Patent Application
20220370991
The embodiments herein generally relate to material synthesis, and more particularly to processing techniques for creating bimetallic-containing lamellar zeolite catalysts.
Conventional state-of-the art technologies for making metal incorporated zeolite structures involve a range of impregnation methods such as wet impregnation techniques to incorporate bimetals on to zeolite supports. These techniques are multi-step. First, the zeolite is synthesized and then the impregnation is carried out over the synthesized zeolite to add the metals to the zeolite catalyst structure. Such impregnation techniques predominantly result in the formation of bulk metal oxides. However, bulk metal oxides usually result in a low catalytic activity especially with the oxidation reactions. Moreover, the conventional techniques for bimetallic-incorporated zeolite catalyst synthesis using the impregnation technique generally result in oligomeric cationic metal complexes and neutral metal-oxide clusters as well as larger metal-oxide aggregates on the zeolite support instead of isolated metal sites in the zeolite framework that have higher activity and/or selectivity for the desired reactions such as deoxygenation of biomass-derived compounds, which lowers the catalytic activity and stability of these bimetallic-zeolite catalysts.
In view of the foregoing, an embodiment herein provides a method to incorporate a bimetal to a lamellar MFI zeolite structure, the method comprising providing a bimetallic-incorporated lamellar zeolite catalyst comprising a sodium source, an aluminum source, a silicon source, a surfactant, sulfuric acid, deionized (DI) water, a metal source, and a molecular template; dissolving the sodium source in the DI water to create a basic solution; adding the sulfuric acid, the aluminum source, the molecular template, and the silicon source to the basic solution to create a mixture and then adding the metal source to the mixture in the basic solution; dissolving the surfactant in the DI water to create a surfactant solution; combining the surfactant solution with the basic solution; heating the combined surfactant solution and the basic solution in a rotating autoclave to create a metal-containing zeolite including the surfactant and the molecular template in the structure of the metal-containing zeolite; removing a synthesized zeolite from the autoclave; drying the synthesized zeolite to create a dry zeolite powder; calcining the dry zeolite powder to remove the surfactant and the molecular template to create a bimetal-containing lamellar MFI zeolite structure; and chemically activating the bimetal-containing lamellar MFI zeolite structure.
The bimetal-containing lamellar MFI zeolite structure may comprise micropores of less than 1 nm and mesopores of 2-50 nm. The sodium source may comprise sodium hydroxide. The aluminum source may comprise aluminum sulfate. The silicon source may comprise tetraethyl orthosilicate (TEOS). The metal source may comprise a metal nitrate solution. The surfactant may comprise a polyquaternary ammonium structure of [C22H45-N+(CH3)2-C6H12-N+(CH3)2-C6H13]Br2, C22-6-6. The molecular template may comprise tetrapropylammonium hydroxide (TPAOH). The bimetallic-incorporated lamellar zeolite catalyst may comprise metal dopants containing any of (i) Ni and Fe, and (ii) Ni and Mn. The weight percent of each metal in the bimetallic-incorporated lamellar zeolite catalyst that is synthesized may be between 0-2.5.
The heating may occur at a temperature of 150° C. The autoclave may rotate at a speed of 30 rpm. The heating may occur for 5 days. The amount of the bimetal-containing lamellar MFI zeolite structure that is produced from 30 mL of the zeolite synthesis solution (e.g., the combined surfactant solution and the basic solution) may be 1-1.8 g. The method may comprise cooling metal-containing zeolite at ambient room temperature prior to removal of the synthesized zeolite from the autoclave. The method may comprise washing and centrifugation of the synthesized zeolite prior to the drying, wherein the washing occurs in DI water until a pH of 9 is obtained. After drying, the synthesized zeolite may be calcined at 600° C. for 6 hours to remove the surfactant and the molecular template. The method may comprise activating the bimetal-containing lamellar MFI zeolite structure by performing a catalyst preparation process comprising performing an ion-exchange process on the calcined dry zeolite powder; drying an ion-exchanged zeolite powder; and activating the dry zeolite powder by heating prior to running a catalytic reaction thereon.
The ion-exchange process may comprise (a) dissolving an ammonium nitrate powder in DI water to create a 1M ammonium nitrate solution; (b) mixing the calcined dry zeolite powder with the 1M ammonium nitrate solution having a weight ratio of 1 to 10 to create an ion-exchange mixture; (c) heating the ion-exchange mixture at 80° C. for 2 hours; (d) washing and centrifugation of the ion-exchange mixture with DI water to separate zeolite from the ion-exchange mixture; and (e) repeating the steps (b) through (d) multiple times. The catalyst preparation method may comprise heating the dry zeolite powder after ion-exchange at 550° C. for 4 hours to activate the dry zeolite powder.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating exemplary embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein provide a one-step hydrothermal synthesis of bimetallic-incorporated lamellar zeolite catalysts that results in the formation of isolated metal sites in the zeolite framework, which can enhance the catalytic activity and/or selectivity as well as stability of the catalyst for oxidation reactions. The catalysts produced in accordance with the embodiments herein may be used for deoxygenation of biomass derived compounds to efficiently produce value added chemicals/fuels, according to an example. Referring now to the drawings, and more particularly to
The creation of value-added chemicals and fuels from biomass-derived compounds through deoxygenation on-site is an important reaction to reduce the logistical burdens and improve the industry to fully utilize biomass sources and lower the impact of the produced waste materials on the environment. One catalyst is not able to perform the different types of elementary reaction steps required to deoxygenate biomass-derived compounds. For this reason, considerable attention has been placed on multifunctional catalysts, such as bimetallic catalysts, where different active materials are used to facilitate these diverse reaction steps. As mentioned, the available bimetallic catalysts are usually produced by an impregnation technique over zeolites, which is a multi-step method and results in formation of metal oxide species on zeolite that are not as active as metals in the zeolite catalyst framework. Accordingly, the embodiments herein provide a technique where the bimetallic (e.g., Ni—Mn and Ni—Fe)-incorporated lamellar MFI zeolite catalysts are synthesized using a one-step hydrothermal synthesis method. The synthesized bimetallic-incorporated zeolites were experimentally characterized, as described below, by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and ultraviolet-visible (UV-Vis)-diffuse reflectance spectroscopy (DRS).
According to an embodiment herein, the method 100 comprises providing (102) a bimetallic-incorporated lamellar zeolite catalyst using a sodium source, an aluminum source, a silicon source, a surfactant, sulfuric acid, deionized (DI) water, a metal source, and a molecular template. The amount of each of these chemicals depends on the amount of zeolite to be produced. For example, an autoclave with 30 mL volume for the zeolite synthesis solution that can produce 1-1.8 gram zeolite at the end may utilize: 0.7 gram sodium source, 0.2373 gram aluminum source, 6.27 gram silicon source, 2.1876 gram surfactant, 0.4 gram sulfuric acid, 23 gram DI water, 0.4 to 0.5 gram metal source, and 0.765 gram molecular template, according to some examples. However, as mentioned, these amounts may be different based on the amount of zeolite to be produced, and the embodiments herein are not restricted to these particular amounts. According to an example, the various components may be provided in separate laboratory dishes and/or beakers, etc. and used as needed in accordance with the subsequent steps of the method 100 as further described below.
In an example, the sodium source may comprise sodium hydroxide. In an example, the aluminum source may comprise aluminum sulfate. In an example, the silicon source may comprise tetraethyl orthosilicate (TEOS). In an example, the metal source may comprise a metal nitrate solution. In an example, the surfactant may comprise a polyquaternary ammonium structure of [C22H45-N+(CH3)2-C6H12-N+(CH3)2-C6H13]Br2, C22-6-6. In an example, the molecular template may comprise tetrapropylammonium hydroxide (TPAOH). The bimetallic-incorporated lamellar zeolite catalyst may comprise metal dopants containing any of (i) Ni and Fe, and (ii) Ni and Mn.
Next, the method 100 comprises dissolving (104) the sodium source in the DI water to create a basic solution. According to an example, for an autoclave with the capacity of a 30 mL zeolite synthesis solution that produces around 1-1.8 gram zeolite at the end of the process, a 4 gram basic solution or 4 mL basic solution may be used. In an example, the dissolving process (104) may be completed in a vial or beaker with gentle agitation using a magnetic stirring bar. According to an example, the dissolving process (104) may take between 60-300 seconds. Moreover, the dissolving process (104) may occur at room temperature, in an example.
Next, the method 100 comprises adding (106) the sulfuric acid, the aluminum source, the molecular template, the silicon source, and the metal source to the basic solution. The adding process (106) may occur according to a specific sequence of adding the various components to the basic solution. First, the sulfuric acid is added to the basic solution, then the aluminum source is added to the basic solution, after that the molecular template is added, and finally the silicon source is added. This mixture is stirred at room temperature using a magnetic stir bar at 800-1000 rpm for 20-24 hours, according to an example. After that, the metal source is added to the resulting mixture and this new mixture is stirred at room temperature for 2-3 hours at 800-1000 rpm (before adding the surfactant solution to the mixture).
Next, the method 100 comprises dissolving (108) the surfactant in the DI water to create a surfactant solution. According to an example, for an autoclave with the capacity of a 30 mL zeolite synthesis solution that produces around 1-1.8 gram zeolite at the end of the process, a 15 gram surfactant solution or 10-15 mL surfactant solution may be used. In an example, the dissolving process (108) may be completed in a plastic vial or beaker with gentle agitation using a magnetic stirring bar at 60° C. According to an example, the dissolving process (108) may take between 5-15 minutes at 60° C. Moreover, the dissolving process (108) may occur at room temperature for a longer time such as 24 hours, in an example.
Next, the method 100 comprises combining (110) the surfactant solution with the basic solution mixture. In an example, the surfactant solution is added to the basic solution mixture. In another example, the basic solution mixture is added to the surfactant solution. Moreover, the combining process (110) may be completed in a vial or beaker with agitation at 800-1000 rpm using a magnetic stirring bar. According to an example, the combining process (110) may take between 1-2 hours to ensure full mixing of the surfactant solution with the basic solution mixture and formation of necessary precursors for zeolite synthesis. Moreover, the combining process (110) may occur at room temperature, in an example.
Next, the method 100 comprises heating (112) the combined surfactant solution and the basic solution in a rotating autoclave to create a metal-containing zeolite including the surfactant and the molecular template in a structure of the metal-containing zeolite. In an example, the autoclave, which is placed in a laboratory oven, may comprise a Teflon®-lined stainless-steel autoclave. According to an example, the heating process (112) may occur at a temperature of 150° C. (e.g., in the laboratory oven) and for approximately 4-6 days, and preferably for 5 days. Additionally, the autoclave may rotate at a speed of 30 rpm, in an example.
Next, after a cooling process, the method 100 comprises removing (114) a cooled synthesized zeolite from the autoclave. Accordingly, in an example, the synthesized zeolite may be cooled prior to removal from the autoclave. In particular, the metal-containing zeolite may be cooled at ambient room temperature prior to removal of the synthesized zeolite from the autoclave.
Next, the method 100 comprises drying (116) the synthesized zeolite to create a dry zeolite powder. The drying process (116) may occur in an oven at 70° C. for 20-24 hours, for example. The method 100 may comprise washing and centrifugation (e.g., in a traditional laboratory centrifuge) of the synthesized zeolite at 5000-10000 rpm for 5-15 minutes, for example, prior to the drying process (116). In an example, the washing and centrifugation occurs using DI water and is repeated until a pH of 9 is obtained.
Next, the method 100 comprises calcining (118) the dry zeolite powder to remove the surfactant and the molecular template to create a bimetal-containing lamellar MFI zeolite structure. In an example, the calcining process (118) may occur in a furnace or kiln, etc. Moreover, after the drying process (116), the synthesized zeolite may be calcined at 600° C. for 6 hours to remove the surfactant and the molecular template, according to an example. Furthermore, the bimetal-containing lamellar MFI zeolite structure may comprise micropores of less than 1 nm and mesopores of 2-50 nm, according to an example. Additionally, in an example, the amount of the bimetal-containing lamellar MFI zeolite structure that is produced from 30 mL of the combined surfactant solution and basic solution may be 1-1.8 g. According to an example, the weight percent of each metal in the bimetallic-incorporated lamellar zeolite catalyst that is synthesized may be between 0-2.5.
Next, the method 100 comprises chemically activating (120) the bimetal-containing lamellar MFI zeolite structure. As shown in the flow diagram of
As shown in the flow diagram of
Next, the ion-exchange process (130) comprises mixing (142) the calcined dry zeolite powder with the 1M ammonium nitrate solution having a weight ratio of 1 to 10 to create an ion-exchange mixture. In an example, the mixing process (142) may occur at room temperature and may take between 60-120 seconds. Furthermore, the calcined dry zeolite powder may be added to the 1M ammonium nitrate solution or the 1M ammonium nitrate solution may be added to the calcined dry zeolite powder, according to various examples.
Next, the ion-exchange process (130) comprises heating (144) the ion-exchange mixture at 80° C. for 2 hours. Next, the ion-exchange process (130) comprises a washing and centrifugation process (146) wherein the ion-exchanged zeolite mixture is washed and centrifuged with DI water to separate zeolite from the ion-exchange mixture. The washing and centrifugation process occur together. First, the ion-exchange zeolite mixture is poured in a centrifuge tube (to fill half of the tube volume) and then DI water is added to the centrifuge tube to fill the centrifuge tube to its full standard capacity, and then the centrifugation is run for 5-15 minutes if the centrifugation rotation speed is between 5000-10000 rpm, for example. Next, the ion-exchange process (130) comprises repeating (148) the steps (142) through (146) multiple times. In an example, the steps (142) through (146) may be repeated three times, although other amounts of repetition may be utilized in accordance with the embodiments herein.
The synthesized catalysts produced in accordance with the embodiments herein can be effectively utilized in the oxidation of aromatic compounds such as benzene and deoxygenation of biomass derived compounds such as phenols. The embodiments herein provide for isolated bimetal sites, which can be incorporated to lamellar zeolite structures using a one-step hydrothermal synthesis method 100. The resulting catalyst shows an efficient catalytic performance due to the multi-functionality that it has due to the presence of both incorporated-metals and active sites of the zeolite (due to the presence of aluminum in zeolite structure which makes the zeolite an active acid catalyst) and also the unique meso-/microporous structure of zeolite originating from its lamellar structure. The embodiments herein provide a useful technique for synthesizing materials to reduce the coke formation and increase the catalyst activity, selectivity, and catalyst lifetime for upgrading the biomass to value added chemicals and fuels. The conventional techniques for incorporation of two metals to a zeolite support is a wet impregnation method, which results in the metal oxide formation on the zeolite catalyst instead of the incorporation of the metal in the zeolite framework. Conversely, the embodiments herein provide a technique in which two different types of metals can be incorporated to the framework of the lamellar zeolite structure successfully without the formation of a significant amount of metal oxides in the resulting catalyst.
The bimetallic-containing zeolite catalysts developed in accordance with the embodiments herein can be utilized for the effective conversion of biomass (e.g., wood, trees, grass, etc.) and/or waste streams (e.g., plastic, paper, etc.) to value added chemicals/fuels, which eventually results in the development of compact energy systems. The compact energy systems can reduce the energy logistic costs as well as increase the range and endurance of robotic autonomous platforms. Moreover, the techniques provided by the embodiments herein can provided for high catalytic activity, selectivity, and stability of the resulting materials, which can enable commercial synthesis of value-added chemicals and fuels from biomass.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others may, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein may be practiced with modification within the spirit and scope of the appended claims.
The embodiments herein may be manufactured, used, and/or licensed by or for the United States Government without the payment of royalties thereon.
