WO2014137293A1

WO2014137293A1 - A method for preparing a highly dispersed supported metal catalyst

Info

Publication number: WO2014137293A1
Application number: PCT/SG2014/000108
Authority: WO
Inventors: Sibudjing Kawi; Liuye MO
Original assignee: National University Of Singapore
Priority date: 2013-03-06
Filing date: 2014-03-06
Publication date: 2014-09-12

Abstract

A process of preparing a highly dispersed supported metal catalyst. The process includes mixing a metal salt, a monofunctional organic acid, and inert oxide powder to form a mixture; drying and calcining the mixture to yield at least one metal oxide on the surface of the powder; and reducing the metal oxide to a particulate metal.

Description

A METHOD FOR PREPARING A HIGHLY DISPERSED

SUPPORTED METAL CATALYST

BACKGROUND

One promising technology to reduce greenhouse gases, such as methane (CH₄) and carbon dioxide (C0₂), is catalytic reforming of CH₄ and C0₂ into synthesis gas, which, as a mixture of carbon monoxide (CO) and hydrogen (H₂) gases, is used in various industrial applications.

The reforming reaction generates carbon deposition, which quickly deactivates any conventional catalysts. For this reason, its commercialization so far remains stalled. Over the past decade, much effort has been directed at the development of a new type of catalyst for this reaction in view of its great economic and environmental impacts.

One possible solution is to use a highly dispersed supported metal catalyst, which is known to exhibit high catalytic performance in many reactions. Yet, preparation of a highly dispersed supported metal catalyst is known to be complex, making its application impractical in an industrial setting.

There is a clear need for a simple and inexpensive process for preparing a highly dispersed supported metal catalyst for use in the above-described reforming reaction, as well as the water gas shift reaction and other reactions.

SUMMARY

This invention is based on an unexpected discovery of a process for preparing a highly dispersed supported metal catalyst that is suitable for the commercial application.

In one aspect, the present invention concerns a process of preparing a highly dispersed supported metal catalyst. The process includes the following steps: (i) preparing a solution that contains a metal salt and a monofunctional organic acid, (ii) mixing an inert oxide powder into the solution to form a homogenous mixture; (iii) drying the homogenous mixture at 50 - 200 °C to yield a dried mass; (iv) calcining the dried mass at 250 - 1000 °C to cause formation of a metal oxide on the surface of the powder; and (v) incubating the calcined mass in a hydrogen atmosphere at 250 - 1000 °C to reduce the metal oxide to a particulate metal. The monofunctional organic acid can be a monocarboxylic acid containing 3 to 40 carbon atoms (e.g., oleic acid, stearic acid, hexanoic acid, butyric acid, propanoic acid, or a combination thereof). The inert oxide powder can be a silica powder, an alumina powder, an aluminum silicate powder, a titanium oxide powder, a zirconium oxide powder, a cerium oxide powder, a lanthanum oxide powder, a carbon powder, a zeolite powder, or a combination thereof. Examples of a metal salt include a copper salt, a nickel salt, a cerium salt, a lanthanum salt, a samarium salt, a magnesium salt, a cobalt salt, a ruthenium salt;, a rhodium salt, a palladium salt, a silver salt, an osmium salt, an iridium salt, a platinum salt, a gold salt, and a combination thereof. Specific examples of a metal salt also include a metal oxide, a metal nitrate, a metal chloride, a metal acetate, a metal formate, and a combination thereof. Preferably, the metal salt can be copper nitrate, nickel nitrate, cerium nitrate, lanthanum nitrate, samarium nitrate, copper oxide, lanthanum oxide, samarium oxide, nickel oxide, or a combination thereof.

In one embodiment, the metal salt is copper nitrate, the monofunctional organic acid is oleic acid, and the inert oxide powder is silica powder.

In another embodiment, the metal salt is nickel nitrate, the monofunctional organic acid is oleic acid, and the inert oxide powder is silica powder.

Another aspect of this invention concerns a different process of preparing a highly dispersed supported metal catalyst. The process includes the following steps: (i) preparing a first solution that contains a metal salt; (ii) preparing a second solution that contains a monofunctional organic acid; (iii) mixing an inert oxide powder into the second solution to form a first homogenous mixture; (iv) mixing the first homogenous mixture with the first solution to form a second homogenous mixture; (v) drying the homogenous mixture at 50 - 200 °C to yield a dried mass; (vi) calcining the dried mass at 250 - 1000 °C to cause formation of a metal oxide on the surface of the powder; and (vii) incubating the calcined mass in a hydrogen atmosphere at 250 - 1000 °C to reduce the metal oxide to a particulate metal. Examples of the monofunctional organic acid, inert oxide powder, and metal oxide are enumerated above.

The details of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims. DETAILED DESCRIPTION

The metal catalyst prepared by the process of the invention includes a transition metal (e.g., copper and nickel) or a noble metal (e.g., platinum and gold), both of which can be doped with other metals to form a bi-metallic or multi-metallic catalyst.

Metal particles are to be prepared by the process of the invention. An inert oxide powder, as a catalyst support, plays a key role in achieving high dispersion of the metal particles over its surface. Preferably, the inert oxide powder has a surface area greater than 200 m²/g. Strong interactions between metal particles and their support, i.e., the inert oxide powder, are necessary to achieve small metal particle sizes, as well as high dispersion and high mobility of metal particles on the support surface.

A monofunctional organic acid and a melt salt are used in the process of the invention. The monofunctional organic acid acts as a promoter to facilitate high dispersion of metal particles. Preferably, the molar ratio of the monofunctional organic acid to the metal in the metal salt is 0.01 to 3. For preparing a copper and nickel catalyst, the molar ratios are preferably ~ 0.05 and ~ 0.5, respectively.

In the method of the present invention, a solvent is used to prepare a solution that contains the metal salt. The solvent may be any liquid which can dissolve the metal salt and can be removed from an inert oxide powder support by drying or vacuum evaporation. Examples of the solvent include, but are not limited to, water, acetic acid, alcohols (e.g., methanol, ethanol, ethylene glycol, and a mixture thereof).

Within this invention are two processes of preparing a highly dispersed supported metal catalyst. One is sequential impregnation in which a proper metal salt is mixed with an acid promoter to form a solution before an inert oxide powder is added. The other is co-impregnation in which an inert oxide powder is mixed in an acid promoter solution before further mixed with a metal salt solution.

Described below is an exemplary procedure of sequential impregnation for preparing a highly dispersed supported metal catalyst.

A solution that contains a metal salt (e.g., copper nitrate) and a monocarboxylic acid (e.g., oleic acid) is prepared. An inert oxide powder (e.g., silica powder) is mixed into the solution to form a homogenous mixture, which is then placed in an oven for drying at 40~90°C (e.g., 50-60°C) overnight. The mixture may then be dried at 80-200 °C (e.g., 100-150°C) in an oven with or without vacuum. Next, the dried mass is calcined at a temperature of 250-1000°C (e.g., 300-900°C) in air or another suitable atmosphere. The preferable temperature for preparing a copper catalyst is 300-500°C and for preparing a nickel catalyst is 600-800 °C. Finally, the calcined mass is reduced at a temperature of 250- 1000° C in an atmosphere containing hydrogen at an amount of 1-100 mol% (e.g., 5-10 mol%). A highly dispersed supported metal catalyst is thus obtained.

An exemplary procedure of co-impregnation for preparing a highly dispersed supported metal catalyst is described below.

An inert oxide powder (e.g., silica powder) is mixed into a solution that contains a monocarboxylic acid (e.g., oleic acid) to form a homogenous mixture. The mixture is further mixed into another solution that contains a metal salt (e.g., copper nitrate) to form yet another homogenous mixture, which is then placed in an oven for drying. The remaining procedure is the same as that for the sequential impregnation described above.

The metal particle size or crystallite size of a catalyst thus obtained is determined by transmission electron microscopy (TEM) or powder X-ray diffraction (XRD), as is well known to those skilled in the art.

Catalytic activities of a catalyst can be measured as follows in one of the two chemical reactions, i.e., reforming of CH₄ and C0₂ (dry reforming of carbon dioxide and methane, DRM) and water gas shift reaction (WGSR). For the DRM reaction, the flow rates of methane, carbon dioxide, and nitrogen are kept at ~20 ml/min. The nitrogen in the feed gas acts as the internal standard. Prior to the DRM reaction, 50 mg of the catalyst is placed in the fixed-bed reactor and plugged with quartz wool. The catalytic activity of the catalyst is determined by the conversion of methane and carbon dioxide to synthesis gas. For the WGSR, the feed composition (with a total flow rate of 50 ml/min) is as follows: 5 mol% CO, 25 mol% H₂0, and 70 mol% He. The effluent gases are analyzed by a Gas Chromatograph equipped with a Hayesep D column. The catalytic activity of the catalyst is measured by the conversion of carbon monoxide into carbon dioxide and hydrogen.

The specific examples below are to be construed as merely illustrative, and not limitati ve of the remainder of the disclosure in any way whatsoever. Without further elaboration, it is believed that one skilled in the art can, based on the description herein, utilize the present invention to its fullest extent. All publications cited herein are incorporated by reference in their entirety.

Example 1 : Preparation and characterization of 10 wt% Cu/Si0₂ catalyst

2.11 g of copper nitrate trihydrate was dissolved in 10 ml D.I. water. 0.650 g of oleic acid or OA (mol(OA/Cu) = 0.25) followed by 5 g of silica (specific surface area = 753 m7g) was then introduced into the aqueous solution.

Subsequently, the sample was impregnated at 60 °C for over 6 hours before dried overnight at 100°C. The dried sample was calcined at 450 °C for 4 hours. The catalyst was reduced at 300 °C for one hour. A 10 wt% Cu/Si0₂ catalyst was thus obtained.

The Cu wt% is calculated as follows: Cu wt% = wt(Cu/(Cu+Si0₂))xl 00%. Ni wt% in Examples 2 and 3 and Cu wt% in Examples 7-9 are calculated by the same formula.

The average copper particle size, as measured by TEM, was 3.8 nm. The catalyst was used in the WGSR reaction at 300 °C and the CO conversion rate was 47%.

Example 2: Preparation and characterization of 5 wt% Ni/Si0₂ catalyst

1.31 g of nickel nitrate hexahydrate was dissolved in 10 ml of D.I. water.

0.126 g of oleic acid (mol(OA/Ni) = 0.1) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60°C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 700 °C for 4 hours. The catalyst was reduced at 700 °C for one hour. The nickel crystallite size, as measured by XRD, was 2.9 nm.

Example 3 : Preparation and characterization of 5 wt% Ni/Si0₂ catalyst

1.31 g of nickel nitrate hexahydrate was dissolved in 10 ml D.I. water.

0.625 g of oleic acid (mol(OA/Ni) = 0.5) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60 °C for > 6 hours before dried overnight at 100° C. The dried sample was calcined at 700 °C for 4 hours. The catalyst was reduced at 700 °C for one hour. The nickel crystallite size, as measured by XRD, was 2.7 nm. The catalyst thus prepared was used in the DRM reaction at 700 °C for 100 hours and the CH₄ and C0₂ conversion rates were 66% and 72%, respectively. In addition, there was no carbon deposition on the spent catalyst.

Example 4: Preparation and characterization of 5 wt% Ni-1 wt% La20₃/Si02 catalyst

1.32 g of nickel nitrate hexahydrate and 0.141 g of lanthanum nitrate hexahydrate were dissolved in 10 ml D.I. water. 0.640 g of oleic acid (mol(OA/Ni) = 0.5) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60 °C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 700 °C for 4 hours. The catalyst was reduced at 700 °C for one hour. Note that La₂0₃ was not reduced under this condition. A 5 wt% Ni-1 wt%

La₂0₃/Si0₂ catalyst was thus obtained.

The Ni wt% is calculated as follows: Ni wt% =

wt(Ni/(Ni+La₂O₃+SiO₂))xl00%, and the La₂0₃ wt% is calculated as follows: La₂0₃ wt% = wt(La₂O₃/(Ni+La₂O₃+SiO₂))xl00%. Ni wt% and Sm₂0₃ wt% in Example 5, Ni wt% and Ce0₂ wt% in Example 6, as well as Cu wt% and Ce0₂ wt% in Example 10, are calculated by the same formula.

The nickel crystallite size, as measured by XRD, was 3.4 nm. The catalyst was used in the DRM reaction at 700 °C and the CH₄ and CQ₂ conversion rates were around 79% and 85%, respectively. TEM images also showed that there was no carbon deposited on the spent catalyst and the nickel particles were still highly dispersed on the support.

Example 5: Preparation and characterization of 5 wt% Ni-1 wt% Sm₂0₃/Si0₂ catalyst

1.32 g of nickel nitrate hexahydrate and 0.136 g of Samarium nitrate hexahydrate were dissolved in 10 ml D.I. water. 0.640 g of oleic acid (mol(OA/Ni) = 0.5) followed by 5 g of silica (specific surface area = 753 m²/g) were then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60 °C for > 6 hours before dried overnight at 100° C. The dried sample was

' calcined at 700 °C for 4 hours. The catalyst was reduced at 700 °C for one hour.

Note that Sm₂0₃ was not reduced under this condition. The nickel crystallite size, as measured by XRD, was 2.8 nm. The catalyst thus prepared was used in the DRM reaction at 700° C. The CH₄ and C0₂ conversion rates were 79% and 85%, respectively. In addition, there was no carbon deposition on the spent catalyst. Example 6: Preparation and characterization of 5 wt% Ni-1 wt% Ce0₂/Si0₂ catalyst

1.32 g of nickel nitrate hexahydrate and 0.134 g of Cerium nitrate

hexahydrate were

dissolved in 10 ml D.I. water. 0.640 g of oleic acid (mol(OA/Ni) = 0.5) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60 °C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 700°C for 4 hours.

The catalyst was reduced at 700 °C for one hour. Note that Ce0₂ was not reduced under this condition. The nickel crystallite size, as measured by XRD, was 3.0 nm. The catalyst thus prepared was used in the DRM reaction at 700 °C and the CH₄ and

CO2 conversion rates were 79% and 84%, respectively. In addition, there was no carbon deposition on the spent catalyst.

Example 7: Preparation and characterization of 10 wt% Cu/Si0₂ catalyst

2.11 g of copper nitrate trihydrate was dissolved in 7 ml D.I. water. 0.192g of butyric acid (B A) (mol(BA/Cu) = 0.25) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60°C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 450°C for 4 hours. The catalyst was reduced at 300°C for one hour. The average copper particle size, as measured by N₂0 chemisotption, was 1.8 nm. The catalyst thus prepared was used in the WGSR W

reaction at 300°C and the CO conversion rate was 47%.

Example 8: Preparation and characterization of 10 wt% Cu/Si0₂ catalyst

2.11 g of copper nitrate trihydrate was dissolved in 7 ml D.I. water. 0.254 g of hexanoic acid (HA) (mol(HA/Cu) = 0.25) followed by 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution.

Subsequently, the sample was impregnated at 60°C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 450 °C for 4 hours. The catalyst was reduced at 300°C for one hour. The average copper particle size, as measured by N₂0 chemisotption, was 2.2 nm. The catalyst thus prepared was used in the WGSR reaction at 300 °C and the CO conversion rate was 46%.

Example 9: Preparation and characterization of 10 wt% Cu/Si0₂ catalyst

0.650 g of oleic acid was added to 9 mL H₂0. 5 g of silica (specific surface area = 753 m²/g) was then introduced into the aqueous solution. Subsequently, the sample was impregnated at 60°C for > 6 hours before dried overnight at 100°C. The dried sample was used as support. 2.1 1 g copper nitrate was dissolved into 9 mL H₂0. The above OA impregnated silica was put to the solution. Next, the sample was impregnated at 60°C for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 450°C for 4 hours. The catalyst was reduced at 300°C for one hour. The average copper particle size, as

measured by N₂0 chemisorption, was 2.0 nm. The catalyst thus prepared was used in the WGSR reaction at 300°C and the CO conversion rate was 51%. Example 10: Preparation and characterization of 10 wt% Cu-10 wt% CeO?/SiQ7

First, 3.154 g Ce(N0₃)₃ 3H₂0 was dissolved in 15 mL D.I. water, and then 0.513 g of oleic acid (mol(OA/Ni) = 0.25) was added into the aqueous solution. At last, 10 g silica was introduced into the same solution. Subsequently, the sample was impregnated at room temperature for > 6 hours before dried overnight at 100°C. The dried sample was calcined at 450 °C for 4 hours to achieve Ce0₂/SiO₂ support. A 10%Cu/10%CeO₂/SiO₂ catalyst was prepared in the presence of OA following the same procedure with Ce0₂/Si0₂ as the support for Copper. The 10 wt%Cu/10 wt%Ce0₂/Si0₂ catalyst thus obtained was reduced at 300 °C for one hour. The average copper particle size, as measured by N₂0 chemisorption, was 1.8 nm. The catalyst thus prepared was used in the WGSR reaction at 300°C and the CO conversion rate was 67%.

OTHER EMBODIMENTS

All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the claims.

Claims

What is claimed is:

1. A process of preparing a highly dispersed supported metal catalyst, the process comprising:

preparing a solution that contains a metal salt and a monofunctional organic acid, the metal salt being a copper salt, a nickel salt, a cerium salt, a lanthanum salt, a samarium salt, a magnesium salt, a cobalt salt, a ruthenium salt, a rhodium salt, a palladium salt, a silver salt, an osmium salt, an iridium salt, a platinum salt, a gold salt, or a combination thereof;

mixing an inert oxide powder into the solution to form a homogenous mixture; drying the homogenous mixture at 50 - 200°C to yield a dried mass; calcining the dried mass at 250 - 1000°C to cause formation of a metal oxide on the surface of the powder; and

incubating the calcined mass in a hydrogen atmosphere at 250 - 1000°C to reduce the metal oxide to a particulate metal,

whereby a highly dispersed supported metal catalyst is obtained.

2. The process of claim 1, wherein the monofunctional organic acid is a monocarboxylic acid containing 3 to 40 carbon atoms.

3. The process of claim 2, wherein the monocarboxylic acid is oleic acid, stearic acid, hexanoic acid, butyric acid, propanoic acid, or a combination thereof.

4. The process of claim 1, wherein the metal salt is a metal oxide, a metal nitrate, a metal chloride, a metal acetate, a metal formate, or a combination thereof. ^"

5. The process of claim 4, wherein the metal salt is copper nitrate, nickel nitrate, cerium nitrate, lanthanum nitrate, samarium nitrate, copper oxide, lanthanum oxide, samarium oxide, nickel oxide, or a combination thereof.

6. The process of claim 3, wherein the metal salt is copper nitrate, nickel nitrate, cerium nitrate, lanthanum nitrate, samarium nitrate, copper oxide, lanthanum oxide, samarium oxide, nickel oxide, or a combination thereof.

7. The process of claim 1, wherein the inert oxide powder is a silica powder, an alumina powder, an aluminum silicate powder, a titanium oxide powder, a zirconium oxide powder, a cerium oxide powder, a lanthanum oxide powder, a carbon powder, a zeolite powder, or a combination thereof.

8. The process of claim 7, wherein the inert oxide powder is a silica powder.

9. The process of claim 6, wherein the inert oxide powder is a silica powder.

10. The process of claim 1, wherein the molar ratio of the monofunctional organic acid to the metal in the metal salt is 0.01 to 3.

11. The process of claim 1 , wherein the inert oxide powder has a surface area greater than 200 m²/g.

12. The process of claim 9, wherein the molar ratio of the monocarboxylic acid to the metal in the metal salt is 0.01 to 3 and the silica powder has a surface area greater than 200 m²/g.

13. A process of preparing a highly dispersed supported metal catalyst, the process comprising:

preparing a first solution that contains a metal salt, the metal salt being a copper salt, a nickel salt, a cerium salt, a lanthanum salt, a samarium salt, a magnesium salt, a cobalt salt, a ruthenium salt, a rhodium salt, a palladium salt, a silver salt, an osmium salt, an iridium salt, a platinum salt, a gold salt, or a combination thereof;

preparing a second solution that contains a monofunctional organic acid;

mixing an inert oxide powder into the second solution to form a first

homogenous mixture;

mixing the first homogenous mixture with the first solution to form a second homogenous mixture;

drying the homogenous mixture at 50 - 200°C to yield a dried mass; calcining the dried mass at 250 - 1000°C to cause formation of a metal oxide on the surface of the powder; and

whereby a highly dispersed supported metal catalyst is obtained.

14. The process of claim 13, wherein the monofunctional organic acid is a monocarboxylic acid containing from 3 to 40 carbon atoms.

15. The process of claim 14, wherein the monocarboxylic acid is oleic acid, stearic acid, hexanoic acid, butyric acid, propanoic acid, or a combination thereof.

16. The process of claim 13, wherein the metal salt is a metal oxide, a metal nitrate, a metal chloride, a metal acetate, a metal formate, or a combination thereof.

17. The process of claim 16, wherein the metal salt is copper nitrate, nickel nitrate, cerium nitrate, lanthanum nitrate, samarium nitrate, copper oxide, lanthanum oxide, samarium oxide, nickel oxide, or a combination thereof.

18. The process of claim 15, wherein the metal salt is copper nitrate, nickel nitrate, cerium nitrate, lanthanum nitrate, samarium nitrate, copper oxide, lanthanum oxide, samarium oxide, nickel oxide, or a combination thereof.

19. The process of claim 13, wherein the inert oxide powder is a silica powder, an alumina powder, an aluminum silicate powder, a titanium oxide powder, a zirconium oxide powder, a cerium oxide powder, a lanthanum oxide powder, a carbon powder, a zeolite powder, or a combination thereof.

20. The process of claim 19, wherein the inert oxide powder is a silica powder.

21. The process of claim 18, wherein the inert oxide powder is a silica powder.

22. The process of claim 13, wherein the molar ratio of the monofunctional organic acid to the metal in the metal salt is 0.01 to 3.

23. The process of claim 13, wherein the inert oxide powder has a surface area greater than 200 m²/g.

24. The process of claim 21, wherein the molar ratio of the monocarboxylic acid to the metal in the metal salt is 0.01 to 3 and the silica powder has a surface area greater than 200 m²/g.