Methane combustion catalyst and method for purifying combustion exhaust gas containing sulfur oxides

Abstract

The present invention relates to a Pt / SnO2-based methane combustion catalyst for combusting methane in a combustion exhaust gas containing sulfur oxides, the methane combustion catalyst being configured such that platinum and / or platinum oxide is supported on a tin oxide-based carrier containing tin oxide as an essential component. In the methane combustion catalyst according to the present invention, the tin oxide-based carrier comprises antimony-doped tin oxide (ATO). At this time, the doping amount of antimony in the tin oxide-based carrier is preferably 0.1-5.0 mass%. In the present invention, the antimony doped in tin oxide improves the ability of the tin oxide to supply oxygen to platinum and the like. As a result, the activity and durability of the methane combustion catalyst can be improved. The Pt / SnO2-based methane combustion catalyst is highly active and excellent in durability even without the additional carrying of iridium or without the application of an overcoat layer.

Description

Methane combustion catalyst and method for purifying combustion exhaust gas containing sulfur oxides

[0001] This invention relates to a methane combustion catalyst for oxidizing and removing methane from combustion exhaust gas containing sulfur oxides. More specifically, it relates to a methane combustion catalyst that suppresses catalyst poisoning by sulfur oxides, is low-cost compared to conventional technologies, and possesses high activity and durability. Furthermore, this invention relates to a method for purifying combustion exhaust gas by oxidizing and removing methane using the catalyst.

[0002] Exhaust gases from engines and boilers that use hydrocarbons such as natural gas, city gas, diesel fuel, and kerosene contain nitrogen oxides (NOx) and sulfur oxides (SO4). ２ In addition to sulfur dioxide (SOx), carbon monoxide (CO), odor-causing substances, and particulate matter, exhaust gases also contain unburned hydrocarbons. Since all of these contribute to environmental pollution, exhaust gases are treated with filters and catalytic converters before being released. In particular, methane has been reported to have more than 20 times the greenhouse effect of carbon dioxide, making its removal extremely important from an environmental protection perspective.

[0003] As a catalyst for oxidizing and removing methane from combustion exhaust gas containing sulfur oxides as described above, a tin oxide support (SnO) made of tin oxide is used. ２ A methane combustion catalyst with platinum supported on a support is known (Patent Document 1). The reason why tin oxide supports are used in methane combustion catalysts is that inorganic oxides such as alumina supports and zirconia supports, which have been used for a long time as catalysts for hydrocarbon purification, are not effective in oxidizing and removing methane. In particular, when treating exhaust gas containing sulfur oxides, catalysts using alumina supports and the like suffer from a significant decrease in activity due to catalyst poisoning.

[0004] Furthermore, improvements have been made to methane combustion catalysts using tin oxide supports, and in particular, the effectiveness of methane combustion catalysts supporting iridium in addition to platinum has been reported (Patent Document 2). This methane combustion catalyst has improved durability against catalyst poisoning by sulfur oxides due to the additional support of iridium. In the following description, a methane combustion catalyst in which platinum, etc., is supported on a tin oxide support is referred to as Pt / SnO ２ Catalyst, Pt-Ir / SnO２ may be referred to as a catalyst. Also, these may be collectively referred to as Pt / SnO ２ -based catalysts.

[0005] The applicant of the present application has disclosed a methane combustion catalyst in which the Pt / SnO ２ -based catalyst has been further improved in activity and durability (Patent Documents 3 and 4). In this improvement, the applicant of the present application has been studying the activation mechanism of the Pt / SnO ２ -based catalyst for methane combustion. According to this study, the methane combustion activity of the Pt / SnO ２ -based catalyst is considered to be important in that platinum is in the state of an oxide (PtO or PtO ２ ).

[0006] And, as a factor of catalyst poisoning of the Pt / SnO ２ -based catalyst by sulfur oxides, it is considered to be due to the alteration of catalyst particles by sulfur oxides. Specifically, sulfur oxides such as SO ２ that fly near platinum oxide, which is a catalyst particle, are easily oxidized, so they reduce platinum oxide,夺取 oxygen, and desorb as SO ３ . Platinum particles reduced and metallized by sulfur oxides such as SO ２ sinter with surrounding metallized platinum particles to form low-activity coarse platinum particles. Catalyst poisoning in the Pt / SnO ２ -based catalyst is caused by the metallization of platinum oxide and the sintering of platinum particles as described above, and as long as these continue, the catalyst activity continues to decrease.

[0007] The above catalyst poisoning mechanism supports the improvement of durability by additional loading of iridium in the Pt / SnO ２ -based catalyst. According to the applicant of the present application, iridium in the Pt-Ir / SnO ２ catalyst, like platinum, is an oxide (IrO ２It exists as iridium oxide, and this iridium oxide has the function of maintaining the oxidized state of platinum by supplying oxygen to the metallized platinum. Iridium oxide is metallized by reduction by oxygen supply to platinum and reduction by sulfur oxide, but it is possible to maintain the iridium oxide state by receiving oxygen supply from the tin oxide support. This cycle of reduction (oxygen supply to platinum) and oxidation (oxygen acceptance from the tin oxide support) of iridium oxide creates a reduction and oxidation cycle in the platinum oxide, and by avoiding the metallic platinum state which is prone to sintering, it contributes to maintaining activity and improving durability.

[0008] Based on the above considerations, the applicant has developed a Pt / SnO2 that enables improved methane combustion activity and durability. ２ Two types of methane combustion catalysts consisting of a Pt / SnO catalyst are disclosed (Patent Documents 3 and 4). In the first methane combustion catalyst by the present applicant, Pt / SnO ２ Considering that the methane combustion activity in the catalyst system is exerted by the presence of platinum oxide, the manufacturing process (platinum loading process) is optimized, and the proportion of platinum oxide on the support is increased, thereby making more effective use of the reduction-oxidation cycle described above (Patent Document 3). Furthermore, in the second methane combustion catalyst by the present applicant, Pt-Ir / SnO ２ A region mainly composed of tin oxide without platinum is formed as an overcoat layer on the surface of the catalyst system, and platinum oxide is supplied from this overcoat layer to make more effective use of the reduction-oxidation cycle described above (Patent Document 4).

[0009] These methane combustion catalysts developed by the present applicant improve activity and durability by optimizing the amount and state of platinum oxide on the tin oxide support while applying an appropriate oxygen supply source (iridium, overcoat layer), thereby efficiently promoting the reduction and oxidation cycle of platinum oxide.

[0010] Patent No. 4283037 Specification Patent No. 4429950 Specification Patent No. 6883135 Specification Patent No. 7038269

[0011] The Pt / SnO of the above-mentioned Patent Documents 3 and 4 by the applicant of this application ２ All methane combustion catalysts are conventional Pt / SnO２ It has been confirmed that this catalyst exhibits high activity compared to conventional catalysts, enabling lower reaction temperatures and improved durability. Therefore, it can be said to be an extremely good methane combustion catalyst in terms of performance, but there are areas that need improvement. This is the need for improvement in terms of manufacturing costs. In other words, although not limited to the methane combustion catalysts of Patent Documents 3 and 4, conventional Pt / SnO ２ In system catalysts, considering the catalyst poisoning mechanism described above, the additional support of iridium is considered essential to improve durability. However, since iridium, like platinum, is a precious metal, it contributes to increased costs for methane combustion catalysts.

[0012] Furthermore, regarding the methane combustion catalyst described in Patent Document 4, the formation of the overcoat layer adds an extra step to the manufacturing process of the methane combustion catalyst. This increase in the number of steps is reflected in the efficiency and cost of catalyst manufacturing. Moreover, there is a demand to reduce costs by minimizing the amount of platinum (platinum oxide), which is the active species in methane combustion, while maintaining its activity.

[0013] The present invention was made against the background described above, and the Pt / SnO ２ The objective is to provide a methane combustion catalyst that is low-cost while exhibiting higher activity and durability than conventional technologies.

[0014] Conventional Pt / SnO ２ In the methane combustion catalyst of the system, the additionally supported iridium or overcoat layer is an oxygen source that promotes the progression of the reduction and oxidation cycle of platinum oxide. The inventors have developed the above-mentioned Pt / SnO ２ Considering the poisoning mechanism of the methane combustion catalyst, we decided to seek an oxygen source in the support material to replace iridium and the overcoat layer. The support material has the closest relationship with platinum (platinum oxide), which is the catalyst component. Furthermore, in the above considerations of the present applicant, the tin oxide support material also acts as an oxygen source and is involved in the reduction and oxidation cycle of iridium (iridium oxide). The inventors considered that by increasing the mobility of oxygen contained in tin oxide, it can function as a more efficient oxygen source and promote the above cycle in platinum (platinum oxide).

[0015] Accelerating the reduction-oxidation cycle of platinum (platinum oxide) provides greater flexibility in setting the relative abundance of platinum oxide. If the reduction-oxidation cycle of platinum (platinum oxide) is accelerated compared to conventional methods, metallic platinum, even at high concentrations, will quickly form oxides in the atmosphere of methane combustion, making sintering less likely. If the reduction-oxidation cycle of platinum and platinum oxide proceeds optimally, there is no need to increase the proportion of platinum oxide as in conventional technology, and the necessary methane combustion activity can be expected even with a reduced amount of supported platinum. This reduction in supported platinum also contributes to lowering catalyst costs.

[0016] Based on the above considerations, the inventors diligently investigated and found that, as a method to enhance the oxygen supply capacity of the support, it is preferable to use a tin oxide-based support that contains other components in addition to tin oxide, as in conventional methods. Specifically, they found that using a tin oxide-based support consisting of antimony-doped tin oxide (ATO), in which tin oxide is doped with antimony (Sb), as a catalyst support is effective, leading to the present invention.

[0017] In other words, the present invention, which solves the above problems, is a methane combustion catalyst for burning methane in combustion exhaust gas containing sulfur oxides, wherein platinum and / or platinum oxide are supported on a tin oxide-based carrier containing tin oxide as an essential component, and the tin oxide-based carrier is characterized in that the tin oxide-based carrier is made of antimond-doped tin oxide.

[0018] The present invention will be described in more detail below. Pt / SnO according to the present invention ２ The methane combustion catalyst, a type of catalytic catalyst, has as its basic structure an antimond-doped tin oxide as a tin oxide-based support, on which platinum (platinum oxide), the catalytic component, is supported. The following description explains each component of the catalyst and provides a detailed explanation of the catalyst manufacturing method. In this specification, a support containing tin oxide as an essential component is referred to as a tin oxide-based support. Furthermore, among tin oxide-based supports, a support composed solely of tin oxide is referred to as a tin oxide support.

[0019] (A) Structure of the methane combustion catalyst according to the present invention (A-1) Catalyst support (antimony-doped tin oxide) As described above, the methane combustion catalyst according to the present invention is characterized by using antimony-doped tin oxide, which is tin oxide doped with antimony, as the tin oxide-based support. Doping tin oxide having a rutile-type crystal structure with antimony increases the mobility (ease of movement) of interstitial oxygen. This increases the efficiency of oxygen supply from the support, and the rate of the reduction-oxidation cycle of platinum oxide during the methane oxidation reaction can be increased. Such high efficiency of oxygen supply eliminates the need for oxygen supply by iridium or an overcoat layer. Furthermore, according to the present invention, methane combustion activity can be exhibited with high efficiency even with a relatively small amount of supported platinum. This, along with the elimination of iridium support, contributes to reducing the cost of the methane combustion catalyst.

[0020] Antimond-doped tin oxide is tin oxide (SnO ２ )An antimony atoms, which act as dopants, are incorporated into the crystal, and the Sn sites are replaced by antimony atoms.In this invention, SnO ２ Antimony is used as a dopant element for the support because it is particularly effective in increasing the oxygen supply efficiency mentioned above, and is thought to be effective in improving both the initial activity and durability of the catalyst. Furthermore, the valency of the antimony doped into tin oxide is not limited. Antimony is trivalent (Sb ３＋ ), tetravalent (Sb ４＋ ), pentavalent (Sb ５＋ Antimony with different valencies exists, but any antimony with any valency may be doped, or multiple types of antimony with different valencies may be doped.

[0021] Furthermore, the above-mentioned effects in the present invention are exhibited with antimony-doped tin oxide, and these effects are not exhibited with a simple mixture of tin oxide and an antimony compound (such as antimony oxide). The increase in oxygen supply efficiency in tin oxide-based carriers is due to a change in their crystal structure. Therefore, the above-mentioned effects are not exhibited with mixtures that do not affect the crystal structure of tin oxide. Accordingly, although a mixture of tin oxide and an antimony compound may be considered a tin oxide-based carrier under the wording, it is not a carrier of the present invention.

[0022] The fact that the support used in the catalyst of the present invention is a tin oxide-based support and antimony-doped tin oxide can be confirmed by performing both compositional analysis and structural analysis on the support or the entire catalyst. Specifically, in compositional analysis such as ICP (inductively coupled plasma emission), antimony is detected along with tin in doped tin oxide. On the other hand, in structural analysis such as XRD (X-ray diffraction), only peaks derived from tin oxide are observed in the diffraction pattern of doped tin oxide, and no peaks derived from antimony compounds are seen. However, a peak shift of the peak derived from tin oxide may be observed in doped tin oxide. Thus, when compositional analysis and structural analysis are performed on the support or the entire catalyst, if the presence of antimony is confirmed but the presence of antimony compounds is not confirmed, the support is confirmed to be antimony-doped tin oxide. In addition, in the case of a mixture of tin oxides, peaks derived from the mixed antimony compound appear in the XRD diffraction pattern, so the presence of antimony is detected in both compositional analysis and structural analysis.

[0023] In the antimony-doped tin oxide support, the amount of antimony doped is preferably 0.1% by mass or more and 5.0% by mass or less in terms of antimony relative to the mass of the tin oxide support. In tin oxide support with a doping amount of less than 0.1% by mass, the above-mentioned effects are insufficient. Furthermore, while antimony doped into tin oxide does not improve catalytic activity, tin oxide has the effect of imparting methane combustion activity to the catalyst components. Therefore, if the amount of antimony doping is excessive, there is a risk of decreased activity, so it is preferable to keep the doping amount at 5.0% by mass or less. The amount of doping of the dopant element can be measured by the compositional analysis (ICP, etc.) described above. Also, as described above, in this invention the amount of doping for the tin oxide support is specified, so when analyzing the methane combustion catalyst to measure and calculate the amount of doping, it is preferable to calculate the amount of doping by excluding the mass of components other than tin oxide and antimony (such as platinum (platinum oxide) and the constituent materials of the honeycomb support).

[0024] Furthermore, it is preferable that the doping amount described above is within the above range as an average value for the entire carrier. Although the method for producing doped tin oxide will be described later, the carrier of the present invention can be composed of a single antimond-doped tin oxide with equal doping amounts. Moreover, it may be formed by mixing antimond-doped tin oxides with different doping amounts.

[0025] The form of the tin oxide-based support made of antimond-doped tin oxide in the present invention is adopted according to the form of the methane combustion catalyst. Here, the form of the methane combustion catalyst can be granular, pelletized, or tablet-shaped. In such a methane combustion catalyst, the tin oxide-based support also takes the same granular, pelletized, or tablet-shaped form. In such a tin oxide-based support, the specific surface area is 10 m². ２ / g or more 60m ２ Preferably, the amount is less than / g, and more preferably 20m ２ / g or more 40m ２ The amount should be less than or equal to / g.

[0026] Furthermore, in the form of gas-phase purification catalysts such as methane combustion catalysts, there are many examples of applications where the methane combustion catalyst is supported on a suitable support. In this case, support structures known to exist are plate-shaped, cylindrical, spherical, or honeycomb-shaped. In such catalysts, a tin oxide-based support is applied to the support as a so-called wash coat to form the tin oxide-based support.

[0027] When applying a tin oxide-based carrier to a support in this form, the preferred amount of tin oxide-based carrier is preferably 250 g / L or more and 400 g / L or less based on the volume of the support. If the amount of carrier is too small, less than 250 g / L, the dispersibility of platinum will decrease, which may make sufficient methane combustion difficult. Also, if the amount of carrier is too large, exceeding 400 g / L, areas that do not come into contact with the processing gas will be formed, and in this case as well, the efficiency of methane combustion will decrease. It is also preferable that the specific surface area of ​​the tin oxide-based carrier in this form be the same as that of the pellet-shaped carrier described above.

[0028] (A-2) Catalyst component (platinum and / or platinum oxide) The catalyst component of the methane combustion catalyst according to the present invention is platinum and / or platinum oxide, and these are essential, just like in conventional methane combustion catalysts. In the present invention, the amount of platinum and / or platinum oxide that serves as the catalyst component is preferably 1.0% by mass or more and 10.0% by mass or less in terms of metallic platinum relative to the total catalyst. In the present invention, by applying antimond-doped tin oxide as the support, efficient utilization of platinum (oxide) can be achieved, and the desired methane combustion activity can be obtained even with a relatively low amount of platinum supported. The amount of platinum supported is more preferably 1.0% by mass or more and 6.0% by mass or less.

[0029] Furthermore, the catalyst component supported on the tin oxide-based support is platinum and / or platinum oxide, and it is not necessary for all of the catalyst component to be metallic platinum or platinum oxide. In the manufacturing process of the methane combustion catalyst according to the present invention, the platinum compound is impregnated and supported on the support, and then subjected to heat treatment by drying or calcination, so at least a portion of the supported platinum can become platinum oxide. Therefore, it is not necessary to limit the catalyst component on the tin oxide-based support to either platinum or platinum oxide.

[0030] Regarding the proportion of platinum oxide (metallic platinum) in the catalyst component, as mentioned above, the prior art (Patent Document 3) states that it is preferable to increase the proportion of platinum oxide on the support, taking into account the behavior of platinum (platinum oxide) during methane combustion. However, in the present invention, it is not necessary to increase the proportion of platinum oxide. In the present invention, which applies a tin oxide-based support with enhanced oxygen supply capacity, the metallic platinum on the support is rapidly converted to platinum oxide during the methane combustion reaction. Then, activity and durability can be ensured by the efficient oxidation-reduction cycle carried out by the tin oxide-based support.

[0031] Rather, in the methane combustion catalyst according to the present invention, it is preferable that the proportion of metallic platinum in the catalyst component is high in the state before methane combustion. This is because the catalytic activity for the methane combustion reaction should be considered to be exerted in the state of metallic platinum. And, by increasing the proportion of metallic platinum, it is thought that methane combustion activity can be secured with a small amount of platinum.

[0032] In the present invention, when increasing the proportion of metallic platinum on a tin oxide-based support, the proportion can be determined in the same manner as the method used in the prior art (Patent Document 3). In the prior art, the platinum oxidation state is determined based on the results of analysis by X-ray photoelectron spectroscopy (XPS), and the relative abundance R of platinum in the respective states of metallic platinum and platinum oxide (divalent and tetravalent) is determined. Ｐｔ , R ＰｔＯ , R ＰｔＯ２ Using the proportion of all platinum oxides (R ＴＯ ) identifies (R ＴＯ = (R ＰｔＯ +R ＰｔＯ２ ) / R Ｐｔ ). And, in conventional technology, it is assumed that the higher the proportion of platinum oxide, the higher the proportion of platinum atoms in an oxidized state.

[0033] In the methane combustion catalyst according to the present invention, based on the results of XPS analysis, the ratio of metallic platinum and platinum oxide R Ｐｔ , R ＰｔＯ、 R ＰｔＯ２ (All units can be calculated as %). And in this invention, the abundance ratio R of metallic platinum ＰｔA catalyst with a high R is considered suitable. Specifically, R Ｐｔ It is preferable that the methane combustion catalyst has a content of 70% or more.

[0034] Ratio of metallic platinum Ｐｔ This can be determined from the detection intensity at the bond energy corresponding to each bond state, based on the platinum 4f (Pt4f) spectrum observed when the catalyst is analyzed by XPS. In this case, in the platinum 4f spectrum obtained by XPS, the peak of metallic Pt is in the range of 71.0 eV to 72.0 eV, and the peak of PtO is in the range of 72.8 eV to 73.2 eV. ２ The peak occurs within the range of 74.6 eV to 75.0 eV. The relative abundance of each state of platinum R Ｐｔ , R ＰｔＯ、 R ＰｔＯ２ This is calculated from the peak area of ​​each state.

[0035] Furthermore, the abundance ratio R of metallic platinum Ｐｔ There is no need to specifically set an upper limit. However, the manufacturing process of methane combustion catalysts requires various heat treatment steps after supporting metallic platinum, and it is difficult to avoid the formation of platinum oxides during these processes. Furthermore, the presence of a certain amount of platinum oxide is thought to help suppress the sintering of metallic platinum. Considering these factors, the ratio of metallic platinum R Ｐｔ It is preferable to set the upper limit at 90%.

[0036] As described above, the catalytic component of the methane combustion catalyst of the present invention is platinum and / or platinum oxide. Furthermore, in the present invention, iridium, which was substantially an essential catalytic component in conventional methane combustion catalysts, is unnecessary. This is because antimond-doped tin oxide, etc., acts as the oxygen source instead of iridium, which was the oxygen source in the prior art. Moreover, additional structures such as an overcoat layer are unnecessary. However, this does not mean that additional iridium support and overcoat layer formation are prohibited in the methane combustion catalyst of the present invention.

[0037] (B) Method for Manufacturing the Methane Combustion Catalyst According to the Present Invention Next, the method for manufacturing the methane combustion catalyst according to the present invention will be described. The manufacturing of the methane combustion catalyst according to the present invention can basically be done using the conventional impregnation method for precious metal catalysts, and the catalyst can be manufactured by supporting platinum on a tin oxide-based support made of antimond-doped tin oxide. The impregnation method is a method in which the precious metal is precipitated by impregnating the support with a solution of a precious metal salt (precious metal compound) and then performing a calcination heat treatment. The manufacturing process of the methane combustion catalyst of the present invention by the impregnation method will be described below.

[0038] (B-1) Pre-processing before platinum loading (preparation of doped tin oxide) The methane combustion catalyst according to the present invention uses antimond-doped tin oxide as a support. There are several known methods for producing antimond-doped tin oxide, the most well known being the coprecipitation method and the calcination method.

[0039] For example, in a method for producing antimond-doped tin oxide by coprecipitation, a tin compound and an antimony compound are used as raw materials. Tin hydroxide and antimony hydroxide are coprecipitationd from a solution of these mixed materials, and the coprecipitationd hydroxide is calcined to obtain antimond-doped tin oxide. The tin compound and antimony compound used as raw materials are chlorides (tin chloride (SnCl) ４ ), antimony chloride (SbCl ３ SbCl ４ SbCl ５ ) is often used. In addition, water is generally used as the solvent for the mixed solution of these compounds, and the hydroxide coprecipitation occurs when an alkaline solution (sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, etc.) is reacted with the mixed aqueous solution. The amount of antimony doping can be adjusted by the mixing ratio of the tin compound and the antimony compound when preparing the above-mentioned mixed solution.

[0040] In the method for producing antimond-doped tin oxide by calcination, tin oxide (SnO ２ ) and antimony oxide (Sb ２ O ３ SbO ２ Sb ２ O ５Antimony-doped tin oxide can be obtained by mixing it with other materials and firing it at high temperature. The amount of antimony doping can be adjusted by the mixing ratio when mixing the oxides.

[0041] The antimond-doped tin oxide used in this invention can be obtained by any of the above methods. Furthermore, commercially available antimond-doped tin oxides are relatively easy to obtain and may be used.

[0042] As a manufacturing process for the methane combustion catalyst, the antimond-doped tin oxide prepared as described above may be used directly as a support to support platinum. Alternatively, when supporting the methane combustion catalyst on a support such as a honeycomb, it is preferable to prepare a support slurry by slurring the antimond-doped tin oxide powder before supporting the platinum, and then apply this slurry to the support. The support slurry can be prepared by mixing antimond-doped tin oxide with a binder using water or an organic solvent as a dispersion medium. Various known methods such as air blowing, spraying, and dipping can be applied to apply the support slurry to the support.

[0043] (B-2) Platinum Loading Process Platinum is loaded onto a tin oxide-based support by impregnation with a platinum salt solution and calcination heat treatment. Examples of platinum salt solutions to be impregnated into the support include aqueous solutions of platinum nitrate, platinum chloride, and platinum acetate, as well as platinum complex solutions such as aqueous solutions of tetraammineplatinum salt, dinitrodiammineplatinum-nitric acid, dinitrodiammineplatinum-ammonia, and dinitrodiammineplatinum-ethanolamine. There are no particular restrictions on the method of impregnating the tin oxide-based support with the platinum salt solution; spraying, dropping, or dipping are all acceptable. The amount of platinum loaded into the methane combustion catalyst can be adjusted by the platinum concentration of the platinum salt solution and the amount of liquid impregnated.

[0044] After impregnation with the platinum salt solution, the material is dried as appropriate before the calcination process. The calcination process is a process in which the platinum salt is decomposed and platinum, which serves as an active source for methane combustion, is precipitated. The calcination temperature is preferably between 350°C and 550°C. Below 350°C, the formation of platinum will be insufficient. Above 550°C, there is a risk of platinum aggregation. The processing time for the calcination process is preferably between 1 hour and 5 hours. The atmosphere for the calcination process is not particularly limited as long as it is an oxidizing atmosphere such as air.

[0045] The methane combustion catalyst according to the present invention is produced through the above calcination process. Note that in the prior art (Patent Document 3), the proportion R of platinum oxide in the catalyst is... ＴＯ As a means to increase the platinum load, a divided loading process is applied, which involves repeatedly impregnating and drying with a platinum salt solution, and the drying temperature is strictly controlled, in order to achieve the desired amount of platinum loaded. However, such treatment is unnecessary in the methane combustion catalyst according to the present invention. In the methane combustion catalyst according to the present invention, by using antimond-doped tin oxide as the support that acts as the oxygen supply source, the proportion of platinum oxide R ＴＯ This is because it allows for proper handling. Furthermore, in this invention, the amount of platinum supported can be reduced by optimizing the tin oxide-based support, so the required amount of platinum can be supported without relying on divided loading.

[0046] (C) Methane combustion method using the methane combustion catalyst according to the present invention The methane combustion method to which the methane combustion catalyst according to the present invention described above is applied is basically the same as the conventional method. The target of the methane combustion method according to the present invention is combustion exhaust gas containing sulfur oxides along with methane. In addition to methane and sulfur oxides, other combustible components such as ethane and propane, carbon monoxide, oxygen, oxygen-containing compounds, and nitrogen oxides may also be present.

[0047] In the combustion of methane in combustion exhaust gas, the gas to be treated is passed through a combustion apparatus equipped with the methane combustion catalyst according to the present invention and brought into contact with the methane combustion catalyst. Known combustion apparatuses can be used, such as fixed-bed flow reactors. The amount of catalyst used in such a combustion apparatus is generally set by the space velocity per gas hour (GHSV). In the present invention, the space velocity is set to 100,000 h in order to ensure the combustion rate of methane. －１ The following is preferable. Since catalytic activity is improved by lowering the space velocity, the lower the space velocity, the better. However, considering catalytic activity, economy, and pressure loss, the space velocity should be 1,000 h. －１ It is preferable to keep it as described above.

[0048] The heating temperature of the methane combustion catalyst for purifying combustion exhaust gas, i.e., the reaction temperature, shall be between 300°C and 500°C. A reaction temperature of 350°C and 475°C is more preferable.

[0049] As described above, the Pt / SnO according to the present invention ２ The methane combustion catalyst of this system utilizes a tin oxide-based support with high oxygen supply capacity as the support material, thereby accelerating the reduction (metalization) and oxidation (oxideization) cycle of platinum oxide, which is the active source, and suppressing the decrease in activity due to sintering of the metallized platinum. In conventional technology, the above cycle was promoted by additional iridium support or the formation of an overcoat layer, but these are unnecessary in the present invention. As a result, the present invention can provide a methane combustion catalyst that is highly active and highly durable while reducing costs.

[0050] XRD diffraction profiles of methane combustion catalysts of Example 1, Comparative Example 1, and Comparative Example 2 manufactured in the first embodiment. Diagram illustrating the configuration of the test apparatus for the methane combustion tests conducted in each embodiment. Graph showing the change in methane conversion rate over time for various methane combustion catalysts manufactured in the first embodiment. Graph showing the results of combustion tests (constant temperature tests) for methane combustion catalysts with various Sb doping amounts manufactured in the second embodiment. Graph showing the results of combustion tests (heating tests) for methane combustion catalysts (fresh catalysts and post-endurance catalysts) with various Sb doping amounts manufactured in the second embodiment. Pt4f spectrum obtained by XPS analysis of the methane combustion catalyst of Example 2 in the second embodiment. Graph showing the relationship between the abundance ratio of metallic platinum measured for the methane combustion catalyst manufactured in the second embodiment and the methane conversion rate. Graph showing the results of combustion tests (constant temperature tests) for methane combustion catalysts of Example 2 (antimond doping 1.30 mass%) and the conventional example (no antimond doping, iridium supported, with overcoat layer) examined in the third embodiment.

[0051] First Embodiment: A preferred embodiment of the present invention will be described. In this embodiment, antimony (antimony oxide (Sb ２ O ５ )) to SnO ２ A methane combustion catalyst was fabricated by supporting platinum on a tin oxide-based support doped with antimony. The effect of antimony doping on the tin oxide-based support was confirmed by evaluating its methane combustion activity.

[0052] [Preparation of Antimony-Doped Tin Oxide Powder (Tin Oxide-Based Carrier)] An aqueous solution of tin chloride (234 g of tin chloride) and an aqueous solution of antimony chloride (21.6 g of antimony chloride) were added to 5 L of water. While maintaining this mixture at 80°C, an aqueous solution of sodium hydroxide was added to adjust the pH to 6-7. The mixture was reacted in this state for 1 hour to produce a coprecipitation of tin oxide hydrate and antimony oxide hydrate. This coprecipitation was then filtered, collected, and washed. After that, the coprecipitation was calcined at 550°C for 3 hours. The calcined material was crushed and pulverized to obtain antimony-doped tin oxide.

[0053] The antimony content of the antimony-doped tin oxide produced as described above was analyzed using ICP (Agilent 5800, manufactured by Agilent Technologies, Inc.) (selective wavelength: Sb = 217.582 nm). As a result, the antimony doping amount of the antimony-doped tin oxide was 0.97% by mass.

[0054] [Platinum Supporting Process] Next, the antimond-doped tin oxide powder produced above was dispersed in water and mixed and pulverized in a ball mill to produce a carrier slurry. This carrier slurry was applied to a commercially available cordierite honeycomb (manufactured by NGK Insulators, Ltd.: φ30 mm × 12.5 mm L, 400 cells) by air blowing. Then, it was fired at 600°C in the air to form a honeycomb-shaped carrier (carrier specific surface area: 12 m²). ２ ( / g). The amount of antimond-doped tin oxide powder applied to the honeycomb at this time was 300 g / L.

[0055] The above honeycomb-shaped support was impregnated with a dinitrodiammineplatinum-nitric acid aqueous solution as a platinum salt solution by air blowing. In this embodiment, the amount of platinum supported was 3.23% by mass (excluding the mass of the honeycomb support) in terms of metallic platinum.

[0056] After impregnation with a platinum salt solution, the honeycomb-shaped support underwent a drying process followed by calcination. In the drying process, the honeycomb-shaped support, after impregnation with the solution, was placed in a dryer maintained at 110°C and held for 30 minutes. Then, the dried honeycomb-shaped support was calcined. The calcination conditions were to heat in air at a calcination temperature of 450°C for 1 hour. The methane combustion catalyst of this embodiment was obtained through the above process (Example 1). ICP analysis was performed on the manufactured methane combustion catalyst, and the antimony content relative to the tin oxide-based support was calculated to be 0.97% by mass, the same as during support production.

[0057] Comparative Examples 1 and 2: To compare with the methane combustion catalyst of Example 1, SnO without antimony was used as the support. ２ A tin oxide support made of powder was prepared (Comparative Example 1). Also, SnO ２ Powder and Sb ２ O ５A carrier composed of a mixed powder with powder was prepared (Comparative Example 2). Then, a methane combustion catalyst was produced from the tin oxide carrier and the mixed powder carrier. In addition, the SnO ２ powder in Comparative Example 1 used commercially available SnO ２ powder. Also, the mixed powder in Comparative Example 2 was prepared by physically mixing commercially available SnO ２ powder and commercially available Sb ２ O ５ powder in a mass ratio of SnO ２ : Sb ２ O ５ = 99:1 using a mill, and this was used.

[0058] For these methane combustion catalysts of Comparative Examples 1 and 2, a carrier slurry was produced in the same manner as in Example 1, coated on a cordierite honeycomb, and fired to obtain a honeycomb-shaped carrier. Further, after impregnating with a dinitrodiammine platinum-ammonia aqueous solution under the same conditions as in Example 1, it was dried and fired to obtain a methane combustion catalyst. The platinum loading was also 3.23% by mass as in Example 1.

[0059] [XRD Analysis] XRD analysis was performed on the methane combustion catalyst produced in this embodiment to confirm the state of antimony in the tin oxide-based carrier of the methane combustion catalyst of Example 1. For the XRD analysis, Ultima IV manufactured by Rigaku Corporation was used as the analyzer, and the X-ray source was Cukα ray, and the measurement was performed in the range of 2θ = 20° to 90°.

[0060] Figure 1 shows the XRD diffraction patterns of the methane combustion catalysts of Example 1, Comparative Example 1, and Comparative Example 2. The diffraction patterns of the methane combustion catalyst of Example 1 with an antimony-doped tin oxide powder as the carrier and the methane combustion catalyst of Comparative Example 1 with an undoped tin oxide powder as the carrier are substantially the same, and diffraction peaks of SnO ２ are observed at around 2θ = 26.5° and around 34°. On the other hand, the methane combustion catalyst of Comparative Example 2 with a mixed powder of SnO ２ powder and Sb ２ O ５ powder as the carrier has a basic diffraction pattern the same as that of Example 1 and Comparative Example 1, but in addition to the diffraction peak of SnO ２ , a diffraction peak of Sb ２ O ５The diffraction peak of the origin is observed. From the results of this XRD analysis and the above-mentioned ICP analysis, it can be confirmed that the carrier of the methane combustion catalyst of Example 1 is a tin oxide-based carrier composed of antimony-doped tin oxide in which antimony is solid-dissolved in tin oxide.

[0061] Evaluation test of methane combustion performance A test for evaluating the methane combustion performance was conducted using each of the methane combustion catalysts produced above. In this evaluation test, each catalyst was set in a test apparatus simulating the fixed-bed reactor of FIG. 2, and the test gas was passed through to measure the methane conversion rate. The evaluation test of this embodiment is a constant-temperature test in which the inlet gas temperature, which is the reaction temperature (catalyst temperature), is set to a constant temperature, and the conversion rate at the reaction temperature is evaluated. The test conditions were as follows. - Reaction temperature: 400 ° C - Test gas composition CH ４ : 2000 ppm CO ２ : 5% O ２ : 10% H ２ O: 10% SO ２ : 3 ppm N ２ : Balance Space velocity (GHSV): 100,000 h －１ - Test time: 24 hours

[0062] In the evaluation test, the test gas was passed through the catalyst under the above conditions, and the composition of the exhaust gas was analyzed at 5-hour intervals from the start of the test to measure the methane conversion rate. The measurement of the methane conversion rate was performed by analyzing the CH of the exhaust gas with a FID type THC gas analyzer, a non-dispersive infrared analyzer, and a magnetic oxygen meter ４ 、CO ２ 、O ２ concentrations. Then, the methane conversion rate was calculated from the measured values using the following formula.

[0063]

[0064] Figure 3 shows a graph illustrating the change in methane conversion rate over time for each methane combustion catalyst, as a result of this evaluation test. Comparing the catalyst of Example 1, which uses antimony-doped tin oxide as a support, with the catalyst of Comparative Example 1, which uses undoped tin oxide as a support, the methane conversion rate at the start of the test was approximately 10% higher for Example 1. Furthermore, while the methane conversion rate of the methane combustion catalyst of Comparative Example 1 showed a tendency to decrease with the progress of the test time, the methane combustion catalyst of Example 1 did not show a significant decrease in the methane conversion rate. As a result, a large difference in methane conversion rate was observed between Example 1 and Comparative Example 1 after 24 hours. These results indicate that doping tin oxide with antimony improves the initial methane combustion activity, maintains the activity, and clearly improves durability.

[0065] Furthermore, comparing Example 1 with Comparative Example 2, it can be seen that the antimony must be in a doped (solid solution) state in the tin oxide-based support. It can be seen that the desired performance is not achieved in the simple mixture of tin oxide and antimony oxide in Comparative Example 2. The methane combustion catalyst using the mixed powder of Comparative Example 2 as a support has higher initial activity and durability than Comparative Example 1, but the difference is slight. And there is a significant difference compared to the methane combustion of Example 1.

[0066] Second Embodiment: In this embodiment, multiple methane combustion catalysts using antimony-doped tin oxide as a support were manufactured, each with a different amount of antimony doping in the tin oxide support. The activity of these methane combustion catalysts was then evaluated. In addition, the state of platinum (proportion of metallic platinum) in the methane combustion catalysts manufactured using each tin oxide support was investigated.

[0067] [Preparation of Tin Oxide-Based Support] The antimond-doped tin oxide-based support was manufactured by the coprecipitation method, as in the first embodiment. In this embodiment, the mixing ratio of tin chloride and antimony chloride during the production of antimond-doped tin oxide was changed to produce several types of antimond-doped tin oxide powder with different antimond-doping amounts (these are designated as Examples 2, 3, 5, and Reference Example 1). The antimond-doped tin oxide-based support of Example 1 of the first embodiment was also examined. Furthermore, the antimond-doped tin oxide powder produced in this embodiment, specifically the antimond-doped tin oxide powder of Example 5 and the antimond-doped tin oxide powder of Example 1 (first embodiment), was uniformly mixed in equal amounts using a ball mill to obtain antimond-doped tin oxide powder (this is designated as Example 4). The antimony doping amounts for the antimond-doped tin oxide in Examples 1 to 5 and Reference Example 1 are as follows.

[0068]

[0069] [Production of Methane Combustion Catalyst] Using the antimond-doped tin oxide powders of Examples 1 to 5 and Reference Example 1, a carrier slurry was prepared in the same manner as in the first embodiment. The carrier slurry was then applied to the same cordierite honeycomb as in the first embodiment and calcined to form a honeycomb-shaped carrier. Then, in the same manner as in the first embodiment, the honeycomb-shaped carrier was impregnated with a dinitrodiammineplatinum-nitrate aqueous solution, dried, and calcined to form a methane combustion catalyst. In this embodiment, the amount of platinum supported was 3.23% by mass in terms of platinum.

[0070] When the methane combustion catalysts produced as described above were subjected to ICP analysis in the same manner as in the first embodiment, there was virtually no change in the amount of antimondope in the support (antimondope-doped tin oxide) in each methane combustion catalyst.

[0071] Evaluation Test of Methane Combustion Performance The methane combustion catalysts manufactured in this embodiment, Examples 1 to 5 and Reference Example 1, were subjected to evaluation tests of their methane combustion performance. The evaluation apparatus used for this evaluation test was the same as in the first embodiment. In this embodiment, in addition to a constant temperature test similar to that in the first embodiment, two types of tests were performed: a temperature-increasing test in which the methane conversion rate was measured while increasing the reaction temperature. The reaction conditions and test method in the constant temperature test were the same as in the first embodiment (only the test time was set to 50 hours).

[0072] In the heating test, the inlet gas temperature was raised from 300°C to 500°C at a heating rate of 10°C / min, and the methane conversion rate was measured. The test gas composition and space velocity in the heating test were the same as in the first embodiment. The methane conversion rate in the heating test was calculated by continuously analyzing the composition of the exhaust gas. The heating test was performed on two types of catalysts: a fresh catalyst immediately after manufacturing and a post-treatment catalyst that had been heated to 500°C in the atmosphere for 24 hours.

[0073] As a result of the methane combustion test in this embodiment, Figure 4 shows the results of the constant temperature test, and Figure 5 shows the results of the heating test.

[0074] Referring to the results of the constant-temperature test in Figure 4, the methane combustion catalysts of Example 1 (antimond dope amount: 0.97 mass%), Example 2 (antimond dope amount: 1.30 mass%), and Example 3 (antimond dope amount: 1.93 mass%) showed good changes in methane conversion rate over time. In particular, the methane combustion catalysts of Example 2 and Example 3 maintained a methane conversion rate of over 90% even after 50 hours of testing. On the other hand, the methane combustion catalyst of Reference Example 1 (antimond dope amount: 7.55 mass%) had an initial methane conversion rate of approximately 80%, but the methane conversion rate decreased with increasing test time, showing a relatively fast degradation rate. Furthermore, good results were also obtained for the methane combustion catalyst of Example 4 (antimond dope amount: 2.57 mass%), which was mixed with antimond dope tin oxide powder.

[0075] Referring to the results of the temperature increase test in Figure 5, the methane conversion rate of the fresh catalysts in each example increased with increasing reaction temperature, and there was no significant difference in the methane conversion rates. However, when the reaction temperature was set to a relatively low temperature (350°C to 400°C), the methane combustion catalysts of Example 2 (antimond doping amount: 1.30 mass%), Example 3 (antimond doping amount: 1.93 mass%), and Example 4 (antimond doping amount: 2.57 mass%) exhibited excellent methane conversion rates.

[0076] Furthermore, when examining the change in methane conversion rate of the post-hardened catalyst heated to 500°C, the catalyst in Reference Example 1 (antimony doping amount: 7.55 mass%) shows a significant drop in methane conversion rate at reaction temperatures above 350°C. Considering this result together with the results of the constant-temperature test described above, it can be concluded that it is preferable to dope the tin oxide with antimony at 5 mass% or less.

[0077] Measurement of the proportion of metallic platinum by XPS: XPS analysis was performed on the methane combustion catalyst to which the tin oxide-based support manufactured in this embodiment was applied, and the proportion of metallic platinum (R Ｐｔ The following was determined. For XPS analysis, a sample was prepared by taking a portion of the catalyst and grinding it in an agate mortar, and XPS analysis was performed under the following conditions. XPS analysis involved survey scans and narrow scans, and the Pt4f spectrum was measured. • Analytical instrument: ULVAC-PHIE Quantera II • X-ray source: Monochromatic Al (1486.6 eV) • Detection area: 100 μmφ • Detection depth: Approximately 4-5 nm (extraction angle 45°)

[0078] Figure 6 shows an example of XPS analysis results, specifically the Pt4f spectrum measured by narrow scan for Example 2 (antimond doping amount 1.30 mass%). In the platinum XPS spectrum, peak tops are obtained in the bond energy range of 71–75 eV. Within this range, the peak in the 71.0–72.0 eV range is identified as metallic Pt. Additionally, the peak in the 72.8–73.2 eV range is identified as PtO, and the peak in the 74.6–75 eV range is identified as PtO. ２ This applies.

[0079] Ratio of metallic platinum (R ＰｔThe calculation of the metal Pt and PtO involves performing waveform separation processing on the obtained XPS profile. ２ The peak areas for each state of PtO were measured. The peak areas for each element, oxygen (O), tin (Sn), and carbon (C), were also measured simultaneously. The peak areas for each component (Pt, O, Sn, and C) were then corrected using their respective relative sensitivity factors (RSF), and the sum of the peak areas for each component was used as the baseline (100) to calculate the percentage of metallic platinum.

[0080] The above XPS analyses were performed on the methane combustion catalysts of Example 1 (antimond doping amount: 0.97 mass%), Example 2 (antimond doping amount: 1.30 mass%), Reference Example 1 (antimond doping amount: 7.55 mass%), and the methane combustion catalyst of Comparative Example 1 without antimond doping and supported by tin oxide. In addition, the analyses were performed on both fresh catalysts immediately after manufacturing and durable catalysts that had been heat-treated at 500°C for 24 hours. Metal Pt, Pt oxide (PtO, PtO) in each methane combustion catalyst. ２ The measurement results for the percentage of ) are shown in Table 2.

[0081]

[0082] Table 2 shows that the methane combustion catalysts of Example 1, Example 2, and Reference Example 1 have a ratio of metallic platinum (R) in the fresh catalyst. Ｐｔ It can be seen that the ) is increasing. Furthermore, in the catalysts of Example 1 and Example 2, the abundance of metallic platinum is maintained at a high value even in the durable catalyst after heat treatment. Regarding the durable catalyst, Figure 7 shows the relationship between the abundance of metallic platinum and the methane conversion rate, based on the results of the methane combustion test described above (Figure 5). From this figure, it can be seen that there is a correlation between the abundance of metallic platinum and the methane conversion rate, and an increase in the methane conversion rate is observed as the proportion of metallic platinum increases. The reason why the proportion of metallic platinum increases with the application of antimond-doped tin oxide-based support is not clear, but it is thought to be due to an improvement in the balance between the oxidation rate and reduction rate of platinum. From the results in Figure 7, it is thought that by applying antimond-doped tin oxide, it may be possible to obtain methane combustion activity while keeping the platinum load low.

[0083] Gas adsorption analysis (CO, N ２) Investigation of catalytic properties of the methane combustion catalyst produced in this embodiment N ２ Specific surface area analysis was performed using gas adsorption and CO gas adsorption methods. The specific surface area obtained by CO gas corresponds to the specific surface area of ​​the active species, metallic platinum, on the support, and N ２ The specific surface area of ​​the gas is related to the specific surface area including the pores of the tin oxide-based support. Specific surface area analysis was performed on the methane combustion catalysts of Example 1 (antimond doping amount: 0.97 mass%), Example 2 (antimond doping amount: 1.30 mass%), Example 4 (antimond doping amount: 2.57 mass%), Reference Example 1 (antimond doping amount: 7.55 mass%), and Comparative Example 1 (no antimond doping). Furthermore, analysis was performed on both fresh catalysts and post-treatment catalysts (heat-treated at 500°C for 24 hours).

[0084] N ２ For gas adsorption analysis, the BET specific surface area was determined using the BET multipoint method with a Belsort mini analyzer manufactured by Microtrac-Bel. ２ For the gas adsorption method measurement, the sample mass was set to 100 mg and N was heated at 300°C. ２ Measurements were taken after a 2-hour gas flow pretreatment.

[0085] For the CO gas adsorption analysis, a pulse method was used with a Belmetal3 analyzer manufactured by Microtrac-Bel. In the CO gas adsorption method, a sample mass of 50 mg was used, and after pretreatment with He gas flow at 50°C for 2 hours, CO gas adsorption measurement was performed at 50°C.

[0086]

[0087] Referring to Table 3, N ２ Gas adsorption analysis results show that the methane combustion catalysts in each example exhibit small changes in specific surface area before and after heat treatment. The antimond-doped tin oxide support is considered to have good heat resistance. Furthermore, CO gas adsorption analysis allows for the estimation of the amount of active sites (metallic platinum) in the fresh catalyst and the endurance catalyst from the amount of CO adsorbed. In each example, the methane combustion catalysts exhibited greater CO adsorption at every stage compared to the catalyst without antimond doping in Comparative Example 1.

[0088] Third Embodiment: In this embodiment, the methane combustion catalyst of Example 2 of the second embodiment (antimond dope amount: 1.30 mass%) is used, and the methane combustion catalyst (Pt-Ir / SnO) described in the prior art (Patent Document 4) is supported with platinum and iridium and further has an overcoat layer. ２ This was compared to a catalyst.

[0089] Conventional example: Pt-Ir / SnO ２ The catalyst was manufactured based on the description in Patent Document 4. After calcining the same tin oxide powder as in the first embodiment at 600°C, a carrier slurry was manufactured in the same manner as in the first embodiment. Furthermore, the carrier slurry was applied to a cordierite honeycomb in the same manner to obtain a honeycomb-shaped carrier.

[0090] In conventional methane combustion catalysts, partial loading is applied during platinum loading. Here, a dinitrodiammineplatinum-ammonia aqueous solution was used, and the partial loading was performed four times. A drying process was carried out at 110°C after each impregnation with the platinum salt solution. After the fourth partial loading, the final drying process was performed, and the temperature was raised from the drying temperature to 275°C for a calcination treatment of 3 hours. In this conventional example, the amount of platinum loaded was 9.69 mass% (30 g / L). That is, the amount of platinum loaded in the conventional example was three times that of the second embodiment (Example 2) (3.23 mass% (10 g / L)).

[0091] Next, iridium was supported on a platinum-supported tin oxide-based carrier and calcined. Here, an aqueous solution of hexachloroiridium acid was used as the iridium salt solution, and the entire amount of the prepared solution was impregnated in one step. After iridium salt impregnation, it was dried at 110°C and calcined at 450°C for 3 hours.

[0092] Furthermore, an overcoat layer was formed by applying the same tin oxide slurry used during support production to the catalyst manufactured above using an air blower. In this conventional example, an overcoat layer (thickness 30 μm to 60 μm) was formed by applying 150 g / L of tin oxide based on the volume of the support. Through the above process, a conventional methane combustion catalyst (Pt-Ir / SnO) was produced. ２ They manufactured a catalyst.

[0093] Comparison of Methane Combustion Activity: Methane combustion tests were conducted on the methane combustion catalysts of Example 2 (antimond dope amount: 1.30 mass%) and the conventional example (no antimond dope, iridium supported, and with an overcoat layer) to compare their initial activity and durability. The same methane combustion test apparatus as in the first embodiment was used. The evaluation test was a constant-temperature test (reaction temperature 400°C) as in the first embodiment, and the reaction conditions and test method were the same as in the first embodiment. The test time was 100 hours, and the methane conversion rate for Example 2 and the conventional example was measured at regular intervals. The test results are shown in Figure 8.

[0094] Referring to Figure 8, it can be seen that the methane combustion catalyst of Example 2 has an initial activity that is about 10% higher than that of the conventional example. Furthermore, in terms of durability, Example 2 consistently showed a higher methane conversion rate than the conventional example from the start to the end of the test (after 100 hours). Thus, the methane combustion catalyst using the antimond-doped tin oxide support of Example 2 surpasses the conventional technology in terms of performance, and in addition, improvements in cost are also observed. Specifically, the conventional example has three times the amount of platinum supported as Example 2, and also has additional iridium support. Furthermore, the conventional example also has an overcoat layer. Since all of these differences affect the catalyst cost, the methane combustion catalyst of Example 2 can be said to be significantly superior to the conventional technology in terms of cost as well.

[0095] The methane combustion catalyst according to the present invention uses antimond-doped tin oxide as a support. This tin oxide-based support acts as an effective oxygen source for the platinum (platinum oxide) catalyst particles. In conventional methane combustion catalysts, additionally supported iridium or an overcoat layer acts as an oxygen source, but the present invention eliminates the need for these. According to the present invention, methane combustion activity equivalent to or better than that of conventional technology can be obtained at a low cost. The methane combustion catalyst according to the present invention can be suitably applied to the purification of various exhaust gases from engines, boilers, power generation systems, etc., that use hydrocarbon fuels such as natural gas and city gas. Furthermore, the present invention is also useful for power generation systems such as cogeneration systems and gas heat pumps (GHP).

Claims

1. A methane combustion catalyst for burning methane in combustion exhaust gas containing sulfur oxides, comprising a tin oxide-based carrier containing tin oxide as an essential component, on which platinum and / or platinum oxide is supported, characterized in that the tin oxide-based carrier is made of antimond-doped tin oxide.

2. The methane combustion catalyst according to claim 1, wherein the amount of antimony doping in the tin oxide-based carrier is 0.1% by mass or more and 5.0% by mass or less, based on the mass of the tin oxide-based carrier.

3. The methane combustion catalyst according to claim 1 or claim 2, wherein the amount of platinum and / or platinum oxide supported on the entire catalyst is 1.0% by mass or more and 10.0% by mass or less in terms of metallic platinum.

4. When a methane combustion catalyst is measured by X-ray photoelectron spectroscopy (XPS), the abundance ratio of metallic platinum R obtained from the platinum 4f spectrum is... Ｐｔ A methane combustion catalyst according to claim 1 or claim 2, wherein the content is 70% or more.

5. The methane combustion catalyst according to claim 1 or claim 2, which is in the form of granules, pellets, or tablets.

6. The methane combustion catalyst according to claim 1 or claim 2, which is supported by a support having one of the following shapes: plate, cylindrical, spherical, or honeycomb.

7. A method for purifying combustion exhaust gas that oxidizes and removes methane in combustion exhaust gas containing sulfur oxides, characterized in that the reaction temperature is 300°C or higher and 500°C or lower, and the combustion exhaust gas is brought into contact with the methane combustion catalyst described in claim 1 or claim 2.

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