Porous alumina and catalysts

Abstract

To provide a porous alumina excellent in heat resistance and coking resistance.SOLUTION: A porous alumina includes an aluminum oxide with a silica and a barium oxide added. The silica and the barium oxide are added to the aluminum oxide so that, if a SiO2 addition rate (mass%) is a rate of SiO2 added with regard to total mass of the aluminum oxide and the SiO2 added, and a BaO addition rate (mass%) is a rate of BaO added with regard to total mass of the aluminum oxide and the SiO2 added, within a range of the SiO2 addition rate 3 mass% or lower and the BaO addition rate 14 mass% or lower, a specific surface area measured by a prescribed measuring method after heat treatment at 1200°C for 30 hours of the porous alumina is equal to or higher than a reference specific surface area measured in a similar manner of a reference porous alumina for comparison with the SiO2 addition rate 3 mass% and the BaO addition rate 0 mass%, set to the porous alumina.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to porous alumina obtained by adding silica and a solid basic oxide to aluminum oxide, and a catalyst using porous alumina as a catalyst support, and in particular to porous alumina and a catalyst to which barium oxide is added as a solid basic oxide. [Background technology]

[0002] Porous alumina materials with a large specific surface area, such as γ-alumina, are useful as catalyst supports for supporting catalytic substances, filters, etc., and studies have been conducted to improve their properties (see, for example, Patent Documents 1 to 5, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-203654 [Patent Document 2] International Publication No. 2014 / 051091 [Patent Document 3] International Publication No. 2012 / 096386 [Patent Document 4] International Publication No. 2013 / 111457 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-061383 [Non-patent literature]

[0004] [Non-Patent Document 1] Toru Numaguchi et al., "Evaluation of activity and carbon deposition of methane steam reforming catalysts," Journal of the Petroleum Society, Vol. 39, No. 3, 1996. [Non-patent document 2] Ki-Yong Lee, et al., "Deactivation by coke deposition on the HZSM-5 catalysts in the methanol-to-hydrocarbon conversion", Journal of Physics and Chemistry of Solids 73 (2012) 1542-1545. Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional porous alumina materials with large specific surface areas, such as gamma-alumina, readily transition to the alpha phase, resulting in a significant decrease in specific surface area, when heated to temperatures above 1000°C in a very short time, or even at lower temperatures over a long period of time. The transition to the alpha phase tends to be even more pronounced in a water vapor atmosphere or under high pressure.

[0006] The use of solid acidic additives such as silica (SiO2) to suppress the transition to the α-phase significantly improves heat resistance and allows a large specific surface area to be maintained even at high temperatures, but at the same time increases the solid acidity of the porous alumina material. Therefore, when a porous alumina material containing a solid acidic additive is used as a catalyst support, carbon deposition (coking) is likely to occur on the catalyst surface in reactions targeting hydrocarbons, leading to catalyst deactivation. Therefore, catalyst supports used in reactions using hydrocarbons, such as steam reforming reactions, are required to have not only heat resistance but also coking resistance. It is well known that coking becomes more likely as the solid acidity of the porous support increases, as disclosed in the above-mentioned Non-Patent Documents 1 and 2.

[0007] Figure 1 shows the relationship between the SiO2 addition rate and the specific surface area of ​​porous alumina to which only silica has been added, prepared using the same kneading method as the comparative sample described below. The specific surface areas of Sample A, obtained by firing in air at 1000°C for 5 hours, Sample B, which was obtained by adding a heat treatment at 1200°C for 5 hours to Sample A, and Sample C, which was obtained by adding a heat treatment at 1200°C for 30 hours to Sample A, were measured using the nitrogen adsorption BET method. As shown in Figure 1, the specific surface area after heat treatment increased significantly as the SiO2 addition rate increased, demonstrating the effectiveness of silica in improving the heat resistance of porous alumina. It is clear that this is effective.

[0008] Figure 2 shows the results of measuring the amount of solid acid and the amount of solid base on the porous alumina surface by temperature programmed desorption (TPD, base probe molecule: NH3, acid probe molecule: CO2) for sample A. As the SiO2 addition rate increases, the amount of NH3 adsorption increases and the amount of CO2 adsorption decreases, indicating that the amount of solid acid on the porous alumina surface increases and the amount of solid base decreases.

[0009] Acidic and basic sites on a solid surface coexist because they are difficult to neutralize. Silica, alumina, and their mixed oxides are both solid acids and solid bases, so as shown in Figure 2, both the amount of solid acid and the amount of solid base are measured without being neutralized on the solid surface.

[0010] 1 and 2, it is clear that simply adding solid acidic silica is difficult to achieve both improved heat resistance of γ-alumina and suppressed increase in solid acidity (coking resistance). Furthermore, methods have been reported in which barium, lanthanum, or the like is added to alumina for the purpose of improving heat resistance, but neither of these methods can be said to have sufficient heat resistance (see Patent Documents 4 and 5).

[0011] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide porous alumina having excellent heat resistance and coking resistance, and further to provide a catalyst using the porous alumina as a catalyst support. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have discovered that by combining silica with barium oxide, which is a solid basic oxide, as an additive to be added to porous alumina having a large specific surface area, such as γ-alumina, and by appropriately adjusting the amounts of silica and barium oxide added, it is possible to obtain porous alumina that is superior in heat resistance and coking resistance to porous alumina to which only silica is added, and have arrived at the invention described below.

[0013] Porous alumina made by adding silica (SiO) and barium oxide (BaO) to aluminum oxide (Al2O3), The ratio of the amount of added SiO2 to the total mass of the aluminum oxide and the amount of added SiO2 is defined as the SiO2 addition rate (mass%), The ratio of the amount of BaO added to the total mass of the aluminum oxide and the amount of SiO added is defined as the BaO addition rate (mass%), The amount of SiO2 added is the amount obtained by converting the content of silicon (Si) in the porous alumina into the content of SiO2, The BaO addition amount is the amount obtained by converting the content of barium (Ba) in the porous alumina into the content of BaO, When the SiO2 addition rate is within a range of 3 mass% or less and the BaO addition rate is within a range of 14 mass% or less, The specific surface area of ​​the porous alumina measured by a predetermined measuring method after heat treatment at 1200°C for 30 hours is equal to or greater than a reference specific surface area measured in the same manner as a reference porous alumina for comparison, in which the SiO2 addition rate is set to 3 mass% and the BaO addition rate is set to 0 mass% relative to the porous alumina, The first feature is that the silica and the barium oxide are added to the aluminum oxide.

[0014] It is needless to say that the same method for measuring the specific surface area is used for the porous alumina according to the present invention and the reference porous alumina for comparison. For example, the well-known nitrogen adsorption BET method similar to that used for measuring the specific surface area shown in FIG. 1 can be used.

[0015] Furthermore, the amount of SiO2 added is defined as the amount obtained by converting the content of silicon (Si) in the porous alumina into the content of SiO2, and the amount of barium added is defined as the amount obtained by converting the content of barium (Ba) in the porous alumina into the content of BaO. However, these definitions take into consideration the fact that, in the prepared porous alumina, the amounts of each added are measured by an X-ray fluorescence analyzer as the amounts of silicon and barium element, rather than as the amounts of silica and barium oxide added, and further, that when part of the added silica enters the alumina framework as silicon, the added silica and barium oxide may form an aluminate phase through a solid-phase reaction with the alumina.

[0016] According to the porous alumina having the first characteristic, when the SiO2 addition rate is within a range of 3 mass% or less and the BaO addition rate is within a range of 14 mass% or less, the solid acid amount is equal to or less than the reference solid acid amount, and the SiO2 addition rate and the BaO addition rate are set so that the specific surface area after heat treatment at 1200°C for 30 hours is equal to or more than the reference specific surface area. Therefore, for the reasons explained below, it is possible to obtain porous alumina having better heat resistance and coking resistance than porous alumina to which only silica is added.

[0017] First, the reason for using porous alumina with SiO2 and BaO additive rates of 3 mass % and 0 mass %, respectively, as the reference porous alumina serving as the evaluation standard for heat resistance and coking resistance will be explained.

[0018] Figure 3 shows the results of evaluating the amount of coking after a steam reforming reaction was performed on a steam reforming catalyst supported on porous alumina with an SiO2 loading in the range of 0.5 mass% to 20 mass% and a BaO loading of 0 mass%, which supported Ni (15 mass%) and La (10 mass% in terms of La2O3).

[0019] The porous alumina was prepared in the same manner as the comparative sample with a BaO addition rate of 0 mass % prepared by the kneading method described below.

[0020] The steam reforming catalyst was prepared by impregnation as follows: the porous alumina was impregnated with a mixed aqueous solution of nickel nitrate and lanthanum nitrate at room temperature for 1 hour, and then evaporated to dryness using an evaporator. After solidifying, it was calcined for 5 hours at 450° C. The powder catalyst supporting Ni-La was pressure molded using a press, then pulverized in a mortar until it became granular, and sieved to size between 180 μm and 250 μm.

[0021] The steam reforming reaction was carried out as follows. 0.5 ml of catalyst was weighed in a measuring cylinder and placed in a stainless steel reaction tube. The catalyst was pretreated by reduction in a hydrogen stream at 600°C for 1 hour. The steam reforming reaction was then carried out at flow rates of C3H8: 60 ml / min, N2: 60 ml / min, H2: 6 ml / min, and H2O: 360 ml / min. The reaction conditions were S / C = 2.0, SV = 60,000 h -1 The temperature was raised from room temperature at a rate of 10°C / min, and when it reached 600°C, it was held for 43 minutes. The product gas was sampled and the composition of the product gas was analyzed by gas chromatography.

[0022] The amount of coking was measured using a carbon-sulfur analyzer (CS-200, manufactured by LECO Japan LLC). A sample made by mixing 0.03 g of the catalyst sample that underwent steam reforming reaction with 1 g of combustion improver (tin-plated copper) was placed in a crucible, and the carbon in the sample was burned in a high-frequency combustion furnace using oxygen as the carrier gas (flow rate 3 L / min). The carbon gasified by high-temperature combustion was detected using infrared absorption, and the amount of carbon was measured.

[0023] Figure 4 shows the porous alumina of the steam reforming catalyst in Figure 3, which was prepared using the same method as the SiO2-added porous alumina. The results of measuring the phase transition temperature to the α phase are shown below using five samples (indicated by ●) of porous alumina with an SiO2 addition rate in the range of 0 mass% to 5 mass% and a BaO addition rate of 0 mass%, and one sample (indicated by ○) of porous alumina with an SiO2 addition rate of 1 mass% and a BaO addition rate of 5 mass%, prepared in the same manner as the evaluation sample prepared by the kneading method described below.

[0024] The phase transition temperature was measured using a thermogravimetric analyzer (Rigaku, differential thermobalance, Thermo Using a differential thermal analysis (DTA) instrument (plus EVO2 TG-DTA TG8120), 20 mg of sample was placed in a platinum pan and measured by heating from room temperature at a rate of 20°C / min. An exothermic reaction is observed when alumina undergoes a phase transition from δ,θ-alumina to α-alumina. Therefore, the exothermic peak temperature of the differential thermal analysis (DTA) curve was determined as the phase transition temperature.

[0025] The measurement results of the amount of coking shown in Figure 3 show that when the SiO2 addition rate is 3 mass% or less, almost no coking occurs, whereas when the SiO2 addition rate exceeds 3 mass%, the amount of coking increases roughly in proportion to the SiO2 addition rate.

[0026] The phase transition temperature measurement results shown in Figure 4 indicate that when the BaO content is 0% by mass, the phase transition temperatures increase to 1201°C, 1282°C, 1290°C, 1396°C, and 1416°C as the SiO2 content increases from 0% by mass to 3% by mass. This indicates that the heat resistance improves with increasing SiO2 content. While the phase transition temperature increases by 195°C (from 1201°C to 1396°C) with increasing SiO2 content from 0% by mass to 3% by mass, the phase transition temperature increases by only 20°C (from 1396°C to 1416°C) with increasing SiO2 content from 3% by mass to 5% by mass. Therefore, the improvement in heat resistance with increasing SiO2 content is evident at SiO2 content levels of 3% by mass or less. The measurement results in Figure 4 are consistent with the relationship shown in Figure 1.

[0027] On the other hand, when comparing two samples with an SiO2 addition rate of 1 mass% and BaO addition rates of 0 mass% and 5 mass%, it is found that when the BaO addition rate increases from 0 mass% to 5 mass%, the phase transition temperature increases by 129°C, from 1282°C to 1411°C.

[0028] The measurement results shown in Figures 3 and 4 show that the increase in the amount of coking can be suppressed by keeping the SiO2 addition rate at 3 mass% or less, and that the heat resistance can be significantly improved by setting the BaO addition rate within a predetermined preferred range including 5 mass% when the SiO2 addition rate is 3 mass% or less.

[0029] From the above explanation, it can be seen that porous alumina (reference porous alumina) with SiO2 and BaO addition rates of 3% and 0% by mass, respectively, has a certain degree of heat resistance and coking resistance. However, when the SiO2 addition rate decreases below 3% by mass, heat resistance decreases, and conversely, when the SiO2 addition rate increases above 3% by mass, coking resistance decreases. Therefore, an SiO2 addition rate of 3% by mass is a unique point where heat resistance and coking resistance can be achieved simultaneously. In other words, porous alumina containing only silica cannot achieve both heat resistance and coking resistance that exceed those of the reference porous alumina. Therefore, when porous alumina containing both silica and barium oxide is to be improved in both heat resistance and coking resistance compared to porous alumina containing only silica, the reference porous alumina can be said to be appropriate as an evaluation standard for heat resistance and coking resistance.

[0030] The effect of improving heat resistance by adding barium oxide in addition to silica can be explained as follows.

[0031] The ionic radius of Si is almost the same as that of aluminum (Al), and Si ions are incorporated into the structure of γ-alumina by the decomposition of the alumina precursor at around 450°C. In γ-alumina with a spinel structure, there are many vacancies in the octahedral sites. By adding Si ions to alumina, Al ions in tetrahedral sites are replaced by Si ions, reducing the total number of vacancies, suppressing alpha phase formation and improving heat resistance. In addition, adding silica is effective in preventing the clogging of alumina micropores, improving heat resistance in the temperature range below 1100°C.

[0032] It is known that Ba ions react with alumina in a solid phase at temperatures above 1000°C, resulting in the formation of aluminates (barium hexaaluminate: BaO·6Al2O3, barium monoaluminate: BaO·Al2O3) (see Figures 9 and 10). Aluminates are formed on the surface of alumina particles and suppress the formation of alpha phases inside the particles. Because the aluminates on the particle surface are cubic (fcc) and have the same structure as gamma-alumina, strong interactions occur by sharing oxygen ions on the surface of the alumina particles. This interaction suppresses the formation of alpha phases inside the alumina particles.

[0033] When Ba is added alone to alumina, aluminate formation based on a solid-state reaction is required. This requires calcination at 1000°C or higher, and the alpha phase transformation is not suppressed during the temperature rise process before aluminate formation, resulting in the loss of alumina micropores and a significant decrease in specific surface area. However, when silica is added to alumina, the silica addition effect can suppress the blockage of micropores and the decrease in specific surface area in the temperature range of 1100°C or less during the temperature rise process before aluminate formation. Furthermore, at temperatures above this temperature range, aluminate is formed by a solid-state reaction of Ba, suppressing the alpha phase transformation of alumina.

[0034] Furthermore, as will be described later, the inventors of the present invention have conducted extensive research to confirm that, for a given SiO2 addition rate of 3 mass% or less, when the BaO addition rate is increased from 0 mass% within a range of 14 mass% or less, the specific surface area after heat treatment at 1200°C for 30 hours increases beyond the reference specific surface area, and once it exceeds its maximum value, decreases toward the reference specific surface area (see Figures 11 and 14). Therefore, when the SiO2 addition rate is within a range of 3 mass% or less and the BaO addition rate is within a range of 14 mass% or less, the specific surface area after heat treatment at 1200°C for 30 hours is equal to or greater than the reference specific surface area. In other words, there is certainly a combination of SiO2 addition rate and BaO addition rate that improves heat resistance compared to the reference porous alumina (SiO2 addition rate: 3 mass%, BaO addition rate: 0 mass%), and by employing this combination, heat resistance is reliably improved.

[0035] Furthermore, the relationship between the SiO2 addition rate and BaO addition rate and the solid acidity shown in Figures 13 and 15 (described later) reveals that, at a given SiO2 addition rate of 3 mass% or less, increasing the BaO addition rate monotonically decreases the solid acidity (decreasing solid acidity). Therefore, as described above, since the relationship exists in which the greater the solid acidity of the porous carrier, the more likely it is that coking will occur, by limiting the SiO2 addition rate to 3 mass% or less and further increasing the BaO addition rate, the increase in the amount of coking is further suppressed, and coking resistance is improved. In other words, by adopting a combination of SiO2 addition rate and BaO addition rate that improves heat resistance, coking resistance is also reliably improved.

[0036] Therefore, when only silica is added, it is difficult to achieve both heat resistance and coking resistance. However, by reducing the amount of silica added and adding barium oxide in addition to silica, both heat resistance and coking resistance can be significantly improved compared to when only silica is added.

[0037] Furthermore, in the porous alumina of the first characteristic, it is preferable that the silica and the barium oxide are added to the aluminum oxide so that the specific surface area of ​​the porous alumina is equal to or greater than the reference specific surface area, with the SiO2 addition rate being within a range of 0.7 mass % to 3 mass %.

[0038] Furthermore, in the porous alumina according to the first aspect, it is preferable that the silica and the barium oxide are added to the aluminum oxide so that the specific surface area of ​​the porous alumina is equal to or greater than the reference specific surface area, with the BaO addition rate being within a range of 0.5% by mass to 14% by mass.

[0039] According to a preferred embodiment of the porous alumina having the first characteristic, a combination of the SiO2 addition rate and the BaO addition rate that improves both the heat resistance and the coking resistance is more reliably present when the SiO2 addition rate is in the range of 0.7 mass % or more and 3 mass % or less, or when the BaO addition rate is in the range of 0.5 mass % or more and 14 mass % or less.

[0040] Furthermore, in the porous alumina according to the first aspect, when the SiO2 addition rate is Xs (mass%) and the BaO addition rate is Xb (mass%), The second feature is that 0.7 mass%≦Xs<1 mass%, and 5 mass%≦Xb≦10 mass%, or 1 mass%≦Xs<2 mass%, and 3 mass%≦Xb≦10 mass%, or 2 mass%≦Xs≦3 mass%, and 1 mass%≦Xb≦14 mass%.

[0041] Furthermore, the porous alumina according to the present invention is porous alumina obtained by adding silica (SiO) and barium oxide (BaO) to aluminum oxide (AlO), The SiO2 addition rate (mass %) defined as the ratio of the amount of SiO2 added to the total mass of the aluminum oxide and the amount of SiO2 added is Xs (mass %), and the amount of SiO2 added is the amount obtained by converting the content of silicon (Si) in the porous alumina into the content of SiO2, When the BaO addition rate (mass%) defined as the ratio of the BaO addition amount to the total mass of the aluminum oxide and the SiO addition amount is Xb (mass%), the BaO addition amount is the amount obtained by converting the content of barium (Ba) in the porous alumina into the content of BaO, The third feature is that 0.7 mass%≦Xs<1 mass%, and 5 mass%≦Xb≦10 mass%, or 1 mass%≦Xs<2 mass%, and 3 mass%≦Xb≦10 mass%, or 2 mass%≦Xs≦3 mass%, and 1 mass%≦Xb≦14 mass%.

[0042] According to the porous alumina having the second or third characteristic, both the heat resistance and the coking resistance are reliably improved compared to the reference porous alumina (SiO2 addition rate: 3 mass%, BaO addition rate: 0 mass%) within the respective specified ranges of the SiO2 addition rate Xs and the BaO addition rate Xb.

[0043] Furthermore, it is preferable that the porous alumina having the second or third characteristic satisfies 1 mass %≦Xs≦3 mass % and 3 mass %≦Xb≦10 mass %.

[0044] According to a preferred embodiment of the porous alumina of the second or third aspect, both the heat resistance and the coking resistance can be further improved.

[0045] Furthermore, the catalyst according to the present invention is characterized by comprising the porous alumina according to the first or second aspect above, and a catalytic substance supported on the porous alumina.

[0046] The catalyst having the above characteristics can improve heat resistance and coking resistance compared to conventional catalysts that use porous alumina as a carrier. [Effects of the Invention]

[0047] According to the porous alumina of the present invention, the use of barium oxide, which is a solid basic oxide, makes it possible to By appropriately adjusting the amounts of silica and barium oxide added, it is possible to provide a high heat resistance that allows a large specific surface area to be maintained even at high temperatures, while suppressing the amount of silica added and suppressing an increase in the amount of solid acid, thereby achieving high coking resistance and providing a high-performance porous alumina that is excellent in both heat resistance and coking resistance.Furthermore, by using this porous alumina as a catalyst support, it is possible to provide a catalyst that is excellent in both heat resistance and coking resistance. [Brief explanation of the drawings]

[0048] [Figure 1] Figure showing the relationship between the SiO2 addition rate and specific surface area of ​​porous alumina to which only silica was added under three different heat treatment conditions [Figure 2] Figure showing the SiO2 addition rate and solid acid and solid base amounts of porous alumina to which only silica was added [Figure 3] Figure showing the results of measuring the SiO2 loading rate and coking amount for a steam reforming catalyst in which Ni-La is supported on porous alumina to which only silica is added. [Figure 4]Figure 1 shows the results of measuring the phase transition temperature to the α phase in porous alumina with only silica added and porous alumina with silica and barium oxide added. [Figure 5] A process flow diagram showing an outline of the method for preparing porous alumina according to the present invention by the kneading method. [Figure 6] A process flow diagram showing an outline of the method for preparing porous alumina according to the present invention using the first type of impregnation method. [Figure 7] A process flow diagram showing an outline of the method for preparing porous alumina according to the present invention using the second type of impregnation method. [Figure 8] A diagram showing the measurement results of the specific surface area of ​​an evaluation sample and a comparison sample prepared by the kneading method under three different heat treatment conditions. [Figure 9] Graph showing XRD diffraction patterns indicating the crystalline structures of evaluation samples and comparative samples prepared by the kneading method under three different heat treatment conditions. [Figure 10] Graph showing an XRD diffraction pattern showing the crystal structure of the evaluation sample shown in FIG. [Figure 11] A table showing the measurement results of the specific surface area of ​​several evaluation samples and comparison samples with different SiO2 and BaO addition rates prepared by the kneading method after heat treatment at 1200°C for 30 hours. [Figure 12] FIG. 1 shows the measurement results of the solid acid amount and solid base amount of an evaluation sample and a comparative sample prepared by a kneading method. [Figure 13] FIG. 1 shows the results of measuring the solid acidity of a plurality of evaluation samples and comparative samples with different SiO2 and BaO addition rates prepared by the kneading method. [Figure 14] A table showing the measurement results of the specific surface area of ​​several evaluation samples and comparison samples with different SiO2 and BaO addition rates prepared by the first type of impregnation method after heat treatment at 1200°C for 30 hours. [Figure 15] FIG. 1 shows the measurement results of the solid acidity of a plurality of evaluation samples and a comparison sample prepared by the first type impregnation method and having different SiO2 and BaO addition rates. [Figure 16]A process flow diagram showing an outline of the method for preparing porous alumina according to the present invention by precipitation method. DETAILED DESCRIPTION OF THE INVENTION

[0049] A preferred embodiment of the porous alumina according to the present invention (hereinafter, appropriately referred to as "the present embodiment") will be described.

[0050] The porous alumina according to this embodiment (hereinafter referred to as "the present alumina") is a porous alumina in which two types of oxides, silica (SiO) and barium oxide (BaO), are added to alumina (aluminum oxide, Al2O3). In the following description, the "present alumina" is , is alumina to which silica and barium oxide have been added, and when simply referred to as "alumina," it is alumina to which silica and barium oxide have not been added.

[0051] [1] Preparation method of this alumina: Next, a method for preparing the present alumina will be described. The method for preparing the present alumina basically comprises a step of adding silica to alumina and a step of adding barium oxide to alumina. Depending on the step of adding barium oxide, the preparation method may be an impregnation method, a kneading method, a precipitation method, a sol-gel method, or the like. In this embodiment, the kneading method and the impregnation method are used to prepare samples for evaluating the heat resistance and coking resistance of the present alumina.

[0052] Before describing the details of the kneading method and the impregnation method, the respective addition rates of silica and barium oxide added to the present alumina in this embodiment are defined as follows: The units of the SiO2 addition rate and BaO addition rate below are "mass%."

[0053] SiO2 addition rate = SiO2 addition amount / (alumina mass + SiO2 addition amount) x 100 BaO addition rate = BaO addition amount / (alumina mass + SiO2 addition amount) x 100

[0054] The amount of SiO2 added is the amount of Si content in the present alumina converted into the amount of SiO2 added, and the amount of BaO added is the amount of Ba content in the present alumina converted into the amount of BaO added. The Si content is the total content of Si present in the present alumina as a simple substance and as a compound, and the Ba content is the total content of Ba present in the present alumina as a simple substance and as a compound.

[0055] In this embodiment, the reference mass used as the basis for calculating the SiO2 addition rate and the BaO addition rate does not include the BaO addition rate. This is because it is more convenient to standardize the SiO2 addition rate and the BaO addition rate to (mass of alumina + SiO2 addition rate) in setting them in the alumina preparation method described below. The SiO2 addition rate and the BaO addition rate can be easily converted to addition rates based on a reference mass including the BaO addition rate. Furthermore, the unit of each addition rate can be converted from "mass%" to "mol%" as needed.

[0056] [1.1] Preparation of this alumina by kneading method: As shown in Figure 5, the method for preparing the present alumina using the kneading method can be broadly divided into the following steps: (1) mixing an alkoxysilane solution containing an alkoxysilane, a mixed solvent containing water and alcohol, and an inorganic acid with an aluminum solution containing an aluminum compound and water to prepare a mixed solution in which the aluminum compound and alkoxysilane are dissolved in the mixed solvent; (2) coprecipitating aluminum hydroxide with a silicon compound in the mixed solvent to form a precipitate; (3) adding an aqueous solution of a barium compound to the precipitate and kneading it; and (4) drying and firing the precipitate kneaded with the barium compound to form porous alumina (the present alumina) containing alumina, silica, and barium oxide.

[0057] The alkoxysilane contained in the alkoxysilane solution in step #K1 is preferably, for example, tetraethoxysilane (hereinafter referred to as "TEOS"); the alcohol is preferably, for example, ethanol; and the inorganic acid is preferably, for example, hydrochloric acid or nitric acid, but is not limited to these.

[0058] From the viewpoint of improving heat resistance, the aluminum solution in Step #K1 is preferably prepared by dissolving aluminum nitrate in water or by dissolving aluminum hydroxide in an aqueous nitric acid solution.

[0059] The mixing ratio of the alkoxysilane and the aluminum compound in the mixed solution prepared in step #K1 is adjusted so that the silica addition rate (SiO2 addition rate) in the porous alumina formed in step #K3 is a desired value.

[0060] The alkoxysilane and aluminum compound in the mixed solution prepared in step #K1 are uniformly dissolved in the mixed solvent composed of water and alcohol. In other words, the mixed solution forms a single liquid phase without phase separation.

[0061] In step #K2, a precipitating agent containing a basic compound is added to the acidic mixed solution while heating it preferably to 40°C to 100°C (for example, while heating it to reflux at 100°C). By adding the basic compound until the pH of the mixed solution reaches about 8 (for example, 8 to 8.5), aluminum hydroxide and a silicon compound are coprecipitated. The silicon compound contained in the precipitate produced by coprecipitation may be an alkoxysilane or a hydrolysis condensate thereof.

[0062] The precipitating agent includes, for example, at least one basic compound selected from the group consisting of aqueous ammonia, sodium hydroxide, potassium hydroxide, and urea, of which aqueous ammonia is preferred.

[0063] In step #K3, the precipitate is preferably removed from the mixed solution by a conventional method such as filtration and washed with room temperature water (distilled water). After washing, an aqueous solution of a barium compound is added to the precipitate and kneaded. The aqueous solution of the barium compound is preferably prepared by dissolving barium nitrate in water to form a barium nitrate aqueous solution, or by dissolving barium hydroxide in water to form a barium hydroxide aqueous solution.

[0064] In step #K4, the precipitate kneaded with the barium compound is dried, for example, in a dryer at 150°C for a predetermined time, and then the dried precipitate is pulverized, for example, in a mortar or the like to form powder. The dried and powdered precipitate is fired, for example, in air at 1000°C for 5 hours to form porous alumina (the present alumina) containing alumina, silica, and barium oxide. The alumina formed in the porous alumina is mainly composed of intermediate aluminas such as γ-alumina and θ-alumina.

[0065] [1.2] Preparation of this alumina by impregnation method: There are two types of impregnation methods for preparing the present alumina: a first type in which silica and barium oxide are added to pre-made porous alumina by impregnation to prepare the present alumina; and a second type in which silica is added to alumina to prepare silica-added porous alumina, and barium oxide is then added to the silica-added porous alumina by impregnation to prepare the present alumina.

[0066] [1.2.1] First type of impregnation method: As shown in Figure 6, the first type of impregnation method can be broadly divided into two steps: impregnating pre-made porous alumina (Al2O3 powder) with an alkoxysilane solution and an aqueous solution of a barium compound (step #I11); and drying and firing the porous alumina impregnated with the alkoxysilane solution and the aqueous solution of a barium compound to form porous alumina containing alumina, silica, and barium oxide (this alumina) (step #I12).

[0067] The ready-made porous alumina used in step #I11 is porous alumina mainly composed of intermediate alumina such as γ-alumina and θ-alumina. For example, in the examples of this embodiment, C20 manufactured by Nippon Light Metal is used as ready-made porous alumina, but it is not limited to the porous alumina manufactured by Nippon Light Metal, and an independently prepared alumina may also be used. In addition, the alkoxysilane contained in the alkoxysilane solution in step #I11 is kneaded As in step #K1 of the kneading method, TEOS is preferably used. As in step #K3 of the kneading method, the aqueous solution of the barium compound in step #I11 is preferably prepared by dissolving barium nitrate in water to form an aqueous barium nitrate solution, or by dissolving barium hydroxide in water to form an aqueous barium hydroxide solution.

[0068] In step #I12, the porous alumina impregnated with the alkoxysilane solution and the aqueous solution of the barium compound is dried, for example, in air at 150°C or in a rotary evaporator, and then calcined, for example, in air at 1000°C for 5 hours to obtain porous alumina containing alumina, silica, and barium oxide (the present alumina).

[0069] [1.2.2] Second type of impregnation method: As shown in Figure 7, the second type of impregnation method can be broadly divided into the following steps: mixing an alkoxysilane solution containing an alkoxysilane, a mixed solvent containing water and alcohol, and an inorganic acid with an aluminum solution containing an aluminum compound and water to prepare a mixed solution in which the aluminum compound and alkoxysilane are dissolved in the mixed solvent (Step #I21); co-precipitating aluminum hydroxide with a silicon compound in the mixed solvent to form a precipitate (Step #I22); drying and calcining the precipitate to form porous alumina containing alumina and silica (silica-added porous alumina) (Step #I23); impregnating the silica-added porous alumina with an aqueous solution of a barium compound (Step #I24); and drying and calcining the silica-added porous alumina impregnated with the aqueous solution of the barium compound to form porous alumina containing alumina, silica, and barium oxide (this alumina) (Step #I25).

[0070] Steps #121 and #122 of the second type of impregnation method are essentially the same as steps #K1 and #K2 of the kneading method described above, and redundant explanations will be omitted. Furthermore, the method for preparing silica-doped porous alumina in steps #121 to #123 is the same as the method for preparing a comparative sample with a BaO doping rate of 0% by mass by the kneading method described below, except for the firing temperatures in steps #K4 and #123.

[0071] In the second type of impregnation method, the silica-added porous alumina used in step #I24 may be a ready-made silica-added porous alumina instead of the one prepared in steps #I21 to #I23.

[0072] In step #123, the precipitate is preferably removed from the mixed solution by a conventional method such as filtration and washed with room temperature water (distilled water). The precipitate is dried to remove most of the solvent, and then crushed into powder in a mortar or the like.

[0073] The dried and powdered precipitate is then calcined to form silica-doped porous alumina, which is primarily composed of intermediate aluminas such as γ-alumina and θ-alumina.

[0074] The firing temperature is preferably 400 to 1000° C. If the firing temperature is too high, the transition of aluminum oxide to the α phase may proceed, resulting in a decrease in the specific surface area. The firing time is preferably about one hour to several tens of hours.

[0075] In step #I24, similar to step #K3 of the kneading method, the aqueous solution of the barium compound is preferably prepared by dissolving barium nitrate in water to form a barium nitrate aqueous solution, or by dissolving barium hydroxide in water to form a barium hydroxide aqueous solution.

[0076] In step #I25, similar to step #I12 of the first type of impregnation method, the silica-added porous alumina impregnated with the aqueous solution of a barium compound is dried, for example, in air at 150°C or in a rotary evaporator, and then calcined, for example, in air at 1000°C for 5 hours to obtain porous alumina containing alumina, silica, and barium oxide (the present alumina).

[0077] The alumina prepared by the kneading method or the first or second type of impregnation method is mainly composed of intermediate alumina such as γ-alumina or θ-alumina. The alumina is, for example, in the form of powder obtained by crushing secondary particles formed by agglomeration of acicular or fibrous primary particles and sieving them to a predetermined particle size range (e.g., 100 μm to 500 μm). The alumina can be in various shapes, such as powder, pellets, disks, honeycombs, etc.

[0078] In the above kneading method and the first or second type impregnation method, the amounts of silicon and barium added to alumina are determined by the amount of each solution added. In other words, the total amount of silicon and barium in the added solution is added to alumina by evaporating the added solution to dryness, so the above-mentioned SiO2 addition rate and BaO addition rate are uniquely determined by the mass of a given alumina or the amount of alkoxysilane solution used and the amount of each solution added.

[0079] [2] Evaluation of heat resistance and coking resistance of this alumina prepared by the kneading method: [2.1] Preparation of evaluation samples and comparative samples: The evaluation sample was prepared by the kneading method shown in FIG. 5 in the following manner.

[0080] To prepare the alkoxysilane solution for step #K1, 7.52 g of ethanol was added to 5.00 g of TEOS and stirred at room temperature for 5 minutes. Next, 1.25 g of hydrochloric acid (37% by mass) was added and stirred at room temperature for an additional 5 minutes. 71.23 g of water was added to this mixture to obtain a transparent, uniform 5.88% by mass TEOS solution.

[0081] In step #K1, the TEOS solution obtained as described above was added to a predetermined amount of 20% by mass aluminum nitrate aqueous solution to obtain a homogeneous mixed solution. The amounts of TEOS solution and aluminum nitrate aqueous solution required for the desired SiO2 loading were used. This mixed solution was heated to reflux, and 28% by mass ammonia water was added dropwise until the pH reached 8.5, followed by stirring. As the ammonia water was added, aluminum hydroxide and silicon compounds co-precipitated, forming a precipitate in the solution. This precipitate was separated by suction filtration using No. 1 filter paper. This precipitate was washed with distilled water. A predetermined amount of barium nitrate aqueous solution was added to the washed precipitate and kneaded. It was then dried in a dryer at 150°C for 20 hours. The dried precipitate was crushed in a mortar and calcined in air at 1000°C for 5 hours to obtain an evaluation sample of this alumina.

[0082] Three comparative samples were also prepared: one with 0% SiO2 addition, one with 0% BaO addition, and one with both 0% SiO2 and BaO addition. The evaluation samples and comparative samples are denoted by the symbol SK(Xs, Xb). Xs represents the SiO2 addition (mass%) and Xb represents the BaO addition (mass%).

[0083] A comparative sample with Xs = 0% by mass was prepared by using a blank solution containing no TEOS (a solution containing ethanol and hydrochloric acid whose concentration was adjusted with water) instead of the TEOS solution in step #K1. A comparative sample with Xb = 0% by mass was prepared by omitting the step of adding an aqueous solution of a barium compound to the precipitate after suction filtration and water washing and kneading it in step #K3.

[0084] [2.2] Sample evaluation method: The specific surface area of ​​each sample was measured using a fully automatic gas absorption spectrometer under the following three heat treatment conditions: The nitrogen adsorption BET method was performed using a deposition measurement device (MicrotracBEL BELSORP-max). The first heat treatment condition was the state before the other two heat treatments (before heat treatment). The second heat treatment condition was the state after the temperature was raised from room temperature to 1200°C at 10°C / min, heating was stopped, and the temperature was held at 1200°C for 5 hours (1200°C 5 hours). The third heat treatment condition was the state after the temperature was raised from room temperature to 1200°C at 10°C / min, heating was stopped, and the temperature was held at 1200°C for 30 hours (1200°C 30 hours).

[0085] The crystal structure of each sample was measured using an X-ray diffractometer (ULTIMA III manufactured by Rigaku) ​​by irradiating CuKα and using a two-dimensional high-speed detector. The amounts of Al, Si, and Ba in each sample were measured using an X-ray fluorescence analyzer (Supermini manufactured by Rigaku) ​​by the glass bead method. The solid acid-base content of each sample was analyzed using a catalyst evaluation device (MicrotracBEL BELCAT) by temperature programmed desorption (TPD, base probe molecule: NH3, acid probe molecule: :CO2).

[0086] The sample evaluation method was the same as that for evaluating the heat resistance and coking resistance of the present alumina prepared by the first type of impregnation method described below.

[0087] [2.3] Heat resistance evaluation results: Figure 8 shows the results of measuring the specific surface area of ​​one evaluation sample and five comparison samples prepared by the kneading method before heat treatment, at 1200°C for 5 hours, and at 1200°C for 30 hours. The evaluation sample and comparison samples used were SK(1,7), SK(0,0), SK(1,0), SK(3,0), SK(5,0), and SK(0,7).

[0088] Figure 9 shows XRD diffraction patterns indicating the crystal structure of one evaluation sample and three comparative samples prepared by the kneading method before heat treatment, at 1200°C for 5 hours, and at 1200°C for 30 hours. The evaluation sample and comparative samples used were SK(1,7), SK(0,0), SK(1,0), and SK(0,7). Figure 10 also shows the XRD diffraction patterns of evaluation sample SK(1,7) shown in Figure 9 under the three heat treatment conditions.

[0089] Figure 11 shows the results of measuring the specific surface area of ​​evaluation samples and comparative samples prepared by the kneading method after heat treatment at 1200°C for 30 hours, using an increased number of samples. The number of samples was 90 for evaluation samples and 24 for comparison samples, and the ranges of the SiO2 addition rate and BaO addition rate were wide, 0≦Xs≦30 and 0≦Xb≦100.

[0090] As shown in Figure 8, the comparative sample SK(0,7), which contained only barium oxide, did not exhibit a significant improvement in specific surface area compared to the addition of silica, regardless of the heat treatment conditions. However, after 5 hours of heat treatment at 1200°C, the evaluation sample SK(1,7) had a higher specific surface area than the comparative samples SK(1,0) and SK(0,7). Furthermore, even after 30 hours of heat treatment at 1200°C, the evaluation sample SK(1,7) maintained a larger specific surface area than the comparative samples SK(1,0) and SK(0,7). This confirmed that the combined addition of silica and barium oxide is effective in improving heat resistance. Furthermore, after heat treatment at 1200°C for 5 hours and 1200°C for 30 hours, the specific surface area of ​​the evaluation sample SK(1,7) was improved compared to the comparison sample SK(3,0). It was confirmed that even when the SiO2 addition rate was reduced from 3% by mass to 1% by mass, by adding an appropriate amount of barium oxide, a larger specific surface area (corresponding to the standard specific surface area) could be obtained than the specific surface area of ​​the comparison sample (corresponding to the standard porous alumina for comparison) to which only 3% by mass of silica was added.

[0091] From Figure 9(A), before heat treatment, peaks of θ-Al2O3 and γ-Al2O3 were confirmed in SK(0,0) and SK(1,0), and peaks of γ-Al2O3 and barium monoaluminate (BaO·Al2O3) were confirmed in SK(0,7) and SK(1,7). This was confirmed. Figure 9(B) confirms that after heat treatment at 1200°C for 5 hours, SK(0,0) and SK(1,0) were completely transformed into α-Al2O3. SK(0,7) and SK(1,7) exhibited peaks for barium monoaluminate and barium hexaaluminate (BaO 6Al2O3) in addition to the α-Al2O3 peak. Figure 9(C) shows that after heat treatment at 1200°C for 30 hours, the same products were observed as after heat treatment at 1200°C for 5 hours. However, the α-Al2O3 peak intensity of SK(1,7) was lower than that of the other comparative samples. Furthermore, as shown in Figure 8, the specific surface area remained high even after heat treatment at 1200°C for 30 hours. This indicates that the coexistence of silica and barium oxide suppresses the formation of α-Al2O3 and contributes to heat resistance.

[0092] Figure 11 shows that within the range of SiO2 addition rate Xs between 0.7% and 3% by mass and BaO addition rate Xb between 0.5% and 14% by mass, there exists a wide first effective range of SiO2 addition rate Xs and BaO addition rate Xb within which the specific surface area after heat treatment at 1200°C for 30 hours is equal to or greater than the specific surface area of ​​the comparative sample SK(3,0) (corresponding to the reference specific surface area) of the reference porous alumina (the area enclosed by the bold line in Figure 11). Furthermore, for the same SiO2 addition rate Xs, as the BaO addition rate Xb increases from 0.5% by mass, the specific surface area exceeds the reference specific surface area, reaches a maximum value, and then drops below the reference specific surface area. It can be seen that the range of BaO addition rate Xb within which the specific surface area is equal to or greater than the reference specific surface area becomes wider as the SiO2 addition rate Xs increases.

[0093] 11, by setting the BaO addition rate Xb as shown below depending on the SiO2 addition rate Xs, it is possible to maintain or improve the specific surface area after heat treatment at 1200°C for 30 hours within a range of 1 to 1.724 times that of the reference porous alumina. Even when the SiO2 addition rate Xs is reduced from 3 mass% to 0.7 mass%, the specific surface area is 1 to 1.034 times that of the reference specific surface area when the BaO addition rate Xb is in the range of 5 mass%≦Xb≦10 mass%, achieving heat resistance almost equivalent to that of the reference porous alumina. Furthermore, even when the SiO2 addition rate Xs is reduced from 3 mass% to 1 mass%, the specific surface area is 1 to 1.414 times that of the reference specific surface area when the BaO addition rate Xb is in the range of 3 mass%≦Xb≦10 mass%, achieving heat resistance almost equivalent to or better than that of the reference porous alumina. Furthermore, even when the SiO2 addition rate Xs is reduced from 3% by mass to 2% by mass, the specific surface area is 1 to 1.655 times the reference specific surface area when the BaO addition rate Xb is in the range of 1% by mass≦Xb≦14% by mass, achieving heat resistance roughly equivalent to or better than that of standard porous alumina. Furthermore, when the SiO2 addition rate Xs is 3% by mass, the specific surface area is 1.207 to 1.724 times the reference specific surface area when the BaO addition rate Xb is in the range of 0.5% by mass≦Xb≦14% by mass, achieving heat resistance 20% or higher than that of standard porous alumina. In particular, when the SiO2 addition rate Xs is in the range of 1 to 3% by mass, increasing the BaO addition rate Xb to around 5% by mass improves the specific surface area by approximately 1.4 to 1.7 times the reference specific surface area, further improving heat resistance.

[0094] From the above, the first effective range of the SiO2 addition rate Xs and the BaO addition rate Xb, in which the specific surface area after heat treatment at 1200°C for 30 hours is equal to or greater than the reference specific surface area, is approximately as follows: 0.7 mass%≦Xs<1 mass% and 5 mass%≦Xb≦10 mass%, or 1 mass%≦Xs<2 mass% and 3 mass%≦Xb≦10 mass%, or 2% by mass≦Xs≦3% by mass, and 1% by mass≦Xb≦14% by mass.

[0095] However, even if it is outside the first effective range, for example, the specific surface area of ​​the evaluation sample SK(3,0.5) having an SiO2 addition rate Xs of 3 mass % and a BaO addition rate Xb of 0.5 mass % is In the vicinity of the thick line frame in FIG. 11, the specific surface area after heat treatment at 1200° C. for 30 hours may be larger than the reference specific surface area.

[0096] [2.4] Coking resistance evaluation results: The results of measuring the solid acid content and solid base content of one evaluation sample and five comparative samples prepared by the kneading method are shown in Figure 12. The evaluation sample and comparative samples used were SK(1,7), SK(0,0), SK(1,0), SK(3,0), SK(5,0), and SK(0,7).

[0097] The solid acidity of the evaluation samples and the comparative samples prepared by the kneading method was measured using an increased number of samples, and the results are shown in Figure 13. The number of samples was 15 for the evaluation samples and 9 for the comparative samples, and the ranges of the SiO2 addition rate and the BaO addition rate were wide, 0≦Xs≦5 and 0≦Xb≦14.

[0098] 12, in the comparative sample with a BaO addition rate Xb of 0 mass%, the solid acid amount increases and the solid base amount decreases as the SiO2 addition rate Xs increases, similar to the measurement results shown in FIG. 2. In contrast, in the evaluation sample SK(1,7) and the comparative sample SK(0,7), which contain barium with a BaO addition rate Xb of 7 mass%, the solid acid amount decreases and the solid base amount increases compared to the comparative samples SK(1,0) and SK(0,0) with the same SiO2 addition rate Xs. The solid acid amount of the evaluation sample SK(1,7) has decreased to a level equivalent to or below that of the comparative sample SK(0,0), which has a SiO2 addition rate Xs and a BaO addition rate Xb of 0 mass%.

[0099] 13, it was confirmed that when the SiO2 addition rate Xs is in the range of 0 mass% to 5 mass%, and the SiO2 addition rate Xs is the same, the solid acid amount monotonically decreases as the BaO addition rate Xb increases from 0 mass% to 14 mass%. Also, when the BaO addition rate Xb is in the range of 0 mass% to 14 mass%, and the BaO addition rate Xb is the same, the solid acid amount monotonically increases as the SiO2 addition rate Xs increases from 0 mass% to 5 mass%.

[0100] Furthermore, Figure 13 shows that when the SiO2 addition rate Xs is 3 mass% or less and the BaO addition rate Xb is 14 mass% or less, the solid acidity of this alumina is less than the solid acidity of the comparison sample SK(3,0), which corresponds to the standard porous alumina, and the coking resistance is improved compared to the standard porous alumina.

[0101] [2.5] Summary of evaluation results: 8 and 12, it can be seen that the evaluation sample SK(1,7) had an improved specific surface area and a reduced solid acidity after heat treatment at 1200°C for 5 hours and 1200°C for 30 hours compared to the comparison sample SK(3,0), which corresponds to the standard porous alumina. This confirms that the addition of a mixture of silica and barium oxide is effective in improving both heat resistance and coking resistance.

[0102] 11 and 13, it was found that within the range of SiO2 addition rate Xs of 3% by mass or less and BaO addition rate Xb of 14% by mass or less, the specific surface area of ​​the present alumina after heat treatment at 1200°C for 30 hours is equal to or greater than the specific surface area (reference specific surface area) of comparative sample SK(3,0), and the solid acidity of the present alumina is equal to or less than the solid acidity of comparative sample SK(3,0). This confirmed that the addition of silica and barium oxide within this effective range is effective in improving both heat resistance and coking resistance. This effective range is the first effective range of SiO2 addition rate Xs and BaO addition rate Xb within which the specific surface area of ​​the present alumina after heat treatment at 1200°C for 30 hours is equal to or greater than the reference specific surface area.

[0103] Furthermore, as is clear from FIG. 11, by narrowing the ranges of the SiO2 addition rate Xs and the BaO addition rate Xb to 1 mass%≦Xs≦3 mass% and 3 mass%≦Xb≦10 mass% relative to the above-mentioned effective ranges, the specific surface area of ​​this alumina after heat treatment at 1200°C for 30 hours is further increased, and the heat resistance is further improved while maintaining the coking resistance.

[0104] [3] Evaluation of heat resistance and coking resistance of this alumina prepared by the first type of impregnation method: [3.1] Preparation of evaluation samples and comparative samples: C20 manufactured by Nippon Light Metal Co., Ltd. was used as the pre-made porous alumina, and the alkoxysilane solution and barium compound aqueous solution were prepared using a TEOS solution and a barium nitrate aqueous solution in amounts corresponding to the desired SiO2 and BaO addition rates. The processes in steps #I11 and #I12 described above were carried out to obtain an evaluation sample of this alumina.

[0105] Three comparative samples were also prepared: one with 0% SiO2 content by mass, one with 0% BaO content by mass, and one with both 0% SiO2 and BaO content by mass. In step #I11 above, the comparative sample with 0% SiO2 content was impregnated without the TEOS solution, and the comparative sample with 0% BaO content was impregnated without the barium nitrate aqueous solution. The evaluation samples and comparative samples are denoted by the symbols SI(Xs, Xb). Xs represents the SiO2 content (mass%), and Xb represents the BaO content (mass%).

[0106] [3.2] Heat resistance evaluation results: Figure 14 shows the results of measuring the specific surface area of ​​the evaluation samples and the comparative samples prepared by the first type of impregnation method after heat treatment at 1200°C for 30 hours. There were 20 evaluation samples and 3 comparative samples, and the ranges of the SiO2 addition rate and BaO addition rate were 0≦Xs≦3 and 0≦Xb≦14.

[0107] 14, it can be seen that within the range of 0.7% by mass or more and 3% by mass or less of SiO2 addition rate Xs and 1% by mass or more and 14% by mass or less of BaO addition rate Xb, there exists a wide second effective range of SiO2 addition rate Xs and BaO addition rate Xb where the specific surface area after heat treatment at 1200°C for 30 hours is equal to or greater than the specific surface area (corresponding to the reference specific surface area) of the comparative sample SI(3,0) corresponding to the reference porous alumina (the region surrounded by a thick line frame in FIG. 14). This second effective range coincides with the first effective range for the evaluation sample prepared by the kneading method shown in FIG. 11. Furthermore, at the same SiO2 addition rate Xs, when the BaO addition rate Xb increases from 1 mass%, the specific surface area exceeds the reference specific surface area, reaches a maximum value, and then decreases to a value equal to or less than the reference specific surface area. Also, the range of the BaO addition rate Xb where the specific surface area is equal to or greater than the reference specific surface area becomes wider as the SiO2 addition rate Xs increases. These are consistent with the measurement results shown in FIG. 11.

[0108] Therefore, the explanation regarding the heat resistance of the evaluation sample prepared by the kneading method shown in FIG. 11 also applies to the evaluation sample prepared by the first type of impregnation method shown in FIG.

[0109] [3.3] Evaluation results of coking resistance: The measurement results of the solid acidity of the evaluation samples and the comparative samples prepared by the first type of impregnation method are shown in Figure 15. The number of samples was 12 for the evaluation samples and 8 for the comparative samples, and the ranges of the SiO2 addition rate and the BaO addition rate were 0≦Xs≦5 and 0≦Xb≦20, respectively.

[0110] From Figure 15, when the SiO2 addition rate Xs is in the range of 0 mass% to 5 mass%, When Xs was the same, it was confirmed that the solid acid amount monotonically decreased as the BaO addition rate Xb increased from 0 mass% to 20 mass%, compared to the solid acid amount of the comparative sample with a BaO addition rate Xb of 0 mass%. This monotonically decreasing solid acid amount as the BaO addition rate Xb increased is consistent with the case of the evaluation sample prepared by the kneading method shown in FIG.

[0111] Furthermore, Figure 15 shows that within the range where the SiO2 addition rate Xs is 3 mass% or less and the BaO addition rate Xb is 14 mass% or less, the solid acidity of the alumina prepared by the first type impregnation method, as well as the evaluation sample prepared by the kneading method shown in Figure 13, is less than the solid acidity of the comparison sample SI(3,0), which corresponds to the standard porous alumina, and the coking resistance is improved compared to the standard porous alumina.

[0112] [3.4] Summary of evaluation results: 14 and 15, similar to the evaluation samples prepared by the kneading method shown in Figures 11 and 13, the present alumina prepared by the first impregnation method also shows a wide effective range of SiO2 addition rate Xs and BaO addition rate Xb within which the specific surface area of ​​the present alumina after heat treatment at 1200 °C for 30 hours is equal to or greater than the specific surface area (reference specific surface area) of the comparative sample SI(3,0), and the solid acidity of the present alumina is equal to or less than the solid acidity of the comparative sample SI(3,0). As a result, it was confirmed that the mixed addition of silica and barium oxide within this effective range is effective in improving both heat resistance and coking resistance. The effective range is the second effective range of the SiO2 addition rate Xs and the BaO addition rate Xb in which the specific surface area of ​​the present alumina after heat treatment at 1200°C for 30 hours is equal to or greater than the reference specific surface area.

[0113] As described above, regardless of the preparation method, the addition of silica and barium oxide improves both heat resistance and coking resistance within the same effective ranges of SiO2 addition rate Xs and BaO addition rate Xb (the same as the first and second effective ranges). This is due to the fact that the components contained in samples fired at 1000°C are the same regardless of the preparation method, whether kneading or impregnation. Furthermore, when the sample is fired at 1200°C for a long time, solid-state reactions between silica and alumina and between barium oxide and alumina begin. As described above, with the addition of barium alone, the alpha phase of gamma-alumina is formed faster than the formation of barium hexaaluminate, which is essential for sintering suppression, and high-temperature heat treatment reduces the specific surface area. Furthermore, while the addition of silica can delay the alpha phase to some extent in the early stages of sintering, it still cannot completely prevent alpha phase during long firing at 1200°C. On the other hand, when silica and barium oxide are added together, the silica delays the initial alpha phase, and the subsequent formation of barium hexaaluminate suppresses the formation of alpha-alumina, presumably maintaining a high specific surface area. These trends can be explained by Figures 8, 9, and 10.

[0114] [4] Another embodiment of the method for preparing the alumina: In the above embodiment, the kneading method and the first and second types of impregnation methods have been described as methods for preparing the present alumina, but the method for preparing the present alumina is not limited to a specific preparation method as long as it is a preparation method that can accurately control the SiO2 addition rate and the BaO addition rate. Other preparation methods for the present alumina include preparation methods using a precipitation method, a sol-gel method, etc. Below, a brief description will be given of the preparation method using the precipitation method.

[0115] [4.1] Preparation of this alumina by precipitation method: As shown in FIG. 16, the method for preparing the present alumina by the precipitation method can be roughly divided into two steps: mixing an alkoxysilane solution containing an alkoxysilane, a mixed solvent containing water and alcohol, and an inorganic acid, and mixing an aqueous solution of a barium compound with an aluminum solution containing an aluminum compound and water. The method comprises the steps of: preparing a mixed solution in which an aluminum compound, an alkoxysilane, and a barium compound are dissolved in a mixed solvent (Step #P1); coprecipitating aluminum hydroxide with a silicon compound in the mixed solvent to form a first precipitate (Step #P2); cooling the solution containing the precipitate to 60°C or below and then adding ammonium carbonate to precipitate barium as a carbonate to form a second precipitate (Step #P3); and filtering and washing the precipitate containing the barium compound by suction filtration, drying and calcining the filtered and washed precipitate to form porous alumina (the present alumina) containing aluminum oxide, silica, and barium oxide.

[0116] The alkoxysilane solution, aluminum solution, and aqueous solution of barium compound used in step #P1 are the same as the alkoxysilane solution, aluminum solution, and aqueous solution of barium compound used in step #K1 and step #K3 of the kneading method described above, and a duplicated description will be omitted. Note that in Figure 16, a TEOS solution is exemplified as the alkoxysilane solution, and a barium nitrate aqueous solution is exemplified as the aqueous solution of the barium compound. Furthermore, step #P2 is basically the same as step #K2 of the kneading method described above, and a duplicated description will be omitted. However, in step #P2, the barium compound does not co-precipitate as barium hydroxide with the aluminum hydroxide and silicon compound, so step #P3 is required.

[0117] In Step #P3, the solution containing the precipitate is cooled to 60°C or below in order to avoid decomposition of ammonium carbonate, which decomposes into carbon dioxide gas, ammonia, and water at temperatures above 60°C.

[0118] [5] Modifications of this alumina: This alumina is a porous alumina prepared by, for example, the above-mentioned kneading method, impregnation method, precipitation method, etc., so that the SiO2 addition rate and BaO addition rate fall within the above-mentioned effective ranges, and then mixed with two oxides, silica and barium oxide, to prepare the alumina. Therefore, the SiO2 addition rate and BaO addition rate are on average within the above-mentioned effective ranges with respect to the total amount of the prepared alumina.

[0119] However, when a heterogeneous porous alumina having an SiO2 addition rate and a BaO addition rate outside the effective ranges (e.g., alumina alone, alumina containing only silica, alumina containing only barium oxide, alumina containing silica and barium oxide, alumina containing an oxide other than silica and barium oxide, etc.) is mixed with the present alumina and presents partially or locally, even if the SiO2 addition rate and the BaO addition rate are outside the effective ranges on average relative to the total amount of the present alumina and the heterogeneous porous alumina, as long as the present alumina exists separately from the heterogeneous porous alumina and has the desired properties (specific surface area and solid acidity after heat treatment at 1200°C for 30 hours), the portion present as the present alumina can naturally achieve the desired effect of providing a porous alumina with excellent heat resistance and coking resistance. Therefore, as one embodiment of the present alumina, the present alumina can take a form in which the above-mentioned heterogeneous porous alumina is present partially or locally.

[0120] Furthermore, as long as the SiO2 addition rate and BaO addition rate of the present alumina are within the above-mentioned effective ranges and the desired properties (specific surface area and solid acidity after heat treatment at 1200°C for 30 hours) are maintained, components other than silica and barium oxide (oxides, etc.) may be added to the alumina in small amounts relative to the silica and barium oxide.

[0121] [6] Application examples of this alumina: As mentioned above, this alumina has excellent heat resistance, and therefore it is suitable for use as a catalyst supporting catalytically active components. It is useful as a catalyst carrier, a filter, etc. Furthermore, since the present alumina has excellent heat resistance as well as excellent coking resistance as described above, it is suitable as a catalyst carrier used in reactions using hydrocarbons, such as steam reforming reactions. [Industrial Applicability]

[0122] The present invention is suitably used for porous alumina in which silica and barium oxide are added to aluminum oxide, and for catalysts using the porous alumina as a carrier.

Claims

1. Aluminum oxide (Al ２ O ３ ) to silica (SiO ２ ) and barium oxide (BaO) are added to the porous alumina, The barium oxide is barium monoaluminate (BaO.Al ２ O ３ ) or as barium monoaluminate (BaO.Al ２ O ３ ) and barium hexaaluminate (BaO.6Al ２ O ３ ) exists as The aluminum oxide and SiO ２ The amount of SiO relative to the total mass of the added amount ２ The proportion of the added amount is SiO ２ The addition rate (mass%) is The aluminum oxide and the SiO ２ The ratio of the amount of BaO added to the total mass of the added amounts is defined as the BaO addition rate (mass%). The SiO ２ The amount of addition is determined by adjusting the content of silicon (Si) in the porous alumina to SiO ２ The amount converted into the content of The amount of BaO added is the amount obtained by converting the content of barium (Ba) in the porous alumina into the content of BaO, The SiO ２ When the BaO content is in the range of 3% by mass or less, and the BaO content is in the range of 14% by mass or less, The specific surface area of ​​the porous alumina measured by a predetermined measuring method after heat treatment at 1200° C. for 30 hours is ２ The specific surface area of ​​the porous alumina was determined to be equal to or greater than the specific surface area of ​​a reference porous alumina for comparison, which was prepared by the same preparation method except that the BaO content was set to 3 mass % and the BaO content was set to 0 mass %. Porous alumina, characterized in that said silica and said barium oxide are added to said aluminum oxide.

2. The SiO ２ When the addition rate is in the range of 0.7 mass% or more and 3 mass% or less, and the BaO addition rate is in the range of 14 mass% or less, so that the specific surface area of ​​the porous alumina is equal to or greater than the reference specific surface area.

2. The porous alumina according to claim 1, wherein said silica and said barium oxide are added to said aluminum oxide.

3. The SiO ２ the BaO addition rate is in the range of 3 mass% or less or in the range of 0.7 mass% to 3 mass%, and the BaO addition rate is in the range of 0.5 mass% to 14 mass%, so that the specific surface area of ​​the porous alumina is equal to or greater than the reference specific surface area.

2. The porous alumina according to claim 1, wherein said silica and said barium oxide are added to said aluminum oxide.

4. Aluminum oxide (Al ２ O ３ ) to silica (SiO ２ ) and barium oxide (BaO) are added to the porous alumina, The barium oxide is barium monoaluminate (BaO.Al ２ O ３ ) or as barium monoaluminate (BaO.Al ２ O ３ ) and barium hexaaluminate (BaO.6Al ２ O ３ ) exists as The aluminum oxide and SiO ２ The amount of SiO relative to the total mass of the added amount ２ SiO specified by the ratio of added amount ２ The addition rate (mass%) is Xs (mass%), where ２ The amount of addition is determined by adjusting the content of silicon (Si) in the porous alumina to SiO ２ The amount converted into the content of The aluminum oxide and the SiO ２ When the BaO addition rate (mass%) defined as the ratio of the BaO addition amount to the total mass of the addition amounts is set to Xb (mass%), the BaO addition amount is the amount obtained by converting the content of barium (Ba) in the porous alumina into the content of BaO, 0.7 mass%≦Xs<1 mass% and 5 mass%≦Xb≦10 mass%, or 1 mass%≦Xs<2 mass% and 3 mass%≦Xb≦10 mass%, or 2% by mass≦Xs≦3% by mass, and 1% by mass≦Xb≦14% by mass, The porous alumina is characterized in that:

5. A steam reforming catalyst comprising the porous alumina according to any one of claims 1 to 4 and a catalytic substance supported on the porous alumina.

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