Method for preparing an iron-chromium catalyst with a platinum promoter, and a catalyst comprising iron-chromium with a platinum promoter

Abstract

PROBLEM TO BE SOLVED: To provide a preparation method of an iron-chromium catalyst accompanying a platinum accelerator and a catalyst including iron-chromium accompanying a platinum accelerator.SOLUTION: Iron and chromium catalysts accompanying a platinum accelerator are to be used in water-gas-shift reaction at both low temperature (LTS) and high temperature (HTS). In comparison to a conventional catalyst, these are superior to a catalyst in the market under a same operational condition due to their characteristics of higher activity by addition of Pt. A precursor of an active phase (FeO) can be obtained at a larger volume per unit area, so that a more promising catalyst can be prepared with a smaller area.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to iron and chromium catalysts with a platinum promoter for use in the water gas shift reaction, and methods for preparing those catalysts.

[0002] [Cross - reference to Related Applications] This application claims the benefit of priority to BR102016022962 - 6, filed on October 3, 2016, which is incorporated herein by reference in its entirety.

Background Art

[0003] Due to the need for better utilization of heavy oil fractions, gasification is an interesting alternative technology. The tendency to use heavy oil as a feedstock processed at refineries results in higher yields of lower - value residues such as fuel oil and coke. The use of gasification technology in an integrated refinery system enables the maximization of hydrogen production and increases the overall efficiency of the refinery.

[0004] The gasification of refinery residues has some specific characteristics compared to coal gasification. The low - cost synthesis gas obtained as an intermediate can be used to produce hydrogen, methane, and other compounds. The synthesis gas produced by gasification has a very high carbon monoxide / hydrogen ratio (CO / H2), and as a result, when it is used to produce products other than hydrogen, the CO / H2 ratio must be adjusted using the water gas shift reaction (WGSR).

[0005] Another important aspect of the reduction of the CO / H2 molar ratio is related to the activity of the catalysts in the next process because, in the presence of an excess of CO, they are either deactivated or their activity decreases. In this way, the water gas shift reaction increases the useful life of the catalysts used in various industrial processes such as ammonia synthesis and hydrogenation reactions.

[0006] Currently, the most common method for producing hydrogen is the steam reforming of hydrocarbons, mainly methane, and the product is a mixture of carbon monoxide (CO), hydrogen gas (H2), carbon dioxide (CO2), and unreacted reactants. For the purpose of increasing hydrogen production, the oxidation of carbon monoxide is carried out by the water-gas shift reaction. In this reaction, steam reacts with carbon monoxide in the presence of a catalyst and is then oxidized to carbon dioxide, generating an additional amount of hydrogen: CO + H2O ⇔ CO2 + H2

[0007] The water-gas shift reaction is well known enough from the prior art. It became one of the most important catalytic reactions in 1915 when the first plant for coal-based ammonia synthesis was developed. The water-gas shift reaction (WGSR) is an important step both in the treatment of syngas derived from coal and in the purification in hydrogen production and the adjustment of the CO / H2 molar ratio for fuel production from syngas.

[0008] Industrially, the water-gas shift reaction (WGSR) is usually carried out in two steps, one is carried out at a low temperature of 200 - 250 °C and is called the low-temperature shift (LTS), and the other is carried out at a higher temperature in the range of 310 - 450 °C and is called the high-temperature shift (HTS).

[0009] Typical catalysts for HTS consist of Fe3O4 and Cr2O3 and have been used since the first commercial process developed by BASF in 1915. However, it changes over time to optimize its stability. The active phase of the catalyst is magnetite (Fe3O4), and the role of Cr2O3 is to prevent the sintering of the microcrystals of Fe3O4 and the inevitable loss of the active surface area. Fresh catalysts contain 90 - 95% hematite (Fe2O3) together with 5 - 10% Cr2O3 by the manufacturer. The catalyst is activated by a controlled reduction of Fe2O3 to Fe3O4. The reduction is carried out as follows by H2 and CO present in the reactor feed in the presence of H2O and CO2, and additional reduction to FeO and metallic Fe is avoided. 3Fe2O3 + H2 ⇔ 2Fe3O4 + H2O 3Fe2O3 + CO ⇔ 2Fe3O4 + CO2

[0010] The equilibrium between the phases Fe2O3 and Fe3O4 is determined by the ratios of H2 / H2O and CO / CO2. It is important to emphasize that in the conventional way of using pure H2 or a mixture of H2 and N2, the reduction cannot be carried out to prevent the formation of metallic Fe. Any formation of metallic Fe will catalyze the methanation reaction and the Boudouard reaction (disproportionation of CO) as follows, leading to coke formation. CO + 3H2 ⇔ CH4 + H2O 2CO ⇔ C + CO2

[0011] From a thermodynamic perspective, the efficiency of the water - gas shift reaction is maximized at low temperatures, higher concentrations of water, and low concentrations of hydrogen. However, under certain conditions, existing catalysts are kinetically limited at the low temperatures required for high conversion of CO. These catalysts also have many disadvantages such as low activity at low temperatures and sensitivity to air. This means that for practical purposes, the process is carried out at high temperatures or using large - volume reactors.

[0012] Thus, in one configuration of the process, the first stage of the reaction is a high-temperature converter, followed by a low-temperature converter. The high-temperature step is typically carried out in the range of 320 - 450 °C using an Fe oxide - Cr catalyst at an overall pressure that varies from 10 to 60 bar. Under standard operating conditions, the temperature in the converter bed continuously rises and can reach 500 °C. The high-temperature water-gas shift reaction uses an iron-based catalyst due to their excellent thermal stability, toxicity resistance, and good selectivity.

[0013] The low-temperature step is carried out at 200 - 250 °C, and the most commonly used catalyst is Cu / ZnO / Al2O3. The concentration of carbon monoxide in this step can vary from 1% to 5%. The outlet temperature can reach 280 °C, and CO is reduced to an amount less than 0.5%. The Cu / ZnO / Al2O3 catalyst is more sensitive to the presence of poisons such as sulfur and chlorides but has higher activity at low temperatures.

[0014] Noble metal catalysts have proven to be an attractive alternative for the water-gas shift reaction as they are more active than Fe-Cr catalysts and are generally poison-resistant to sulfur. In their investigations, several authors used platinum to prepare the catalyst, and a specific resistance of this metal to the presence of sulfur was observed. This was explained by the low stability of the bond between sulfur and platinum.

[0015] Patent Document 1 discloses a catalyst for the water-gas shift reaction comprising a platinum-based catalyst together with at least one alkaline earth metal and at least one third metal. In particular, the catalyst of this patent comprises: a) Pt, b) at least one of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, 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.

[0016] Patent Document 2 discloses a catalyst for the conversion of CO to carbon dioxide (CO2) by the water gas shift reaction. This catalyst includes a carrier formed from a metal oxide, a platinum component and an alkali metal component supported on this carrier. Examples of the catalysts disclosed in this application include Na / Pt / ZrO2, K / Pt / ZrO2 and Rb / Pt / ZrO2.

[0017] Patent Document 3 describes the application of a noble metal catalyst of Pt, Pd or a mixture thereof or other mixtures of Pt-Ir for the water gas shift reaction in the temperature range of 200 - 400 °C, supported on a mixture of oxides of Ce in the range of 20 - 58% or 58 - 80% and Zr in the range of 42 - 20%, together with at least one metal selected from 0.01 - 1% of yttrium, an alkali metal, or an alkaline earth metal as a promoter.

[0018] A platinum-based iron-chromium catalyst for use in the aqueous phase reforming of ethylene glycol was disclosed in Non-Patent Document 1. However, since this catalyst is prepared by the decomposition of nitrates using citric acid as a fuel, involves the use of a relatively high-cost reagent (citric acid), and it is very difficult to control the reaction temperature, it is not attractive for industrial production. Table 1 of that non-patent document discloses that the preferred catalyst has a high specific surface area of 94 m 2 / g.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0020]

Non-Patent Document 1

[0021] However, despite current developments, this technology still requires Fe-Cr catalysts with Pt promoters that are applicable to the water-gas shift reaction in all technologies used in this reaction, such as steam reforming, partial oxidation, and catalytic gasification. Means for Solving the Problems

[0022] The present disclosure relates to iron-chromium catalysts with a platinum promoter. These catalysts are applicable in the water-gas shift reactions of HTS and LTS. Compared to conventional catalysts, due to the addition of Pt, they are superior to commercially available catalysts under the same operating conditions due to their higher activity characteristics. Since a larger amount of the precursor of the active phase (Fe3O4) is obtained per unit surface area, it has become possible to prepare highly active catalysts with a small surface area.

[0023] In addition, a method for preparing these iron-chromium catalysts with a platinum promoter is described.

[0024] One aspect of the present disclosure provides a method for preparing an iron-chromium catalyst with a platinum promoter, comprising the following steps: (a) synthesis of oxides of iron and chromium by a coprecipitation method to obtain Fe2O3 and Cr2O3; and (b) addition of platinum to the catalyst obtained in (a). Another aspect of the present invention provides a catalyst obtained by this method.

[0025] Another aspect of the present disclosure is the following steps: (a) synthesis of iron and chromium oxides by coprecipitation to obtain Fe2O3 / Cr2O3 at a ratio of 85 - 95%:15 - 5%; (b) addition of 0.01 - 1.5 wt% of platinum to the catalyst obtained in (a) by dry impregnation; and (c) drying at least some at a temperature varying in the range of 110 - 130 °C for 20 - 28 hours, and provides a method for preparing an iron-chromium catalyst with a platinum promoter, characterized by comprising the above.

[0026] In some embodiments, the method further comprises the step of calcining the catalyst at a temperature varying between 440 - 460 °C for 1 - 3 hours at a heating rate varying between 5 - 15 °C / min.

[0027] In some embodiments, the method is further characterized in that the iron and chromium oxides are synthesized from Fe(NO3)3·9H2O and Cr(NO3)3·9H2O respectively at a temperature varying between 60 - 80 °C.

[0028] In some embodiments, the method is further characterized in that in the step of Fe-Cr synthesis, a base is added until the solution reaches a pH of 8.0 - 9.0.

[0029] In some embodiments, the method is further characterized in that the base is Na2CO3.

[0030] In some embodiments, the method is further characterized in that the iron-chromium catalyst is aged for 1 - 10 hours.

[0031] In some embodiments, the method is further characterized in that the platinum precursor is hexachloroplatinic acid.

[0032] In another aspect of the present disclosure, an iron-chromium with a platinum promoter, obtained by the method defined in any one of the above aspects, and having a surface area of 35 - 45 m 2 ·g-1 There is provided a catalyst further characterized by having a specific surface area.

[0033] In some embodiments, the catalyst is further characterized by being suitable for use in the water gas shift reaction in LTS and HTS.

[0034] In some embodiments, the catalyst is further characterized by being suitable for use in the water gas shift reaction in the temperature range of 200 to 450 °C.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0036] The Fe-Cr catalyst with the Pt promoter of the present disclosure can be applied to the water gas shift reaction in all technologies where this reaction is used, such as steam reforming, partial oxidation, and catalytic gasification. Due to their higher activity, they are superior to commercially available catalysts under the same operating conditions.

[0037] Depending on the carrier used, the catalyst with the platinum promoter is active in the water gas shift reaction. The interaction of Pt with the components of the Fe-Cr catalyst causes the formation of additional active sites, improving the activity of the catalyst.

[0038] Due to its activity over a wide temperature range, the catalyst of the present disclosure can be used under conditions from low to high temperatures and is therefore applicable to both low temperature shift (LTS) and high temperature shift (HTS) water gas shift reactions (WGSR).

[0039] As described above, the water-gas shift reaction (WGSR) is maximized at low temperatures, high water concentrations, and low hydrogen concentrations. However, existing catalysts are kinetically limited at low temperatures. In fact, the process operates at a temperature higher than that indicated by thermodynamics. In the case of a more active catalyst, the reaction rate is more favorable, the volume of the catalyst can be minimized, and it can operate at a lower temperature, promoting a higher conversion from a thermodynamic perspective.

[0040] The catalyst of the present disclosure is an Fe-Cr catalyst prepared, for example, by a coprecipitation method from iron and chromium salts such as Fe(NO3)3·9H2O and Cr(NO3)3·9H2O. In some embodiments, this can be carried out at a temperature of 60 - 80 °C. These reagents can be added to a base until the solution reaches a pH of, for example, 8.0 - 9.0. In some embodiments, the base used is Na2CO3. The precipitate can be matured under these conditions for 1 - 10 hours. It can then be filtered and dried, for example, at 100 - 120 °C for 10 - 14 hours. At the end of the preparation, in some embodiments, the catalyst has an Fe2O3 / Cr2O3 weight ratio of 85 - 95%:15 - 5% respectively. In a preferred embodiment, the catalyst has 90% Fe2O3 and 10% Cr2O3.

[0041] In the synthesis method of the Fe-Cr catalyst of the present disclosure, the iron and chromium oxides are formed simultaneously. This promotes crystal formation by a greater dispersion of the existing species' oxides. This can increase the interaction between iron and chromium. In addition, the catalyst has a low specific surface area of 35 - 45 m 2 ·g -1 . This reduces the exposure of iron oxide sites. Such a reduction in exposure, combined with a better Fe-Cr interaction, promotes the partial reduction of hematite (Fe2O3) sites to magnetite (Fe3O4), increasing the overall activity of the catalyst.

[0042] The Fe-Cr catalyst thus prepared is promoted with platinum by the dry impregnation method. In some embodiments, the impregnation is in the range of weight % varying from 0.01% to 1.5%. An example of a platinum precursor is hexachloroplatinic acid. Accordingly, a solution of H2PtCl6 can be prepared and diluted in a volume corresponding to the pore volume. This solution can be slowly added to the support and continuously stirred to make the impregnation uniform.

[0043] After impregnation, the sample can be subjected to a temperature of 110 - 130 °C for a time that each sample can survive for 20 - 28 hours. After this time, the sample is heated to a temperature of 440 - 460 °C at an initial heating rate varying from 5 - 15 °C / min and then calcined by maintaining the temperature of 440 - 460 °C for 1 - 3 hours.

[0044] The method used to add platinum (dry impregnation) promotes proper dispersion of the particles on the surface of the support. The presence of platinum promotes partial reduction of hematite occurring at lower temperatures, along with a decrease in platinum oxide and chromium oxide. This reduces the possibility of complete reduction to metallic Fe, which, as described above, would undesirably promote the methanation reaction and the Boudouard reaction and lead to coke formation.

[0045] Furthermore, under clean conditions, i.e., in the absence of the presence of impurities such as sulfur, the catalyst of the present disclosure shows an initial conversion of CO in the range of 30% - 40%.

Example

[0046] Table 1 shows the specific surface area (S BET ), average pore diameter (D p ), and total pore volume (V p ) in the range of 0.05 - 0.20 w / w of commercially available catalysts (HTS Com 1, HTS Com 2), Fe-Cr catalysts, and Fe-Cr catalysts impregnated with 1% platinum according to the present disclosure, based on the BET method. These experiments were carried out on an ASAP 2020 apparatus from MICROMERITICS.

Table 1

[0047] Furthermore, to determine the chemical composition of the synthesized catalyst, the technique of X-ray spectroscopy (EDX) was used, where the sample was exposed to X-rays under vacuum. The apparatus used was a BRUKER spectrometer, model S4 Explorer equipped with an X-ray tube of rhodium (Rh).

[0048] Table 2 represents the results obtained to determine the chemical composition of the oxide of the catalyst, determined by energy-dispersive X-ray spectroscopy (EDX).

Table 2

[0049] [Catalyst Test] The catalytic test was carried out in a unit connected to a SHIMADZU gas chromatograph equipped with a SUPELCO CARBOXEN 1010 PLOT 30 m×0.53 mm column, a thermal conductivity detector (TCD) and a flame ionization detector (FID). A quartz reactor containing approximately 200 mg of sample was used for the reaction.

[0050] All the catalysts were subjected to the same steps of drying and activation (shown in Table 3).

Table 3

[0051] Various commercially available catalysts (HTS Com 1, HTS Com 2), Fe-Cr catalysts and Fe-Cr catalysts impregnated with 1% platinum according to the present disclosure were provided to the reaction using the conditions shown in Table 4.

Table 4

[0052] [Results] The results obtained from the above tests are presented in Figures 1 and 2.

[0053] Figure 1 shows a diagram of the influence of temperature on the conversion of CO using a commercially available catalyst and an Fe-Cr supported catalyst. In the water-gas shift reaction, a very surprising beneficial effect is found by incorporating 1% Pt as compared to the already conventional Fe-Cr catalyst. Under these conditions, the 1% Pt / Fe-Cr catalyst shows very interesting potential for application in this reaction.

[0054] The prepared Fe-Cr catalyst has active analysis results similar to those of the commercially available catalyst. However, the use of Pt as a promoter provides activity at a lower temperature, and the results are seen from 200 °C, which is the temperature at which the commercially available catalyst and the Fe-Cr catalyst without a promoter did not show activity, and it is thought to start at 150 - 200 °C.

[0055] Furthermore, it can be seen that the activity of the catalyst with a platinum promoter at 350 - 400 °C is more than twice that of the catalyst without a promoter.

[0056] Therefore, it can be concluded that the Fe-Cr catalyst with a Pt promoter prepared according to the present disclosure can be used for the water-gas shift reaction in LTS and HTS.

[0057] Figure 2 shows a diagram of the stability in the conversion of CO for the tested catalysts. As can be seen, for the commercially available catalyst, there is a slight tendency to deactivate with reaction time.

[0058] Despite the differences in the results (due to the condensation of H2O in the catalyst test unit), a significant tendency for conversion is observed for the Fe-Cr catalyst with a Pt promoter, especially when compared to the conventional Fe-Cr, which indicates great potential for the use of this catalyst.

[0059] Table 5 below shows a comparison between various catalysts for the conversion of CO under clean conditions and provides a time-average of the results in Figure 2.

Table 5

[0060] Surprisingly, in addition to the catalysts of the present disclosure that do not suffer a significant decrease in catalytic activity, a substantial increase in the conversion of CO has been found compared to known catalysts from the prior art. This is at least partially due to the preparation method of the material, which is advantageous for the formation of species that are more susceptible to partial reduction and results in a larger amount of the active phase (Fe3O4) per unit area.

[0061] Modifications of the devices and methods described above, combinations between various executable variations, and variations of aspects of the invention that will be apparent to those skilled in the art are intended to be within the spirit and scope of the claims.

Claims

1. (a) Synthesis of an iron-chromium catalyst of iron and chromium oxides by coprecipitation to obtain Fe ２ O ３ and Cr ２ O ３ without ammonia, and (b) Addition of platinum to the catalyst obtained in (a) and A method for preparing an iron-chromium catalyst with a platinum promoter, which is a catalyst for the water-gas shift reaction, comprising: The coprecipitation method in (a) is carried out by adding a base Na ３ ) ３ ·9H ２ O and Cr(NO ３ ) ３ ·9H ２ O to a solution of CO ２ CO ３ and (a) does not include a degassing step, The addition of platinum in (b) is carried out by dry impregnation and includes the addition of hexachloroplatinic acid as a platinum precursor, and the method is The prepared catalyst does not contain oxides other than iron and chromium oxides.

2. The coprecipitation provides Fe in a ratio of 85 to 95 wt%: 15 to 5 wt% ２ O ３ and Cr ２ O ３ The method according to claim 1.

3. The method according to claim 1, wherein the platinum is added in an amount of 0.01 to 1.5 wt% of the catalyst.

4. The method according to claim 1, further comprising a step of drying at a temperature of 110 to 130 °C after the addition of platinum.

5. The method according to claim 4, wherein the drying step is carried out for 20 to 28 hours.

6. The method according to claim 1, further comprising a step of firing the catalyst.

7. The method according to claim 6, wherein the firing step is carried out at a temperature of 440 to 460 °C.

8. The method according to claim 7, wherein the firing step comprises maintaining a temperature of 440 to 460 °C for 1 to 3 hours.

9. The method according to claim 8, wherein the firing step comprises an initial heating step of heating at a rate of 5 to 15 °C / min to reach a temperature of 440 to 460 °C.

10. The method according to claim 1, wherein the oxides of iron and chromium are synthesized at a temperature of 60 to 80 °C.

11. The method according to claim 1, wherein the iron-chromium catalyst is matured in the solution containing the base for 1 to 10 hours.

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