Catalyst particles and methods for producing catalyst particles

Abstract

This invention provides a highly active photocatalyst that promotes both oxidation and reduction reactions in the decomposition of water, thereby efficiently generating hydrogen and oxygen. [Solution] The solution includes a photocatalyst 2 and a co-catalyst 3 supported on the photocatalyst 2, wherein the co-catalyst 3 includes a first co-catalyst 31 and a second co-catalyst 32, the first co-catalyst 31 having at least one of the elements from groups 3 to 7, and the second co-catalyst 32 having at least one of the elements from groups 8 to 11, and the photocatalyst 2 contains 16 at% or more of titanium, and the highly active catalyst particles decompose water to produce hydrogen and oxygen when irradiated with light.

Description

[Technical Field]

[0001] This invention relates to catalyst particles that decompose water molecules to produce hydrogen and oxygen when irradiated with light, and to a method for producing such catalyst particles. [Background technology]

[0002] Patent Document 1 discloses a photocatalytic laminate having a photocatalytic particle layer in which multiple hydrogen-generating photocatalytic particles and multiple oxygen-generating photocatalytic particles are dispersed amongst themselves. However, this method required synthesizing multiple different photocatalysts and dispersing them. Furthermore, despite using multiple photocatalysts, they were dispersed and did not act synergistically. [Prior art document] [Patent] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-059920 [Overview of the project] [Means for solving the problem]

[0003] In a first embodiment of the present invention, catalyst particles are provided that decompose water molecules upon irradiation with light to produce hydrogen and oxygen, wherein the catalyst particles comprise a photocatalyst and a co-catalyst supported on the photocatalyst, the co-catalyst comprises a first co-catalyst and a second co-catalyst, and the first co-catalyst comprises at least one of the elements of Groups 3 to 7.

[0004] A second embodiment of the present invention provides a method for producing catalyst particles according to the first embodiment, comprising the step of supporting the first co-catalyst and the second co-catalyst on the photocatalyst, wherein the supporting step is one of the following: a step of supporting both the first co-catalyst and the second co-catalyst on the photocatalyst by photodeposition, a step of supporting both the first co-catalyst and the second co-catalyst on the photocatalyst by impregnation, or a step of supporting the first co-catalyst and the second co-catalyst individually on the photocatalyst by photodeposition.

[0005] It should be noted that the above summary of the invention does not enumerate all of its features. Furthermore, subcombinations of these features may also constitute an invention. [Brief explanation of the drawing]

[0006] [Figure 1] The schematic structure of the catalyst particles is shown below. [Figure 2A] The distribution of the first and second co-catalysts on photocatalyst 2 is schematically shown. [Figure 2B] This shows the distribution of the first and second co-catalysts, supported by the SPD method, on the photocatalyst. [Figure 2C] This shows the distribution of the first and second co-catalysts, supported by the PD method, on the photocatalyst. [Figure 3] This paper describes a method for producing catalyst particles by supporting a co-catalyst on a photocatalyst using the SPD method. [Figure 4] The results of water splitting tests using catalyst particles with molybdenum and nickel supported on calcium titanium oxide (CTO), catalyst particles consisting of CTO alone, catalyst particles consisting of nickel oxide alone, catalyst particles consisting of molybdenum oxide alone, and catalyst particles in which nickel oxide and molybdenum oxide were simply mixed with CTO are shown. [Figure 5] The results of water splitting tests using catalyst particles in which two types of co-catalysts were supported on a photocatalyst by the SPD method, and catalyst particles in which a noble metal was supported as a co-catalyst on a photocatalyst are shown. [Figure 6] The results of water splitting tests using catalyst particles with nickel nitrate as a co-catalyst, catalyst particles with sodium molybdate as a co-catalyst, and catalyst particles with nickel nitrate and sodium molybdate as co-catalysts are shown. [Figure 7] The results of water splitting tests using catalyst particles with different methods of supporting the first and second co-catalysts on the photocatalyst are shown. [Figure 8] The results of water splitting tests using catalyst particles with varying amounts of the first co-catalyst are shown. [Figure 9] The results of water splitting tests using catalyst particles with varying amounts of the second co-catalyst are shown. [Figure 10] The results of water splitting tests using catalyst particles with varying composition ratios of the first and second co-catalysts are shown. [Modes for carrying out the invention]

[0007] The present invention will be described below through embodiments of the invention, but these embodiments are not intended to limit the invention as defined in the claims. Furthermore, not all combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0008] Figure 1 shows a schematic diagram of the catalyst particle structure. Catalyst particle 1 comprises a photocatalyst 2 and a co-catalyst 3 supported on the photocatalyst 2. When irradiated with light, it decomposes water molecules to produce hydrogen and oxygen.

[0009] Photocatalyst 2 is a particle that, when irradiated with light, is excited by the energy of the light (photoexcitation), causing electrons to transition from the valence band to the conduction band. After the electron transition, holes are created in the valence band, and through a redox reaction, water molecules are decomposed to produce hydrogen (hydrogen molecules) and oxygen (oxygen molecules). The particles of photocatalyst 2 are polyhedra that reflect the crystal structure of the substance contained in the particle, and have oxidation faces and reduction faces. The oxidation faces are facets that promote oxidation reactions. The reduction faces are facets that promote reduction reactions. Photocatalyst 2 preferably contains a substance with a titanium content of 16 at% or more, more preferably 18 at% or more, and even more preferably 20 at% or more. Such substances include titanium dioxide (TiO2), fluoride titanate (TiOF2), barium titanium oxide (BaTiO3), calcium titanium oxide (CaTiO3), strontium titanium oxide (SrTiO3), and potassium titanium oxide (K2Ti). n O 2n+1 ), sodium titanium oxide (Na2Ti n O 2n+1) Substances such as lead titanate (PbTiO3) and lanthanum titanate (La2Ti2O7) can be mentioned. By using a substance containing 16 at% or more of titanium, which is known to be chemically stable, as the photocatalyst 2, high durability against corrosion and aging can be achieved.

[0010] Among substances containing 16 at% or more of titanium, the photocatalyst 2 more preferably contains titanates such as barium titanate (BaTiO3), calcium titanate (CaTiO3), strontium titanate (SrTiO3), potassium titanate (K2TiO3), sodium titanate (Na2TiO3), lead titanate (PbTiO3), and lanthanum titanate (La2Ti2O7).

[0011] Among substances containing 16 at% or more of titanium, the photocatalyst 2 more preferably contains substances having a perovskite-type crystal structure such as barium titanate (BaTiO3), calcium titanate (CaTiO3), strontium titanate (SrTiO3), and lead titanate (PbTiO3). The perovskite-type crystal structure is represented by the general formula ABX3. Since A, B, and X are regularly arranged, there are few crystal defects, and the band gap tends to be larger than that of photocatalysts such as titanium dioxide. A represents cations such as calcium (Ca), strontium (Sr), and barium (Ba), B represents cations smaller than A such as titanium (Ti), manganese (Mn), and iron (Fe), and X represents anions such as oxygen (O), fluorine (F), and chlorine (Cl). By using the photocatalyst 2 having a perovskite-type crystal structure with few crystal defects and an appropriate band gap, the recombination of carriers can be suppressed and the redox reaction can be promoted. Also, the heat resistance and durability can be improved.

[0012] In the photocatalyst 2, the valence band is an allowed band (band) that is completely filled with electrons at absolute zero. The conduction band is a band that exists separated from the valence band by a forbidden band (band gap). When light having energy corresponding to or higher than the band gap energy is irradiated, electrons in the valence band are excited and transition to the conduction band, and holes are generated in the valence band after the electrons have transitioned. Thereby, electron-hole pairs are generated.

[0013] When the energy level at the apex of the valence band of the photocatalyst 2 is expressed by the standard hydrogen electrode potential, it is higher than +1.23 V, which is the oxygen generation potential (oxidation potential), and the energy level at the bottom of the conduction band is lower than 0 V, which is the hydrogen generation potential (reduction potential). That is, the band gap of the photocatalyst 2 is 1.23 eV or more.

[0014] The light to be irradiated is selected according to the band gap of the photocatalyst 2. For example, in the case of rutile-type titanium dioxide, since the band gap energy is about 3.0 eV (corresponding to a light wavelength of about 414 nm), electrons are photoexcited by irradiation with visible light or ultraviolet light having a wavelength of about 414 nm or less, and electron-hole pairs are generated. In the case of calcium titanate, since the band gap energy is about 3.4 eV (corresponding to a light wavelength of about 365 nm), electrons are photoexcited by irradiation with ultraviolet light having a wavelength of about 365 nm or less, and electron-hole pairs are generated. The light to be irradiated needs to include light having a wavelength that satisfies these conditions, and light that does not meet the conditions may be irradiated simultaneously.

[0015] The hole (h + )夺取水分子(H2O)中的电子(氧化反应),生成氧气(O2)气体和质子(H + )。<> 2H2O + 4h + → O2 + 4H +

[0016] The excited electrons (e - ) in the conduction band, as shown in the following chemical formula, protons (H +It reacts with (reduction reaction) to produce hydrogen (H2) gas. 2H + +2e - →H2

[0017] The co-catalyst 3 includes an oxidation co-catalyst 31 and a reduction co-catalyst 32, which trap holes and electrons respectively on the photocatalyst 2 to promote the oxidation-reduction reaction. For example, if a high-performance co-catalyst such as rhodium (Rh) is used alone, it may promote not only the decomposition reaction of water but also the formation reaction, potentially causing the decomposition reaction to stall. To address this problem, by supporting the oxidation co-catalyst 31 and the reduction co-catalyst 32 on the photocatalyst 2, both the oxidation and reduction reactions can be promoted, thereby improving the activity of the photocatalyst 2.

[0018] The first co-catalyst 301 is supported on both the oxidation and reduction surfaces of the photocatalyst 2. On the oxidation surface, it forms an oxidation co-catalyst 31, and on the reduction surface, it forms a reduction co-catalyst 32 together with the second co-catalyst 302. The first co-catalyst 301 assists in the efficient consumption of holes on the oxidation surface and exhibits high co-catalyst activity on the reduction surface by being present simultaneously with the second co-catalyst 302. The first co-catalyst contains at least one of the group 3 to 7 elements, preferably a group 5 or 6 element, and more preferably vanadium (V), molybdenum (Mo), or tungsten (W). Among these, molybdenum (Mo) is particularly preferred. The content of any of the group 3 to 7 elements is preferably 0.01 wt% or more by weight relative to the catalyst particle 1, more preferably 0.1 wt% or more, and even more preferably 0.2 wt% or more. The oxidation co-catalyst 31 traps holes on the photocatalyst 2 and promotes the oxidation reaction. The first co-catalyst 301 is, for example, vanadium oxide (V2O5), molybdenum oxide (MoO5) x )(x≦3), or tungsten oxide (WO3) may be present. The elements contained in the first co-catalyst 301 can take on multiple oxidation states and can exist in different oxidation states on the oxidation surface and the reduction surface, respectively. Examples of materials (precursors) for the first co-catalyst 31 include sodium molybdate (Na2MoO4), ammonium molybdate ((NH4)6Mo7O 24Examples include 4H2O, potassium molybdate (K2MoO4), molybdic acid (H2MoO4), sodium tungstate (Na2WO4), and ammonium vanadate (Na3VO4).

[0019] The group 3-7 elements contained in the first co-catalyst 301 need to be stable at their highest oxidation state and supported on the oxidation surface in order to exert their effect as an oxidation co-catalyst 31 that assists in the efficient consumption of holes. Furthermore, the group 3-7 elements contained in the first co-catalyst 301 need to be stable at oxidation states lower than their highest oxidation state and supported on the reduction surface in order to exert their effect as a highly efficient reduction co-catalyst 32 when present simultaneously with the second co-catalyst 302. An example that satisfies these conditions is the group 6 element M, which exists stably as a hexavalent oxide MO3 on the oxidation surface and as a tetravalent oxide MO2 on the reduction surface.

[0020] The second co-catalyst 302 becomes the reduction co-catalyst 32. The reduction co-catalyst 32 is a co-catalyst that traps electrons on the photocatalyst 2 and promotes the reduction reaction, and preferably contains any of the group 8 to 11 elements, more preferably a group 10 element, and even more preferably nickel (Ni). The content of any of the group 8 to 11 elements is preferably 0.01 wt% or more by weight relative to the catalyst particle 1, and more preferably 0.1 wt% or more. The second co-catalyst 302 is, for example, nickel oxide (NiO x The catalyst may contain (x≦2), nickel phosphide (Ni2P), or nickel sulfide (NiS,Ni3S2). Examples of materials (precursors) for the second co-catalyst 302 include nickel nitrate (Ni(NO3)2), iron nitrate (Fe(NO3)3), copper nitrate (Cu(NO3)2), cobalt nitrate (Co(NO3)2), etc.

[0021] The second co-catalyst 302 is supported on the reducing surface and needs to work synergistically with the oxidizing co-catalyst 31 to promote hydrogen production. Because it is supported on the reducing surface, the second co-catalyst 302 (second co-catalyst species) needs to be more easily reduced than the first co-catalyst 301 (first co-catalyst species). In transition metals, the electronegativity increases as the group number increases, making it easier to capture electrons, and thus easier to reduce. For this reason, the second co-catalyst has one of the elements from groups 8 to 11, preferably a group 10 element, and more preferably Ni.

[0022] In particular, by including one of the group 3-7 elements in the first co-catalyst 301 and one of the group 8-11 elements in the second co-catalyst 302, the activity of the photocatalyst can be significantly improved compared to other combinations of oxidation co-catalysts and reduction co-catalysts. Here, the activity is further improved if the first co-catalyst 301 includes a group 5 or 6 element, further improved if it includes vanadium (V), molybdenum (Mo), or tungsten (W), and even further improved if it includes molybdenum (Mo). Furthermore, the activity is improved if the second co-catalyst 302 includes a group 10 element, and further improved if it includes nickel (Ni).

[0023] The weight ratio of the second co-catalyst 302 to the photocatalyst 2 is preferably equal to or greater than the weight ratio of the first co-catalyst 301 to the photocatalyst 2. By having a weight ratio of the second co-catalyst 302 to the photocatalyst 2 that is equal to or greater than the weight ratio of the first co-catalyst 301 to the photocatalyst 2, the oxidation-reduction reaction can be further promoted. The weight ratio of the second co-catalyst 302 to the photocatalyst 2 is preferably twice or more than the weight ratio of the first co-catalyst 301 to the photocatalyst 2, and more preferably three times or more.

[0024] The weight ratio of the first co-catalyst 301 to the photocatalyst 2 is not particularly limited, but is preferably 0.5 wt% or more and less than 3.0 wt%, and more preferably 0.5 to 2.0 wt%. By having the weight ratio of the first co-catalyst 301 to the photocatalyst 2 within this range, the oxidation-reduction reaction can be further promoted.

[0025] The weight ratio of the second co-catalyst 302 to the photocatalyst 2 may be 0.5 wt% or more, preferably 1.0 wt% or more, more preferably 2.0 wt% or more, and even more preferably 3.0 wt% or more. By having such a weight ratio of the second co-catalyst 302 to the photocatalyst 2, the oxidation-reduction reaction can be further promoted.

[0026] Figure 2A schematically shows the distribution of the first co-catalyst 301 and the second co-catalyst 302 on the photocatalyst 2. The photocatalyst 2 comprises an oxidation surface 310 on which the first co-catalyst 301 is supported (boundary indicated by a dashed line) and a reduction surface 320 on which the first co-catalyst 301 and the second co-catalyst 302 are supported (boundary indicated by a dotted line). In this way, it is preferable that a portion of the first co-catalyst 301 and the second co-catalyst 302 are localized on specific facets of the photocatalyst 2. By localizing the first co-catalyst 301, which is an oxidation co-catalyst, and the first co-catalyst 301 and the second co-catalyst 302, which are reduction co-catalysts, on specific facets of the photocatalyst 2 that become the oxidation surface and facets that become the reduction surface, respectively, the oxidation-reduction reaction can be promoted.

[0027] Furthermore, it is preferable that portions of the first co-catalyst 301 and the second co-catalyst 302, which are localized on different facets of the photocatalyst 2, overlap on the photocatalyst 2 to form a reduction surface 320. By overlapping portions of the first co-catalyst 301 and the second co-catalyst 302 on the photocatalyst 2, the functions of the first co-catalyst 301 and the second co-catalyst 302 can be coordinated to promote the oxidation-reduction reaction.

[0028] Catalyst particles 1 are produced by supporting co-catalysts 3 on a synthesized photocatalyst 2. Methods for supporting co-catalysts 3 on the photocatalyst 2 include photodeposition (SPD) and impregnation (IMP) methods, which precipitate both the first co-catalyst 301 and the second co-catalyst 302, and photodeposition (PD) methods, which precipitate the first co-catalyst 301 and the second co-catalyst 302 individually. Among these, the SPD method is preferred from the viewpoint of promoting the redox reaction. The SPD method promotes the formation of oxidation co-catalysts and reduction co-catalysts on the oxidation surface 310 and the reduction surface 320.

[0029] Figure 2B shows the distribution of the first co-catalyst 301 and the second co-catalyst 302, supported by the SPD method, on photocatalyst 2. The center image is an energy-dispersive X-ray spectroscopy (EDS) mapping image showing the distribution of Lα1X rays of molybdenum (Mo), the bottom image is an EDS mapping image showing the distribution of Kα1X rays of nickel (Ni), and the top image is an image of the distribution of molybdenum and nickel superimposed on a scanning electron microscope (SEM) image of the catalyst particles. The area enclosed by the dashed line is the area where molybdenum has precipitated, and the area enclosed by the dotted line is the area where nickel has precipitated. The area where molybdenum has precipitated is the oxide surface 310, and the area where nickel, or both molybdenum and nickel, have precipitated is the reduction surface 320. According to these images, by supporting the catalyst particles by the SPD method, molybdenum and nickel precipitate on the facets of the catalyst particles, with molybdenum added to the oxide surface 310 and the reduction surface 320, and nickel added to the reduction surface 320. In other words, molybdenum and nickel are superimposed on the reduction surface 320.

[0030] Figure 2C shows the distribution of the first co-catalyst 301 and the second co-catalyst 302, supported by the PD method, on photocatalyst 2. The center image is an EDS mapping image showing the distribution of Lα1X rays of molybdenum (Mo), the bottom image is an EDS mapping image showing the distribution of Kα1X rays of nickel (Ni), and the top image is a SEM image of the catalyst particles. According to these images, the nickel supported by the PD method is segregated but not deposited on specific facets of the catalyst particles, while the molybdenum is deposited evenly across the surface of the catalyst particles.

[0031] Figure 3 shows a method for producing catalyst particles 1 by supporting a co-catalyst 3 on a photocatalyst 2 using the SPD method.

[0032] In step S11, photocatalyst 2 is synthesized using a flux method or the like.

[0033] In step S12, in the dark, both the aqueous solution of the material for the first co-catalyst 301 and the aqueous solution of the material for the second co-catalyst 302 are added to the photocatalyst 2.

[0034] In step S13, in the dark, an inert gas, such as a noble gas, is continuously supplied to the photocatalyst 2 to which aqueous solutions of the materials for the first co-catalyst 301 and the second co-catalyst 302 have been added, and air (oxygen) is purged.

[0035] In step S14, ultraviolet light is irradiated from a mercury (Hg) lamp or the like in the dark to excite the photocatalyst 2, and the holes and excited electrons generated by the transition of electrons from the valence band of the photocatalyst 2 to the conduction band oxidize the material of the first co-catalyst 301 and reduce the material of the second co-catalyst 302, causing the oxidation co-catalyst 31 and reduction co-catalyst 32 to be photodeposited together on the surface of the photocatalyst 2. By producing catalyst particles 1 in this manner, the formation of an oxidation surface 310 on the photocatalyst 2 where the oxidation co-catalyst is present and a reduction surface 320 where the reduction co-catalyst is present can be promoted. [Examples]

[0036] (Example 1) (Synthesis of photocatalysts) Calcium carbonate (CaCO3) and titanium dioxide (TiO2) were added to twice the volume of ethanol in a molar ratio of 1:1 and mixed. Sodium chloride (NaCl) was then added as a flux and mixed for 5 minutes. The mixture was calcined at 1100°C (heating rate 200°C / h) for 10 hours. After that, it was cooled to 500°C at a rate of 100°C / h to obtain calcium titanium oxide (CaTiO3), which is a photocatalyst. CaTiO3 will hereafter be referred to as CTO. (Supporting of co-catalysts) The co-catalysts were supported on CTO by the SPD method as follows. First, in the dark, 1.0 wt% of sodium molybdate (Na2MoO4), the material for the first co-catalyst, was added to the CTO as an aqueous solution. Then, nickel nitrate (Ni(NO3)2), the material for the second co-catalyst, was added as an aqueous solution so that the nickel (Ni) content was 1.0 wt% relative to the CTO. After the addition, argon (Ar) gas was supplied at 30 mL / min for 1 hour in the dark, and the air (oxygen) was purged. After purging, the co-catalysts were supported on the photocatalyst by irradiating with ultraviolet light from a mercury lamp (100 W) for 3 hours, thereby obtaining catalyst particles. (Water splitting test) 0.3 g of catalyst particles were suspended in 0.36 L of water. In the dark, air (oxygen) was purged from the suspension over 1 hour while supplying argon gas at 30 mL / min. The components of the generated gas were analyzed using GC-TCD (Gas Chromatography - Thermal Conductivity Detector) while irradiating with a mercury lamp (100 W).

[0037] (Example 2) The water splitting test was performed in the same manner as in Example 1, except that 0.5 wt% sodium molybdate was added to the CTO.

[0038] (Example 3) The water splitting test was performed in the same manner as in Example 1, except that 2.0 wt% sodium molybdate was added to the CTO.

[0039] (Example 4) The water splitting test was performed in the same manner as in Example 1, except that 3.0 wt% sodium molybdate was added to the CTO.

[0040] (Example 5) The water splitting test was performed in the same manner as in Example 1, except that nickel nitrate equivalent to 0.5 wt% nickel was added to CTO.

[0041] (Example 6) The water splitting test was performed in the same manner as in Example 1, except that nickel nitrate equivalent to 2.0 wt% nickel was added to CTO.

[0042] (Example 7) The water splitting test was performed in the same manner as in Example 1, except that nickel nitrate equivalent to 3.0 wt% nickel was added to CTO.

[0043] (Example 8) The water splitting test was performed in the same manner as in Example 1, except that nickel nitrate equivalent to 4.0 wt% nickel was added to CTO.

[0044] (Example 9) The water splitting test was performed in the same manner as in Example 1, except that 0.5 wt% sodium molybdate and nickel nitrate equivalent to 3.0 wt% nickel were added to CTO.

[0045] (Example 10) The water splitting test was performed in the same manner as in Example 1, except that silver nitrate (AgNO3) was added instead of nickel nitrate.

[0046] (Example 11) The water splitting test was carried out in the same manner as in Example 1, except that cobalt nitrate (Co(NO3)2) was added instead of nickel nitrate.

[0047] (Example 12) A water splitting test was performed in the same manner as in Example 1, except that 1.0 wt% sodium tungstate (Na2WO4) was added to CTO instead of sodium molybdate (Na2MoO4).

[0048] (Example 13) A water splitting test was conducted in the same manner as in Example 1, except that a co-catalyst was supported using the impregnation method (IMP method), that is, 3 wt% nickel nitrate (Ni(NO3)2) and 1 wt% sodium molybdate (Na2MoO4) were added to CTO in aqueous solution, the water was evaporated, and the catalyst particles were obtained by calcining at 400°C for 2 hours.

[0049] (Example 14) A water splitting test was conducted in the same manner as in Example 1, except that a co-catalyst was supported using the impregnation method (IMP method), that is, 1 wt% nickel nitrate (Ni(NO3)2) and 1 wt% sodium molybdate (Na2MoO4) were added to CTO in aqueous solution, the water was evaporated, and the catalyst particles were obtained by calcining at 500°C for 2 hours.

[0050] (Example 15) The water splitting test was conducted in the same manner as in Example 1, except that the first and second co-catalysts were not both supported in a single loading treatment, but rather a loading treatment using nickel nitrate (Ni(NO3)2) was performed first, followed by a loading treatment using sodium molybdate (Na2MoO4).

[0051] (Example 16) The water splitting test was conducted in the same manner as in Example 1, except that the first and second co-catalysts were not both supported in a single loading treatment, but rather a loading treatment using sodium molybdate (Na2MoO4) was performed first, followed by a loading treatment using nickel nitrate (Ni(NO3)2).

[0052] (Comparative Example 1) The water splitting test was conducted in the same manner as in Example 1, except that a co-catalyst was not supported.

[0053] (Comparative Example 2) The water splitting test was performed in the same manner as in Example 1, except that nickel nitrate equivalent to 1.0 wt% nickel was added to CTO instead of sodium molybdate (Na2MoO4), and cobalt nitrate (Co(NO3)2) was added instead of nickel nitrate.

[0054] (Comparative Example 3) A water splitting test was conducted in the same manner as in Example 1, except that 0.003 g of molybdenum oxide (MoO3) catalyst particles were used instead of CTO, and no co-catalyst was supported on them. 0.003 g corresponds to the amount of co-catalyst used in Example 1.

[0055] (Comparative Example 4) A water splitting test was conducted in the same manner as in Example 1, except that 0.003 g of elemental nickel oxide (NiO) catalyst particles were used instead of CTO, and no co-catalyst was supported on them. 0.003 g corresponds to the amount of co-catalyst used in Example 1.

[0056] (Comparative Example 5) The water splitting test was conducted in the same manner as in Example 1, except that molybdenum oxide (MoO3) was used instead of sodium molybdate (Na2MoO4), nickel oxide (NiO) was used instead of nickel nitrate (Ni(NO3)2), and these were simply mixed with CTO without any treatment of supporting them on the CTO.

[0057] (Comparative Example 6) The water splitting test was conducted in the same manner as in Example 1, except that sodium molybdate (Na2MoO4) was not used.

[0058] (Comparative Example 7) The water splitting test was carried out in the same manner as in Example 1, except that nickel nitrate (Ni(NO3)2) was not used.

[0059] (Comparative Example 8) The water splitting test was performed in the same manner as in Example 1, except that 0.01 wt% of rhodium (Rh) relative to CTO was used as a co-catalyst.

[0060] (Comparative Example 9) The water splitting test was performed in the same manner as in Example 1, except that 0.01 wt% of platinum (Pt) relative to CTO was used as a co-catalyst.

[0061] Table 1 shows the results of the water splitting tests for Examples 1-16 and Comparative Examples 1-9. [Table 1]

[0062] (Examination of the effects of support) Figure 4 shows the results of water splitting tests using catalyst particles with molybdenum and nickel supported on CTO (actual 1), catalyst particles consisting of CTO alone (ratio 1), catalyst particles consisting of molybdenum oxide (MoO3) alone (ratio 3), catalyst particles consisting of nickel oxide (NiO) alone (ratio 4), and catalyst particles in which NiO and MoO3 were simply mixed with CTO (ratio 5). The vertical axis represents the amount of substance produced per hour (μ mol h). -1The graph shows the hydrogen production rate in each example, and the oxygen production rate in the left bar. Note that the hydrogen production rate is approximately twice that of the oxygen production rate. It can be seen that the activity of Example 1, which consists of catalyst particles supported with one of the group 3-7 elements and one of the group 8-11 elements on the photocatalyst, is more than 10 times higher than that of the other examples.

[0063] Comparative Example 1, which used catalyst particles made solely of CTO, exhibited the lowest activity. In comparison, Example 1 showed a significant improvement in the photocatalytic performance of CTO due to the co-catalyst. Comparative Examples 3 and 4, which used catalyst particles equivalent to the co-catalyst amounts in Example 1 (MoO3 and NiO respectively), showed only slight activity compared to Example 1. Comparative Example 5, in which NiO and MoO3 were simply mixed with CTO, showed lower activity than Comparative Example 10, which used NiO alone. This decrease is thought to be due to the CTO blocking the irradiation light, thereby suppressing the photocatalytic activity of the NiO support. As can be seen from the above, any of the group 3-7 elements and any of the group 8-11 elements exhibit high activity when supported on CTO as co-catalysts.

[0064] (Consideration of combinations of co-catalysts) Figure 5 shows the results of water splitting tests using catalyst particles with two types of co-catalysts supported on the photocatalyst by the SPD method (actual values ​​1, 10-12, ratio 2), catalyst particles consisting of CTO alone (ratio 1), and catalyst particles with noble metals supported as co-catalysts on the photocatalyst (ratios 8, 9). The vertical axis represents the amount of substance produced per hour (μ mol h). -1The graph shows the hydrogen production rate, with the left bar representing hydrogen production and the right bar representing oxygen production. Examples 1 and 10-12, which are catalyst particles supported with any of the group 3-7 elements and any of the group 8-11 elements on a photocatalyst, showed significantly higher water-splitting performance than Comparative Example 1, which is a catalyst particle made of CTO alone. Furthermore, they were superior in hydrogen production to Comparative Example 2, which has two co-catalysts but does not contain any of the group 3-7 elements. Among Examples 1 and 10-12, Example 1, which contains molybdenum as the first co-catalyst and nickel as the second co-catalyst, showed particularly high activity, more than 10 times higher than Comparative Example 2. Moreover, Example 1 showed twice the activity compared to Comparative Examples 8 and 9, which have precious metal co-catalysts known to be expensive but high-performance. Example 12, which contains group 6 and group 10 elements, also showed excellent activity comparable to that of precious metal co-catalysts. From the above, it can be concluded that by including one of the group 3-7 elements as the first co-catalyst and a group 8-11 element as the second co-catalyst, the activity of the photocatalyst can be improved compared to other combinations of oxidation and reduction co-catalysts. The combination of group 6 and group 10 elements significantly improves activity, and the combination of molybdenum and nickel in particular dramatically improves activity.

[0065] (Investigation of the effects of supporting the first and second co-catalysts) Figure 6 shows the results of water splitting tests using catalyst particles with nickel nitrate and sodium molybdate as co-catalysts (actual 1), catalyst particles with pure nickel nitrate as a co-catalyst (ratio 6), and catalyst particles with pure sodium molybdate as a co-catalyst (ratio 7). The vertical axis represents the amount of substance produced per hour (μ mol h). -1The graph shows the hydrogen production rate, with the left bar representing hydrogen production and the right bar representing oxygen production. The hydrogen production capacity of Example 1, which used nickel nitrate and sodium molybdate as co-catalyst materials, was more than 15 times greater than that of Comparative Example 6, which used nickel nitrate alone as a co-catalyst material, and Comparative Example 7, which used sodium molybdate alone as a co-catalyst material. The combined hydrogen production amounts of Comparative Examples 6 and 7 were nowhere near the amount of hydrogen production in Example 1. This indicates that including both nickel and molybdenum in the co-catalyst significantly improves the photocatalytic activity compared to catalyst particles containing only either nickel or molybdenum.

[0066] (Consideration of carrying method) Figure 7 shows the results of water splitting tests using catalyst particles (actual 1, actual 13-16) with different methods of supporting the first and second co-catalysts on the photocatalyst. The vertical axis represents the amount of substance produced per hour (μ mol h). -1 The graph shows the hydrogen production rate in each example, with the bar on the left representing the hydrogen production rate and the bar on the right representing the oxygen production rate. Example 1, in which the molybdenum compound and nickel compound were supported together by the SPD method, showed approximately three times higher activity than Examples 13 and 14, in which they were supported using the IMP method, and Examples 15 and 16, in which the molybdenum compound and nickel compound were sequentially supported by the PD method. From the above, it can be concluded that the activity of the photocatalyst can be further improved by supporting the first and second co-catalysts together by the SPD method.

[0067] (Investigation of the amount of the first co-catalyst supported) Figure 8 shows the results of water splitting tests using catalyst particles (actuals 2, 1, 3, 4) with varying amounts of the first co-catalyst. The vertical axis represents the amount of substance produced per hour (μ mol h). -1The graph shows the hydrogen production rate in each example, with the left bar representing the hydrogen production rate and the right bar representing the oxygen production rate. The hydrogen and oxygen production rates in Examples 2, 1, 3, and 4 did not vary significantly, indicating that the amount of Mo, the first co-catalyst, supported does not significantly affect the activity of the catalyst particles. In Example 4, the hydrogen and oxygen production rates decreased slightly, suggesting that the amount of the first co-catalyst supported is preferably 0.5 wt% or more and less than 3.0 wt%, and more preferably 0.5 wt% or more and 2.0 wt%, relative to the amount of photocatalyst 2.

[0068] (Investigation of the amount of the second co-catalyst supported) Figure 9 shows the results of water splitting tests using catalyst particles (actuals 5, 1, 6, 7, 8) with varying amounts of the second co-catalyst. The vertical axis represents the amount of substance produced per hour (μ mol h). -1 The graph shows the amount of hydrogen produced in each example, with the bar on the left representing the amount of oxygen produced. Examples 5, 1, 6, 7, and 8 show that increasing the amount of Ni, the second co-catalyst, has a significant effect on the activity of the catalyst particles. The activation due to the increase in Ni is particularly pronounced in Example 6, and is maximized in Example 7, with only a slight difference between Examples 7 and 8. Therefore, the amount of the second co-catalyst may be 0.5 wt% or more relative to the amount of photocatalyst 2, preferably 1.0 wt% or more, more preferably 2.0 wt% or more, and even more preferably 3.0 wt% or less.

[0069] (Investigation of the composition ratio of the first and second auxiliary catalysts) Figure 10 shows the results of water splitting tests using catalyst particles (actual values ​​5, 1, 6, 7, 8, 9) with varying composition ratios of the first and second co-catalysts. The vertical axis represents the amount of substance produced per hour (μ mol h). -1The graph shows the amount of hydrogen produced in each example, with the bar on the left representing the amount of hydrogen produced and the bar on the right representing the amount of oxygen produced. A comparison of Example 5 with Examples 1, 6, 7, 8, and 9 shows that the amount of hydrogen and oxygen produced increases when the weight ratio of the second co-catalyst, Ni, to the photocatalyst is greater than or equal to the weight ratio of the first co-catalyst, Mo, to the photocatalyst. Activation is significant in Example 6 and maximum in Example 7, with only slight differences between Examples 7-9. Therefore, the weight ratio of the first co-catalyst to photocatalyst 2 is preferably 2 times or more, and more preferably 3 times or more, than the weight ratio of the first co-catalyst to photocatalyst 2.

[0070] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0071] It should be noted that the execution order of operations, procedures, steps, and stages in the apparatus, systems, programs, and methods shown in the claims, specifications, and drawings is not explicitly stated as "before," "prior to," etc., and that these can be implemented in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," "next," etc. for convenience, it does not mean that it is essential to perform the operations in that order. [Explanation of Symbols]

[0072] 1... Catalyst particles, 2... Photocatalyst, 3... Co-catalyst, 31... Oxidation co-catalyst, 32... Reduction co-catalyst, 301... First co-catalyst, 302... Second co-catalyst, 310... Oxidation surface, 320... Reduction surface.

Claims

1. Catalyst particles that decompose water molecules upon irradiation with light, producing hydrogen and oxygen, The catalyst particles include a photocatalyst and a co-catalyst supported on the photocatalyst. The aforementioned co-catalyst includes a first co-catalyst and a second co-catalyst. The first co-catalyst is a catalyst particle having at least one of the elements from groups 3 to 7.

2. The catalyst particle according to claim 1, wherein the first co-catalyst particularly has a group 5 or 6 element.

3. The catalyst particle according to claim 1, wherein the first co-catalyst particularly comprises vanadium (V), molybdenum (Mo), or tungsten (W).

4. The catalyst particle according to claim 1, wherein the first co-catalyst particularly contains molybdenum (Mo).

5. The catalyst particle according to claim 1, wherein the second co-catalyst has at least one of the elements from groups 8 to 11.

6. The catalyst particle according to claim 1, wherein the second co-catalyst particularly has a group 10 element.

7. The catalyst particle according to claim 1, wherein the second co-catalyst particularly contains Ni.

8. The catalyst particles according to claim 1, wherein the photocatalyst contains 16 at% or more of titanium.

9. The catalyst particles according to claim 8, wherein the photocatalyst is a titanate.

10. The catalyst particles according to claim 8, wherein the photocatalyst has a perovskite-type crystal structure.

11. The catalyst particle according to claim 1, wherein the weight ratio of the second co-catalyst to the photocatalyst is equal to or greater than the weight ratio of the first co-catalyst to the photocatalyst.

12. The catalyst particle according to claim 1, wherein a portion of the first co-catalyst and a portion of the second co-catalyst are localized on different facets of the photocatalyst, respectively.

13. The catalyst particle according to claim 12, wherein a portion of the first co-catalyst and the second co-catalyst overlap on the photocatalyst.

14. A method for producing catalyst particles according to any one of claims 1 to 13, The process includes the step of supporting the first co-catalyst and the second co-catalyst on the photocatalyst, A method for producing catalyst particles, wherein the supporting step is one of the following: a step of supporting both the first co-catalyst and the second co-catalyst on the photocatalyst by photodeposition; a step of supporting both the first co-catalyst and the second co-catalyst on the photocatalyst by impregnation; or a step of supporting the first co-catalyst and the second co-catalyst individually on the photocatalyst by photodeposition.

15. The method for producing catalyst particles according to claim 14, wherein the supporting step comprises supporting both the first co-catalyst and the second co-catalyst on the photocatalyst by photodeposition.

Images