Process for preparing a water gas shift catalyst, catalyst and process for reducing carbon monoxide content

Abstract

This invention relates to HTS catalysts used in hydrogen or syngas production plants, whether in steam reforming, autothermal reforming, dry reforming, or gasification processes. The HTS catalyst is chromium-free and comprises iron oxide containing platinum at levels between 0.1% and 0.4% m / m, promoted by sodium at levels between 0.1% and 0.3% m / m and optionally aluminum at levels between 5.0% and 6.0% m / m, the aluminum being intercalated into the lattice of the iron oxide having a hematite crystal structure (Fe₂O₃), thereby combining high activity with excellent resistance to deactivation upon exposure to high temperatures. In a second aspect, the invention provides a method for converting carbon monoxide by contacting the catalyst with a syngas gas stream, wherein the maximum temperature of the bed can be limited by injecting water or steam together with a CO-containing gas feed at the reactor inlet.

Description

Invention Field

[0001] This invention relates to a method for preparing a water-gas shift catalyst (chromium-free) and a method for its application in a hydrogen or syngas production plant, which aims to reduce the safety, environmental and health impacts associated with the manufacture, handling and disposal of the materials used, through reforming steam, autothermal reforming, dry or gasification reforming.

[0002] Description of the prior art

[0003] The water-gas shift reaction (“water-gas shift” or simply “shift”) is an integral step in the steam reforming process used for hydrogen production. The reaction can be represented by Equation 1; it is exothermic and is typically limited by thermodynamic equilibrium.

[0004] CO + H₂O = CO₂ + H₂ (Equation 1)

[0005] This reaction produces H2 while simultaneously reducing CO levels. CO is a contaminant in catalysts used in ammonia synthesis, hydrotreating processes, and fuel cells using high-purity hydrogen. In syngas generation processes, the water-gas shift reaction is used to adjust the desired ratio of CO to H2. The water-gas shift reaction is also part of other H2 production processes, such as partial oxidation, autothermal reforming, and hydrocarbon gasification processes, including biomass.

[0006] In steam reforming processes, a typical configuration involves a water-gas shift reaction in the first stage, known as the "high-temperature shift" (HTS), where the catalyst is operated at a typical temperature between 330°C at the reactor inlet and up to 450°C at the reactor outlet. A second stage, cooling the effluent and initiating further reactions, is then performed, known as the "low-temperature shift" (LTS), where the catalyst is operated at a typical temperature between 180°C at the reactor inlet and 240°C at the reactor outlet. In variations of the process configuration, the LTS reactor and subsequent CO2 separation system via amines are replaced with a pressure swing adsorption (PSA) step. The pressure conditions during the shift stages are determined by the amount of hydrogen used and are typically between 10 and 40 bar.

[0007] Commercial LTS catalysts consist of copper oxide, zinc oxide, and alumina, typically in concentrations between 40% and 35% m / m, and 27% to 44% m / m, with alumina as the balance. They may also contain small amounts of basic promoters such as cesium (Cs) or potassium (K). LTS catalysts rapidly lose activity when exposed to high temperatures, which is why they are typically used in a temperature range of 180°C to 240°C, or in their “Medium Temperature Shift” (MTS) versions, at temperatures between 180°C and 330°C. The lower temperature range is usually determined by the requirement that no steam condensation occurs in the reactor at the operating pressure of the unit.

[0008] In industry, large-scale installations (here considered to have a capacity greater than 50,000 Nm) are used. 3 The HTS catalyst used in the hydrogen production unit (with a capacity of 1000 m³ / d) consists of iron (Fe), chromium (Cr), and copper (Cu) (mainly in oxide form) before operation begins, and then consists of metallic copper and oxides of iron and chromium after operation begins. Despite its widespread use, this catalyst formulation has the disadvantage of containing chromium. Specifically, during the calcination step in the production of this catalyst, chromium (CrO₃ or Cr₂O₃) at different oxidation states VI is inevitably formed. 6+ Cr(II) compounds, which are known carcinogens and environmentally damaging, are subject to increasingly stringent legislation worldwide. For example, OSHA (Occupational Health and Safety Organization) regulations on workplace exposure to Cr(II) can be cited. 6+ Strict regulations. Therefore, Cr 6+ The presence of chromium can negatively impact the manufacturing process, handling, transportation, loading, unloading, and disposal of materials. Therefore, it is desirable to produce HTS catalysts with chromium-free formulations.

[0009] The logical solution for producing chromium-free catalysts is simply to remove them from the catalyst composition. However, the literature teaches that chromium plays an essential role in the formulation of HTS catalysts, reducing the surface area loss of the iron oxide phase present in the catalyst at typical process temperatures (i.e., between 330°C and 500°C). Therefore, it reduces the deactivation rate of the material, allowing the catalyst to maintain good performance throughout the entire active life of the unit (typically lasting 3 to 5 years), a function known in catalysis as a structure promoter.

[0010] Several studies have reported on replacing chromium in HTS catalyst formulations with iron-, chromium-, and copper-based compositions. In PAL, DB et al. (2018), “Performance of water gas shift reaction catalysts: A review,” *Renewable and Sustainable Energy Reviews*, Vol. 93, pp. 549-565, studied the replacement of chromium with several elements (e.g., cerium, silicon, titanium, magnesium, zirconium, and aluminum oxides). However, in industrial practice, an effective method for preparing HTS catalysts using chromium as a substitute (while maintaining high resistance to deactivation upon exposure to high temperatures) remains unavailable.

[0011] A solution to improve the thermal stability of chromium-free HTS catalysts would be to use them at low temperatures. However, an activation promoter would be necessary because the iron oxide phase is only active at typical temperatures of 320°C to 330°C. Copper would be a candidate for an activation promoter due to its low cost and widespread use in LTS catalysts; however, it suffers from a relatively high deactivation rate when exposed to temperatures in the 250°C to 350°C range. Other candidates would be noble metals, particularly platinum, given their greater availability and lower relative cost compared to other noble metals.

[0012] Several teachings exist regarding the use of platinum (Pt) in shift catalyst formulations. Patent 7744849 teaches a catalyst for a water-gas shift reaction comprising a platinum-based catalyst having at least one alkaline earth metal and at least one third metal. Specifically, the catalyst in this patent comprises: a) Pt, b) at least one of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, their oxides and mixtures, and c) at least one of Sc, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ir, Ni, Pd, La, Ce, Pr, Nd, Sm, Eu, their oxides and mixtures, and may be supported in one or a combination of oxides of aluminum, zirconium, titanium, cerium, magnesium, lanthanum, niobium, yttrium, or iron. The catalyst can be used in compact hydrogen production equipment.

[0013] Patent application US2012 / 0063989 discloses a catalyst for converting CO to carbon dioxide (CO2) via a water-gas shift reaction. The catalyst comprises a noble metal at a level between 0.001% and 1.10% m / m on a support material (containing Ce or Zr), at least one alkali metal or alkaline earth metal at a level between 1.0% and 4% m / m, and at least one dopant composed of Fe, Cr, Cu, Zn, or mixtures thereof.

[0014] Patent 7824455 describes the application of a noble metal catalyst of Pt, Pd or a mixture thereof or a mixture of Pt-Ir for a shift exchange reaction in a temperature range of 200°C to 400°C, wherein the catalyst is supported on a mixture of oxides of Ce and Zr having Ce in the range of 20% to 58% or 58% to 80% and Zr in the range of 42% to 20%, wherein at least one metal selected from yttrium, alkali metals or alkaline earth metals in the range of 0.01% to 1% is used as a promoter.

[0015] Patent application US2018 / 0093261 discloses a catalyst composed of oxides of iron and chromium and containing platinum at levels between 0.01% and 1.5% m / m. Several other teachings regarding the use of platinum in formulations of conversion catalysts can be found.

[0016] In their article “Water Gas Shift Catalysis”, Catalysis Reviews, Vol. 51, pp. 325–440, Ratnasamy, C.; Wagner, JP (2009), “Water Gas Shift Catalysis”, Catalysis Reviews, Vol. 51, pp. 325–440, they reviewed the literature and taught the use of platinum deposited on several oxides, such as zirconium, vanadium, alumina and cerium oxide.

[0017] A key consideration in using noble metals in HTS catalyst formulations is to maximize the possible activity of the metal phase. The high cost of noble metals makes their commercial application in large-capacity hydrogen production plants impractical. Literature guides the addition of alkali metals to formulations of "conversion" catalysts containing Pt as an activity promoter. Beneficial results were observed for CO conversion activity via the water-gas shift reaction with sodium contents between 1% and 10% m / m in Pt-Na / TiO2 catalysts prepared by co-impregnation, as described in ZHU, X. et al. (2011), “Structural effects of Na promotion for high water gasshift activity on Pt-Na / TiO2”, Journal of Catalysis, Vol. 278, pp. 123-132, and in Pt / CeO2 catalysts prepared by impregnation with 1% sodium content, as described in JEONG, DW. et al. (2011), “The Effect of Sodium in Activity Enhancement of Nano-sized Pt / CeO2 Catalyst for Water Gas Shift Reaction at Low Temperature”, Bulletin of Korean Chemical Society, Vol. 32, pp. 3557-3558. The literature teaches that alkali metals are incorporated through additional specific and additional preparation steps, typically at levels higher than 1% m / m, and using oxides. Regarding alkali metals, there is no teaching on their effect on the thermal stability of catalysts, nor is there a report on the effect of sodium content on the thermal stability of catalysts.

[0018] Document US 7160533 seeks protection for catalysts containing Pt and Ru. The Ru phase is highly active but exhibits low selectivity. Catalyst formulations containing Pt, Ru, and alkali metals attempt to mitigate methanation reactions. Impregnation methods are also used to prepare catalysts, in which noble metals are deposited onto pre-formed supports. The use of combinations of noble metals increases costs and is difficult for large-scale catalyst production, especially when using noble metals with limited reserves.

[0019] Therefore, although there are many references in the literature regarding the use of Pt in water-gas shift catalyst formulations, there is still a need to provide methods and formulations for the preparation of chromium-free (Cr) "high-temperature shift" catalysts that exhibit high activity associated with excellent resistance to deactivation upon exposure to high temperatures, using the lowest possible Pt level and employing practical, low-cost methods and incorporation promoters to enhance passivity and resistance to deactivation upon prolonged exposure to high temperatures.

[0020] To address these problems, the present invention was developed, which employs a chromium- and copper-free catalyst formulation consisting of iron oxide containing platinum (Pt), sodium (Na), and optionally aluminum (Al), wherein the aluminum is inserted into the lattice of the iron oxide having a hematite (Fe2O3) crystal structure.

[0021] In a second aspect of the invention, a method for reducing CO content using the catalyst via a water-gas shift reaction is disclosed.

[0022] This invention decisively contributes to reducing CO content effluent during the process, which improves energy efficiency and facilitates better operation in PSA systems. The more active HTS catalyst has the estimated potential to help reduce production costs by approximately 1%.

[0023] Eliminating chromium, especially its carcinogenic Cr, from HTS catalyst formulations. 6+ This format minimizes the risks associated with catalyst handling, loading, and unloading processes.

[0024] Using a more active HTS catalyst can tolerate greater anomalies in the steam reforming process for hydrogen production, which can lead to increased pressure losses and / or the formation of byproducts in the reactor, thus increasing the risk of unplanned shutdowns.

[0025] Furthermore, the use of a more active catalyst in the H2 production process allows for greater energy efficiency and thus helps reduce CO2 emissions, estimated at 10 t CO2 / t H2 in conventional configurations. The H2 production process, along with the FCC process, is one of the two largest sources of CO2 emissions from refining.

[0026] Brief Description of the Invention

[0027] This invention relates to HTS catalysts (chromium-free (Cr)) containing between 0.1% and 0.4% m / m of Pt in the balance of iron oxide, which is promoted by sodium (Na) having a content between 0.1% and 0.3% m / m and optionally aluminum content between 5.0% and 6.0% m / m, allowing high activity in combination with excellent resistance to deactivation due to exposure to high temperatures.

[0028] In a second aspect, the present invention provides a method for converting carbon monoxide from a syngas feed stream using the catalyst, wherein the steam / gas ratio is between 0.2 and 1.0 mol / mol, the pressure is between 10 and 40 atm, and the temperature is between 250°C and 450°C, or preferably between 250°C and 370°C, wherein the maximum bed temperature can be limited by injecting water or steam and a CO-containing gas feed at the reactor inlet.

[0029] This invention is applicable to hydrogen or syngas production facilities, whether by steam, autothermal reforming, dry or gasification reforming.

[0030] Brief description of the attached figures

[0031] The invention will be described in more detail below with reference to the accompanying drawings, which represent embodiments of the invention in a schematic and not limiting manner. In the drawings, we see:

[0032] - Figure 1 The graph illustrates the CO conversion activity in the water-gas shift reaction of catalysts with different residual sodium contents prepared according to Example 1.

[0033] - Figure 2 The graphs illustrate the CO conversion activity in the water-gas shift reaction of catalysts with different residual sodium contents prepared according to Example 2. Results obtained for commercial catalysts based on iron, chromium, and copper oxides and for the catalyst prepared according to Example 1 are also shown in the graphs.

[0034] - Figure 3 The graph illustrates the correlation between the conductivity of the washing water and the sodium content in the catalyst prepared according to the present invention (Example 2).

[0035] Detailed description of the invention

[0036] In summary, the present invention relates to a catalyst that can be used to convert CO to CO2 and H2 via a water-gas shift reaction. This catalyst comprises an iron oxide support having a crystalline structure of hematite, as determined by X-ray diffraction, promoted by a platinum (Pt) content between 0.1% and 0.4% m / m based on the oxide material and a sodium (Na) content between 0.1% and 0.3% m / m. Optionally, the catalyst contains aluminum at a content of 5.0% to 6.0% m / m.

[0037] The catalyst thus formed is prepared using the method described in the following steps:

[0038] 1) An aqueous solution containing a soluble iron salt (preferably ferric nitrate Fe(NO3)3·9H2O), a soluble platinum compound (preferably hexachloroplatinic acid (H2PtCl6·6H2O)) and optionally a soluble aluminum salt (preferably aluminum nitrate Al(NO3)3·9H2O)) is co-precipitated with an aqueous solution of sodium carbonate and optionally sodium hydroxide. The pH of the suspension is maintained between 7.5 and 8.0 at a temperature between 20°C and 80°C, preferably between 50°C and 70°C, with stirring. The precipitate is then aged under these conditions for 0.5 to 2.0 h.

[0039] 2) Filter the precipitate and then wash with water or ethanol until the residual sodium content of the product is 0.1% to 0.3% m / m;

[0040] 3) The precipitate obtained is dried at a temperature between 60°C and 150°C for 1 to 6 hours, and then calcined at a temperature between 300°C and 400°C for 1 to 5 hours;

[0041] 4) The material is shaped to obtain catalyst sheets with typical dimensions of between 0.3 and 0.7 cm in diameter and between 0.5 and 1.0 cm in length, and then calcined at a temperature between 300°C and 450°C to obtain hematite promoted by platinum and sodium, and optionally by aluminum intercalated into the crystalline structure of iron oxide, such that, in the balance of iron oxide, the platinum content is between 0.1% and 0.4% m / m, the sodium content is between 0.1% and 0.3% m / m, and optionally the aluminum content is between 5.0% and 6.0% m / m, having a hematite structure and greater than 50 m 2 Specific surface area per g.

[0042] The material can be shaped into a cylindrical shape with a hole in the middle or a cylinder with a wavy outer surface.

[0043] The catalyst thus prepared avoids an additional sodium incorporation step. Surprisingly, the presence of controlled levels of sodium allows for high CO conversion activity while maintaining high resistance to deactivation upon exposure to high temperatures, as extensively demonstrated in the examples. Very low sodium content in the final product produces a catalyst with lower activity, while very high sodium content produces a catalyst with low resistance to deactivation upon prolonged exposure to high temperatures.

[0044] As measured by X-ray diffraction, catalysts containing aluminum (Al) intercalated into the hematite crystalline structure showed cell parameters varying to values ​​between 0.5005 and 0.5010 nm. Aluminum provided greater catalytic activity, allowing for a reduction in the desired Pt level in the final product.

[0045] The catalyst thus prepared is a hematite-based catalyst promoted by platinum, sodium, and optionally aluminum, activated by a reduction process to convert the hematite phase (Fe2O3) into the magnetite phase (Fe3O4). This process has been well established industrially, and consists of the transfer of a gas containing H2 or CO and water vapor (with a vapor / gas ratio typically between 2 and 6 mol / mol) at temperatures between 250°C and 400°C for 1 to 3 hours.

[0046] The catalyst thus prepared and activated can be used for the conversion reaction of CO with water vapor to produce hydrogen at reactor inlet temperatures between 250°C and 350°C, preferably between 280°C and 300°C. Optionally, to reduce the CO content and increase the service life of the catalyst according to the invention, it is advantageous to maintain the highest temperature in the entire reactor at 370°C by injecting steam or condensate at the reactor inlet or at multiple points along the bed. The operating pressure in the reactor can be from 10 to 40 kgf / cm³. 2 Within the range of 20 and 30 kgf / cm², it is preferred. 2 The steam / dry gas molar ratio at the reactor inlet is between 0.2 and 1.0 mol / mol, preferably between 0.3 and 0.8 mol / mol. The dry gas at the reactor inlet typically contains CO content between 5% and 30% v / v, preferably between 8% and 20% v / v. Example

[0047] The embodiments shown below are intended to illustrate some ways of implementing the present invention and to demonstrate the practical feasibility of its application, and do not constitute any limitation on the present invention.

[0048] Example 1:

[0049] This comparative example illustrates the detrimental effect of sodium on catalysts containing iron oxide. A 1.0 M aqueous solution of ferric nitrate (Fe(NO3)3·9H2O) and a second 1.5 M aqueous solution of sodium carbonate (Na2CO3) were simultaneously added under stirring for 1 h, maintaining a temperature between 45°C and 50°C and a pH between 7.5 and 8.0. After precipitation, the suspension was maintained at the same temperature, pH, and stirring conditions for an additional 1 h to age the precipitate. The precipitate was then filtered and separated into fractions, which were washed with varying amounts of water to obtain different levels of residual sodium in the product.

[0050] The monitoring parameter for the washing step was the conductivity of the washing water. The washed material was then dried at 100°C for 5 hours and calcined at 400°C for 2 hours to obtain FeO. x -yNa catalyst, where yNa is the content of sodium (Na) in the oxidized form in the product.

[0051] The crystalline phases in the samples were characterized by X-ray diffraction (XRD) using a Rigaku Miniflex II diffractometer with a copper tube and monochromator, employing a speed of 2° / min and angle variations from 5° to 90°. The catalyst exhibited X-ray diffraction profiles corresponding to the presence of hematite. Structural analysis by nitrogen adsorption (BET) was performed to determine the specific surface area on a Micromeritics ASAP2400 instrument. For this determination, the samples were previously treated in vacuum at 300°C. Compositional analysis was performed by X-ray fluorescence (XRF) on a PANAlytical MagiX PRO instrument equipped with a 4kW Rh tube.

[0052] The activity of the catalyst in the water-gas shift reaction was measured in a commercial facility (AutoChem Micromeritcs) under fixed-bed reactor and atmospheric pressure. The sample was initially heated to 100 °C in an argon stream and then to 350 °C in a stream of 5% H2 saturated with water vapor at 73 °C. Following this pretreatment, the gas mixture was replaced with a mixture containing 10% v / v CO, 10% v / v CO2, and 2% v / v methane in the balance of H2, and the temperature of the saturator (using water) was maintained at 73 °C, corresponding to a steam / gas ratio of 0.55 mol / mol. The reaction was carried out at different temperatures, and the reactor effluent was analyzed by gas chromatography. The catalyst activity is expressed as CO conversion (% v / v).

[0053] Table 1 and Figure 1 The results shown allow us to conclude that, in order to obtain high activity in catalysts composed of iron oxide, it is necessary to reduce the residual sodium content to less than 0.02% m / m. Therefore, the effect of sodium on catalyst performance depends on its concentration, and its complete elimination is desirable when the catalyst consists solely of iron oxide.

[0054] Table 1 - Comparison of CO conversion activity with sodium content in water-gas shift reaction (Example 1).

[0055]

[0056] Note: The remaining balance in the composition of the completed sample is oxygen (O).

[0057] Example 2

[0058] This embodiment of the invention illustrates a method for preparing a hematite-based catalyst promoted by low levels of platinum and sodium. A 1.0 M aqueous solution of ferric nitrate (Fe(NO3)3.9H2O) and a second 1.5 M aqueous solution of sodium carbonate (Na2CO3) containing platinum compounds soluble in water or polar solvents (e.g., but not limited to Pt(NH3)4(NO3)2 (CAS20634-12-2), H2PtC15.xH2O (CAS26023-84-7), PtCl4 (CAS13454-96-1), (NH4)2PtCl4 (CAS13820-41-2), and (NH4)2PtCl6 (CAS16919-58-7)) are simultaneously added under stirring for 1 h, wherein the temperature is maintained between 45°C and 50°C, and the pH between 7.5 and 8.0. After precipitation, the suspension was maintained at the previous temperature, pH, and stirring conditions for an additional 1 hour to allow the precipitate to age. The precipitate was then filtered and separated into several fractions, which were washed with different amounts of water to obtain different levels of residual sodium in the product.

[0059] Monitoring the conductivity of the wash water allows for a simple way to obtain different sodium (Na) contents in the final product. Figure 3 The washed material was then dried at 100°C for 5 hours and calcined at 400°C for 2 hours to obtain Pt-FeO. x The sample contained yNa, where yNa is the content of sodium (Na) in the oxidized form in the product. The catalyst was characterized, and its CO conversion activity was measured by a water-gas shift reaction as described in Example 1.

[0060] Furthermore, the platinum metal region was characterized by a cyclohexane dehydrogenation reaction in a fixed-bed reactor at atmospheric pressure, using a saturator with cyclohexane maintained at 10 °C and hydrogen as the carrier gas. Catalyst reduction was carried out at 300 °C with a hydrogen flow (40 ml / min) for 2 h, followed by the reaction at the same temperature.

[0061] Table 2 and Figure 2 The results shown allow us to conclude that, in order to obtain high activity in the conversion of CO, the presence of a sodium promoter (above 0.04% m / m) is necessary and, in principle, above 2.0% m / m, is desirable, unlike the catalysts observed with the catalysts composed of iron oxide and platinum (Table 2).

[0062] Catalysts containing platinum and promoted by sodium exhibit significantly higher CO conversion activity than commercial catalysts based on iron, chromium, and copper oxides. Figure 2Although the results do not allow for definitive conclusions, it is believed that sodium interacts with Pt atoms to form a substance with high CO conversion activity. Since Pt-containing catalysts exhibit dehydrogenation activity, the zero activity in dehydrogenation is an unusual result, raising doubts about the influence of the interaction between Na and Pt. This interaction can reduce the dehydrogenation activity of cyclohexane, a characteristic of platinum, which has a predominantly metallic function (Table 2). To evaluate this hypothesis, a series of catalysts with different sodium contents were evaluated, and the dehydrogenation activity of samples with low Na contents was observed, as can be seen in Table 2.

[0063] Table 2 - Comparison of CO conversion activity with sodium content in water-gas shift reaction at different temperatures (Example 2).

[0064]

[0065] Note: The Pt content in the sample, determined by XRF technology, is 0.20 ± 0.01, and the Fe content is 69 ± 1 m / m, with oxygen as the balance. RD refers to the rate of cyclohexane dehydrogenation.

[0066] The activity of the catalyst in the water-gas shift reaction was measured in a commercial facility (AutoChem Micromeritcs) under fixed-bed reactor and atmospheric pressure. The sample was initially heated to 100 °C in an argon stream and then to 350 °C in a stream of 5% H2 saturated with water vapor at 73 °C. Following this pretreatment, the gas mixture was replaced with a mixture containing 10% v / v CO, 10% v / v CO2, and 2% v / v methane in the H2 balance, and the temperature of the saturator with water was maintained at 73 °C, corresponding to a steam / gas ratio of 0.55 mol / mol, to measure the initial activity at 350 °C. Next, the gas mixture was replaced with hydrogen and the temperature was raised to 500 °C and maintained under these conditions for 18 h. The temperature was then lowered to 350 °C, the hydrogen was replaced with the reaction gas, and a new measurement of catalyst activity was performed. The reactor effluent was analyzed by gas chromatography. The catalyst activity is expressed as CO conversion (% v / v).

[0067] Table 3 shows the initial activity and stability results. Surprisingly, however, the present invention teaches that high sodium content, while allowing for greater activity, reduces the stability of the catalyst when exposed to high temperatures, where sodium content between 0.1% and 0.3% m / m allows for the optimal combination of activity and stability performance.

[0068] Table 3 - Comparison of CO activity with sodium content after initial conversion and accelerated deactivation over a period of time in water-gas shift reaction (Example 2).

[0069] Pt-FeOx>2.0Na 70.0 25.0 Pt-FeOx-1.58Na 62.3 27.8 Pt-FeOx-0.66Na 64.6 31.0 Pt-FeOx-0.28Na 68.4 40.0 Pt-FeOx-0.09Na 59.8 35.2 Pt-FeOx-0.04Na 47.0 33.0

[0070] Example 3:

[0071] This comparative example demonstrates that a catalyst with lower activity than that obtained by the catalyst preparation method described in this invention (i.e., by co-precipitation) was produced by impregnating platinum with the hematite phase. The catalyst prepared according to Example 2, containing less than 0.05% m / m sodium, was impregnated by a wet-point method with an aqueous solution of a water-soluble platinum compound (e.g., but not limited to compounds Pt(NH3)4(NO3)2 (CAS20634-12-2), H2PtC15.xH2O (CAS26023-84-7), PtCl4 (CAS13454-96-1), (NH4)2PtCl4 (CAS13820-41-2), and (NH4)2PtCl6 (CAS16919-58-7)) or a polar solvent. The catalyst was then dried at 100°C for 2 h and calcined at 400°C for 2 h to obtain a hematite-based catalyst promoted by 0.2% platinum (Pt) based on oxidation products. The catalyst was characterized by measuring its CO conversion activity through a water-gas shift reaction as described in Example 1 and by measuring its cyclohexane dehydrogenation activity as described in Example 2.

[0072] Table 4 shows that the catalyst prepared by co-precipitation according to the present invention (Example 2) allows for higher CO conversion activity than the catalyst prepared by impregnation (Example 3), despite a smaller metal region assessed by cyclohexane dehydrogenation activity. Although the results do not allow for definitive conclusions, it is believed that sodium interacts more effectively with Pt atoms in the co-precipitation method, thereby forming a substance with high CO conversion activity. The greater interaction between sodium and platinum will decrease the dehydrogenation activity of cyclohexane, a characteristic of platinum with its dominant metallic function (Table 4), but will increase the activity of the CO conversion reaction via the water-gas shift reaction.

[0073] Table 4 - CO conversion activities of the catalyst prepared by impregnation (Example 3) and the catalyst prepared according to the present invention (Example 2) in the water-gas shift reaction.

[0074]

[0075] Note: The Fe content is 69±1 m / m, with an oxygen balance. RD refers to the rate of cyclohexane dehydrogenation [gmol / gs].

[0076] Example 4:

[0077] This embodiment of the invention illustrates a method for preparing a hematite-based catalyst promoted by low levels of aluminum, platinum, and sodium. The catalyst is prepared by simultaneously adding, under stirring, a 1.0 M aqueous solution of ferric nitrate (Fe(NO3)3.9H2O) and a second 1.5 M aqueous solution of sodium carbonate (Na2CO3) containing platinum compounds soluble in water or polar solvents (e.g., but not limited to compounds Pt(NH3)4(NO3)2 (CAS20634-12-2), H2PtC15.xH2O (CAS26023-84-7), PtCl4 (CAS13454-96-1), (NH4)2PtCl4 (CAS13820-41-2), and (NH4)2PtCl6 (CAS16919-58-7)) and aluminum salt Al(NO3)3.9H2O, to a solution of ferric nitrate (Fe(NO3)3.9H2O) and ferric nitrate (Na2CO3) to a solution of ferric nitrate (Fe(NO3)3.9H2O) to a solution of ferric nitrate (Na2CO3) to a solution of ferric nitrate (Al ... After precipitation, the suspension was maintained at the previous temperature, pH, and stirring conditions for an additional 1 hour to allow the precipitate to age. The precipitate was then filtered and separated into several fractions, which were washed with different amounts of water to obtain different levels of residual sodium in the final product.

[0078] Monitoring the conductivity of the wash water allows for easy and simple determination of the varying sodium (Na) content in the final product. The washed material was then dried at 100°C for 5 h and calcined at 400°C for 2 h. The catalyst exhibited the CO conversion activity measured as described in Example 1.

[0079] According to the present invention, aluminum is inserted into the crystalline structure of hematite, thereby reducing the size of parameter "a" of the hematite unit cell to a value between 0.05005 and 0.5010 nm (Table 5).

[0080] Table 5 - Crystalline phase types and their unit cell sizes measured using X-ray diffraction techniques.

[0081]

[0082] Note: tC = average size of hematite crystallites. Cell parameters A, B, and C.

[0083] Table 6 illustrates that introducing aluminum into the formulation yields the hematite phase at higher calcination temperatures. Furthermore, a higher specific surface area was observed (Table 7), which contributes to greater catalyst activity.

[0084] Table 6 - Crystal structure and crystallite size of samples prepared according to Examples 1, 2 and 4, determined by X-ray diffraction (XRD).

[0085] T＝60℃ Goetita 14nm Goethite (8nm) Hydroxide mixture T＝300℃ Hematite (24nm) Hematite (24nm) Hydroxide mixture T＝400℃ Hematite (43nm) Hematite (44nm) Hematite (34nm)

[0086] Note: The sodium content in the sample is <0.1% m / m, the Pt content in Examples 2 and 4 is 0.2% m / m, and the aluminum content in Example 4 is 5.2% m / m.

[0087] Table 7 - Changes in compositional properties, specific surface area, and CO conversion activity with temperature in the water-gas shift reaction.

[0088]

[0089] Note: S = Specific surface area measured by N2 adsorption technology after calcination at 400℃.

[0090] It should be noted that although the invention has been described with reference to the accompanying drawings, those skilled in the art may modify and alter it according to the specific circumstances, provided that they are within the scope of the invention as defined herein.

Claims

1. A method for preparing a water-gas shift catalyst, characterized in that... Includes the following steps: 1) A solution containing soluble iron salts, soluble platinum compounds and soluble aluminum salts in a polar solvent is co-precipitated with soluble sodium salts. The pH of the suspension is maintained between 7.5 and 8.0 under stirring and at a temperature between 20°C and 80°C. The precipitate is then aged under these conditions for 0.5 h to 2.0 h. 2) Filter and wash the precipitate formed with a polar solvent until the residual sodium content of the final product is between 0.1% w / w and 0.3% w / w; 3) The precipitate obtained by drying at a temperature between 60°C and 150°C for 1 h to 6 h, and then calcining at a temperature between 300°C and 400°C for 1 h to 5 h; 4) Shape the material and then calcine it at a temperature between 300°C and 450°C to obtain hematite promoted by platinum and sodium and aluminum.

2. The method according to claim 1, characterized in that... The soluble iron salt is ferric nitrate.

3. The method according to claim 1, characterized in that... The soluble platinum compound is hexachloroplatinic acid.

4. The method according to claim 1, characterized in that... The polar solvent is water or ethanol.

5. The method according to claim 1, characterized in that... The soluble sodium salt is sodium carbonate or sodium hydroxide.

6. The method according to claim 1, characterized in that... Co-precipitation occurs at temperatures between 50°C and 70°C.

7. The method according to claim 1, characterized in that... Aluminum is inserted into a hematite lattice having a cell parameter between 0.5005 nm and 0.5010 nm and a density greater than 100 nm. 2 Specific surface area per g.

8. A water-gas shift catalyst, obtained by the method according to claim 1, characterized in that it has a platinum content between 0.1% w / w and 0.4% w / w, a sodium content between 0.1% w / w and 0.3% w / w, and an aluminum content between 5.0% w / w and 6.0% w / w, with the balance being iron oxide, and has a hematite structure and a particle size greater than 50 m. 2 Specific surface area per g.

9. A method for reducing carbon monoxide content via water-gas shift reaction, characterized in that... The catalyst prepared by the method according to claim 1 is brought into contact with syngas containing between 5% and 30% CO, a steam / dry gas ratio between 0.2 mol / mol and 1.0 mol / mol, and a reactor inlet temperature between 250°C and 350°C.

10. The method according to claim 9, characterized in that... The synthesis gas contains between 8% and 20% CO, the steam / dry gas ratio is between 0.3 mol / mol and 0.8 mol / mol, and the reactor inlet temperature is between 280°C and 300°C.

11. The method according to claim 9, characterized in that... The reactor outlet temperature is a maximum of 370°C, which is controlled by the combined supply of the synthesis gas and the steam or condensate stream.

Images