Process for preparing an iron-chromium catalyst with a platinum promoter, and catalyst consisting of iron chromium with a platinum promoter

Abstract

The present invention relates to catalysts of iron and chromium with a platinum promoter for use in water-gas shift reactions, both at low temperatures (LTS) and at high temperatures (HTS). Their characteristics of higher activity due to the addition of Pt compared to the conventional catalysts make them superior to the commercial catalysts in the same operating conditions. Because precursors of the active phase (Fe.sub.3O.sub.4) are obtained in greater quantity per unit area, it was possible to prepare catalysts that are more promising with a smaller surface area.

Claims

1. A process for preparing an iron-chromium water-gas shift reaction catalyst with a platinum promoter, wherein the process consists of the following steps: (a) synthesizing iron and chromium oxides by a method of co-precipitation so as to obtain Fe.sub.2O.sub.3 and Cr.sub.2O.sub.3; and (b) adding platinum to the catalyst obtained in (a), wherein the process excludes addition of oxides other than iron and chromium oxide.

2. The process according to claim 1, wherein the co-precipitation provides Fe.sub.2O.sub.3 and Cr.sub.2O.sub.3 in a ratio of 85-95%:15-5% by weight.

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

4. The process according to claim 1, wherein the platinum is added by a method of dry impregnation of the catalyst.

5. The process according to claim 1, wherein the iron and chromium oxides are synthesized from Fe(NO.sub.3).sub.30.9H.sub.20 and Cr(NO.sub.3).sub.30.9H.sub.2O, respectively.

6. The process according to claim 5, wherein the iron and chromium oxides are synthesized at a temperature from 60 to 80° C.

7. The process according to claim 5, wherein a base is added to the solution of Fe(NO.sub.3).sub.30.9H.sub.2O and Cr(NO.sub.3).sub.30.9H.sub.2O in the step of synthesis of the iron and chromium oxides.

8. The process according to claim 7, wherein the base is Na.sub.2CO.sub.3.

9. The process according to claim 7, wherein the iron-chromium catalyst is matured in the solution containing the base for 1 to 10 hours prior to the step of adding platinum to the catalyst.

10. The process according to claim 1, wherein the addition of the platinum comprises the addition of hexachloroplatinic acid as a platinum precursor.

11. A catalyst consisting of iron-chromium with a platinum promoter prepared by the process as defined in claim 1, wherein the catalyst has a specific surface area between 35 and 45 m.sup.2.g.sup.−1.

12. The catalyst according to claim 11, wherein the catalyst is used in water-gas shift reactions in both low-temperature shift and high-temperature shift.

13. The catalyst according to claim 11, wherein the catalyst is used in water-gas shift reactions in the temperature range of from 200 to 450° C.

14. The process according to claim 1, wherein the iron-chromium catalyst is filtered and dried for 10-14 hours at 100-120° C. prior to the step of adding platinum to the catalyst.

15. A process for preparing an iron-chromium water-gas shift reaction catalyst with a platinum promoter, wherein the process consists of the following steps: (a) synthesizing iron and chromium oxides by a method of co-precipitation so as to obtain Fe.sub.2O.sub.3 and Cr.sub.2O.sub.3; (b) adding platinum to the catalyst obtained in (a), and (c) drying at a temperature from 110 to 130° C., wherein the process excludes addition of oxides other than iron and chromium oxide.

16. The process according to claim 15, wherein the step of drying is performed for 20 to 28 hours.

17. A process for preparing an iron-chromium water-gas shift reaction catalyst with a platinum promoter, wherein the process consists of the following steps: (a) synthesizing iron and chromium oxides by a method of co-precipitation so as to obtain Fe.sub.2O.sub.3 and Cr.sub.2O.sub.3; (b) adding platinum to the catalyst obtained in (a), and calcinating the catalyst, wherein the process excludes addition of oxides other than iron and chromium oxide.

18. The process according to claim 17, wherein the step of calcination is performed at a temperature of from 440 to 460° C.

19. The process according to claim 18, wherein the step of calcination comprises maintaining the temperature between 440 and 460° C. for 1 to 3 hours.

20. The process according to claim 19, wherein the step of calcination comprises an initial heating step, heating at a rate of from 5 to 15° C./min, to reach the temperature of from 440 to 460° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a diagram of the conversion of CO carried out with commercial catalysts and with the catalysts according to the present disclosure in a range varying from 150° C. to 400° C.

(2) FIG. 2 shows a diagram of the conversion of CO carried out with commercial catalysts and with the catalysts according to the present disclosure at a temperature of 300° C. for 15 hours.

DETAILED DESCRIPTION OF THE INVENTION

(3) The Fe—Cr catalysts with Pt promoter of the present disclosure can be applied to the water-gas shift reactions in all the technologies in which this reaction is used, such as steam reforming, partial oxidation and catalytic gasification. Their higher activity makes them superior to the commercial catalysts in the same operating conditions.

(4) Depending on the support used, catalysts with a platinum promoter are active in the water-gas shift reaction. Interaction of Pt with the components of the Fe—Cr catalyst leads to the formation of additional active sites, improving the activity of the catalyst.

(5) Owing to its activity over a wide temperature range, the catalyst of the present disclosure may be used in conditions from low to high temperature, and is therefore applicable in both low-temperature shift (LTS) and high-temperature shift (HTS) water-gas shift reactions (WGSR).

(6) As described above, the water-gas shift reaction (WGSR) is maximized at low temperatures, high concentration of water and low concentration of hydrogen. However, the existing catalysts are kinetically limited at low temperatures. In practice, processes work at higher temperatures than is indicated by the thermodynamics. With catalysts that are more active, the reaction kinetics are more favourable, the volume of catalyst can be minimized, and it is possible to work at lower temperatures, promoting higher conversions from the thermodynamic standpoint.

(7) The catalyst of the present disclosure is an Fe—Cr catalyst, prepared by the method of co-precipitation from iron and chromium salts such as, for example, Fe(NO.sub.3).sub.3.9H.sub.2O and Cr(NO.sub.3).sub.3.9H.sub.2O. In some embodiments, this can be done at a temperature between 60 and 80° C. These reagents can be added to a base until the solution reaches a pH between 8.0 and 9.0, for example. In some embodiments, the base used is Na.sub.2CO.sub.3. The precipitate can be matured in these conditions for a period from 1 to 10 hours. It can then be filtered and dried for 10-14 hours at 100-120° C., for example. At the end of preparation, in some embodiments, the catalyst has Fe.sub.2O.sub.3/Cr.sub.2O.sub.3 in a weight ratio of 85-95%:15-5%, respectively. In preferred embodiments, the catalyst has 90% Fe.sub.2O.sub.3 10% Cr.sub.2O.sub.3.

(8) In the method of synthesis of the Fe—Cr catalyst of the present disclosure, the iron and chromium oxides are formed at the same time. This promotes the formation of crystals with greater dispersion of the oxides of the species present. This can increase the interactions between the iron and chromium. In addition, the catalyst has a low specific surface area, between 35 and 45 m.sup.2.g.sup.−1. This reduces the exposure of the iron oxide sites. This reduced exposure, combined with the better Fe—Cr interaction, promotes the partial reduction of the sites of haematite (Fe.sub.2O.sub.3) to magnetite (Fe.sub.3O.sub.4), increasing the overall activity of the catalyst.

(9) The Fe—Cr catalysts thus prepared are promoted with platinum by a method of dry impregnation. In some embodiments, the impregnation is in a percentage by weight varying from 0.01 to 1.5%. An example of a platinum precursor is hexachloroplatinic acid. Thus, a solution of H.sub.2PtCl.sub.6 can be prepared, and diluted in a volume of water corresponding to the pore volume. This solution can be added slowly to the support, stirring continuously to make the impregnation uniform.

(10) After impregnation, the samples can be subjected to a temperature between 110 and 130° C., at which each sample can remain for a period of time between 20 and 28h. After this time the samples can be calcined by heating with an initial heating rate varying from 5 to 15° C./min to a temperature between 440 and 460° C., and then maintaining the temperature between 440 and 460° C. for 1 to 3 hours.

(11) The method used for adding platinum (dry impregnation) promotes suitable dispersion of the particles on the surface of the support. The presence of platinum promotes the partial reduction of haematite, which occurs at lower temperatures, together with the reduction of platinum oxide and chromium oxides. This reduces the possibility of complete reduction to the metallic form of Fe (which, as explained above, would undesirably catalyse the methanation reaction and the Boudouard reaction, leading to the formation of coke.

(12) Furthermore, in clean conditions, i.e. without the presence of impurities such as sulphur, the catalyst of the present disclosure displays initial conversion of CO in the range from 30 to 40%.

EXAMPLES

(13) Table 1 presents the results obtained for specific surface area (S.sub.BET) based on the BET method in a w/w range from 0.05 to 0.20, average pore diameter (D.sub.p) and total pore volume (V.sub.p) of the commercial catalysts (HTS Com 1, HTS Com 2), of the Fe—Cr catalyst and of the Fe—Cr catalyst impregnated with 1% platinum, according to the present disclosure. These experiments were carried out in ASAP 2020 equipment from MICROMERITICS.

(14) TABLE-US-00001 TABLE 1 Surface properties of the catalysts Catalysts S.sub.BET (m.sup.2 .Math. g.sup.−1) D.sub.p(Å) V.sub.p(cm.sup.3 .Math. g.sup.−1) HTS Com 1 60.20 168.0 0.278 HTS Com 2 30.10 186.3 0.148 Fe—Cr 45.50 149.4 0.194 1% Pt/Fe—Cr 41.10 151.4 0.176

(15) Furthermore, to determine the chemical compositions of the synthesized catalysts, the technique of X-ray spectrometry (EDX) was used, in which the samples are exposed to an X-ray beam under vacuum. The equipment used was a spectrometer of BRUKER make, model S4 Explorer, equipped with a rhodium (Rh) X-ray generating tube.

(16) Table 2 presents the results obtained for determining the chemical composition of the oxides of the catalysts, determined by X-ray fluorescence spectrometry (EDX).

(17) TABLE-US-00002 TABLE 2 Composition of the catalysts obtained by X-ray spectrometry Contents of the oxides (%) Catalysts Pt Cu Al Fe Cr Others HTS Com 1 — — — 89.1 8.5 1.9 Cu 0.4 Mn HTS Com 2 — 3.60 0.2 84.6 8.9 2.6 Na 0.06 S Fe-Cr — — — 90.4 9.6 — 1% Pt/Fe-Cr 1.10 — — 85.8 9.6 2.2 Na 1.1 Cl
Catalytic Tests

(18) The catalytic tests were carried out in a unit coupled to a SHIMADZU gas chromatograph, 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.

(19) All the catalysts underwent the same step of drying and activation (shown in Table 3).

(20) TABLE-US-00003 TABLE 3 Conditions of drying and activation Drying Flow rate: 30 mL/min of He Heating rate: 10° C./min up to 150° C., maintained for 30 min Activation Reaction mixture: 100 mL/min Heating rate: 10° C./min up to 400° C., maintained for 2 hours

(21) The various commercial catalysts (HTS Com 1, HTS Com 2), the Fe—Cr catalyst and the Fe—Cr catalyst impregnated with 1% platinum, according to the present disclosure, were submitted to reaction, adopting the conditions shown in Table 4.

(22) TABLE-US-00004 TABLE 4 Reaction steps and conditions H.sub.2 CO CO.sub.2 H.sub.2O N.sub.2 Reaction mixture 5% 15% 5% 20% 55% Temperatures 150° C., 200° C., 250° C., 300° C., 350° C. and 400° C. Stability test 300° C. for approx. 15 h
Results

(23) The results obtained from the tests described above are presented in FIGS. 1 and 2.

(24) FIG. 1 shows a diagram of the effect of temperature on the conversion of CO using commercial catalysts and Fe—Cr supported catalysts. An extremely surprising positive effect is found on incorporating 1% of Pt compared to the Fe—Cr catalyst that is already conventional in the water-gas shift reaction. In these conditions, the 1% Pt/Fe—Cr catalyst displays very interesting potential for application in this reaction.

(25) The Fe—Cr catalyst prepared has an activity profile similar to the commercial catalysts. The use of Pt as a promoter, however, provides activity at lower temperatures, visible in the results from 200° C., a temperature at which the commercial catalysts and the Fe—Cr catalyst without promoter did not display activity, and appearing to start between 150° C. and 200° C.

(26) Moreover, it can be seen that the activity at 350-400° C. of the catalyst with a platinum promoter is more than twice the activity of the catalysts without promoter.

(27) Thus, it can be concluded that the Fe—Cr catalyst with Pt promoter, prepared according to the present disclosure, can be used for water-gas shift reactions in LTS and HTS.

(28) FIG. 2 shows a diagram of stability in conversion of CO for the catalysts tested. As can be seen, there is a slight tendency for deactivation with the reaction time for the commercial catalysts.

(29) Despite the variations in the result (due to condensation of H.sub.2O in the catalytic testing unit), a tendency for conversion at considerable values is observed for the Fe—Cr catalyst with Pt promoter, especially when compared to the conventional Fe—Cr, which indicates great potential for use of this catalyst.

(30) Table 5 below shows a comparison between the various catalysts with respect to conversion of CO in clean conditions, presenting a time average of the results in FIG. 2.

(31) TABLE-US-00005 TABLE 5 Comparison of the catalysts with respect to conversion of CO Catalyst Conversion of CO (%) HTS Com 1 4.82 HTS Com 2 7.95 Fe—Cr 1.85 1% Pt/Fe—Cr 36.70

(32) It was found, surprisingly, that in addition to the catalyst of the present disclosure not suffering a significant decrease in catalytic activity, there was a substantial increase in conversion of CO relative to the catalysts known from the prior art. It is thought that this is at least partly due to the method of preparation of the material, which favours the formation of species that are more susceptible to partial reduction, obtaining the active phase (Fe.sub.3O.sub.4) in greater quantity per unit of area.

(33) Modification of the above-described apparatuses and methods, combinations between different variations as practicable, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the spirit and scope of the claims.