Next generation modified silica materials for increased performance and industrial applications

Abstract

Disclosed are heterostructured silica catalysts (modified Haider heterostructured silica) and methods of their use and preparation. The heterostructured silica catalysts include a transition metal, an alkaline earth metal oxide, and silica, wherein the transition metal, the alkaline earth metal from the metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst. The catalyst can have application in, e.g., the hydrogenation of carbon monoxide.

Claims

1. A heterostructured silica catalyst comprising a transition metal, an alkaline earth metal oxide, and silica; wherein the heterostructured silica catalyst comprises 0.1 to 10 wt. % of the transition metal, based on the total weight of the catalyst; wherein the alkaline earth metal oxide comprises an alkaline earth metal selected from the group consisting of magnesium, calcium, strontium and barium; wherein the transition metal comprises a member selected from the group consisting of zinc and zirconium, or combinations thereof; wherein the catalyst has a crystal structure; wherein the transition metal, the alkaline earth metal from the alkaline earth metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst; and wherein the weight ratio of silicon (Si) from silica to alkaline earth metal from the metal oxide thereof is from 1.5:1 to 5:1.

2. The heterostructured silica catalyst of claim 1, wherein the weight ratio of silicon (Si) from silica to alkaline earth metal from the metal oxide thereof is 5:1.

3. The heterostructured silica catalyst of claim 1, wherein the weight ratio of silicon (Si) from silica to alkaline earth metal from the metal oxide thereof is 1.5:1.

4. The heterostructured silica catalyst of claim 3, wherein the transition metal comprises zinc.

5. A heterostructured silica catalyst comprising a transition metal, an alkaline earth metal oxide, and silica; wherein the heterostructured silica catalyst comprises 0.1 to 10 wt. % of the transition metal, based on the total weight of the catalyst; wherein the catalyst has a crystal structure; wherein the transition metal, the alkaline earth metal from the alkaline earth metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst; wherein the weight ratio of silicon (Si) from silica to alkaline earth metal from the metal oxide thereof is from 1.5:1 to 5:1; and wherein the transition metal comprises zinc.

6. A heterostructured silica catalyst comprising a transition metal, an alkaline earth metal oxide, and silica; wherein the heterostructured silica catalyst comprises 0.1 to 10 wt. % of the transition metal, based on the total weight of the catalyst; wherein the catalyst has a crystal structure; wherein the transition metal, the alkaline earth metal from the alkaline earth metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst; wherein the weight ratio of silicon (Si) from silica to alkaline earth metal from the metal oxide thereof is from 1.5:1 to 5:1; and wherein the transition metal comprises zirconium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings.

(2) FIG. 1 depicts a system for the hydrogenation of carbon monoxide.

(3) FIG. 2 is an image showing the physical morphology of a filtered support material having uniform single crystal structure.

(4) FIG. 3 is a graph showing the activity/selectivity results of a MHH—SiO.sub.2 catalyst.

DETAILED DESCRIPTION OF THE INVENTION

(5) The catalysts of the present invention offer a solution to the problems associated with currently available silica supported catalysts. The solution is premised on forming a uniform and uniquely heterostructured SiO.sub.2 material (e.g., MHH—SiO.sub.2 material) with an active metal, an alkaline earth metal, and silicon (Si) present in the crystal lattice structure. The resulting catalysts of the present invention can offer non-limiting advantages ranging from increased conversion, increased selectivity, lower catalyst deactivation rates, and/or robust thermal stability in for example, catalyzing the production of methane, olefins, paraffins, and carbon dioxide from syngas (e.g., H.sub.2/CO).

(6) These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the Figures.

(7) A. Heterostructured Silica Catalysts

(8) Embodiments herein describe heterostructured silica catalysts and methods of making and using the heterostructured silica catalysts. The catalysts of the present invention can include a transition metal, an alkaline earth metal oxide, and silica, wherein the transition metal, the alkaline earth metal from the metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst.

(9) The catalytically active material used to prepare the heterostructured silica catalysts of the present invention includes one or more catalytically active metals. The crystal lattice structure of the catalyst can contain one metal (i.e., monometallic), two metals (i.e., bimetallic), three metals (i.e., trimetallic), four metals (i.e., tetrametallic) or more metals. In one embodiment, the catalytic metal is a transition metal. An amount of transition metal can depend inter alia on the desired activity of the catalyst. Non-limiting examples of transition metal include scandium (Sc), yttrium (Y), lanthanum (La), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt, (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), copper (Cu), silver (Ag), and gold (Au). Preferably the transition metal is one or more of iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), aluminum (Al), zirconium (Zr), or titanium (Ti), with iron (Fe) being preferred. The amount of transition metal comprised in the heterostructured silica catalyst can include 0.01 to 20 wt. % or 0.1 to 10 wt. % and all values and ranges there between. For example, the catalyst can include about 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, or 9.9 wt. % of the transition metal based on the total weight of the catalyst. Transition metals and corresponding stable derivatives/precursors thereof (e.g., halides, oxides, etc.) can be purchased from commercial manufactures such as Sigma-Aldrich®, USA.

(10) The heterostructured silica catalysts of the present invention also include an alkaline earth metal oxide. The alkaline earth metal oxide may be inert or be able to participate in catalytic reactions. The alkaline earth metal oxide can be one or more of magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO), or strontium (SrO), with magnesium oxide (MgO) being preferred. The amount of alkaline earth metal from the metal oxide thereof comprised in the heterostructured silica catalyst can include 5 to 40 wt. % or 10 to 20 wt. % and all values and ranges there between. For example, the catalyst can include 5, 5.5, 6, 6.5, 7.0, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 30, 30.5, or 40 wt. % based on the total weight of the catalyst. In some instances, the alkaline earth metal oxide can be present in the crystal lattice structure of the catalyst in a weight ratio of silicon to alkaline earth metal from 0.5:1 to 5:1 with 1:1 to 3:1 and all values and ranges there between (e.g., 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1). Alkaline earth metal oxides and corresponding derivatives/precursors thereof (e.g., halides), can be purchased from commercial manufactures such as Sigma-Aldrich®, USA.

(11) Silica or silicon dioxide (i.e., SiO.sub.2) is the oxide of silicon that is highly abundant in nature (e.g., quartz). Silica more so than almost any material, exists in many crystalline forms (e.g., polymorphs). Due to a range of robust structure properties and high surface area, silica is often included in catalyst support materials to which active metals are affixed. Great effort has been made to maximize the surface area of a catalyst by increasing distribution over and within the support. The amount of silicon (Si) from silica comprised in the heterostructured silica catalyst can include 10 to 50 wt. % or 20 to 40 wt. % and all values and ranges there between (e.g., 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, or 39 wt. %) of silicon, based on the total weight of the catalyst. A wide range of silicon containing precursors can be used to prepare the heterostructured silica catalysts of the present invention. In particular aspects, the sources of silicon can be derived from organic compounds that readily provide soluble sources of silicon in a template reaction. In coordination chemistry, a template reaction is a ligand-based reaction that occurs between two or more adjacent coordination sites on a metal center. Providing silicon under templating conditions effects the pre-organization provided by the coordination sphere which can result in significant modification of physical/chemical/electronic properties of the template complex formed which can have profound effects on the resultant crystal morphology (e.g., size, shape, dispersion, surface area, distribution) of the resultant heterostructured silica catalyst formed. Preferably the organic source of silicon that be used to form the silica comprised in the heterostructured silica catalysts include tetraalkyl orthosilicates. Tetraalkyl orthosilicate derivatives (e.g., tetraethyl orthosilicate (TEOS) can be purchased from commercial manufactures such as Sigma-Aldrich®, USA.

(12) B. Methods of Making the Catalysts

(13) The catalysts of the present invention can be prepared by using the following non-limiting steps. In the method of the invention orthosilicate can be added to heated aqueous alkaline earth metal salt (e.g., MgCl.sub.2). Under these conditions, orthosilicate can be converted into polycondensed silica with an external network of alkaline earth metal atoms (e.g., Mg) along with an organic phase (e.g., ethyl moiety). A transition metal salt (e.g., iron citrate) can then be added in solid form. The transition metal salt dissolves slowly to allow the transition metal (e.g., iron) to network with the existing solution in a regular systematic pattern. This regular patterned solution can then be precipitated by means of precipitating agent to keep the heterostructure intact. Upon drying, interstitial water can be removed producing a uniformly shaped material.

(14) Step 1 of the method can include subjecting an aqueous solution comprising an alkaline earth metal precursor and a silicon containing organic template (e.g., tetraalkyl orthosilicate) to conditions sufficient to form polycondensed silica having an external network of alkali earth metal atoms. The molar ratio of tetraalkyl orthosilicate to alkaline earth metal precursor can be 0.5:1 to 6:1, preferably 1:1 to 4:1 and all ranges and values there between (e.g., 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, or 3.9:1). Non-limiting examples of the alkaline earth metal precursor include magnesium fluoride (MgF.sub.2), magnesium chloride (MgCl.sub.2), magnesium bromide (MgBr.sub.2), magnesium iodide (MgI.sub.2), calcium fluoride (CaF.sub.2), calcium chloride (CaCl.sub.2), calcium bromide (CaBr.sub.2), calcium iodide (CaI.sub.2), barium fluoride (BaF.sub.2), barium chloride (BaCl.sub.2), barium bromide (BaBr.sub.2), barium iodide (BaI.sub.2), strontium fluoride (SrF.sub.2), strontium chloride (SrCl.sub.2), strontium bromide (SrBr.sub.2), strontium iodide (SrI.sub.2), with MgCl.sub.2 being preferred. Non-limiting examples of tetraalkyl orthosilicates or alkoxy silanes include tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraisobutoxysilane, tetrakis(methoxyethoxy)silane, tetrakis(methoxypropoxy)silane, tetrakis(ethoxyethoxy)silane, tetrakis(methoxyethoxyethoxy)silane, trimethoxyethoxysilane, dimethoxydiethoxysilane, triethoxymethoxysilane, tetra-(4-methyl-2-pentoxy)silane, and tetra-(2-ethylhexoxy)silane. Additional examples of tetrafunctional silanes with acyloxy groups include tetraacetoxyoxysilane, silicon tetrapropionate and silicon tetrabutyrate. Preferably the tetraalkyl orthosilicate is TEOS. The aqueous solution can include from 10 to 100 vol. % water and all ranges and values there between (e.g., 10, 20, 30, 40, 50, 60, 70, 80, 90 vol. %) The aqueous solution can also include an alcohol. Non-limiting examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, or glycerol to name a few, preferably the alcohol is ethanol, propanol, butanol, or mixtures thereof. The aqueous solution of alkaline earth metal precursor and an tetraalkyl orthosilicate can be mixed together using suitable mixing equipment and heated to a temperature of room temperature to 90° C., preferably 50° C. to 60° C., and all values and ranges there between (e.g., 51, 52, 53, 54, 55, 56, 57, 58, 59° C.). In other aspects, an alkaline earth metal precursor solution can first be formed. The alkaline earth metal precursor solution can be heated to a temperature ranging from room temperature to 95° C., preferably from 40 to 70° C. and all ranges and values there between (e.g., 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, or 69° C.) followed by adding the tetraalkyl orthosilicate to the solution. In particular aspects, a mixture of TEOS and MgCl.sub.2 results in the formation of a polycondensed support material containing uniform single crystal structure including heterostructures of silica magnesia within an organic template.

(15) Step 2 of the method can include adding a transition metal precursor material to the aqueous solution including polycondensed silica having an external network of alkali earth metal atoms under conditions to incorporate transition metal atoms into the polycondensed silica. The molar ratio of alkaline earth metal precursor to transition metal precursor can be 5:1 to 50:1, preferably 20:1 to 30:1 and all ranges and values there between Non-limiting ratios include about 20.1:1, 20.5:1, 21.0:1, 21.5:1, 22.0:1, 22.5:1, 23.0:1, 23.5:1, 24.0:1, 24.5:1, 25.0:1, 25.5:1, 26:1, 26.5:1, 27.0:1, 27.5:1, 28.0:1, 28.5:1, 29.0:1, 29.5:1, or 30:1. The transition metal precursor can include ferric citrate, nickel citrate, copper citrate, zinc citrate, aluminum citrate, zirconium citrate, or titanium citrate. After adding the transition metal precursor, the aqueous mixture can be stirred (e.g., vigorously) for an appropriate amount of time to incorporate the transition metal precursor. The appropriate amount of time can include from 30 minutes to overnight (e.g., approximately 12 hours), 1 hour to 6 hours, preferably about 2 hours.

(16) Step 3 of the method can include forming a solid material from the polycondensed silica. In some instances, the solid material can be obtained by adding a precipitating agent. The precipitating agent can be one or more of ammonium hydroxide (NH.sub.4OH), ammonium carbonate [(NH.sub.4).sub.2CO.sub.3], ammonium bicarbonate (NH.sub.4HCO.sub.3), sodium carbonate (Na.sub.2CO.sub.3), potassium carbonate (K.sub.2CO.sub.3), sodium bicarbonate (NaHCO.sub.3), or potassium bicarbonate (KHCO.sub.3). Preferably the precipitating agent is NH.sub.4OH. In other instances, the precipitating agent can have a concentration from 1M to 10M of precipitation agent in water. After adding the precipitating agent, the aqueous mixture can be stirred (e.g., vigorously) for an appropriate amount of time to form the solid material. The appropriate amount of time can include from 30 minutes to overnight (e.g., approximately 12 hours), 1 hour to 6 hours, preferably about 2 hours.

(17) Step 4 of the method can include drying and calcining the solid material to form a heterostructured silica catalyst comprising a transition metal, an alkaline earth metal oxide, and silica, wherein the transition metal, the alkaline earth metal from the metal oxide thereof, and silicon (Si) from silica are each present in the crystal lattice structure of the catalyst. After the solid material is formed by precipitation, it can be collected by filtration, washed with hot water, and dried overnight at a temperature of 100 to 150° C., preferably 130° C. In certain instances (e.g., when the transition metal is iron) after drying, the material can be treated with an oxidant (e.g., H.sub.2O.sub.2) under stirring conditions for a period of time (e.g., 30 minutes to 2 hours, preferably approximately 1 hour) followed by isolation by filtration and drying. Drying can include a time of 2 hours to overnight, preferably approximately 4 hours at a temperature of 100 to 150° C., preferably 130° C. Further calcination of the dried solid material can include heating at a temperature from 250 to 800° C. and all ranges and values there between preferably 400 to 500° C. Preferably, calcination is employed under temperature ramping conditions (e.g., 3° C./minute) to a hold temperature (e.g., 450° C.) and holding for 3 to 7 hours, preferably 5 hours in air to form the final heterostructured silica catalysts.

(18) The morphology, structure, and quality of the heterostructured silica catalysts of the present invention can be evaluated using techniques, such as, but not limited to, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, UV-VIS, optical reflectivity, optical microscopy, low-energy electron microscopy (LEEM), low-energy diffraction (LEED), atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning tunnelling microscopy (STM), photoelectron microscopy (PES), angle-resolved photoelectron spectroscopy (ARPES), photoemission electron microscope (PEEM), energy dispersive X-ray spectroscopy (EDS, EDX, or XEDS), X-ray photoelectron spectroscopy (XPS), Image J data analysis software, reflection high-energy electron diffraction (RHEED), or microscope-based videography.

(19) C. Hydrocarbon Production

(20) 1. Methods and Systems

(21) The heterostructured silica catalyst of the present invention can be used to catalyze a chemical reaction, such as the hydrogenation of carbon monoxide. In non-limiting embodiments, the hydrogenation of carbon monoxide includes the conversion of synthesis gas (e.g., gas that include H.sub.2 and CO) to carbon dioxide, methane, olefins (e.g., ethylene, propylene, and butylenes), and and/or paraffins (e.g., C.sub.2+ alkanes). Conditions sufficient for production include temperature, time, syngas ratio and concentration, space velocity, and pressure. The temperature range for hydrocarbon production may range from about 200° C. to 500° C., preferably 250° C. to 350° C. A weighted hourly space velocity (WHSV) of syngas higher than 1000 h.sup.−1 can be used, preferably between 1000 and 10,000 h.sup.−1, most preferably approximately 1875 h.sup.−1. The conversion of syngas can be carried out at a pressure from 0 to 15 bar, preferably approximately 5 bar, or at atmospheric pressure. The conditions for hydrocarbon production may be varied based on the type of the reactor. Prior to using the heterostructured silica catalyst of the present invention, the catalysts can be activated by ramping 3° C./minute to 350° C. and holding for 16 hour under 50:50 H.sub.2/N.sub.2 flow (e.g., WHSV: 3600 h.sup.−1).

(22) The reaction of the methods and system disclosed herein can occur in any type of reactor. Non-limiting examples of reactors include a high throughput fixed bed flow reactor setup housed in a temperature controlled system fitted with regulators to maintain pressure during the reaction. It is also envision the method and systems may also include the ability to regenerate used/deactivated catalyst in a continuous process such as in a fluidized bed reactor. The method and system can further include collecting or storing the produced hydrocarbon product along with using the produced hydrocarbon product to produce downstream petrochemical and/or polymer products. Reaction products of the reactions can be analyzed by online GC analysis for purity.

(23) Referring to FIG. 1, a system 10 is illustrated, which can be used to convert syngas to hydrocarbon products with the heterostructured silica catalysts of the present invention. The system 10 can include a syngas source 11, a reactor 12, and a collection device 13. The syngas source 11 can be configured to be in fluid communication with the reactor 12 via an inlet 17 on the reactor. In a non-limiting aspect, one or more inlets can be present that can deliver syngas in a single feed as a H.sub.2/CO mixture or separately via multiple inlets (not shown). As explained above, the syngas source can be configured such that it regulates the amount of syngas feed entering the reactor 12. The reactor 12 can include a reaction zone 18 having the heterostructured silica catalyst 14 of the present invention (MHH—SiO.sub.2 catalyst). The amounts of the syngas feed 11 and the catalyst 14 used can be modified as desired to achieve a given amount of product produced by the system 10. The reactor 12 can include an outlet 15 for products produced in the reaction zone 18. The products produced can include carbon dioxide, methane, olefins (e.g., ethylene, propylene, and butylenes), and/or paraffins (e.g., C.sub.2+ alkanes). The collection device 13 can be in fluid communication with the reactor 12 via the outlet 15. Both the inlet 17 and the outlet 15 can be open and closed as desired. The collection device 13 can be configured to store, further process, or transfer desired reaction products (e.g., olefins) for other uses. Still further, the system 10 can also include a heating source 16. The heating source 16 can be configured to heat the reaction zone 18 to a temperature sufficient (e.g., 250 to 350° C.) to convert syngas to hydrocarbon products. A non-limiting example of a heating source 16 can be a temperature controlled furnace. Additionally, any unreacted syngas can be recycled and included in the syngas feed to further maximize the overall conversion of syngas to hydrocarbon products. Further, certain products can be separated by known processes in the art and used in other processes to produce commercially valuable chemicals. This increases the efficiency and commercial value of the syngas conversion process of the present invention.

(24) 2. Reactants and Products

(25) Carbon monoxide (CO) gas and hydrogen (H.sub.2) gas can be obtained from various sources. The CO can be obtained from streams coming from other chemical processes, like partial oxidation of carbon-containing compounds, iron smelting, photochemical process, syngas production, reforming reactions, and/or various forms of combustion. H.sub.2 can be obtain from streams coming from other chemical processes, like water splitting (e.g., photocatalysis, electrolysis, or the like), syngas production, ethane cracking, methanol synthesis, or conversion of methane to aromatics. The molar ratio of H.sub.2/CO in the reactant stream can be 1 or more. In some embodiments, the H.sub.2/CO molar ratio can be from 1 to 10, preferably approximately 2. In some examples, the remainder of the reactant gas stream can include another gas or gases provided the gas or gases are inert, such as argon (Ar), nitrogen (N.sub.2), or methane and further provided that they do not negatively affect the reaction. All possible percentages of CO plus H.sub.2 plus inert gas in the current embodiments can have the described H.sub.2/CO ratios herein. Preferably, the reactant mixture is highly pure and devoid of water or steam. In some embodiments, the feed gases can be dried prior to use (e.g., pass through a drying media) or contain a minimal amount of water or no water at all.

(26) The process of the present invention can produce a product stream that includes a mixture of carbon dioxide, methane, olefins (e.g., ethylene, propylene, and butylenes), and/or paraffins (e.g., C.sub.2+ alkanes). In particular instances, the carbon monoxide conversion can be 70 to 78% at 300° C., 67 to 80% at 325° C., and 14 to 53% at 350° C. The selectivity of methane can be 11 to 28%, the selectivity of olefins can be 24 to 41%, the selectivity of paraffins can be 13 to 21%, and the selectivity of carbon dioxide can be 13 to 41%, based on a reaction mass balance of 95±5%.

EXAMPLES

(27) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

(28) Aqueous magnesium chloride (1M), tetraethyl orthosilicate (98%, TEOS), ferric citrate (16.5 to 18.5 wt %, based on total weight of solution), aqueous ammonium hydroxide (1M, 3M, 5M, and 7M), and aqueous hydrogen peroxide (15%) were used without further purification.

Example 1