Electric field catalyst and gas reforming method using the same

Abstract

Provided is an electrocatalyst having high catalytic activity. An electrocatalyst composed of Ni, Y, Zr, and O, the electrocatalyst having a composition such that x and y in NixYyZr1–x–yO2 satisfy formulas (1) and (2), the crystal structure of the electrocatalyst being free of monoclinic crystals, the electrocatalyst containing metallic Ni and hydroxide Ni as the Ni, and the metallic Ni content A (at%) and the hydroxide Ni content B (at%) being such that the content A satisfies formula (3) and the ratio α of the content B to the content A satisfies formula (4), where the total amount of Ni is designated as 100 at%.　Formula (1): 0.10≤x≤0.45; Formula (2): 0.05≤y≤0.30; Formula (3): A≥30 at%; Formula (4): 0.15≤α≤0.63

Description

[Technical Field]

[0001] The present invention relates to an electric field catalyst and a method for reforming gas using the same. [Background technology]

[0002] Conventionally, as a hydrocarbon reforming catalyst, a hydrocarbon reforming catalyst containing an oxide support, and Ni, a metal oxide, and an alkali metal or an alkaline earth metal supported on the oxide support has been known (for example, Patent Document 1). In recent years, electrocatalysts, which are used by applying an electric field, have become known (for example, Patent Documents 2 and 3). Electrocatalysts are attracting attention as a new type of catalyst because, by applying electrical energy to them, they can cause catalytic reactions to occur at lower temperatures than conventional catalysts.

[0003] Patent Document 2 describes that the electric field catalyst may contain at least one component selected from the group consisting of Pt, Rh, Pd, Ru, Ir, Ni, Co, CeO2, CoO, Co3O4, CuO, ZnO, Mn3O4, Bi2O3, SnO2, Fe2O3, Fe3O4, TiO2, Nb2O5, MgO, ZrO2, La2O3, Sm2O3, Al2O3, SiO2, and CaO.

[0004] Patent Document 3 lists carriers for electric field catalysts containing at least one of cerium oxide (ceria), zirconium oxide (zirconia), and bismuth oxide. Also, examples of active metals include rhodium, ruthenium, platinum, iridium, palladium, and nickel, and it is stated that rhodium and ruthenium are particularly suitable for use as electric field catalysts in steam reforming reactions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-155234 [Patent Document 2] Patent No. 5252479 specification [Patent Document 3] Patent No. 6444289 specification Summary of the Invention [Problem to be solved by the invention]

[0006] Since electrocatalysis is a new technology, it cannot be said that the composition, structure, etc. have been fully optimized, and there is still room for improvement. Therefore, an object of the present invention is to provide an electric field catalyst having higher catalytic activity. [Means for solving the problem]

[0007] According to one aspect of the present invention, An electric field catalyst consisting of Ni, Y, Zr and O, Its composition: Ni x Y y Zr 1-x-y x and y of O2 satisfy the following formula (1) and formula (2), respectively: The crystal structure does not include monoclinic crystals, The Ni includes Ni in a metallic state and Ni in a hydroxide state, When the total amount of Ni is taken as 100 atomic %, the content A (atomic %) of Ni in the metallic state and the content B (atomic %) of Ni in the hydroxide state are expressed as follows: The content A satisfies the following formula (3), There is provided an electric field catalyst in which the ratio α of the content B to the content A satisfies the following formula (4). 0.10≦x≦0.45 (1) 0.05≦y≦0.30 (2) A≧30 atomic% (3) 0.15≦α≦0.63 (4)

[0008] According to another aspect of the present invention, A method for reforming gas using an electric field catalyst, comprising: Step 1) providing the electric field catalyst, wherein: The electrocatalyst consists of Ni, Y, Zr and O, and its composition is Ni x Y y Zr 1-x-y x and y of O2 satisfy the following formula (1) and formula (2), respectively: The crystal structure does not include monoclinic crystals, The Ni includes Ni in a metallic state and Ni in a hydroxide state, When the total amount of Ni is taken as 100 atomic %, the content A (atomic %) of Ni in the metallic state and the content B (atomic %) of Ni in the hydroxide state are expressed as follows: The content A satisfies the following formula (3), The ratio α of the content B to the content A satisfies the following formula (4); and Step 2) heating the electric field catalyst to a reaction temperature of 423 K or more and 673 K or less and applying an electric field to reform the gas. 0.10≦x≦0.45 (1) 0.05≦y≦0.30 (2) A≧30 atomic% (3) 0.15≦α≦0.63 (4) [Effects of the Invention]

[0009] According to the present invention, an electric field catalyst having higher catalytic activity can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] Figure 1(a) is the XRD pattern of ZrO2 containing Y, and Figures 1(b) to (d) are graphs showing the peak positions of the tetragonal, cubic, and monoclinic crystals, respectively. [Figure 2] FIG. 2 is a graph showing the relationship between power efficiency and ratio α. [Figure 3] Figure 3 shows the Ni2p photoelectron spectra of metallic Ni, Ni hydroxide, and Ni oxide. [Figure 4]Figure 4 shows the fitting results of the Ni2p photoelectron spectrum obtained by XPS measurement of the catalyst powder. [Figure 5] FIG. 5 is a schematic diagram showing an example of a reaction apparatus used in a gas reforming method using an electric field catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0011] The inventors conducted extensive research to improve catalytic activity, focusing on an electric field catalyst using Ni as the active metal and yttria-stabilized zirconia as the support. As a result, they discovered for the first time that catalytic activity can be improved by ensuring that the support does not contain monoclinic crystals, that the active metal Ni contains both metallic Ni and hydroxide Ni, and that the ratio of the content of hydroxide Ni to metallic Ni is controlled within a certain range, leading to the completion of the present invention.

[0012] An electric field catalyst according to an embodiment of the present invention will be described below.

[0013] [Embodiment 1] The electric field catalyst according to the first embodiment is composed of Ni, Y, Zr and O, and has a basic structure in which the active metal Ni is supported on an oxide support, yttria-stabilized zirconia (Zr, Y)O2. The composition of the electrocatalyst is the chemical formula Ni x Y y Zr 1-x-y It is expressed as O2, and x and y in the chemical formula satisfy the following formulas (1) and (2), respectively. 0.10≦x≦0.45 (1) 0.05≦y≦0.30 (2)

[0014] The reasons for specifying x and y are as follows: If x is less than 0.10, the Ni content is too low to induce a catalytic reaction, whereas if x exceeds 0.45, the tetragonal and cubic crystals of the zirconia support are not stabilized, resulting in the precipitation of monoclinic crystals. However, if there is too much Ni (for example, x is 0.6 or more), the electrocatalyst becomes a conductor, and electricity flows through the electrocatalyst. As a result, an electric field is not applied to the catalyst, which may reduce the power efficiency of the catalyst.

[0015] If y is less than 0.05, the Y content is low, the tetragonal and cubic crystals of the zirconia support are not stabilized, and monoclinic crystals are precipitated.If y exceeds 0.30, the content of metallic Ni decreases, making it difficult for the ratio α described below to satisfy formula (4).

[0016] The crystal structure of the electric field catalyst according to embodiment 1 (substantially the crystal structure of the oxide support) does not include monoclinic crystals, that is, the crystal structure is composed of only one or both of tetragonal and cubic crystals. If monoclinic crystals are contained, the catalytic activity of the electric field catalyst will decrease, so by not containing monoclinic crystals, the catalytic activity of the electric field catalyst can be increased. The elimination of monoclinic crystals can be achieved by controlling the Ni content and the Y content within appropriate ranges. In other words, by adjusting the composition so that the Ni content satisfies formula (1) and the Y content satisfies formula (2), it is possible to form an electric field catalyst that does not contain monoclinic crystals and is composed only of tetragonal and / or cubic crystals.

[0017] The crystal structure is identified by powder X-ray diffraction. Figure 1 shows the XRD pattern (Figure 1(a)) of a typical Y-containing ZrO2, along with the peak positions of each crystal structure (Figures 1(b)-(d)). The XRD pattern in Figure 1(a) was measured using CuKα radiation. If the peaks around 2θ = 28° ((-111) plane) and 2θ = 32° ((111) plane), which clearly indicate the presence of monoclinic crystals, are present in the XRD pattern of the electrocatalyst, it is determined that monoclinic crystals are present.

[0018] The electric field catalyst according to embodiment 1 contains, as Ni, Ni in a metallic state (hereinafter sometimes referred to as "metallic Ni") and Ni in a hydroxide state (hereinafter sometimes referred to as "Ni hydroxide"), and the contents thereof satisfy the following conditions: When the total amount of Ni is 100 atomic %, the content A (atomic %) of Ni in the metallic state and the content B (atomic %) of Ni in the hydroxide state are as follows: The content A satisfies the following formula (3), The ratio α of the content B to the content A satisfies the following formula (4). A≧30 atomic% (3) 0.15≦α≦0.63 (4)

[0019] The inventors first discovered that catalytic activity can be improved by including a portion of the Ni in the electric field catalyst as Ni hydroxide. Further investigation into the appropriate Ni hydroxide content revealed that the ratio α of the Ni hydroxide content to the Ni metal content has a certain correlation with catalytic activity.

[0020] By satisfying the above formulas (3) and (4), the catalytic activity of the electric field catalyst can be increased. In particular, high catalytic activity can be achieved even at low reaction temperatures (for example, 573 K or less). It is not clear why the presence of Ni hydroxide can improve catalytic activity, but a proposed reaction mechanism for electrocatalytic reactions is that protons adsorbed on the catalyst surface affect activity, and it is speculated that the hydroxyl group (-OH) of Ni hydroxide, which is a bond between this proton and oxygen, promotes the electrocatalytic reaction.

[0021] It is preferable that the ratio α satisfies the following formula (5): This can further enhance the catalytic activity. 0.25≦α≦0.45 (5)

[0022] When the total amount of Ni is taken as 100 atomic %, the content A of metallic Ni is preferably 35 atomic % or more. In other words, the content A preferably satisfies the following formula (6). A≧35 atomic% (6)

[0023] The catalytic activity can be confirmed by the power efficiency. The power efficiency is calculated by the reaction enthalpy Δ r H(Js -1 ) and input power EP(Js -1 ) and is defined by the following equation (7): Power efficiency (%) = Δ r H(Js -1 ) / EP(Js -1 )×100(%)···(7) A power efficiency of 9% or higher can be evaluated as having high catalytic activity, a power efficiency of 12% or higher can be evaluated as having even higher catalytic activity, and a power efficiency of 15% or higher can be evaluated as having extremely high catalytic activity.

[0024] As will be described later, a preferred method for producing the electric field catalyst according to embodiment 1 involves pretreatment with a pretreatment gas containing hydrogen (H). It is more preferable that the electric field catalyst be pretreated with a pretreatment gas containing not only hydrogen (H) but also water vapor (H0), which can achieve extremely high catalytic activity. The results of the examples described below confirm that pretreatment with a pretreatment gas containing H and HO significantly improves catalytic activity compared to an electrocatalyst pretreated with a pretreatment gas containing H but not HO. However, as will be explained below, the change in the electrocatalyst due to whether the pretreatment gas contains HO has not been confirmed by any physical property value (e.g., ratio α).

[0025] Figure 2 is a graph showing the relationship between power efficiency, an index of catalytic activity, and the ratio α of the Ni hydroxide content to the Ni metal content. The results for the electrocatalyst pretreated with a pretreatment gas containing hydrogen (H) but not water vapor (H2O) are plotted with squares, and the results for the electrocatalyst pretreated with a pretreatment gas containing hydrogen (H2) and water vapor (H2O) are plotted with circles.

[0026] For an electrocatalyst pretreated with a pretreatment gas containing hydrogen (H2) but not water vapor (H2O), the power efficiency is low when the ratio α is less than 0.15 or greater than 0.63, but the power efficiency improves significantly to over 9% when the ratio α is between 0.15 and 0.63. The power efficiency further improves to over 12% when the ratio α is between 0.25 and 0.45 (indicated by the square in Figure 2).

[0027] On the other hand, in the case of an electrocatalyst pretreated with a pretreatment gas containing hydrogen (H2) and water vapor (HO), the power efficiency was high, at 15% or more, when the ratio α was between 0.15 and 0.63 (indicated by the dots in Figure 2). However, even with a similar ratio α, different electrode efficiencies could be observed (Examples 9 and 10, described below, both had a ratio α of approximately 0.34, but the power efficiencies were significantly different, at approximately 20% and 16%, respectively).

[0028] In the present invention, it was discovered that the catalytic activity of an electric field catalyst using active metallic Ni can be improved by controlling the ratio α of the Ni hydroxide content to the metallic Ni content, and as can be seen from Figure 2, the electric field catalyst according to embodiment 1 has high catalytic activity when the ratio α is in the range of 0.15 to 0.63. However, it is difficult to explain in terms of the relationship with the ratio α why the electric field catalyst exhibits even higher catalytic activity when pretreatment is performed with a pretreatment gas containing hydrogen (H2) and water vapor (H2O). Furthermore, although other physical properties were also investigated, no physical properties showing a correlation with the improved catalytic activity have been found. Therefore, in this specification, an electric field catalyst that has been pretreated with a pretreatment gas containing hydrogen and water vapor is defined by the fact that it has been pretreated using the pretreatment gas, rather than by specifying it by its physical property values.

[0029] The Ni in the catalyst can be in a metallic state (metallic Ni), a hydroxide state (Ni hydroxide), or an oxide state (hereinafter sometimes referred to as "Ni oxide"). The state of Ni in the catalyst (metallic state, hydroxide state, oxide state) can be identified by X-ray photoelectron spectroscopy (XPS). The identification method using XPS is described in detail below.

[0030] The catalyst powder that has undergone the necessary pretreatment is transferred into a glove box in an Ar atmosphere without being exposed to the atmosphere, and is pressed and fixed against an In foil to prepare a sample for XPS measurement. The sample is fixed to the sample stage for a carbon coater (Gatan, Inc. PECS) with double-sided tape, and a 1.5 nm conductive carbon film is evaporated onto the sample surface using the carbon coater. Note that the sample is exposed to the atmosphere when it is removed from the glove box and transferred to the carbon coater, so the exposure time is limited to 5 minutes to prevent changes to the sample surface due to exposure to the atmosphere. The sample removed from the carbon coater is fixed to an alumina plate with carbon tape, which is then fixed to the XPS sample stage and introduced into the ultra-high vacuum XPS instrument. Since the sample is exposed to the atmosphere when transferred from the carbon coater to the XPS instrument, the exposure time is limited to 5 minutes or less to prevent changes to the state of the sample surface due to exposure to the atmosphere.

[0031] The XPS device may be, for example, PHI Quantes manufactured by ULVAC-PHI, Inc. The X-ray beam is a monochromatic Al-Kα ray (output 100 W, 20 kV) with a beam size of 100 μmφ.

[0032] The pass energy was set to 26.0 eV, the energy step was set to 0.1 eV, and the dwell time per step was set to 100 ms. The core-level photoelectron spectrum was measured within the binding energy range and the number of sweeps shown in Table 1. To compensate for the charging of the sample surface during photoelectron spectrum measurement, the electron beam was set to an accelerating voltage of 30 V and an emission current of 20 μA, and the Ar was set to an accelerating voltage of 10 V and an emission current of 5 mA. + The ion beams are irradiated simultaneously.

[0033] [Table 1]

[0034] In the obtained Ni2p photoelectron spectrum, the ratio of Ni in the metallic state (metallic Ni), Ni in the hydroxide state (Ni hydroxide), and Ni in the oxide state (Ni oxide) is quantified by the following procedure.

[0035] The charge shift energy correction value is determined so that the peak indicating the C-C bond in the C1s photoelectron spectrum is 285 eV, and this is applied to the Ni2p photoelectron spectrum to correct the charge shift. Next, to remove the background, the endpoints on the low and high binding energy sides of the baseline are adjusted within the ranges of 848-850 eV and 888-902 eV, respectively, so that the intersection points of the baseline endpoints and the Ni2p photoelectron spectrum are near the center of the noise in the Ni2p photoelectron spectrum. After these adjustments, the background in the photoelectron spectrum is removed using the Interposed Shirley method.

[0036] The Ni 2p photoelectron spectra obtained from standard materials of metallic Ni foil, Ni hydroxide powder, and Ni oxide powder are used as the references for metallic Ni, Ni hydroxide, and Ni oxide, respectively, and by linearly combining these, fitting is performed using the least squares method on the Ni 2p photoelectron spectrum after data processing obtained above. The Ni2p photoelectron spectrum of the standard material is obtained under the same measurement conditions as the measurement sample, and the data processing is also the same. However, in the case of Ni metal foil, Ar + After removing the oxide layer by ion sputtering, XPS measurement is performed, and charge shift correction is performed so that the binding energy value of the Ni2p3 / 2 peak, which indicates a metallic state, is 852.7 eV.

[0037] In the least-squares fitting, we allow for shifts in the Ni 2p photoelectron spectra of the reference Ni metal, Ni hydroxide, and Ni oxide, taking into account errors in the charge shift correction of the Ni 2p photoelectron spectrum of the sample and differences in the magnitude of charge for each chemical state. Figure 3 shows the Ni 2p photoelectron spectra of the reference Ni metal (Ni-metal), Ni hydroxide (Ni(OH)2), and Ni oxide (NiO). No constraints are placed on the spectral shift of Ni metal, but constraints are placed on the Ni 2p photoelectron spectra of Ni hydroxide and Ni oxide so that the relative binding energy differences with the Ni 2p photoelectron spectrum of Ni metal are 1.4 ± 0.2 eV and 3.2 ± 0.2 eV, respectively (Figure 3). Note that the shift of the Ni 2p photoelectron spectrum during fitting is varied in 0.025 eV steps.

[0038] In fitting by the least squares method, the coefficient multiplied by the intensity of the Ni2p photoelectron spectrum of each reference is changed so that the sum of squares of the fit error at each energy point from 849 to 887 eV is minimized. After fitting, the area intensities of the Ni 2p photoelectron spectra of metallic Ni, Ni hydroxide, and Ni oxide are determined within the above range, and their ratios are calculated as the chemical state ratios. An example of the fitting results is shown in Figure 4. Figure 4 shows the Ni 2p photoelectron spectrum of the catalyst powder (Sample), the Ni 2p photoelectron spectra of references of metallic Ni (Ni-metal), Ni hydroxide (Ni(OH)2), and Ni oxide (NiO), and the fitting curves (fit) created using the above method.

[0039] The atomic concentration of elements was determined by calculating the area intensity of the core-level photoelectron spectrum obtained by XPS measurement, excluding C1s, and performing sensitivity correction. The energy point where the base of the peak of the core-level photoelectron spectrum falls sufficiently was set as the end point of the baseline, and the background was defined using the iterated Shirley method to calculate the area intensity of the core-level photoelectron spectrum of each element. The atomic concentration was calculated by dividing these by the relative sensitivity correction coefficient. This calculation was performed using the analysis software MultiPak manufactured by ULVAC-PHI, Inc., and the relative sensitivity coefficient was determined using the software's built-in value.

[0040] (Manufacturing method) The method for producing the electric field catalyst of embodiment 1 is not particularly limited, but the following production method can be adopted because it allows for the production of an electric field catalyst having the above physical properties with good reproducibility. It should be noted that a person skilled in the art who has access to the disclosure of the present application may arrive at a different method for producing the electric field catalyst of embodiment 1 based on the disclosure.

[0041] The electric field catalyst can be prepared by a complex polymerization method, a solid phase method, or the like. As an example, a production method using complex polymerization will be described below. Nitrates of zirconium, yttrium, and nickel are weighed out to a predetermined composition ratio and dissolved in ethylene glycol and citric acid dissolved in distilled water. The solution is heated at an appropriate temperature and for an appropriate heating time while stirring in an evaporator, and after heating, the mixture is evaporated and solidified using a hot stirrer. The appropriate heating temperature and heating time can be set as appropriate depending on the raw materials used and the amount of raw materials added during production. For example, the heating temperature is 323 K or higher and 363 K or lower (e.g., 343 K), and the heating time is 12 hours or higher and 48 hours or lower (e.g., 24 hours).

[0042] Thereafter, the mixture is calcined at an appropriate temperature for an appropriate period of time, which can be appropriately set depending on the type and amount of the material to be calcined. For example, the calcination temperature is 573 K or higher and 873 K or lower (e.g., 673 K), and the calcination time is 1 hour or higher and 12 hours or lower (e.g., 2 hours).

[0043] The catalyst powder is then obtained by calcining at an appropriate temperature for an appropriate time. The appropriate calcination temperature and time can be set appropriately depending on the type and amount of material to be calcined. For example, the heating temperature is 1073 K or higher and 1473 K or lower (e.g., 1173 K), and the heating time is 1 hour or higher and 24 hours or lower (e.g., 10 hours).

[0044] The obtained catalyst powder is pretreated with a pretreatment gas containing hydrogen (H2) in the powder state, in a molded state, or in the state of granulated powder obtained by crushing the molded powder. By using a pretreatment gas containing hydrogen (H2), Ni contained in the catalyst powder is partially reduced to Ni in a metallic state (metallic Ni). The pretreatment gas preferably contains hydrogen (H2) and water vapor (HO). In addition to hydrogen (H), the pretreatment gas may contain an inert gas such as Ar gas, N gas, or He gas. The pretreatment gas may also contain a reducing gas such as methane or propane in addition to or instead of hydrogen.

[0045] The pretreatment is carried out for 0.5 to 5 hours at a pretreatment temperature of 673 to 1273 K. The flow rate of the pretreatment gas is controlled to an appropriate flow rate depending on the composition of the pretreatment gas and the amount of catalyst powder to be pretreated. Pretreatment can be carried out in a suitable furnace or in a catalytic gas reforming reactor, where the catalyst is loaded into the reactor at a predetermined location and heated while the pretreatment gas is passed through the reactor.

[0046] In this manner, the electric field catalyst according to the first embodiment can be obtained.

[0047] [Embodiment 2] The second embodiment is a method for reforming gas using the electric field catalyst according to the first embodiment. The reforming method of the second embodiment includes the steps of: 1) preparing an electric field catalyst; and 2) reforming.

[0048] Step 1) Preparing an electric field catalyst 1 is a step of preparing an electric field catalyst according to the first embodiment. The step of preparing the electric field catalyst may include, for example, mixing raw materials, sintering, and treating the resulting sintered powder with a pretreatment gas. The prepared electrocatalyst and the preparation process thereof are the same as those described in the first embodiment, and therefore, the description thereof will be omitted.

[0049] Step 2) Modifying step The electric field catalyst is heated to a reaction temperature of 423 K or higher and 673 K or lower, and an electric field is applied. The gas to be reformed (e.g., hydrocarbon) is brought into contact with the electric field catalyst in this state, causing the gas to react (be reformed). The reforming step can be carried out, for example, using an atmospheric pressure fixed-bed flow reactor equipped with electrodes. FIG. 5 shows an example of an atmospheric pressure fixed-bed flow reactor (reactor) 10 equipped with a pair of electrodes 13, 14. The atmospheric pressure fixed-bed flow reactor (reactor) 10 is equipped with a support means 16 for supporting a catalyst 15 inside a reaction vessel 12, and the catalyst 15 is placed on the support means 16. The pair of electrodes 13, 14 are in direct contact with the catalyst 15. When carrying out the reforming step, a voltage is applied between the pair of electrodes 13, 14 to apply an electric field to the catalyst 15.

[0050] The amount of catalyst 15 used is not particularly limited and is adjusted appropriately depending on the reactor 10 used, the type of gas to be reformed, and the supply amount. The catalyst 15 may be filled in a powder state into the reaction vessel 12, or may be molded into a disk shape beforehand and then placed in the reaction vessel 12. Furthermore, catalyst granulated powder obtained by molding and then pulverizing and granulating may also be used. [Example]

[0051] (Preparation of catalyst powder for measurement) Nitrates of zirconium, yttrium, and nickel were weighed out to obtain the composition ratios shown in Table 2, and dissolved in ethylene glycol and citric acid dissolved in distilled water. The solution was heated at a holding temperature of 343 K for 24 hours while stirring in an evaporator, and after heating, evaporated and solidified using a hot stirrer. The mixture was pre-baked at a holding temperature of 673 K for 2 hours, and then calcined at a holding temperature of 1173 K for 10 hours to obtain catalyst powder for measurement.

[0052] (crystal structure) The resulting catalyst powder was subjected to powder XRD measurement to confirm the crystal structure. The XRD measurement was carried out using CuKα radiation at an output of 50 kV and 30 mA. The presence or absence of monoclinic crystals (peaks at 2θ=28° and 32°) was confirmed from the XRD pattern. If peaks were observed at 2θ = 28° and 32° in the XRD pattern, it was determined that monoclinic crystals were present; if peaks were not observed, it was determined that monoclinic crystals were not present. The results are shown in Table 2.

[0053] (Ni state) The state of Ni (metal state, hydroxide state, oxide state) was confirmed by XPS analysis, and the content (atomic %) of Ni atoms in each state was measured.

[0054] (Activity evaluation) The obtained catalyst powder was filled into a mold and pressed with a press at 60 kN for 10 minutes to form a disk shape. The formed sample was crushed in a mortar and classified into particles of 355 to 500 μm using a sieve. Activity evaluation was performed using the classified catalyst granules. Activity evaluation was performed using an atmospheric pressure fixed-bed flow reactor. A quartz tube with an outer diameter of 8.0 mm and an inner diameter of 6.0 mm was used as the reaction tube, and 80 mg of the classified catalyst granules was packed into it. Electrodes with an outer diameter of 2 mm were inserted from the top and bottom of the reaction tube and brought into contact with the catalyst.

[0055] As a pretreatment, a pretreatment gas of H2:Ar=1:1 was passed through at a total flow rate of 120 CCM, and reduction treatment was carried out at a furnace temperature of 873 K for a holding time of 1 hour. Then, the reaction gas was passed through the reactor to carry out the catalytic reaction under the following reaction conditions: Reactant gas flow rate: 120 CCM Reactant gas composition: CH4:H2O:Ar = 1:2:7 Applied current: 9mA Reaction temperature (furnace temperature): 473K

[0056] The gas composition after the reaction was analyzed by gas chromatography. The results of the confirmed gas composition are used as the "Δ r H(Js -1 ) was used to find the The reaction formula of the reactive gas is as follows: CH4+H2O→CO+3H2 CO+H2O→CO2+4H2

[0057] (power efficiency) To investigate the efficiency of the electrocatalysis, the power efficiency was calculated. The results are shown in Table 2. The power efficiency is calculated by the reaction enthalpy of formation Δ r H(Js -1 ) and input power EP(Js -1 ) and is defined by the following equation (7): Power efficiency (%) = Δ r H(Js -1 ) / EP(Js -1 )×100(%)···(7) Here, the reaction formation enthalpy Δ r H(Js -1 ) is the reaction formation enthalpy calculated based on the reaction formula of the above-mentioned reaction gas, and is defined by the following formula (8). Δ r H=r CO ×ΔH CO +rCO2 ×ΔH CO2 -r CO ×ΔH CH4 -(r CO +2r CO2 ) × ΔH H2O ···(8) Here, ΔH CO , ΔH CO2 , ΔH CH4 , and ΔH H2O are the enthalpy values ​​(kJ / mol) of CO, CO2, CH4, and H2O, respectively, and are constants specific to each chemical. r CO , and r CO2 are the production rates (mol / sec) of CO and CO2, respectively, and are determined from the results of activity evaluation tests. The input power EP is calculated by multiplying the current I by the voltage V, as shown in the following equation (9). EP(Js -1 ) = I (mA) × V (kV) (9)

[0058] The measurement results are shown in Table 2. In Table 2, underlined values ​​indicate values ​​outside the range of the present invention. Furthermore, since monoclinic crystals were confirmed in Comparative Examples 1 to 4, XPS measurement was not performed. Therefore, in Table 2, a line (-) is entered in the "Ni" column for Comparative Examples 1 to 3 and 6.

[0059] [Table 2]

[0060] The results in Table 2 are discussed. In Comparative Examples 1 to 3, the Y content (y) was below the lower limit of the appropriate range, so that the tetragonal and cubic crystals were not stabilized and monoclinic crystals were precipitated, resulting in low power efficiency. In Comparative Example 4, the Y content (y) was greater than the upper limit of the appropriate range, so the proportion of metallic Ni was low, α deviated from the appropriate range, and the power efficiency was also low. In Comparative Example 5, the Ni content was low and no catalytic reaction occurred. In Comparative Example 6, the Ni content was high and zirconia could not be stabilized, so tetragonal and cubic crystals were not stabilized and monoclinic crystals were precipitated.

[0061] In Examples 1 and 2, when Ni=0.30, Y=0.05 and 0.10, respectively, and were within the range of 0.25<α<0.40, so that the power efficiency was high. In Example 3, Ni=0.30 and Y=0.30, and the content of metallic Ni was low and the content of Ni hydroxide was high, so α tended to be large. The power efficiency was sufficiently high, but lower than Examples 1 and 2. In Example 4, Ni=0.10 and Y=0.10, and although the content of metallic Ni was high, the content of Ni hydroxide was also high, which tended to increase α. Therefore, although the power efficiency was sufficiently high, it was lower than in Examples 1 and 2.

[0062] In Example 5, Ni=0.40 and Y=0.10, which were within the range of 0.25<α<0.40, and therefore the power efficiency was high. In Example 6, Ni=0.45 and Y=0.10, and the content of metallic Ni was high and the content of Ni hydroxide was low, so the ratio α tended to be small. The power efficiency was sufficiently high, but lower than Examples 1 and 2. [Example]

[0063] The effect of pretreating the electrocatalyst with a pretreatment gas containing hydrogen (H2) and water vapor (H2O) was investigated.

[0064] (Preparation of catalyst powder for measurement) Nitrates of zirconium, yttrium, and nickel were weighed out so as to have the composition ratios shown in Table 3, and catalyst powders for measurement were obtained in the same manner as in [Example 1].

[0065] (crystal structure) The resulting catalyst powder was subjected to powder XRD measurement to confirm the crystal structure. The measurement conditions and confirmation method were the same as those in [Example 1].

[0066] (Ni state) The state of Ni (metal state, hydroxide state, oxide state) was confirmed by XPS analysis, and the content (atomic %) of Ni atoms in each state was measured. The measurement conditions and confirmation method were the same as those in [Example 1].

[0067] (Activity evaluation) The evaluation was carried out in the same manner as in Example 1, except that a gas having the composition shown in Table 3 was used as the pretreatment gas.

[0068] The measurement results are shown in Table 3.

[0069] [Table 3]

[0070] In Examples 8 to 10, the catalyst material had a composition of x = 0.30 and y = 0.05, and by adding water vapor (HO) together with H as a pretreatment gas, the power efficiency increased compared to Example 1 (no water vapor added). The ratio α in Examples 8 to 10 was in the range of 0.20 to 0.40.

[0071] This application claims priority based on Japanese Patent Application No. 2021-182616, filed on November 9, 2021, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0072] 10 Atmospheric pressure fixed-bed flow reactor (reactor) 12 Reaction vessel 13, 14 Pair of electrodes 15 Catalyst 16 Support means

Claims

1. An electric field catalyst for use in a hydrocarbon reforming reaction, comprising: the electric field catalyst comprises Ni, Y, Zr, and O; Its composition: Ni ｘ Y ｙ Zr １－ｘ－ｙ O ２ x and y satisfy the following formula (1) and formula (2), respectively: The crystal structure does not include monoclinic crystals, The Ni includes Ni in a metallic state and Ni in a hydroxide state, The content A (atomic %) of Ni in the metallic state and the content B (atomic %) of Ni in the hydroxide state are expressed as follows, where the total amount of Ni is taken as 100 atomic %: The content A satisfies the following formula (3), An electric field catalyst in which the ratio α of the content B to the content A satisfies the following formula (4). 0.10≦x≦0.45 (1) 0.05≦y≦0.30 (2) A≧30 atomic%...(3) ０．１５≦α≦０．６３・・・（４）

2. The electric field catalyst of claim 1 , wherein the ratio α satisfies the following formula (5): ０．２５≦α≦０．４５・・・（５）

3. 3. The electric field catalyst according to claim 1, which is pretreated with a pretreatment gas containing hydrogen and water vapor.

4. A method for reforming hydrocarbon gas using an electric field catalyst for a hydrocarbon reforming reaction, comprising: Step 1) providing the electric field catalyst, wherein: The electrocatalyst is composed of Ni, Y, Zr and O, and the composition is Ni ｘ Y ｙ Zr １－ｘ－ｙ O ２ x and y satisfy the following formula (1) and formula (2), respectively: The crystal structure does not include monoclinic crystals, The Ni includes Ni in a metallic state and Ni in a hydroxide state, The content A (atomic %) of Ni in the metallic state and the content B (atomic %) of Ni in the hydroxide state are expressed as follows, where the total amount of Ni is taken as 100 atomic %: The content A satisfies the following formula (3), The ratio α of the content B to the content A satisfies the following formula (4); and Step 2) heating the electric field catalyst to a reaction temperature of 423 K or higher and 673 K or lower and applying an electric field to reform the hydrocarbon gas. 0.10≦x≦0.45 (1) 0.05≦y≦0.30 (2) A≧30 atomic%...(3) ０．１５≦α≦０．６３・・・（４）

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