DISSIMILAR METAL-SUPPORTED CATALYST FOR THE PRODUCTION OF AROMATICS BY METHANE DEHYDROAROMATIZATION AND METHOD FOR PRODUCING AROMATICS USING THE SAME

Abstract

Disclosed is a dissimilar metal-supported catalyst for the production of aromatics by methane dehydroaromatization. In the dissimilar metal-supported catalyst, a noble metal such as gold (Au), silver (Ag), platinum (Pt), and/or rhodium (Rh) is introduced into a catalyst supported with iron (Fe) on a zeolite support to promote the dehydrogenation of methane and the formation of iron carbide (Fe.sub.3C) as an active species for dehydroaromatization, achieving a greatly improved yield of aromatics. Also disclosed is a method for producing aromatics using the dissimilar metal-supported catalyst.

Claims

1. A dissimilar metal-supported catalyst comprising a zeolite support, iron (Fe) as a first metal supported on the zeolite support, and at least one metal selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), and rhodium (Rh) as a second metal supported on the zeolite support wherein the dissimilar metal-supported catalyst is used for methane dehydroaromatization to aromatics.

2. The dissimilar metal-supported catalyst according to claim 1, wherein the first metal is supported in an amount of 0.5 to 4% by weight, based on the total weight of the zeolite support.

3. The dissimilar metal-supported catalyst according to claim 1, wherein the second metal is supported in an amount of 0.5 to 2% by weight, based on the total weight of the zeolite support.

4. The dissimilar metal-supported catalyst according to claim 1, wherein the iron (Fe) is converted to iron carbide (Fe.sub.3C) during the methane dehydroaromatization.

5. The dissimilar metal-supported catalyst according to claim 1, wherein the zeolite support is selected from the group consisting of HZSM-5, ZSM-5, MCM-22, and MCM-41.

6. The dissimilar metal-supported catalyst according to claim 1, wherein the ratio Si/Al in the zeolite support is 15 to 140.

7. A method for producing aromatics comprising dehydroaromatizing methane as a reactant in the presence of the dissimilar metal-supported catalyst according to claim 1.

8. The method according to claim 7, wherein the reaction is performed in a gas phase reactor comprising a column filled with the dissimilar metal-supported catalyst.

9. The method according to claim 7, wherein the reactant further comprises argon gas.

10. The method according to claim 7, wherein the reaction is performed at 600 to 800° C.

11. The method according to claim 7, wherein aromatics are selected from the group consisting of benzene, toluene, xylene, naphthalene, and coke.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The patent or application file contains a least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0022] These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

[0023] FIG. 1 shows the calculated formation rates of aromatics through methane dehydroaromatization according to the amount of iron supported;

[0024] FIG. 2 shows XRD patterns of catalysts 2Fe/HZSM-5 (a), 2Fe-0.5Au/HZSM-5 (b), 2Fe-0.5Ag/HZSM-5 (c), 2Fe-0.5Pt/HZSM-5 (d), and 2Fe-0.5Rh/HZSM-5 (e);

[0025] FIG. 3 shows the formation rates of aromatics in the initial stage of methane dehydroaromatization in the presence of different catalysts 2Fe/HZSM-5, 2Fe-0.5Au/HZSM-5, 2Fe-0.5Ag/HZSM-5, 2Fe-0.5Pt/HZSM-5, and 2Fe-0.5Rh/HZSM-5;

[0026] FIG. 4 shows the formation rates of aromatics through methane dehydroaromatization with time on stream in the presence of different catalysts 2Fe/HZSM-5, 2Fe-0.5Au/HZSM-5, 2Fe-0.5Ag/HZSM-5, 2Fe-0.5Pt/HZSM-5, and 2Fe-0.5Rh/HZSM-5;

[0027] FIG. 5 shows the cumulative formation rates of aromatics through methane dehydroaromatization with time on stream in the presence of different catalysts 2Fe/HZSM-5, 2Fe-0.5Au/HZSM-5, 2Fe-0.5Ag/HZSM-5, 2Fe-0.5Pt/HZSM-5, and 2Fe-0.5Rh/HZSM-5;

[0028] FIG. 6 shows the selectivities of catalysts 2Fe/HZSM-5 and 2Fe-0.5Au/HZSM-5 to aromatics and cock when methane dehydroaromatization was carried out using the catalysts;

[0029] FIG. 7 shows the profiles of CH.sub.4-TPSR of catalysts 2Fe/HZSM-5 and 2Fe-0.5Au/HZSM-5 for measuring the activation temperatures of methane;

[0030] FIGS. 8A to 8C show XPS curves for C1s (FIG. 8A), Fe2p (FIG. 8B), and Au4f (FIG. 8C) orbitals of catalysts 2Fe/HZSM-5 and 2Fe-0.5Au/HZSM-5 before and after use for methane dehydroaromatization; and

[0031] FIG. 9 shows the calculated formation rates of aromatics through methane dehydroaromatization according to the amount of gold supported;

DETAILED DESCRIPTION OF THE INVENTION

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly employed in the art.

[0033] The present invention will now be described in more detail.

[0034] The present invention is directed to a dissimilar metal-supported catalyst for the production of aromatics by methane dehydroaromatization. Specifically, the present invention intends to provide a dissimilar metal-supported catalyst in which a metal such as gold (Au), silver (Ag), platinum (Pt), and/or rhodium (Rh) is further introduced into a catalyst supported with iron (Fe) as an active metal on a zeolite support to promote the dehydrogenation of methane, with the result that the formation of iron carbide is promoted, achieving an improved yield of aromatics.

[0035] More specifically, the present invention provides a dissimilar metal-supported catalyst including a zeolite support, iron (Fe) as a first metal supported on the zeolite support, and at least one metal selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), and rhodium (Rh) as a second metal supported on the zeolite support wherein the dissimilar metal-supported catalyst is used for methane dehydroaromatization to aromatics.

[0036] The first metal and the second metal can be supported by suitable methods known in the art, preferably an incipient wetness impregnation method.

[0037] The following Examples section reveals that the first metal iron is preferably supported in an amount ranging from 0.5 to 4% by weight, based on the total weight of the zeolite support. Within this range, the supported first metal promotes the dehydrogenation of methane, resulting in a significant increase in the formation rate of aromatics.

[0038] The following Examples section reveals that the second metal is preferably supported in an amount of 0.5 to 2% by weight, based on the total weight of the zeolite support. The use of the second metal in an amount less than the lower limit or exceeding the upper limit has little or no effect in promoting the dehydrogenation of methane during the methane dehydroaromatization, leading to a significant reduction in the yield of final products (i.e. aromatics).

[0039] The zeolite support used in the supported catalyst of the present invention may be any of those commonly used as catalyst supports in the art. For example, the zeolite support may be selected from the group consisting of HZSM-5, ZSM-5, MCM-22, and MCM-41.

[0040] The ratio Si/Al in the zeolite support is preferably 15 to 140.

[0041] The present invention also provides a method for producing aromatics including dehydroaromatizing methane as a reactant in the presence of the dissimilar metal-supported catalyst.

[0042] The dehydroaromatization is preferably performed in a gas phase reactor including a column filled with the dissimilar metal-supported catalyst, for example, in a fixed bed gas phase reactor.

[0043] The reactant for the dehydroaromatization may further include argon gas in addition to methane.

[0044] The dehydroaromatization is preferably performed at 600 to 800° C.

[0045] The aromatics as the dehydroaromatization products may be selected from the group consisting of benzene, toluene, xylene, naphthalene, and coke.

[0046] The following Examples section reveals that the dehydroaromatization of the reactant methane in the presence of the dissimilar metal-supported catalyst is most preferably performed using a mixture of methane and argon in a 2:1 volume ratio at a GHSV of 4,500 ml/h.Math.g.sub.cat and 750° C. for 1 hour.

[0047] The present invention will be explained in more detail with reference to the following examples. It will be appreciated by those skilled in the art that these examples are merely illustrative and the scope of the present invention is not construed as being limited to the examples. Thus, the true scope of the present invention should be defined by the appended claims and their equivalents.

PREPARATIVE EXAMPLE 1. PREPARATION OF ZEOLITE CATALYSTS SUPPORTED WITH DIFFERENT AMOUNTS OF IRON

[0048] First, NH.sub.4-ZSM-5 with ammonium cations (CBV 3024E, Zeolyst) was heated at a rate of 5° C./min and calcined at 500° C. for 5 h to obtain a zeolite support HZSM-5 with protons, which was used as a catalyst support.

[0049] Next, different amounts (0.036, 0.072, 0.145, 0.29, 0.435, and 0.725 g) of iron nitrate hydrate (Fe(NO.sub.3).Math.9H.sub.2O, Sigma-Aldrich) were separately dissolved in distilled water, supported on 1.0 g of the support HZSM-5 by an incipient wetness impregnation method, dried at 110° C. for 12 h, heated at a rate of 5° C./min under normal air conditions, and calcined at 500° C. for 5 h to prepare zeolite catalysts supported with different amounts (0.5, 1, 2, 4, 6, and 10 wt. %) of iron, based on the weight of the support (0.5Fe/HZSM-5, 1 Fe/HZSM-5, 2Fe/HZSM-5, 4Fe/HZSM-5, 6Fe/HZSM-5, and 10Fe/HZSM-5), respectively.

PREPARATIVE EXAMPLE 2. PREPARATION OF GOLD-SUPPORTED CATALYST, SILVER-SUPPORTED CATALYST, PLATINUM-SUPPORTED CATALYST AND RHODIUM-SUPPORTED CATALYST on the Iron-Supported Zeolite Catalyst

Preparative Example 2-1. Preparation of Silver-Supported Catalyst, Platinum-Supported Catalyst and Rhodium-Supported Catalyst on the Iron-Supported Zeolite Catalyst

[0050] The iron (2 wt. %)-supported zeolite catalyst prepared in Preparative Example 1 was dried at 110° C. for 12 h. Next, 0.0079 g of silver nitrate (Ag(NO.sub.3), Sigma-Aldrich), 0.0086 g of platinum chloride (PtCl.sub.4, Sigma-Aldrich), and 0.0080 g of rhodium nitrate (Rh(NO.sub.3).sub.3.Math.xH.sub.2O, Sigma-Aldrich, ˜36%) were separately dissolved in distilled water, supported on 1.0 g of the iron-supported HZSM-5 by an incipient wetness impregnation method, dried at 110° C. for 12 h, heated at a rate of 5° C./min under normal air conditions, and calcined at 500° C. for 5 h to prepare zeolite catalysts supported with 0.5 wt. % of silver, 0.5 wt. % of platinum, and 0.5 wt. % of rhodium together with 2 wt. % of iron, based on the weight of the support (2Fe-0.5Ag/HZSM-5, 2Fe-0.5Pt/HZSM-5, and 2Fe-0.5Rh/HZSM-5), respectively.

Preparative Example 2-2. Preparation of Catalysts Supported with Different Amounts of Gold on the Iron-Supported Zeolite Catalyst

[0051] The iron (2 wt. %)-supported zeolite catalyst prepared in Preparative Example 1 was dried at 110° C. for 12 h. Next, different amounts (0.002 g, 0.001 g, 0.02 g, 0.03 g, 0.04 g, and 0.06 g) of gold chloride trihydrate (Au(III)Cl trihydrate, Sigma-Aldrich) were separately dissolved in distilled water, supported on 1.0 g of the iron-supported HZSM-5 by an incipient wetness impregnation method, dried at 110° C. for 12 h, heated at a rate of 5° C./min under normal air conditions, and calcined at 500° C. for 5 h to prepare zeolite catalysts supported with 2 wt. % of iron and different amounts (0.1, 0.5, 1, 1.5, 2, and 3 wt. %) of gold, based on the weight of the support (2Fe-0.1Au/HZSM-5, 2Fe-0.5Au/HZSM-5, 2Fe-1Au/HZSM-5, 2Fe-1.5Au/HZSM-5, 2Fe-2Au/HZSM-5, and 2Fe-3Au/HZSM-5), respectively.

EXPERIMENTAL EXAMPLE 1. PRODUCTION OF AROMATICS THROUGH METHANE DEHYDROAROMATIZATION ACCORDING TO AMOUNT OF IRON SUPPORTED

[0052] Aromatics were produced by methane dehydroaromatization using the catalysts prepared in Preparative Example 1. Specifically, 0.2 g of each of the catalysts prepared in Preparative Example 1 was filled in a fixed bed gas phase reactor having an outer diameter of 6.35 mm and heated to a reaction temperature of 750° C. in an ultrahigh purity argon gas (99.999%) atmosphere. When the reaction temperature was reached, the argon gas was replaced by a mixture of methane and argon (2:1, v/v) as a reaction gas. The reaction was allowed to proceed for 1 h under a flow of the reaction gas at a rate of 15 ml/min. The reactants and final products having passed through the catalyst bed of the fixed bed reactor were injected into a gas chromatograph connected on-line to the fixed bed reactor while maintaining a temperature of 230° C. Gas components were analyzed by the gas chromatography and used to calculate the formation rates of aromatics as the products. The results are shown in FIG. 1.

[0053] Referring to FIG. 1, the formation rates of aromatics through dehydroaromatization were significantly high when the amounts of the supported iron were 0.5-4 wt. % compared to those when the amounts of the supported iron were 6 and 10 wt. %. Particularly, the highest formation rate of aromatics was observed when the amount of the supported iron was 2 wt. %.

EXPERIMENTAL EXAMPLE 2. ANALYSIS OF XRD PATTERNS

[0054] FIG. 2 shows XRD patterns of the catalysts 2Fe/HZSM-5, 2Fe-0.5Au/HZSM-5, 2Fe-0.5Ag/HZSM-5, 2Fe-0.5Pt/HZSM-5, and 2Fe-0.5Rh/HZSM-5.

[0055] Referring to FIG. 2, the pattern of crystalline ZSM-5 was prominent in all of the catalysts. In addition, since the supported active metal iron was uniformly dispersed on the support, its peak was not distinct. No distinct peaks were observed for the gold-supported catalyst, the silver-supported catalyst, the platinum-supported catalyst, and the rhodium-supported catalyst due to the loading of small amounts of the noble metals.

EXPERIMENTAL EXAMPLE 3. PRODUCTION OF AROMATICS THROUGH METHANE DEHYDROAROMATIZATION USING THE GOLD (AU)-SUPPORTED CATALYST, THE SILVER (AG)-SUPPORTED CATALYST, THE PLATINUM (PT)-SUPPORTED CATALYST AND THE RHODIUM (RH)-SUPPORTED CATALYST ON THE IRON-SUPPORTED ZEOLITE CATALYST

[0056] Aromatics were produced by methane dehydroaromatization using the iron (2 wt. %)-supported zeolite catalyst unsupported with a noble metal (2Fe/HZSM-5), the gold (0.5 wt. %)-supported catalyst (2Fe-0.5Au/HZSM-5), the silver (0.5 wt. %)-supported catalyst (2Fe-0.5Ag/HZSM-5), the platinum (0.5 wt. %)-supported catalyst (2Fe-0.5Pt/HZSM-5), and the rhodium (0.5 wt. %)-supported catalyst (2Fe-0.5Rh/HZSM-5). Specifically, 0.2 g of each of the supported catalysts was filled in a fixed bed gas phase reactor having an outer diameter of 6.35 mm and heated to a reaction temperature of 750° C. in an ultrahigh purity argon gas (99.999%) atmosphere. When the reaction temperature was reached, the argon gas was replaced by a mixture of methane and argon (2:1, v/v) as a reaction gas. The reaction was allowed to proceed for 1 h under a flow of the reaction gas at a rate of 15 ml/min. The reactants and final products having passed through the catalyst bed of the fixed bed reactor were injected into a gas chromatograph connected on-line to the fixed bed reactor while maintaining a temperature of 230° C. Gas components were analyzed by the gas chromatography and used to calculate the formation rates of aromatics as the products and the selectivity of the catalyst to the aromatics. The results are shown in FIGS. 3 to 6.

[0057] Referring to FIGS. 3 to 6, the use of the catalyst unsupported with a noble metal (2Fe/HZSM-5) did not lead to the production of aromatics due to carbonization in the initial stage of the reaction, whereas the formation rates of aromatics were ˜1080.3 nmol/g.sub.cat.Math.s, ˜875.3 nmol/g.sub.cat.Math.s, ˜802.8 nmol/g.sub.cat.Math.s, and ˜825.6 nmol/g.sub.cat.Math.s when the gold (0.5 wt. %)-supported catalyst (2Fe-0.5Au/HZSM-5), the silver (0.5 wt. %)-supported catalyst (2Fe-0.5Ag/HZSM-5), the platinum (0.5 wt. %)-supported catalyst (2Fe-0.5Pt/HZSM-5), and the rhodium (0.5 wt. %)-supported catalyst (2Fe-0.5Rh/HZSM-5) were used, respectively. The additional support with gold, silver, platinum or rhodium was found to significantly improve the formation rate of aromatics. Particularly, the highest formation rate of aromatics was found when gold was further supported. The selectivity of the catalyst unsupported with a noble metal (2Fe/HZSM-5) to aromatics was compared with that of the catalyst additionally supported with gold (2Fe-0.5Au/HZSM-5). As a result, the additional gold support was confirmed to increase the selectivity to aromatics from 6.65% to 23.5% and reduce the selectivity to coke from 89.47% to 67.56%. In conclusion, the inventive iron-supported zeolite catalyst additionally supported with gold, silver, platinum or rhodium significantly increases the formation rate of aromatics and the selectivity to aromatics and reduces the selectivity to coke.

EXPERIMENTAL EXAMPLE 4. CH.SUB.4.-TEMPERATURE-PROGRAMMED SURFACE REACTION (CH.SUB.4.-TPSR)

[0058] FIG. 7 shows the profiles of CH.sub.4-TPSR of the catalysts 2Fe/HZSM-5 and 2Fe-0.5Au/HZSM-5 for measuring the activation temperatures of methane.

[0059] Referring to FIG. 7, methane began to be activated at around 752° C. in the presence of the catalyst 2Fe/HZSM-5 supported with only iron, whereas methane was activated at a lower temperature of ˜742° C. in the presence of the catalyst 2Fe-0.5Au/HZSM-5 supported with iron and gold, demonstrating that the loading of gold promoted the dehydrogenation of methane.

EXPERIMENTAL EXAMPLE 5. X-RAY PHOTOELECTRON SPECTROSCOPY (XPS)

[0060] FIG. 8A to 8C show XPS curves for C1s (FIG. 8A), Fe2p (FIG. 8B), and Au4f (FIG. 8C) orbitals of the catalysts 2Fe/HZSM-5 and 2Fe-0.5Au/HZSM-5 before and after use for methane dehydroaromatization.

[0061] Referring to FIG. 8A to 8C, a higher degree of reduction to iron carbide (Fe.sub.3C) was observed after the reaction in the presence of the catalyst 2Fe-0.5Au/HZSM-5 than in the presence of the catalyst 2Fe/HZSM-5. For the catalyst 2Fe-0.5Au/HZSM-5 in which gold (Au) was further supported on the catalyst 2Fe/HZSM-5, Fe became deficient in electrons due to the interaction between Fe and Au. This electron deficiency played a role in promoting the reduction of Fe to iron carbide (Fe.sub.3C) during the reaction, leading to an improvement in the dehydrogenation ability of the catalyst.

[0062] In other words, the introduction of gold (Au) into the catalyst 2Fe/HZSM-5 caused Fe to be deficient in electrons due to the interaction between iron (Fe) and gold (Au) during methane dehydroaromatization, and as a result, the reduction of the electron-deficient Fe to iron carbide (Fe.sub.3C) was promoted, markedly improving the yield of aromatics.

EXPERIMENTAL EXAMPLE 6. PRODUCTION OF AROMATICS THROUGH METHANE DEHYDROAROMATIZATION ACCORDING TO AMOUNT OF GOLD SUPPORTED

[0063] Aromatics were produced by methane dehydroaromatization using the catalysts prepared in Preparative Example 2-2. Specifically, 0.2 g of each of the catalysts was filled in a fixed bed gas phase reactor having an outer diameter of 6.35 mm and heated to a reaction temperature of 750° C. in an ultrahigh purity argon gas (99.999%) atmosphere. When the reaction temperature was reached, the argon gas was replaced by a mixture of methane and argon (2:1, v/v) as a reaction gas. The reaction was allowed to proceed for 1 h under a flow of the reaction gas at a rate of 15 ml/min. The reactants and final products having passed through the catalyst bed of the fixed bed reactor were injected into a gas chromatograph connected on-line to the fixed bed reactor while maintaining a temperature of 230° C. Gas components were analyzed by the gas chromatography and used to calculate the formation rates of aromatics as the products. The results are shown in FIG. 9.

[0064] Referring to FIG. 9, the formation rates of aromatics through dehydroaromatization were significantly high when the amounts of the supported gold were 0.5-2 wt. % compared to those when the amounts of the supported gold were 0.1 and 3 wt. %. Particularly, the highest formation rate of aromatics was observed when the amount of the supported gold was 1.5 wt. %.

[0065] Although the particulars of the present disclosure have been described in detail, it will be obvious to those skilled in the art that such particulars are merely preferred embodiments and are not intended to limit the scope of the present invention. Therefore, the true scope of the present invention is defined by the appended claims and their equivalents.