Method of manufacturing a porous gallium (III) oxide photocatalyst for preparation of hydrocarbons

This application claims priority from Korean Patent Application No. 10-2012-0008307, filed on Jan. 27, 2012 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.

The present invention relates to a method of manufacturing a porous gallium (III) oxide [Ga 2 O 3 ] photocatalyst for production of hydrocarbons, and more particularly, to a method of manufacturing a porous gallium (III) oxide photocatalyst for production of hydrocarbons, comprising: adding a base and a surfactant to a solvent and agitating the mixture to prepare a solution containing micelles formed therein; adding a solution containing a gallium precursor to the micelle-containing solution to conduct a reaction; and washing and drying a precipitate obtained by filtering reactants after the reaction, and heating the precipitate to remove the micelles from a surface and an inner part of the precipitate, followed by forming pores therein.

The present invention also relates to a porous gallium oxide photocatalyst for production of hydrocarbons, manufactured by the foregoing method, and a process of producing hydrocarbons using the porous gallium oxide photoctalyst for production of hydrocarbons, manufactured by the foregoing method.

The hydrocarbons described above may include hydrocarbons having 1 to 4 carbon atoms, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane.

Artificial photo-synthesis technologies that use a photocatalyst to produce useful fuel from carbon dioxide and/or conversion of carbon dioxide to the same are now a global issue. Such a method of preparing a useful fuel using carbon dioxide and/or converting carbon dioxide to the same substantially utilizes only water and solar light, therefore, may be the most eco-friendly and sustainable technique. The fuel produced by the foregoing method may include hydrocarbons having 1 to 4 carbon atoms, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane.

Methane has the simplest form among hydrocarbons, however, is a main component of natural gas generating the largest energy (55.7 kJ/g) per unit mass and hence is generally known as a useful fuel.

In order to convert carbon dioxide (CO 2 ) to methane using solar energy, it is important to use an excellent photocatalyst.

Recently, gallium (III) oxide (Ga 2 O 3 ) has attracted worldwide attention since it has superior photo-catalytic properties and high reduction potential to render CO 2 to be converted to methane. However, studies on conversion of CO 2 to methane using gallium (III) oxide have not yet been reported.

Accordingly, the present invention relates to a method of manufacturing a porous gallium (III) oxide photocatalyst with novel structure and form, and a method for production of hydrocarbons, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane from CO 2 or for conversion of CO 2 to any of the foregoing hydrocarbons or methane by using the aforesaid porous gallium (III) oxide photocatalyst.

In this regard, prior arts to which the present invention pertains may include the following:

Grimes et al. have disclosed photo-synthesis wherein titanium dioxide nanotubes (TiO 2 nanotubes) synthesized through anodization is used to generate methane from CO 2 and water [High-Rate Solar Photocatalytic Conversion of CO 2 and Water Vapor to Hydrocarbon fuels, Nano Lett., 2009, 9, 731]. However, it is known that such TiO 2 material is less effective in reducing CO 2 to produce methane due to a relatively low chemical reduction potential thereof [Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons, ACS nano, 2010, 4, 1259].

Further, Tanaka et al. have conducted reduction of CO 2 from hydrogen as well as CO 2 using a β-Ga 2 O 3 photocatalyst, which is known to have high reduction potential [Effect of H 2 gas as a reductant on photoreduction of CO 2 over a Ga 2 O 3 Photocatalyst, Chem. Phys. Lett., 2008, 467, 191]. However, it was found that the above photocatalyst did not produce methane, but instead generated carbon monoxide (CO), which is substantially an intermediate stage of the reduction.

Therefore, an object of the present invention is to provide a method of manufacturing a porous gallium (III) oxide (Ga 2 O 3 ) photocatalyst which can produce hydrocarbons, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane by using carbon dioxide (CO 2 ) and water under a light source with high reaction efficiency and/or productivity; or, otherwise, which can conduct conversion of the above materials (that is, CO 2 and water) to the foregoing, that is, hydrocarbons, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane.

Another object of the present invention is to provide the porous Ga 2 O 3 photocatalyst for production of hydrocarbons, manufactured by the foregoing method.

Another object of the present invention is to provide a process of producing hydrocarbons using the porous Ga 2 O 3 photocatalyst for production of hydrocarbons, manufactured by the foregoing method.

According to the present invention, there is a method of manufacturing a porous gallium (III) oxide photocatalyst for production of hydrocarbons, comprising: adding a base and a surfactant to a solvent and agitating the mixture to prepare a solution containing micelles foamed therein (‘micelle-containing solution’); adding a solution containing a gallium precursor to the micelle-containing solution to conduct a reaction; and washing and drying a precipitate obtained by filtering reactants after the reaction, and heating the precipitate to remove the micelles from a surface and an inner part of the precipitate, followed by forming pores therein.

The present invention may also provide a porous Ga 2 O 3 photocatalyst for production of hydrocarbons, manufactured by the foregoing method.

Further, the present invention may provide a process of producing hydrocarbons using the porous Ga 2 O 3 photocatalyst for production of hydrocarbons, manufactured by the foregoing method.

The porous Ga 2 O 3 photocatalyst manufactured by the present invention includes pores afforded therein to increase an amount of CO 2 adsorption as a product of photo-reaction and, since such a photo-reaction is a reaction occurring at the surface of the Ga 2 O 3 photocatalyst, an increase in CO 2 adsorption on the pores present inside the Ga 2 O 3 may contribute to improvement in efficiency of the photo-reaction, thereby rendering hydrocarbons, preferably, aliphatic hydrocarbons having 1 to 4 carbon atoms, and more preferably, methane to be produced in large quantities.

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is schematic views illustrating a method of manufacturing a porous Ga 2 O 3 photocatalyst and the production of methane as a hydrocarbon from raw materials such as CO 2 and water using the manufactured porous Ga 2 O 3 photocatalyst;

FIG. 2 illustrates an SEM image of the porous Ga 2 O 3 photocatalyst with low magnification;

FIG. 3 a is an SEM image (top view) of the porous Ga 2 O 3 photocatalyst, FIG. 3 b is an SEM image illustrating a cross-section of the porous Ga 2 O 3 photocatalyst, FIG. 3 c is a TEM image of the porous Ga 2 O 3 photocatalyst with low magnification, FIG. 3 d is a TEM image of the porous Ga 2 O 3 photocatalyst with high magnification, FIG. 3 e illustrates XRD pattern of the porous Ga 2 O 3 photocatalyst, FIG. 3 f illustrates nitrogen adsorption of the porous Ga 2 O 3 photocatalyst, and FIG. 3 g illustrates a distribution of pore sizes of the porous Ga 2 O 3 photocatalyst; and

FIG. 4 a is graphs illustrating recycling features of the porous Ga 2 O 3 photocatalyst producing methane from CO 2 , FIG. 4 b is graphs illustrating redox potential of CO 2 and energy band position of Ga 2 O 3 , FIG. 4 c is graphs illustrating photocatalytic properties of the porous Ga 2 O 3 photocatalyst in regard to methane conversion (10 hours reaction), and FIG. 4 d is graphs illustrating analyzed results of CO 2 adsorption of the porous Ga 2 O 3 photocatalyst, compared to a typical Ga 2 O 3 photocatalyst.

The present invention discloses a method of manufacturing a porous Ga 2 O 3 photocatalyst used for production of hydrocarbons.

The present invention also discloses a method of manufacturing a porous gallium (III) oxide photocatalyst used for production of hydrocarbons, which includes: adding a base and surfactant to a solvent and agitating the mixture to prepare a solution containing micelles formed therein; adding a solution containing a gallium precursor to the micelle-containing solution to initiate a reaction therebetween; and washing and drying a precipitate obtained by filtering the mixture after the reaction described above, and heating the precipitate to remove the micelles from the surface of the precipitate as well as inside the same while forming pores therein.

In the formation of micelles, a solvent may be purified water (‘water’).

In the formation of micelles, a solvent may be ethanol.

In the formation of micelles, a solvent may be methanol.

In the formation of micelles, a solvent may include at least one selected from water, ethanol and methanol.

In the formation of micelles, a base may be ammonium hydroxide (NH 4 OH).

In the formation of micelles, a base may be sodium hydroxide (NaOH).

In the formation of micelles, a base may be potassium hydroxide (KOH)

In the formation of micelles, a base may include at least one selected from NH 4 OH, NaOH and KOH.

In the formation of micelles, a surfactant may be tetradecyltrimethylammonium bromide (TTAB).

In the formation of micelles, a surfactant may be hexadecyltrimethylammonium bromide (CTAB).

In the formation of micelles, a surfactant may comprise TTAB and CTAB.

In the formation of micelles, agitation may be implemented at 100 to 500 rpm for 30 minutes to 1 hour.

In the formation of micelles, 5 to 10 ml of at least one base selected from NH 4 OH, NaOH and KOH, and 100 to 300 mg of at least one surfactant selected from TTAB and CTAB may be added to 100 ml of at least one solvent selected from water, ethanol and methanol, followed by agitating the above mixture at 100 to 500 rpm for 30 minutes to 1 hour, to thereby form micelles.

The formation of micelles may further comprise using an additive helpful to form the micelles as a component added to the solvent, other than the base and surfactant described above.

Such an additive helpful to form the micelles may include, for example, 1-dodecanethiol.

Alternatively, the formation of micelles may include adding 5 to 10 ml of at least one base selected from NH 4 OH, NaOH and KOH, 100 to 300 mg of at least one surfactant selected from TTAB and CTAB and, as an additive helpful to form the micelles, and 0.01 to 0.1 ml of 1-dodecanethiol to 100 ml of at least one solvent selected from water, ethanol and methanol, and then, agitating the above mixture at 100 to 500 rpm for 30 minutes to 1 hour, to thereby form micelles.

The solution containing a gallium precursor may be prepared by adding the gallium precursor to a solvent.

The solution containing a gallium precursor may be a solution prepared by adding at least one gallium precursor selected from gallium nitrate hydrate (Ga(NO 3 ) 3 .xH 2 O), gallium sulfate hydrate (Ga 2 (SO 4 ) 3 .xH 2 O) and gallium perchlorate hydrate (Ga(ClO 4 ) 3 .xH 2 O) to a solvent selected from water, ethanol and methanol.

In this regard, the solution containing a gallium precursor may be a solution prepared by adding gallium nitrate hydrate (Ga(NO 3 ) 3 .xH 2 O) as the gallium precursor to an ethanol solvent.

More particularly, the solution containing a gallium precursor may be a solution prepared by adding 0.5 to 1.5 g of at least one gallium precursor selected from gallium nitrate hydrate (Ga(NO 3 ) 3 .xH 2 O), gallium sulfate hydrate (Ga 2 (SO 4 ) 3 .xH 2 O) and gallium perchlorate hydrate (Ga(ClO 4 ) 3 .xH 2 O) to 100 ml of any one solvent selected from water, ethanol and methanol.

Preferably, the solution containing a gallium precursor may be a solution prepared by adding 0.5 g of gallium nitrate hydrate (Ga(NO 3 ) 3 .xH 2 O) to 100 ml of an ethanol solvent.

The prepared gallium precursor-containing solution may be added to a solution containing micelles formed therein, followed by agitating the mixture at 65 to 75° C. and 100 to 500 rpm for 1 to 3 hours to initiate a reaction therebetween.

The gallium precursor-containing solution may be added to a solution containing micelles formed therein, followed by agitating the mixture at 70° C. and 300 rpm for 2 hours to initiate a reaction therebetween.

The precipitate obtained after filtration may be subjected to washing, drying under vacuum and heating at 500 to 700° C. for 5 to 8 hours to remove the micelles from the surface of the precipitate as well as inside the same, thereby resulting in a porous gallium nitride catalyst.

More particularly, the precipitate obtained after filtration may be washed using distilled water and dried under vacuum, followed by heat treatment at 600° C. for 6 hours, to remove the micelles from the surface of the precipitate as well as inside the same, thereby manufacturing a porous gallium nitride catalyst.

FIG. 1 is schematic views illustrating a method of manufacturing a porous gallium oxide photocatalyst according to the present invention, as well as a photo-reaction which is performed using CO 2 and water as raw materials under a light source to produce methane and is promoted by the porous gallium oxide photocatalyst manufactured by the foregoing method.

According to the inventive method of manufacturing the porous gallium oxide photocatalyst, a porous gallium oxide photocatalyst having pores formed therein may be prepared using a surfactant, base and nitric acid precursor.

The surfactant may contribute to formation of micelles, the base may reduce the gallium precursor while promoting gelling. When the solution containing a gallium precursor is added to the solution containing the micelles formed therein, a gallium hydroxide phase in which the micelles are contained may be generated.

In this case, heat treatment at a high temperature may burn out the micelles present on the surface of gallium hydroxide as well as inside the same, to thereby remove the micelles. Instead, pores may be formed on the surface of gallium hydroxide as well as inside the same, which are free from the micelles. Moreover, controlling a heat treatment temperature in the range of 500 to 700° C. may convert a gallium phase to Ga 2 O 3 .

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may produce hydrocarbons from raw materials such as CO 2 and water and/or convert the raw materials into hydrocarbons.

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may conduct reaction using CO 2 and water as raw materials under a light source to produce aliphatic hydrocarbons having 1 to 4 carbon atoms and/or convert the raw materials into the foregoing hydrocarbons.

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may conduct reactions using CO 2 and water as raw materials under a light source to produce methane and/or convert the raw materials into methane.

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may be prepared in a rod shape wherein pores having a diameter of 0.1 to 100 μm are formed.

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may have a specific surface area (BET) in the range of 40 to 48 m 2 /g.

The porous Ga 2 O 3 photocatalyst manufactured according to the foregoing method may have a specific surface area (BET) in the range of 40 to 48 m 2 /g as well being prepared in a rod shape wherein pores having a diameter of 0.1 to 100 μm are formed.

As described above, the method of manufacturing a porous Ga 2 O 3 photocatalyst used for production of hydrocarbons according to the present invention has been practically executed under a variety of conditions and it is expected from the results that, in order to accomplish the purposes of the present invention, the method of manufacturing a porous Ga 2 O 3 photocatalyst is preferably conducted under such various conditions as described above.

The present invention may include a porous Ga 2 O 3 photocatalyst used for production of hydrocarbons, manufactured according to the foregoing method.

The porous Ga 2 O 3 photocatalyst described above may be prepared in a rod shape wherein pores having a diameter of 0.1 to 100 μm are formed.

The porous Ga 2 O 3 photocatalyst described above may have a specific surface area (BET) in the range of 40 to 48 m 2 /g.

The porous Ga 2 O 3 photocatalyst described above may have a specific surface area (BET) in the range of 40 to 48 m 2 /g as well being prepared in a rod shape wherein pores having a diameter of 0.1 to 100 μm are formed.

The present invention may further comprise a process of producing hydrocarbons from CO 2 and water as raw materials and/or a process of converting the raw materials described above to hydrocarbons through reaction under a light source by using the porous Ga 2 O 3 photocatalyst used for production of hydrocarbons, which was manufactured according to the foregoing method.

The porous Ga 2 O 3 photocatalyst described above may render production of aliphatic hydrocarbons having 1 to 4 carbon atoms from CO 2 and water as raw materials and/or conversion of the raw materials to the foregoing hydrocarbons, through reaction under a light source.

The porous Ga 2 O 3 photocatalyst described above may produce methane from CO 2 and water as raw materials and/or covert the raw materials to methane, through reaction under a light source.

Such a light source may be solar light or a xenon (Xe) lamp.

Hereinafter, preferred embodiments of the present invention will be described in detail to more concretely understand the present invention with reference to examples, comparative examples, practical examples and experimental examples. However, it will be apparent to those skilled in the art that such embodiments are provided for illustrative purposes and do not limit subject matters to be protected as defined by the appended claims.