WO2007015620A1

WO2007015620A1 - Steam reforming ni-based catalyst without pre-reduction treatment

Info

Publication number: WO2007015620A1
Application number: PCT/KR2006/003017
Authority: WO
Inventors: Byong Sung Kwak; Young Seek Yoon; Jin Hong Kim; Il Su Kim; Keun Seob Choi; Heon Jung; Ho Won La; Jung Il Yang
Original assignee: Sk Energy Co., Ltd.
Priority date: 2005-08-04
Filing date: 2006-08-01
Publication date: 2007-02-08

Abstract

The present invention relates to a steam hydrocarbon reforming nickel-based catalyst requiring no pre-reduction treatment for the activity thereof. More particularly, the present invention relates to a steam hydrocarbon reforming nickel-based catalyst impregnated with Ru, Pt or a combination thereof in an amount of 0.001 wt% to 1.0 wt%, which can catalyze the reforming reaction even at 380 to 400 °C without being reduced with hydrogen in advance. According to the present invention, if it is impregnated with a small amount of ruthenium, platinum or a combination thereof, a nickel-based catalyst for use in small-sized fuel cells or in hydrogen stations can show steam reforming activity at low temperatures even without being reduced in advance. Thus, the catalyst requires neither apparatus nor complicated processes relevant to pre-reduction treatment, such as those for controlling reduction temperatures and flow rates, thereby being economically advantageous.

Description

[DESCRIPTION] [INVENΗON TITLE]

STEAM REFORMING NI-BASED CATALYST WITHOUT PRE-REDUCTION TREATMENT [TECHNICAL FIELD]

The present invention relates to a steam hydrocarbon reforming nickel-based catalyst requiring no pre-reduction treatment for the activity thereof. More particularly, the present invention relates to a steam reforming nickel-based catalyst impregnated with a small amount of ruthenium, platinum, or a combination thereof, which is capable of catalyzing the reaction of hydrocarbons, such as methane, natural gas, liquefied gas (LPG), naphtha, gasoline and diesel, with steam to yield hydrogen even at around a temperature as low as 380~400°C without prereduction treatment with hydrogen gas. [BACKGROUND ART]

Hydrogen is the fuel of fuel cells, which have recently received intensive attention as promising energy technology. Typically, hydrogen is obtained from various sources, including methanol, natural gas, which consists mainly of methanol, synthetic liquid fuels prepared from natural gas, petroleum hydrocarbons, such as liquefied petroleum gas (LPG), naphtha, kerosene, etc. These fuels are converted into hydrogen, which is directly fed into fuel cells. Also, there is an increasing demand for small-sized hydrogen stations where hydrogen is supplied for automobiles.

Usually used to prepare hydrogen from natural gas or petroleum hydrocarbons is a steam reforming reaction, in which hydrocarbons are converted into a mixture of hydrogen and carbon monoxide through reaction with water steam in the presence of a catalyst. A nickel- based catalyst is typically used as a catalyst for steam reforming reactions for such hydrocarbons. Thanks to the high activity thereof, the nickel-based catalysts are industrially very important, and useful in a wide spectrum of reduction reactions, including reformation, hydrogenation, methanation, etc.

Typically, nickel-based catalysts for steam reforming processes are in the form of nickel oxides before use. Most nickel-based catalysts are reduced from nickel oxides to nickel with a reducing agent such as hydrogen, ammonia, methanol, etc., before the introduction of the reactants hydrocarbons and steam, because unreduced forms thereof are almost completely inactive, particularly at low temperatures. When the reactions in which the reduced steam reforming catalysts are involved are stopped, the catalysts are reoxidized by steam. Upon restart of the processes, the catalysts have to be reduced to realize their catalytic activity (Catalyst Handbook, Ed. 2, p274-275, written by M. V. Twigg).

However, a steam reformer, which is a hydrogen (or hydrogen compound) production device for use in small-sized fuel cells or in hydrogen stations, must be designed to readily operate even upon frequent operational termination/restart, must be simple in structure, and must be small in size so as to occupy a small space. For the reduction of the catalysts, small- or medium-size steam reformers require additional equipment necessary, for example, for providing reducing agents, such as hydrogen or ammonia, thereto and controlling their flow rate, as well as additional operational processes, for example, control of reducing temperatures, flow rates, etc., and thus the structure thereof is complicated. Japanese Pat. Laid-Open Publication No. 2001-342004 teaches a hydrocarbon steam reforming process in which a nickel-based catalyst is used in combination with a ruthenium catalyst to reduce carbon deposition and maintain the nickel-based catalyst at high activity for an extended time. This patent features an industrially favorable bilayer reformer structured to contain ruthenium in an upstream catalytic layer and nickel in a downstream catalytic layer, which is, however, different from the present invention in technical subject. International Patent Publication No. WO2000/043121 describes a steam reforming catalyst, composed of nickel, ruthenium, lanthanide, and alumina, featuring the maintenance of high activity even upon carbon deposition, which is outside the scope of the present invention, which targets a steam reforming catalyst needing no reduction treatment. Meanwhile, the addition of a small amount of ruthenium to facilitate the reduction of cobalt catalysts for use in the Fischer-Tropsch process for synthesizing hydrocarbons from synthetic gas has been reported (A. Kogelbauer, J.G. Goodwin, Jr., R. Oukaci, Journal of Catalysis, vol. 160, 125-133, 1996).

The use of ruthenium in activating steam reforming catalysts can be read in many patent documents. For example, International Patent Publication No. WO2002/038268 and Korean Pat. Laid-Open Publication No. 2003-61395 disclose catalysts comprising ceria-alumina supports on which at least one platinum group metal selected from among ruthenium, platinum, rhodium, palladium and iridium, either or both of cobalt and nickel, and an alkali earth metal are supported. Enhancement in catalyst activity with ruthenium supported on a support containing manganese oxide is described in Japanese Pat. Laid-Open Publication No. 2003-265963.

Additionally, U.S.Pat. Publication Nos. 2004-0266615 and 2004-0265225 introduce catalysts for steam methane reforming, which comprise rhodium (Rh) supported on magnesium-alumina supports. These catalysts are reported to be of high stability.

As described in all of the aforementioned literature, the role of the ruthenium supported on various supports is to improve the activity of steam reforming catalysts. Nowhere does the literature mention the subject of the present invention, that is, elimination of the pre-reduction treatment and improvement in steam reforming activity at low temperatures.

Japanese Pat. Laid-Open Publication No. 1997-131533 describes, as a solution to the problem difficulty in the reduction of nickel-based catalysts, a nickel-based reforming catalyst with at least one platinum group metal such as Pt, Os, Ir, Pd, Ru, or Rh supported thereon. Featuring the easy reduction of particularly limited catalysts consisting of nickel and alkali earth metal (aNi.bMg.cCa.dO) with one or more of the precious metals supported thereon, this patent differs from the present invention, which is characterized by the elimination of a reduction process in activating a wide range of nickel-based catalysts impregnated with ruthenium or platinum.

[DISCLOSURE] [TECHNICAL PROBLEM]

Leading to the present invention, intensive and thorough research into nickel-based reforming catalysts, conducted by the present inventors, resulted in the finding mat when impregnated with a small amount of ruthenium, platinum or a combination thereof, a wide range of nickel catalysts can continue to be used without pre-reduction treatment, and exhibits steam reforming activity even at low temperatures, particularly, from about 380 to 400°C.

Therefore, it is an object of the present invention to provide a steam hydrocarbon reforming nickel-based catalyst which exhibits superb steam reforming activity even at low temperatures without pre-reduction treatment. [TECHNICAL SOLUTION]

In accordance with the present invention, the object can be accomplished by the provision of a steam hydrocarbon reforming nickel-based catalyst, impregnated with ruthenium, platinum or a combination thereof in an amount from 0.001 wt% to 1.0 wt%, capable of showing steam reforming activity from a temperature range of 380 to 400°C without prereduction treatment. [ADVANTAGEOUS EFFECT]

Although not pretreated for reduction in advance of a reforming reaction, the nickel- based catalyst impregnated with a small amount of ruthenium, platinum or a combination thereof in accordance with the present invention shows as high catalytic activity as in conventional pre-reduced nickel-based catalysts, with neither ruthenium nor platinum supported thereon, at approximately 450⁰C, and starts to catalyze the reforming reaction from a temperature as low as about 380°C to 400°C. Accordingly, the nickel-based catalyst impregnated with ruthenium, platinum, or a combination thereof in accordance with the present invention requires neither pre-reduction treatment nor apparatus and process for storing reductants, controlling the flow rate of reductants, regulating a reduction period of time, or the like, and is sufficiently simple in structure to respond to frequent operational termination/restart. These advantages are expected to make the catalyst according to the present invention industrially highly available. [DESCRIPTION OF DRAWINGS]

FIG. 1 is a graph in which methane conversion rates are plotted against reaction temperatures for a nickel catalyst treated with hydrogen (Comparative Example 1), an unreduced nickel catalyst (Comparative Example 2), and a ruthenium-supported nickel catalyst (Example 1). FIG. 2 is a graph in which methane conversion rates are plotted against reaction temperatures for a nickel catalyst treated with hydrogen (Comparative Example 1), an unreduced nickel catalyst (Comparative Example 2), a platinum-supported nickel catalyst (Example 1), and an iridium-supported nickel catalyst (Comparative Example 3). [BEST MODE] Below, a detailed description will be given of the present invention.

The steam reforming catalyst of the present invention is a nickel-based catalyst impregnated with ruthenium, platinum or a combination thereof, and needs no pre-reduction treatment for recovering its catalytic activity. The catalyst of the present invention shows steam reforming activity even at temperatures as low as 380 to 400 °C . Any of the nickel-based catalysts which are usually used in steam reforming processes are available in the present invention. For example, a catalyst comprising nickel, alumina, magnesium oxide and a potassium compound may be used, and may be in the form of pellets, fine powder, or a coating on metal or ceramic monolith.

In accordance with the present invention, the impregnation of a small amount of ruthenium, platinum or a combination thereof into a steam reforming nickel-based catalyst allows the catalyst to maintain its activity for a long period of time without pre-reduction treatment. Preferably, ruthenium, platinum or a combination thereof is impregnated in an amount from 0.001 wt% to 1.0 wt% based on the total weight of the nickel-based catalyst. If the content is less than 0.001 wt%, self reduction of the catalyst does not occur. On the other hand, a content of the precious metal exceeding 1.0 wt% gives rise to an increase in production cost, so that the production of the catalyst is economically disadvantageous.

The nickel-based catalyst impregnated with ruthenium, platinum or a combination thereof, according to the present invention can be prepared using a typical impregnation method. In an embodiment of the present invention, for example, a solution of a ruthenium compound in deionized water or nitric acid is evenly impregnated in a nickel catalyst, which is then dried at 120°C for 4 hours in an oven and calcinated at 900⁰C for 9 hours in air to yield a ruthenium-supported nickel-based catalyst.

Examples of the ruthenium compound useful in the present invention include ruthenium chloride, ruthenium chloride hydrate, ruthenium nitrosyl chloride hydrate, and ruthenium nitrosyl nitrate, but are not limited thereto. The platinum compounds useful in the present invention can be exemplified by, but are not limited to, platinum chloride, hydrogen hexachloroplatinate hydrate, and platinum acetylacetonate.

In the present invention, hydrogen production is preferably achieved using a contact method in which hydrocarbon, such as methane, natural gas, LPG, naphtha, gasoline, diesel, etc., is fed, together with water steam, into a reactor which contains the catalyst. As for the hydrocarbon steam reforming reaction conditions of the catalyst, the reaction temperature is approximately 380°C or higher, preferably in a range from 600 to 850 °C, the reaction pressure is 50 atm or lower, preferably in a range from 1 to 35 atm, and the reactants are present in a molar ratio of steam : carbon of hydrocarbon 1-5 : 1. In the present invention, the GHSV of a mixture of hydrocarbon and steam falls into a range from 1000 to 50,000 hr^'1. If necessary, hydrogen, carbon dioxide and/or nitrogen may be introduced into the reactor.

The nickel-based catalyst impregnated with ruthenium, platinum or a combination thereof in accordance with the present invention shows significantly high steam reforming activity even at temperatures as low as about 380 to 400 °C. In addition, the catalyst of the present invention needs neither pre-reduction treatment nor additional equipment for the reduction thereof. Thus, the catalyst of the present invention enjoys economic advantage because it is not restricted by apparatus size.

[MODE FOR INVENTION] A better understanding of the present invention may be realized with the following examples, which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE l Preparation of Rh-Supported Ni-Based Catalyst

A nickel-based catalyst impregnated with a small amount of ruthenium was prepared.

A commercially available, steam reforming nickel-alumina catalyst with a nickel content of

10% was finely powdered. 20 g of the powder was immersed in 200 cc of a solution containing 8.2g ruthenium chloride, followed by drying at 120 °C for 4 hours and calcinating at up to 900 ^°C for 9 hours. The ruthenium-supported nickel-based catalyst thus obtained was measured to contain 0.1 g (0.1 %)of ruthenium per 100 g of the catalyst.

EXAMPLE 2 Preparation of Pt-Supported Ni-Based Catalyst

A platinum-supported nickel-based catalyst was prepared.

A commercially available, steam reforming nickel-alumina catalyst with a nickel content of 10% was finely powdered. 20 g of the powder was immersed in 200 cc of a solution containing 2.1 g of hydrogen hexachloroplatinate hydrate, followed by drying at 120 °C for 4 hours and calcinating at up to 900 ^°C for 9 hours. The platinum-supported nickel-based catalyst thus obtained was measured to contain 0.025 g (0.025%) of platinum per 100 g of the catalyst.

COMPARATIVE EXAMPLE 1

For comparison with the ruthenium-supported catalyst of Example 1, the same commercially available steam reforming nickel-based pellet-type catalyst as used in Example 1 was pulverized. The powdered catalyst was reduced at 600 °C for 4 hours under conditions such that a gas mixture of 10% hydrogen and 90% nitrogen was allowed to flow at a rate of 100 cc per min per 1.5 g of the catalyst, and was stored in an air-free container until its use in steam reforming reaction.

COMPARATIVE EXAMPLE 2 Without being reduced, the same nickel-based pellet-type catalyst as used in Comparative Example 1 was used in steam reforming processes.

COMPARATIVE EXAMPL 3 Preparation of Ir-Supported Ni-Based Catalyst

A commercially available, steam reforming nickel-alumina catalyst with a nickel content of 10% was finely powdered. 20 g of the powder was immersed in 200 cc of a solution containing 2.1g of hydrogen hexachloroiridate, followed by drying at 120°C for 4 hours and baking at up to 900 ^°C for 9 hours. The iridium-supported nickel-based catalyst thus obtained was measured to contain 0.025 g (0.025%) of indium per 100 g of the catalyst.

EXAMPLE 3

Assay for Catalytic Activity

The catalysts (1.5 g of nickel-based catalyst) prepared in Examples and Comparative Examples were charged in respective quartz reactors, followed by steam methane reforming. The catalysts were measured for temperature by means of a thermocouple installed in a lower portion of a catalyst bed. A mixture of methane and steam was used as a reaction gas with a volume ratio of steamimethane 3:1. The reaction gas flowed at a speed of 1200 cc per min at 2O⁰C. While the reactors were heated using an external heating furnace, observations of the steam methane reforming performance of each of the catalysts were made. The results are given in Table 1 , below, and in FIG. 1.

In Table 1 and FIG. 1, the methane conversion rate is defined as follows. Methane Conversion Rate(%)=(l - Flow Rate of Methane from Reactor/Flow Rate of Methane into Reactor) x 100

Thanks to their self-reduction ability, the ruthenium-supported nickel-based catalysts of the present invention, as apparent from data of Table 1 and FIG. 1, exhibit superior steam reforming activity at the same temperature over commercially available nickel-based catalysts which are reduced in advance. It was observed that a temperature as high as 800°C was required to confer reforming activity on the commercially available catalyst of Comparative Example 2, which was not reduced in advance. The pre-reduction treatment, as conducted in Comparative Example 1, was found to decrease the reaction starting temperature of the commercially available catalyst to 500°C. In contrast, the ruthenium-supported nickel-based catalyst of Example 1, although not reduced in advance, exhibited catalyst activity even at temperatures as low as 380 to 400 °C .

On the other hand, as shown in FIG. 2, the steam reforming activity of the platinum- supported nickel-based catalyst prepared in Example 2 was silent up to 400 °C, but started to appear at 500°C or higher due to the self reduction property, and increased from 600⁰C to a level higher than that of the ruthenium-supported nickel-based catalyst. The iridium-supported catalyst of Comparative Example 2 did not show steam reforming activity until the reaction temperature reached 700⁰C.

Therefore, as described hitherto, the nickel-based catalysts impregnated with ruthenium, platinum or a combination thereof in accordance with the present invention show excellent steam reforming activity even at low temperatures without pre-reduction treatment.

Eliminating the requirement for additional apparatus for catalyst reduction, the present invention is not restricted by the scale of apparatus and enjoys a great economic advantage.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible. Accordingly, the modifications, additions and substitutions should be understood as falling within the scope and spirit of the invention.

Claims

[CLAIMS]

1. A steam hydrocarbon reforming nickel-based catalyst, impregnated with ruthenium, platinum or a combination thereof in an amount from 0.001 wt% to 1.0 wt%, capable of showing steam reforming activity in a temperature range from 380 to 400°C without prereduction treatment.

2. The steam hydrocarbon reforming nickel-based catalyst according to claim 1, wherein the ruthenium is in a form of a ruthenium compound selected from a group consisting of ruthenium chloride, ruthenium chloride hydrate, ruthenium nitrosyl chloride hydrate, and ruthenium nitrosyl nitrate.

3. The steam hydrocarbon reforming nickel-based catalyst according to claim 1, wherein the platinum is in a form of a platinum compound selected from a group consisting of platinum chloride, hydrogen hexachloroplatinate hydrate, and platinum acetylacetonate.

4. The steam hydrocarbon reforming nickel-based catalyst according to claim 1, wherein the hydrocarbon is selected from a group consisting of methane, natural gas, liquefied petroleum gas, naphtha, gasoline, diesel, and combinations thereof.