity decreases.

In the present invention, a small amount of a binder such as silica or cement may be added to the catalyst carrier in order to increase the mechanical strength of the catalyst.

A platinum group metal is used as the active metal in the catalyst of the present invention. Ruthenium (
Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). The active metals may be used alone or in combination of two or more. Ruthenium, rhodium, and platinum are preferred, with ruthenium being particularly preferred.

The amount of platinum group metal supported is not particularly limited, but is 0.1 of the catalyst weight (total weight of catalyst carrier and active metal).
~20wt%, preferably 0.5~10wt%. If the amount of platinum group metal supported is less than 0.1 wt%, the catalytic activity decreases, and if it is more than 20 wt%, the catalytic activity does not increase much, which is uneconomical.

The platinum group metal can be supported on a catalyst carrier by a conventional method. Examples of the method include an impregnation method, a deposition method, a coprecipitation method, a kneading method, an ion exchange method, and a pore filling method. Particularly preferred is the impregnation method.

[0020] The starting material for supporting platinum group metals varies depending on the supporting method, but chlorides and nitrates of platinum group metals are usually used.

The starting material for supporting ruthenium varies depending on the supporting method, but is usually ruthenium chloride (RuCl3
・nH2O), ruthenium nitrate (Ru(NO3)
3 .nH2O) is used.

An example of the method for preparing the catalyst of the present invention will be described below. First, a cerium oxide hydrate is precipitated by reacting an aqueous solution containing a cerium salt with an aqueous solution of a basic compound at around pH 10. Examples of the basic compound include ammonia, sodium hydroxide, potassium hydroxide, and the like. The reaction between the aqueous solution containing the cerium salt and the aqueous solution of the basic compound is preferably carried out at a pH of 6.0 or higher,
More preferably, the pH is in the range of 7.0 to 11.0. Next, the generated precipitate is filtered and washed, and the filtrate is
Dry at 120°C overnight. After drying, apply this to 500 to 70
Ceria is obtained by firing at 0°C. The ceria thus obtained is impregnated with an aqueous solution containing an alkali metal or alkaline earth metal, and after drying at 100-120°C,
Bake at 0°C. The carrier thus obtained was impregnated with an aqueous solution containing ruthenium, dried at 100 to 120°C, and then
Hydrogen reduction is performed at 00 to 900°C.

[0023] The surface area of the catalyst of the present invention is 5 to 200 m2.
/g, and the pore volume is preferably in the range of 0.05 to 1.0 cc/g.

[0024] When carrying out a steam reforming reaction using the catalyst of the present invention, the reaction conditions are a temperature of 400 to 1000°C, preferably a temperature of 450 to 850°C, and a pressure of 50 kgf/cm2.
Below, preferably the pressure is 0.1 to 10 kgf/cm2,
More preferably, the pressure is 0.1 to 2 kgf/cm2, and the steam/carbon ratio is 2.5 or less, preferably steam/carbon.
The carbon ratio is in the range of 2.0 or less. When the catalyst of the present invention is used under these reaction conditions, its superiority becomes remarkable.

[0025] Hydrocarbons as used in the present invention include natural gas, LPG, naphtha, kerosene and the like. The sulfur content in the hydrocarbon is preferably 0.5 wtppm or less. If the hydrocarbon contains more than 0.5 wtppm of sulfur, it is preferable to perform hydrodesulfurization, desulfurization using a sulfur adsorbent, or the like. The superiority of the catalyst of the present invention becomes remarkable when hydrocarbons such as naphtha and kerosene, which are relatively prone to carbon deposition, are used.

The catalyst of the present invention exhibits remarkable effects as a steam reforming catalyst for a fuel cell system equipped with a steam reformer and using hydrocarbons such as naphtha and kerosene as fuel.

[0027]

[Examples] Next, examples of the present invention will be described.

Example 1 (1) Preparation of Catalyst 1000 cc of an aqueous solution containing 50.5 g of cerium nitrate and 2N aqueous ammonia were added to a 5-liter container to adjust the pH to 10 to precipitate a cerium oxide hydrate. This was suction filtered, washed with 2 liters of pure water, and the filtrate was dried at 120° C. all day and night. Next, this was heated to 600℃ for 3 hours.
It was air fired to obtain ceria.

The above ceria was impregnated with an aqueous solution of cesium carbonate, and the water was evaporated to dryness. The amount of cesium added was 1.5 wt% as cesium oxide based on the total amount of ceria and cesium oxide. Next, this was heated to 800℃ for 3 hours.
Air firing was performed to obtain a catalyst carrier.

The catalyst carrier was impregnated with an aqueous solution of ruthenium chloride so that the supported amount of ruthenium metal was 1 wt %, and the water was evaporated to dryness. Next, this is pressure molded (
3 mmφ×3 mm) and then subjected to hydrogen reduction at 700° C. for 3 hours to obtain catalyst A. The surface area of this catalyst was 9 m2/g. If you want to test the activity of the catalyst, add another 30~
It was used after being ground to 80 mesh.

(2) Steam reforming reaction A fixed bed microreactor was used for the steam reforming reaction. The catalyst loading amount was 5 cc. Light naphtha (C/H
Atomic ratio 0.422, specific gravity 0.642, sulfur content 0.2p
pm) was used. The reaction conditions are as follows. Reaction temperature 500℃, reaction pressure 1kgf/cm2, steam/
Carbon ratio 1.5, GHSV9000.

The reaction gas was quantitatively analyzed using a gas chromatograph. Table 1 shows the conversion rate of the raw material naphtha determined from the composition of the produced gas after 10 hours of reaction. Here, the conversion rate in Table 1 is the rate at which raw material naphtha was converted to CO, CH4, and CO2, and was calculated based on carbon.

After the reaction was completed, the catalyst was taken out from the reaction apparatus and the amount of carbon attached to the catalyst was measured, which is also shown in Table 1.
It was shown to.

Example 2 Ceria prepared in the same manner as in Example 1 (1) was impregnated with an aqueous solution of magnesium nitrate, and the water was evaporated to dryness. The amount of magnesium added is 1.5% as magnesium oxide based on the total amount of ceria and magnesium oxide.
It is 5wt%. Next, this was air-calcined at 800°C for 3 hours to obtain a catalyst carrier.

[0035] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst B. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 Ceria prepared in the same manner as in Example 1 (1) was impregnated with an aqueous solution of barium nitrate, and the water was evaporated to dryness. The amount of barium added was 1.5 wt% as barium oxide based on the total amount of ceria and barium oxide. Next, this was air-calcined at 800°C for 3 hours to obtain a catalyst carrier.

[0037] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst C. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 Ceria prepared in the same manner as in Example 1 (1) was impregnated with an aqueous solution of calcium nitrate, and the water was evaporated to dryness. The amount of added calcium was 1.5wt% as calcium oxide based on the total amount of ceria and calcium oxide.
It is. Next, this was air-calcined at 800°C for 3 hours to obtain a catalyst carrier.

[0039] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst D. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Example 5 Ceria prepared in the same manner as in Example 1 (1) was impregnated with an aqueous solution of potassium carbonate, and the water was evaporated to dryness. The amount of potassium added was 1.5 wt% as potassium oxide based on the total amount of ceria and potassium oxide. Next, this was air-calcined at 800°C for 3 hours to obtain a catalyst carrier.

[0041] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst E. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 Ceria prepared in the same manner as in Example 1 (1) was air-calcined at 800° C. for 3 hours to obtain a catalyst carrier.

[0043] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst F. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 In a 5 liter container, 1000 cc of an aqueous solution containing 1475 g of aluminum nitrate and 2N ammonia water were mixed at pH 1.
0 to precipitate alumina hydrate. This was suction filtered, washed with 2 liters of pure water, and the filtrate was dried at 120° C. all day and night. Next, this was air fired at 600°C for 3 hours to obtain alumina.

The above alumina was impregnated with an aqueous solution of cesium carbonate, and water was evaporated to dryness. The amount of cesium added was 1.5 wt% as cesium oxide based on the total amount of alumina and cesium oxide. Next, heat this at 800℃ for 3
A catalyst carrier was obtained by air firing for hr.

[0046] Ruthenium was then supported in the same manner as in Example 1 to obtain Catalyst G. Evaluation of the activity of this catalyst and measurement of the amount of carbon after completion of the reaction were also carried out in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Examples 3 to 4 The activity of commercially available Ni-based catalysts H and I and the amount of carbon after the reaction were measured in the same manner as in Example 1.
The results are shown in Table 1.

[0048]

[Table 1]

Table 1 shows that in the case of the ceria-supported ruthenium catalyst, carbon precipitation is extremely small even under severe steam reforming reaction conditions. Furthermore, the activity of the ceria-supported ruthenium catalyst can be increased by adding an alkali metal or alkaline earth metal to ceria. In particular, the improvement in catalytic activity by the addition of cesium and barium is remarkable.

[0050]

Effects of the Invention The steam reforming catalyst of the present invention exhibits little carbon deposition even when the steam reforming reaction is carried out under conditions of relatively low pressure and low steam/carbon, has high activity, and has a long catalyst life.

Claims (1)

[Claims] Claim 1: Ceria containing 0.2 to 20 wt% of one or more metals selected from alkali metals and alkaline earth metals as a metal oxide, or a rare earth element oxide mainly composed of ceria. A catalyst for steam reforming of hydrocarbons characterized by supporting a platinum group metal.