WO2009064170A2

WO2009064170A2 - Cu-zn-al catalyst promoted with palladium for hydrogen production from methanol

Info

Publication number: WO2009064170A2
Application number: PCT/MY2009/000006
Authority: WO
Inventors: Zahira Yaakob; Wan Ramli Wan Daud; Lorna Jeffery Minggu
Original assignee: Universiti Kebangsaan Malaysia
Priority date: 2007-11-16
Filing date: 2009-01-02
Publication date: 2009-05-22
Also published as: MY151052A; WO2009064170A3

Abstract

The present invention relates to a catalyst for autothermal steam reforming of methanol comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina.

Description

Cu-Zn-Al CATALYST PROMOTED WITH PALLADIUM FOR HYDROGEN PRODUCTION FROM METHANOL

FIELD OF INVENTION

The present invention relates to a catalyst for the hydrogen production from methanol by autothermal steam reforming reaction. In more particular, this invention relates to a catalyst of copper(Cu)-zinc(Zn)-aluminium(Al) promoted with palladium (Pd) which effectively catalyzes the reforming of methanol to hydrogen to be coupled with Proton Exchange Membrane Fuel Cell (PEMFC).

BACKGROUND OF THE INVENTION

The early introduction of fuel cell as a sustainable alternative to the internal combustion engine depends mainly on the use of primary fossil fuels as hydrogen carriers and existing fossil fuel infrastructure. The conversion of methanol into hydrogen gas has gained increasing interests lately because methanol is an attractive hydrogen carrier for the application in the Proton Exchange Membrane Fuel Cell (PEMFC).

Generally, hydrogen gas can be produced from methanol by three types of processes, namely steam reforming (SRM), partial oxidation (POX) and autothermal reforming (ATR). Conventionally, SRM of methanol is the most common and well-established technology. In SRM, methanol is reacted with steam to produce hydrogen gas and carbon dioxide with trace amount of carbon monoxide. SRM is a catalytic reaction where the presence of catalyst plays a significant role in the rate and efficiency of the reaction. SRM is widely used in the hydrogen production method since it produces high hydrogen yield as 3 moles of hydrogen gas produced per mole of methanol converted. There are some inventions disclosed in the prior arts pertaining the development of a catalyst for the SRM reaction and a method of producing the catalyst thereof.

Of interest in respect to a catalyst for steam reforming process of methanol and a method for producing hydrogen therewith is European Patent No. EPl 174386 to Mitsui Chemicals Inc. The catalyst invented is capable of providing sufficient catalytic activity and durability. The catalyst is characterized by comprising copper and zinc, and palladium and/or platinum. The invention also relates to a method of producing hydrogen by using this invented catalyst.

Another steam reforming process of methanol to hydrogen gas is described in PCT publication No. WO2004083116. This invention relates to a method for the production of hydrogen by a steam reforming process wherein a catalyst is used. The catalyst comprises Cu in the form of copper oxide and Zr in the form of zirconia. This catalyst is prepared by a templating method.

As SRM of methanol is highly endothermic and requires high input level of external energy to sustain its reaction, the partial oxidation (POX) reaction that exothermic is occasionally used for hydrogen production. POX reacts methanol with the presence of an oxygen which its quantity inadequate for complete oxidation. However, POX reaction produces significant amount of carbon monoxide and the waste heat production affects overall efficiency as well as possible runaway temperature. Hence, an autothermal steam reforming (ATR) reaction that combines the methods of SRM and POX where methanol is reacted with water and oxygen simultaneously. No external energy is required for the reaction to make place. By using the ATR reaction,

2.5 moles of hydrogen gas can be produced per every mole of methanol coverted. The most common catalyst for the autothermal reforming reaction of methanol is mainly made up of Cu-Zn-Al. There are also a few patented technologies described by the prior arts relating to an autothermal steam reforming process and its catalyst. However, the catalyst described in these patented technologies include a wide variation in the quality of the product and their manufacturing method thereof.

Of interest in connection with a catalyst for oxidative steam reforming of methanol and the synthesis method thereof is European Patent No. EPl 161992 to Agency of Industrial Science and Technology Japan. This invention relates to a catalyst comprising copper, zinc, aluminium and zirconium in combination. The method of producing this Cu-Zn-AL-Zr oxide catalyst includes reacting an aqueous sodium hydroxide solution and aqueous sodium carbonate solution with a mixture of aqueous solutions of Cu, Zn, Al, and Zr, producing a precipitate by co-precipitation, preparing a catalyst precursor of Cu-Zn-Al-Zr layered double hydroxide, and calcining this precursor to obtain the catalyst. The invention also relates to a method of producing hydrogen gas by using this oxide catalyst.

U. S. Patent No. US2006111457 to Industrial Technology Research Institute of Taiwan also relates to a process for the production of a hydrogen-rich reformate gas by methanol autothermal reforming reaction. This prior art provides a catalyst comprising a platinum deposited on a carrier containing mixed oxide of cerium and zirconium. This catalyst is capable of catalyzing a feed of methanol, water vapour and air to form a hydrogen-rich reformate gas by an autothermal reforming reaction.

Since different types of catalysts perform differently to give products of different qualities, an innovative composition of catalyst that manages to provide maximum yield of hydrogen gas and lower carbon monoxide selectivity while consuming minimum level of energy is desirable in the fuel cell industry. SUMMARY OF INVENTION

The primary object of the present invention is to develop a catalyst that composed of palladium, copper and zinc as a metal component supported on alumina which is used for catalyzing the autothermal steam reforming reaction of hydrogen production from methanol.

Another object of the present invention is to provide a catalyst of palladium, copper and zinc supported on alumina which is capable of catalyzing autothermal steam reforming reaction of hydrogen production from methanol at low temperature and low pressure.

Still another object of the present invention is to provide a composition of a catalyst containing palladium, copper, zinc and alumina for the autothermal steam reforming reaction, in which this catalyst can help in the production of the highest yield of hydrogen and the lowest selectivity to carbon monoxide.

Further object of the present invention is to prepare a catalyst which has high surface area and uniform distribution of active species on the surface which are proportional to the increase of catalytic activity.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention describes a catalyst for autothermal steam reforming of methanol comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina.

Another embodiment of the present invention is a method for preparing a catalyst comprising copper, zinc, palladium or any combination thereof which is supported on alumina by incipient wetness impregnation process. Still another embodiment of the present invention is a method for producing hydrogen, comprising the step of converting methanol to hydrogen gas by an autothermal steam reforming process in the presence of both oxygen and steam using a catalyst comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention.

DETAIL DESCRIPTION OF THE INVENTION

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description. However, it is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

The present invention discloses a catalyst for autothermal steam reforming of methanol comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina. In this invention, the conventional Cu-Zn-Al catalyst is promoted with various concentrations of palladium and supported on alumina. According to the preferred embodiment of the present invention, the catalyst is a combination of metals which can be palladium (Pd), copper (Cu), zinc (Zn) or any combination thereof. In the present invention, it is preferably to use the combination of Pd-Cu-Zn. These metals are impregnated and supported on gamma alumina (γ-A^Os).

In accordance with the preferred embodiment of the present invention, the metal component which is the Pd, Cu and Zn are used in different standard values for the preparation of the catalyst. According to the preferred embodiment of the present invention, the amount of metal component which includes copper, zinc and palladium in the catalyst is preferably to be 1% to 5% by weight of the catalyst, respectively.

Preferably, the maximum active metal loading on the support is predetermined at 5%. Therefore, a statistical mixture experimental design of Pd-Cu-Zn- Alumina is applied in the present invention. It is based on the response surface method of the design of experiment, whereby the relationship of the factors (the different types of composition of the three metals in the catalyst) and response (efficiency in the catalytic capability of the catalyst) in a process is represented by mathematical equation which is used to model the blending surface. A standard simplex centroid design is used for determining the amount of different metals added into the mixture.

In another preferred embodiment of the present invention, the amount of a mixture of copper, zinc and palladium in the catalyst is preferably to be 5% by weight of the catalyst. According to the most preferred embodiment of the present invention, all three metals, copper, zinc and palladium are added in a percentage of 1.67% by weight of the catalyst. This optimum weight percentage of these three active metals is able to give high activity since high surface area on the support is impregnated by low active material content of the metals. The amount of different metals added into the mixture is determined by the statistical mixture experimental design which aims to find the effect of the different composition in the mixture to the yield and hydrogen and selectivity of carbon dioxide.

Gamma-alumina is an enormously important material in catalysis. It is commonly used as a catalyst in hydrocarbon conversion or as a support for automotive and industrial catalysts as in the present invention. Alumina has negligible catalytic activity in the production of hydrogen from methanol. It acts as the support for the impregnation of the copper, zinc and palladium. According to the preferred embodiment of the present invention, the amount of alumina in the catalyst is at least 95% by weight of the catalyst. Preferably, the gamma alumina employed in the present invention has a surface area of 228m²/g and its average particle size is approximately 100 micron.

In accordance with the preferred embodiment of the present invention, the palladium employed in the present invention is preferably Pd(NOs) 2.2EkO, the suitable source of Cu is Cu(NO₃) 2.3H₂O, whereas the suitable source of Zn is Zn(NOs)₂-OH₂O.

The catalyst produced is active at low temperature and low pressure for methanol reforming which is favourable when the hydrogen is coupled to PEMFC for automotive application. Besides, the catalyst also has high surface area and uniform distribution of active species on the surface which are proportional to the increase of its catalytic activity.

Another embodiment of the present invention is a method to prepare a catalyst comprising copper, zinc, palladium or any combination thereof which is supported on alumina by incipient wetness impregnation process.

The Pd-Cu-Zn-Y-Al₂O₃ is prepared by a 2-step process. Initially, the pure Cu and Zn powder are dissolved in an aqueous or organic solvent respectively to form Cu and Zn precursor solution. It is then followed by a co-impregnation process of γ- Al₂O₃ with the mixture of Cu and Zn precursor solution which is dried and calcined. Consequently, Pd precursor solution is added to the Cu-Zn- γ-Al₂O₃ by sequential- impregnation. The resulting catalyst is dried at approximately 60°C to 67°C with occasional stirring for one hour and then kept at 110⁰C overnight. The dried catalyst is calcined in nitrogen flow at 500⁰C for 3 hours to decompose the nitrate so as to obtain a pure Pd-Cu-Zn-γ-Al2θ₃ catalyst.

This impregnation method is capable of provide a catalyst which requires less active metal loading to achieve the same catalytic activity and more resistant to sintering. The preparation by co-precipitation method also offers well dispersed active metals throughout the support of alumina.

Still another embodiment of the present invention is a method for producing hydrogen, comprising the step of converting methanol to hydrogen gas by an autothermal steam reforming process in the presence of both oxygen and steam using a catalyst comprising copper, zinc, palladium or any combination thereof which is supported on alumina.

According to the preferred embodiment of the present invention, this autothermal steam reforming reaction is capable of producing hydrogen gas at moderately low temperature which is preferably in a range of 180⁰C to 280⁰C and low pressure of 1 bar to 2 bar. The method for producing hydrogen from methanol as described by the preferred embodiment is a high efficient autothermal reaction where it provides maximum yield of hydrogen and yet consumes minimum level of energy. Accordingly, the maximum yield of hydrogen gas can be 77%. The carbon dioxide selectivity is approximately 1.2% to 73%.

Autothermal steam reforming (ATR) reaction as described in the preferred embodiment of the present invention is a combination of the endothermic steam reforming (SRM) reaction and the exothermic partial oxidation (POX) reaction. The energy generated by the POX is utilized by the endothermic SRM. Thus, the resulting net enthalpy is near zero. The catalyst offered a viable way to harness hydrogen from methanol to be used as an energy source for the future especially when methanol is derived from renewable sources such as biomass. Apart from catalyzing the ATR reaction, the catalyst embodied by the present invention is also applicable for crude oil processing, hydrotreating naphtha, synthesis of methanol from syngas or petrochemicals industry.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A catalyst for autothermal steam reforming of methanol comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina.

2. A catalyst as claimed in claim 1, wherein the metal component is present in an amount of up to 5% by weight of the catalyst.

3. A catalyst as claimed in claim 1 or claim 2, wherein the amount of copper in the catalyst is 1% to 5% by weight of the catalyst.

4. A catalyst as claimed in any one of claims 1 to 3, wherein the amount of zinc in the catalyst is 1% to 5% by weight of the catalyst.

5. A catalyst as claimed in any one of claims 1 to 4, wherein the amount of palladium in the catalyst is 1% to 5% by weight of the catalyst.

6. A catalyst as claimed in any one of claims 1 to 5, wherein the amount of alumina in the catalyst is at least 95% by weight of the catalyst.

7. A method for preparing a catalyst according to any one of claims 1 to 6 by incipient wetness impregnation.

8. A method for producing hydrogen, comprising the step of converting methanol to hydrogen gas by an autothermal steam reforming process in the presence of both oxygen and steam using a catalyst comprising copper, zinc, palladium or any combination thereof as a metal component supported on alumina.

9. A method as claimed in claim 8, wherein the autothermal steam reforming process is performed at a reaction temperature of 180⁰C to 28O⁰C.