Na based support containing catalyst for partial oxidation of substrate to value-added products

Abstract

The present invention relates to a heterogeneous catalyst system comprising bimetallic catalysts (M1M2) supported onto sodium-based support for partial oxidation of substrate (e.g., lower alkane such as methane, ethane, propane etc.) into value-added products under ambient conditions using hydrogen peroxide (H2O2) solution or in-situ formed H2O2 using H2 and O2 gases.

Description

PT / 2024 / 15489 Na BASED SUPPORT CONTAINING CATALYST FOR PARTIAL OXIDATION OF SUBSTRATE TO VALUE-ADDED PRODUCTS FIELD OF THE INVENTION

[0001] The present invention generally relates to a Na-based support containing heterogeneous catalyst for oxidation of substrates into value-added products under ambient conditions. More particularly, the present invention relates to a heterogeneous catalyst system comprising bimetallic catalysts (M1M2) supported onto a sodium-based support for partial oxidation of substrate (e.g., lower alkane such as methane, ethane, propane etc.) into value-added products under ambient conditions using hydrogen peroxide (H2O2) solution or in-situ formed H2O2using H2and O2gases. BACKGROUND OF THE INVENTION

[0002] Lower alkanes e.g. methane, is one of the major constituents of natural gas, and its presence in waste landfills and manure feedstocks adds to the potential list of chemicals contributing to global warming. Methane has a high calorific value and can be directly used as fuel, but its storage and transportation are not practical as it needs to be compressed to 10-100 atm for commercial utility. Alternatively, methane can be converted into chemicals using an indirect route involving the production of synthesis gas (CO+H2) (refer, Hamzehlouia, S. et al., Sci Rep 2018, 8 (1), 8940).

[0003] Methane is envisaged to have tremendous potential to be a raw material that can be converted into various high-value chemicals. One of the biggest obstacles in this direction is the activation of non-polar methane with a central carbon atom surrounded by four hydrogen atoms forming a regular tetrahedron, thereby requiring harsh reaction conditions (refer, Latimer, A. A. et al., Nat Mater 2017, 16 (2), 225–229). More significant challenge is the partial oxidation of methane (POM) to methanol or any other useful platform molecules, as thermodynamics suggests that an activated C-H bond is so reactive that it readily undergoes complete oxidation to CO2 under the activated conditions. Direct conversion of methane into value-added product fuels and chemicals such as methanol, formic acid, olefins, hydrogen, and aromatics has thus become an important research topic attracting interest from industry and academia. Indeed, direct partial oxidation of methane (or lower alkanes) to value-added products is considered a Holy Grail problem in catalysis and is a dream reaction that still eludes the catalysis community.

[0004] Moreover, molecular oxygen and H2O2, the two green oxidants, are targeted because of their better commercialization scope, and if successful, catalytic technologies can be developed through these routes [refer, Qi, G. et al., Nat. Catalo. 2022, 5 (1), 45–54; Agarwal, N. et al., Science (1979) 2017, 358 (6360), 223–227); Xin, J. et al., Nat. Catalo. 2018, 1 (11), 889–896; and Xin, P. et al., Nat. Common. 2022, 13 (1)]. While molecular oxygen is the ideal solution for this problem, the yields reported so far for methanol, and other oxygenates are so poor that any commercialization scope is far in sight. One of commercial production of H2O2by the anthraquinone method suffers from several disadvantages, such as requiring toxic solvents, multiple steps and significant energy and risk during transportation. The direct synthesis of H2O2 from H2 and O2 gases using metal catalysts can be a solution to solve this problem. However, the key problem is stabilizing the resulting H2O2 because H2O2 simultaneously undergoes decomposition to water in the presence of the same catalysts employed for its formation

[0005] Thus, there is still a dire need in the art to produce value-added products from cheaper hydrocarbon sources like lower alkanes effectively with easy and facile methods for the reaction process using intelligent catalyst and efficient oxidant(s). OBJECTSOF THE INVENTION

[0006] Main objective of the present invention is to provide a heterogeneous catalyst system for partial oxidation of substrate to value-added product(s) under ambient conditions wherein the catalyst comprises bimetallic catalysts supported onto sodium based zeolite support (M1M2-Na containing zeolite).

[0007] Another objective of the present invention is to provide a process for the preparation of said heterogeneous catalyst system of bimetallic catalysts.

[0008] Another objective of the present invention is to provide a process for preparing value added products by reacting lower alkane(s) with said heterogeneous catalyst system, in presence of oxidant such as H2O2solution or in-situ H2O2from H2and O2. SUMMARY OF THE INVENTION

[0009] Accordingly, the present invention provides a bimetallic catalyst supported onto sodium based zeolite support (M1M2-Na containing zeolite) for partial oxidation of substrate to value-added product(s) under ambient conditions.

[0010] In an aspect, the present invention relates to a heterogeneous catalyst for partial oxidation of hydrocarbon substrate to value-added product(s), the catalyst comprises:

[0011] bimetallic catalysts (M1M2) supported onto sodium-based zeolite support, wherein the amount of metals M1 and M2 deposited onto said Na based support is in the range from 0.1 to 5.0 wt. % of the total weight of the catalyst; and the amount of sodium in said sodium-based zeolite support is in range of 0.1 wt. % to 3 wt. %. In an embodiment, the M1 metal is transition metal or noble metal.

[0012] In an embodiment, the M2 metal is noble metal or transition metal.

[0013] In an embodiment, the sodium-based zeolite support is selected from Na-ZSM5, Na-LSX, Na-β zeolite, Na-SSZ-13, and Na-ZSM35.

[0014] In an embodiment, M1 metal is selected from Cu, Ni, Fe and Co.

[0015] In an embodiment, M2 metal is selected from Pd, Au, Pt and Ag.

[0016] In an embodiment, the amount of M1 metal in said bimetallic catalysts (M1M2) is in the range of 0.1 to 5 wt. %.

[0017] In an embodiment, the amount of M2 metal in the said bimetallic catalysts (M1M2) is in the range of 0.1 to 5 wt. %.

[0018] In an embodiment, a particle size of M1 metal is in range of 1 to 10 nm; and a particle size of M2 metal is in range of 1 to 5 nm. In another aspect, the present invention relates to a process for the preparation of the heterogeneous catalyst system, the process comprises the steps of: a) reacting alkaline aqueous solution of Na based support with aqueous solution of M1-metal precursor by drop wise addition of said M1-metal precursor solution into alkaline solution of Na based support for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation and drying to obtain powder of M1 metal catalyst supported onto Na based support; b) preparing modified aqueous solution of M1 metal catalyst supported onto Na based support as obtained in step a) with water and a modifier; andc) reacting modified aqueous solution of step b) with aqueous solution of M2-metal precursor by drop wise addition of said M2-metal precursor solution into modified solution of step b) for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation, washing and drying to obtain powder of the heterogeneous catalyst system comprising bimetallic catalysts (M1M2) supported onto sodium-based zeolite support.

[0019] In an embodiment, M1 metal precursor is Iron (III) nitrate nonahydrate, and M2 metal precursor is hydrogen tetrachloroaurate (III) trihydrate.

[0020] In an embodiment, the modifier is ammonium chloride.

[0021] In another aspect, the present invention provides a process for the preparation of value-added products, comprising: reacting a hydrocarbon in the presence of oxidizing agent, optionally CO, and the heterogeneous catalyst, at one or more specific reaction conditions to obtain the value added products.

[0022] In an embodiment, the one or more specific reaction conditions is / are selected from: i) a pressure is of 1 atm or 10 to 30 bar, ii) a temperature is at least 25-120 °C, iii) a feed stream in contact with the heterogeneous catalyst system at a weight hourly space velocity of 12000 cm3STP gcalh-1, iv) stirring the reaction mixture containing substrate, catalyst and oxidant at 900-1100 rpm, v) the H2O2molarity of aqueous solution in a batch process is in the range of 0.1-5M, and / or vi) the molar ratio of H2O2 solution to substrate in the continuous flow feed stream is in the range of 1:1 to 1:10.

[0023] In an embodiment, wherein the hydrocarbon is selected from methane, ethane, propane and butane.

[0024] In an embodiment, the process is done in a batch mode or continuous flow mode.

[0025] In an embodiment, the oxidizing agent is H2O2solution or in-situ generated H2O2.

[0026] In an embodiment, the value-added products are selected from methanol, ethanol, and formic acid with 90% selectivity.

[0027] In an embodiment, the value-added products are selected from carboxylic acids, esters and aldehydes when the process is conducted in the presence of CO, wherein the carboxylic acid is selected from acetic acid and ethanoic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention, which are used to describe the principles of the present invention together with the description.

[0029] Figure 1 represents TEM images of: a) sodium zeolite support, b) Fe as M1 metal supported on sodium zeolite support, c) a bimetallic mixture of Fe as M1 and Au as M2 without support, and d) a bimetallic mixture of Fe as M1 and Au as M2 supported on sodium zeolite support as said heterogeneous catalyst system. In the case of a) sodium zeolite support, there were only big particles of cubic shape. The same was true in the case of b) Fe as M1 metal supported on sodium zeolite support as there were no Fe particles on the surface. TEM analysis of d) bimetallic mixture of Fe as M1 and Au as M2 supported on sodium zeolite confirms the presence of Au particles on the surface, which are seen as small black particles on the edges of the cubic particles. 0.1FeNZ represents the 0.1 wt% Fe loaded on the support, similar to 0.1AuNZ and 0.1Au0.1FeNZ, in accordance with an implementation of the present invention.

[0030] Figure 2 represents the HRTEM images of the 0.1Au0.1FeNZ, which confirms the presence of small Au nanoparticles over the surface of the zeolite support. The particle size of Au particles is ~5nm, in accordance with an implementation of the present invention.

[0031] Figure 3 represents the elemental mapping of the bimetallic catalysts. This confirms the presence of the elements with a homogeneous distribution on the zeolite support's surface, in accordance with an implementation of the present invention.

[0032] Figure 4 represents the XRD pattern of sodium zeolite support and a bimetallic mixture of Fe as M1 and Au as M2 supported on sodium zeolite support as said heterogeneous catalyst system. The XRD pattern well matches the Na-containing zeolite reported before with Ref Code 000480135 and the chemical formula H1.7Na0.6Al2.3Si93.7O192. After the deposition of the metals, no phase changes were observed for the support, in accordance with an implementation of the present invention.

[0033] Figure 5 represents the NMR graph confirming the formation of value-added products e.g. methanol, formic acid, acetic acid and Potassium hydrogen phthalate (KHP) (Sample collected from a batch reactor), in accordance with an implementation of the present invention.

[0034] Figure 6 represents the GC spectrum of gaseous products in the reaction mixture (sample collected from batch reactor), in accordance with an implementation of the present invention.

[0035] Figure 7 represents the product formation in the batch process. Fig. 7a confirms the high production of bimetallic catalyst resulting from the synergistic effect among the metals. Fig. 7b shows the product formation at various temperatures, confirming 60 °C as the optimum temperature, in accordance with an implementation of the present invention.

[0036] Figure 8 represents the methane conversion and selectivity toward the products, indicating the highly selective formation of the formic acid in the case of a bimetallic catalyst, in accordance with an implementation of the present invention.

[0037] Figure 9 represents the product formation in the continuous flow reactor using the bimetallic catalyst, in accordance with an implementation of the present invention. ACRONYMS USED TO DESCRIBE THE INVENTION

[0038] Carbon Monoxide (CO)

[0039] Methane (CH4)

[0040] Carbon dioxide (CO2)

[0041] Hydrogen peroxide (H2O2)

[0042] Copper (Cu), Iron (Fe), Nickel (Ni), Cobalt (Co), Palladium (Pd), Gold (Au), Platinum (Pt) and Silver (Ag).

[0043] NZ means Na Zeolite support (e.g. Na-ZSM-5).

[0044] Fe-NZ means Fe metal supported on Na Zeolite support i.e., monometallic system.

[0045] AuFeNZ means bimetallic mixture of Au and Fe metals supported on Na Zeolite support. DETAILED DESCRIPTION OF THE INVENTION

[0046] It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate relevant elements for a clear understanding of the invention. The detailed description below will be provided in reference to the attached drawing.

[0047] While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.

[0048] Although one or more features and / or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and / or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and / or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[0049] The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As usedherein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0050] The term “substrate” provided herein is “hydrocarbon substrate” that is related to alkanes (C1-C10 or more, straight or branched chains) or alcohols (C1-C10 or more, straight or branched chains) and so on, depending upon the type of product sought to be produced.

[0051] The terms “value-added products”, “platform chemicals”, “platform molecules”, and “value added chemicals” are used throughout the specification interchangeably with the same meaning, and it may be defined as oxidized products such as alcohols (C1-C10 or more, straight or branched chains), C1-C10 oxygenated products, aldehydes (C1-C10 or more, straight or branched chains), esters (C1-C10 or more, straight or branched chains), acids (C1-C10 or more, straight or branched chains), and so on, depending upon the type of substrate used.

[0052] The terms “oxidant” and “oxidizing agent” are used throughout the specification interchangeably with the same meaning.

[0053] The term “ambient conditions” or “specific reaction conditions” provided herein are defined by specific temperature, pressure, weight, hourly space velocity and molar ratio ranges, which are lower or much lower or better than the reported methods for obtaining said value-added products under similar conditions.

[0054] In an embodiment, the present invention provides a heterogeneous catalyst system for partial oxidation of substrate to value-added product(s) under ambient conditions, the catalyst system comprises bimetallic catalysts (M1M2) supported onto sodium based zeolite support (M1M2-Na containing zeolite), wherein the amount of metals M1 and M2 deposited onto said Na based support is in the range from 0.1 to 5.0 wt. % of the total weight of the catalyst; and the amount of sodium in said sodium-based zeolite support is in range of 0.1 wt. % to 3 wt. %.

[0055] In another embodiment, the M1 metal is selected from Cu, Ni, Fe and Co. In particularly useful embodiment, the M1 metal is Fe.

[0056] In yet another embodiment, the M2 metal is selected from Pd, Au, Pt and Ag. In particularly useful embodiment, the M2 metal is Au.

[0057] In another embodiment, the amount of M1 metal in said bimetallic catalysts (M1M2) is in the range of 0.1 to 5 wt. % and the amount of M2 metal in the said bimetallic catalysts (M1M2) is in the range of 0.1 – 5 wt. %.

[0058] In another embodiment, the metals M1M2 deposited overall onto the Na based support or Na based zeolite, may be done by deposition precipitation method.

[0059] In another embodiment, the Na based support disclosed herein comprises specific amounts / proportion of elements comprising mixture of sodium, aluminum, silicon and oxygen.

[0060] In another embodiment, the amount / content of sodium in said support is in range of 0.1 wt. % to 3 wt. %.

[0061] In another embodiment, the particle size of M1 metal in nanoparticle form is in range of 1 to 10 nm.

[0062] In another embodiment, the particle size M2 metal in nanoparticle form is in range of 1 to 5 nm.

[0063] In specific embodiment, the Na based support in combination with said bimetallic components acts in synergistic way to preferably provide acid based value added products, with the large-scale production of value-added products from methane and lower alkanes.

[0064] In another embodiment, the heterogeneous catalyst system containing bimetallic catalysts (M1M2) supported onto sodium based zeolite support (M1M2-Na containing zeolite) is crystalline in nature (refer, XRD graph of Figure 4).

[0065] In another embodiment, Figure 7 confirms the synergism of M1 and M2 metals supported onto Na based support by providing higher yields (in µmol.) of different products like formic acid, methanol, acetic acid, etc. over monometallic system (M1-NZ or M2-NZ) and NZ support alone.

[0066] In another embodiment, the Na based support mainly comprises Na containing zeolite.

[0067] In another embodiment, the Na based support is selected from but not limited to Na-ZSM5, Na-LSX, Na-β zeolite, Na-SSZ-13, Na-ZSM35 and so on.

[0068] In another embodiment, the present invention provides a process for the preparation of heterogeneous catalyst system for partial oxidation of substrate to value- added product(s) under ambient conditions, the catalyst system comprises bimetallic catalysts (M1M2) supported onto sodium based zeolite support (M1M2-Na containing zeolite), the process comprising the steps of: a) reacting alkaline solution of Na based support with aqueous solution of M1-metal precursor by dropwise addition of said M1-metal precursor solution into alkaline solution of Na based support for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation and drying to obtain powder of M1 metal catalyst supported onto Na based support; b) preparing modified aqueous solution of M1 metal catalyst supported onto Na based support as obtained in step a) with water and a modifier; and c) reacting modified aqueous solution of step b) with aqueous solution of M2-metal precursor by dropwise addition of said M2-metal precursor solution into modified solution of step b) for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation, washing and drying to obtain powder of the heterogeneous catalyst system comprising bimetallic catalysts (M1M2) supported onto sodium based zeolite support.

[0065] In another embodiment, the alkaline solution of Na based support used in step a) is prepared by mixing and stirring 0.5 to 2 g of Na based support in water under sonication at the temperature in the range of 25-30 °C for time period of 5 to 10 minutes followed by adding a 1stbase to maintain the pH between 9 to 10.

[0066] In another embodiment, the 1stbase used in preparation of Na based support is selected from sodium hydroxide, potassium hydroxide, sodium carbonate and so on. More particularly, the base is sodium hydroxide solution with 0.1 M concentration.

[0067] In another embodiment, the aqueous solution of M1 metal precursor is prepared by dissolving the fixed amount of the M1 precursor in 20-25 mL of water to synthesize 0.1 to 5 wt. % of M1 supported on Na containing support.

[0068] In another embodiment, prior to the formation of precipitates in step a), the mixture of M1-metal precursor solution and alkaline solution of Na based support is aged for time period of 0.5 to 2 hours.

[0069] In another embodiment, the centrifugation of step a) is done at speed of 5000 to 10000 using Eppendorf.

[0070] In another embodiment, the drying of step a) is done in hot air oven at temperature in the range of 70-90 °C for time period of 12-24 h.

[0071] In another embodiment, after centrifugation and drying of step a), the powder is calcined in the static air with temperature in the range of 300 to 400°C for time period of 4 to 6 h to finally obtain the M1 metal catalyst supported onto Na based support system.

[0072] In another embodiment, the modified aqueous solution of step b) is prepared by mixing and stirring 0.1 to 5 wt. % of the M1 metal catalyst supported onto Na based support in water under sonication at the temperature in the range of 25-30 °C for time period of 5 to 10 minutes followed by adding specific amount of a modifier.

[0073] The modifier used herein is selected from ammonium chloride. The amount of modifier is in range of 15-25 wt. % with respect to the support.

[0074] In another embodiment, the aqueous solution of M2 metal precursor is prepared by dissolving the fixed amount of the M2 precursor in 20-25 mL of water to synthesize 0.1 to 5 wt. % of M2 supported on M1NZ (M1 loaded on NZ).

[0075] In another embodiment, the pH of 9-10 in step c) is maintained using 2ndbase.

[0076] The 2ndbase used herein is selected from sodium hydroxide, potassium hydroxide, sodium carbonate and so on. Specifically, the base is sodium hydroxide solution with 0.1 M concentration.

[0077] In another embodiment, the centrifugation of step c) is done at speed of 5000 to 12000 using Eppendorf.

[0078] In another embodiment, the washing of step c) is done by using water or deionized water.

[0079] In another embodiment, the drying of step c) is done in a hot air oven at a temperature in the range of 70-90 C for a time period of 12-24 hrs.

[0080] In another embodiment, after centrifugation, washing and drying of step c), the powder is calcined in the static air with a temperature in the range of 300 to 400oC for time period of 3 to 6 h to finally obtain the heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support.

[0081] In another embodiment, the heterogeneous catalyst system as prepared is used for partial oxidation of hydrocarbon substrates without any post-treatment.

[0082] In an embodiment, the hydrocarbon substrate is selected from lower alkanes such as methane, ethane, propane and butane.

[0083] Yet another embodiment of the present invention provides a process carried out in the gaseous phase in the continuous flow reactor or liquid phase in the batch reactor, wherein said process comprises of reacting substrate with an oxidizing agent such as H2O2 solution or in-situ generated H2O2 in the presence of said heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support at specific reaction conditions.

[0084] In another embodiment, the present invention provides a process for the preparation of value-added products from the substrate in the presence of oxidizing agent such as H2O2solution or in-situ generated H2O2, optionally CO, and said heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support at specific reaction conditions.

[0085] The in-situ H2O2used herein as oxidizing agent is produced by using H2and O2gases.

[0086] In preferred embodiment, the concentration of H2O2 solution used herein in the batch process is in range of 1 to 25 % w / v. Particularly, the concentration of H2O2solution is 15 % w / v.

[0087] The diluted molar concentration of H2O2solution is in range of 1 to 50 % w / v.

[0088] In another embodiment, the pressure flow of lower alkane in said process or processes is kept in the range of 5 to 40 bar.

[0089] In another embodiment, the ratio of lower alkane to CO in case of production of acids as value added products is in the range of 1:1 to 4:1 respectively with a total pressure of 10-40 bar.

[0090] In another embodiment, the partial oxidation reaction is done by stirring the reaction mixture at 900-1100 rpm.

[0091] In another embodiment, the feed stream of the substrate in a continuous partial oxidation process comprises methane in pure form with the purity of 99.9% and 25-75% w / v of H2O2solution.

[0092] Specifically, the continuous partial oxidation process is done under one or more reaction conditions, as listed above. More specifically, the reaction conditions in continuous partial oxidation process are: i) the temperature range of 30-100oC and under a pressure of 1 atm.

[0093] In the case of the in-situ H2O2 process, the reactant feed comprises pure methane cylinder (CH4) with purity of 99.99%, O2cylinder in which 25% of O2diluted with CO2or N2 (denoted as d-O2), H2 Cylinder of 5% H2 diluted with CO2 or N2 denoted as (d-H2), and millipore water. Specifically, the pressure of this in-situ H2O2 process is kept in between 20-40 bar of feed gas with a ratio of 1:1:2::d-O2:d-H2:CH4i.e., in a typical reaction d-O2= 5bar, d-H2= 5bar and CH4= 10 bar with a total pressure of 20 bar.

[0094] In preferred embodiment, in case of acid production via in-situ H2O2 process, the pure CO gas in feed along with CH4, d-H2, and d-O2 is used wherein the total pressure of 20-50 bar was maintained with the ratio of 1:1:1:2::CO:d-H2:d-O2:CH4,i.e., in a typical reaction CO= 5 bar, d-O2 = 5bar, d-H2 = 5bar and CH4 = 10 bar with a total pressure of 25 bar.

[0095] The utilization of in-situ synthesized H2O2from H2and O2in said partial oxidation reaction in the same vessel (one-pot oxidation reaction), contributes to savingsof both energy and time by avoiding isolation and purification steps as well as minimizes risks involved in the transportation of concentrated H2O2.

[0096] In a specific embodiment, the specific reaction conditions comprise one or more of the: i) a pressure is of 1 atm or 10 to 30 bar, ii) a temperature is at least 25-120°C, iii) a feed stream in contact with the heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support at a weight hourly space velocity of 12000 cm3STP gcal h-1, iv) stirring the reaction mixture containing substrate, catalyst and oxidant at 900-1100 rpm, v) the H2O2 molarity of aqueous solution in batch process is in the range of 0.1-5M, and / or vi) the molar ratio of H2O2solution to substrate in the continuous flow feed stream is in the range of 1:1 to 1:10.

[0097] Another embodiment of the present invention is the generation of in-situ H2O2 at atmospheric pressure as well as at high pressure.

[0098] In yet another embodiment or preferred embodiment, the present invention provides a process of preparation of methanol or ethanol or both, using methane or ethane by the same partial oxidation process as described above.

[0099] In yet another embodiment or preferred embodiment, the present invention provides a process of preparation of acids (e.g. acetic acid, ethanoic acid, propanoic acid, etc.) using methane or ethane by the same partial oxidation process described above with mandatory use of CO.

[0100] In preferred embodiment, the present invention provides a process of preparation of acetic acid using carbon monoxide (CO), methane(CH4) and H2O2 solution or in-situ generated H2O2keeping at said one or more reaction conditions.

[0101] In yet another embodiment or preferred embodiment, the present invention provides a process of preparation of esters (e.g. methyl ester, ethyl ester, etc.) using methane, ethane or propane by the same partial oxidation process described above.

[0102] In yet another embodiment or preferred embodiment, the present invention provides a process of preparation of aldehydes (e.g. formaldehyde, ethanal, propanal etc.) using methane or ethane by the same partial oxidation process described above.

[0103] In preferred embodiment, the present invention provides a process for the preparation of value-added products such as methanol, ethanol, propanol, etc. or mixtures thereof, from substrates such as methane, ethane or propane in the presence of oxidizing agents such as H2O2 solution or in-situ H2O2 and said heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support keeping one or more of said specific reaction conditions, wherein the in-situ H2O2 is produced in said reaction by treating H2 and O2 gases.

[0104] In preferred embodiment, the present invention provides a process for the preparation of value-added products such as acid, acetic acid, aldehydes, esters, etc. or mixtures thereof, from a substrate such as methane, ethane, propane or butane in the presence of oxidizing agent such as H2O2solution or in-situ H2O2, CO and said heterogeneous catalyst system of M1M2 bimetallic catalysts supported onto Na based support at one or more of said specific reaction conditions, wherein the in-situ H2O2 is produced in said reaction by treating H2and O2gases.

[0105] Table 1 below thus summarises the results obtained with the activity of catalysts with two different conditions of pressure. Table-1 Sr. No. Catalyst Pressure Products (µmol) 1 0.1Au0.1FeNZ 10 bar 4203 2. 0.1Au0.1FeNZ 1 atm 26

[0106] 1stentry: Reaction Condition at 10 bar pressure: Catalyst= 50 mg, Methane= 10 bar, H2O2 = 5M, Temperature=60 °C, and Time= 0.5 h.

[0107] 2ndentry: Reaction Condition at 1 atm. pressure: Catalyst= 100 mg, Methane flow= 50 mmol / h, H2O2 flow = 2 mL / h, Temperature=80 °C, Pressure = 1 atm, and Time= 3h. (Note: 1stentry is for batch process reaction under high pressure conditions where inventors kept the pressure as bar unit) and 2ndentry is for continuous flow process under atmospheric conditions so the gases flow are mentioned).

[0108] The selectivity of the liquid oxygenates or value added products is more than 90%. Specifically, the formic acid selectivity is in the range from 75-95 % depending on the reaction conditions.

[0109] Table 2 shows the catalytic activity under various conditions of the reaction. These controlled experiments confirmed the methane as the carbon source for the product formation. Table 2 Sr. No. Catalyst Reaction feed Products (µmol) 1 0.1Au0.1FeNZ CH4+H2O24264.0 3 0.1Au0.1FeNZ N2+ H2O2 0 4 0.1Au0.1FeNZ CH4+ No oxidant 0 5 No Catalyst CH4+H2O20

[0110] Overall, the present invention provides M1-M2 (Au-Fe) bimetallic based catalysts supported over Na containing zeolite to partially oxidize lower alkane (e.g. methane, ethane or propane) to value added products using H2O2(15% w / v) solution or in- situ generated hydrogen peroxide as an oxidant in batch and / or continuous process. It is further shown in the present invention that co-feeding CO with lower alkane (methane) produces acetic acid in excellent yield. The overall conversion achieved through the atmospheric pressure continuous process in the present work is the best reported, surpassing the high-pressure batch process for oxygenates.MATERIALS REQUIRED:

[0111] All chemicals were used without further purification. Metal precursors, Iron (III) nitrate nonahydrate, and hydrogen tetrachloroaurate (III) trihydrate were purchased from Alfa Aesar. Ammonium chloride and sodium hydroxide flakes were purchased from Merck. Hydrogen peroxide (50% w / v) was purchased from Thomas Baker. Methane (99.999% pure), Carbon monoxide (99.999% pure), hydrogen, and oxygen diluted with CO2 or N2 were purchased from Vadilal chemical limited. Na- containing zeolites were purchased from commercially available platforms. Na containing Zeolite (NZNCL) was purchased from the laboratory. EXAMPLES:

[0112] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and the description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all and only experiments performed. The methodology of preparing few of the preferred embodiments shall become clearer with working examples provided below. Example 1: Synthesis of Support NZ:

[0112] The support (NZ) was prepared using a molar gel composition of SiO2 / 0.0125Al2O3 / 0.3Na2O / 0.1TPABr / 36H2O. Typically, 5-8 g of TPABr (98%, LobaChemie) and 20- 40.0g of DI water were dissolved with stirring to produce Solution A. Solution B was prepared separately by mixing 50-70 g sodium silicate (28% SiO2 & 8% Na2O, LobaChemie) in 30.0g water with vigorous stirring. Then, solution B was slowly added to solution A, referred to as solution C. 2-3 g of aluminium sulfate (99%, LobaChemie) was carefully mixed in an acidic solution containing 4-6g of Sulfuric acid (98%, LobaChemie), and 8-12 g of water. This alumina solution (solution D) was then slowly added to solution C, and solution E, with vigorous stirring for 2h. Finally, 60-75 g of water was added to solution E with stirring for 1-2 h to produce a final gel and the pH is maintained at 10.0 -12. The final gel was then transferred to a Stainless steel autoclave and subjected to hydrothermal crystallization at 150- 170 °C for 36-54h. After hydrothermal crystallization, the gel was separated into a wet cake by vacuum filtration, then dried at100-150°C and calcined in a muffle furnace at 450-600°C for 8-10h to obtain a ZSM-5 composite in Na-form. Example 2: Synthesis of Fe (M1) metal supported on Na containing zeolite catalyst:

[0113] Iron (Fe) was deposited over Na containing zeolite (further stated as support) by using the well-known deposition precipitation method. A fixed amount of support (0.3-1 g) of support was typically dispersed in 50 mL millipore water under sonication for 5-10 min. Then the pH of the solution was maintained between 9-10 using 0.1 M NaOH solution under stirring. Then the 25mL aqueous solution of the metal precursor was added to be above solution for 20-30 minutes in a dropwise manner under-maintained pH and the solution was aged for 0.5-2 h. The solid powder was obtained after centrifugation and drying in a hot air oven at 80 °C for several hours. The powder was calcined in the static air of 300 -400oC for 4-6 h and the resulting powder catalyst (Fe-zeolite) was used for the catalytic reactions without any post-treatment. Example 3: Synthesis of Fe (M1) and Au (M2) bi-metallic supported on Na containing zeolite catalyst system:

[0114] Deposition of Au over Fe-zeolite catalyst was performed by deposition precipitation method. Typically, 0.5-1 g of Fe-zeolite catalyst was dispersed in 50 mL millipore water and a fixed amount of ammonium chloride was added to the liquid solution as a modifier. In the next step, the 25 mL aqueous solution of Au precursor was added to the resulting solution in a dropwise manner by maintaining the pH at 9-10 using 0.1M aq. NaOH solution. The obtained precipitate was then centrifuged, washed with deionized water, and dried at 80° C. The dried powder was calcined in static air at 300 – 40° C for 3-6 h and the resulting powder catalyst (Au Fe-zeolite) was used for the catalytic reactions without any post-treatment. Example 4: Catalytic Performance, Testing and Product Analysis: A) Process for methane oxidation using H2O2 in a batch reactor:

[0115] The partial oxidation of methane was performed in an Amar reactor made up of a stainless-steel autoclave with 100 mL capacity. A fixed amount of catalyst was dispersed in 20 mL of Millipore water and then the fixed amount of 50% w / v diluted H2O2 was added. Then the autoclave was sealed and purged three times with methane (CH4) gas at 5bar pressure. It was then pressurized to the desired pressure (10-40 bar) with CH4gas and the solution was heated to desired reaction temperature (typically 60C̊ ). Once the temperature reached the set value, the solution was vigorously stirred at ca. 950 rpm for a fixed amount of time. After the completion of the reaction, the autoclave was subjected to cooling down below 10 C̊ in ice-cold water to minimize the loss of volatile products. The gas sample was collected in a gas bag after cooling the products. Liquid samples were collected after centrifugation and analyzed using gas chromatography and NMR. The same process was used for acetic acid production by adding CO to the reactant feed. The methane and CO ratio was maintained at 1:1- 4:1 respectively with a total pressure of 10- 40 bar. A fixed amount of H2O2 (50 uL) was used to initiate the reaction. B) Process for methane oxidation using H2O2 in a continuous flow reactor:

[0116] Catalytic performance was measured in a continuous flow cotton-plugged quartz reactor having a total length of 50 cm and an internal diameter of 8 mm. By providing the feed stream comprising methane (99.9% pure) and 25-75% w / v diluted H2O2putting in contact with the catalyst in the temperature range of 30- 100 °C and under a pressure of 1 atm. To avoid the loss of volatile products, the products are recovered from the effluents by an ice-cold condensation process below 10 °C. In the feed stream, an aqueous solution of hydrogen peroxide was controlled by a syringe pump and methane flow was controlled by a mass flow controller (Alicat). Both were fed down through the layers of the pelletized catalyst bed. Liquid and gaseous products were separated in a coiled gas condenser and collected periodically for analysis for a 10 h period. C) Process for methane oxidation using in-situ generated H2O2 in a batch reactor:

[0117] In the said process 99.9995 pure methane cylinder (CH4), O2 cylinder in which 25% O2 diluted with CO2 or N2 (denoted as d-O2) and H2 Cylinder 5% H2 diluted with CO2or N2denoted as (d-H2) and millipore water was used as reactant feed.

[0118] Direct oxidation of CH4 with H2 and O2 gasses of all catalysts was evaluated in a 50 mL stainless-steel fixed bed reactor. A fixed amount of catalyst was dispersed in 20 mL of millipore water. Then the autoclave was sealed and purged three times with d-O2gas at 5 bar pressure. It was then pressurized to the desired pressure of 20-40 bar of feed gas in a ratio of 1:1:2: d-O2: d-H2:CH4. Then the solution was heated to desired reaction temperature. Once the temperature reached the set value, the solution was vigorouslystirred at ca. 950 rpm. The reaction was carried out for fix amount of time under the constant circulation of ice-cold water. After completion of the reaction, the gas sample was collected in a gas bag after cooling the products and liquid samples were collected after the centrifugation. Products were analyzed by gas chromatography and NMR technique.

[0119] Acetic acid was produced by using pure CO gas in feed along with CH4, d-H2,and d-O2. The total pressure of 20-50 bar was maintained with the ratio of 1:1:1:2: CO: d-H2: d-O2:CH4. D) Process for methane oxidation using in-situ generated H2O2 in a Continuous flow reactor:

[0120] The process is the same as methane oxidation in a continuous flow reactor using H2O2. But in this process, peroxide was generated in situ and utilized simultaneously by diluting hydrogen and oxygen gases with methane. The flow of gases was maintained using a mass flow controller, water was used to liquefy the products, and a syringe pump controlled the flow. The flow of d-H2 and d-O2 was maintained at 30 mL / min while the flow of methane was 20 mL / min. In the case of acetic acid production, the CO flow was maintained at 5mL / min.

[0121] Qualitative product analysis was done using various techniques like gas chromatography and NMR. 1H, 2H & 13C NMR were recorded in H2O+D2O (90:10) solvent with adding DBM as external standard using Bruker Avance DRX 500 spectrometer.

[0122] The peak values in 1H NMR are as follow: Dissolved methane = 0.13 ppm, acetic acid= 2.04 ppm, methanol= 3.31 ppm, methyl hydroperoxide = 3.82 ppm, DBM = 5.07 ppm and formic acid = 8.4 ppm.

[0123] The GC technique was utilized for the quantitative analysis using the response factor method. A defined amount of products were calibrated in this method and calculation was done using the area under the curve. Products were quantified in NMR using dibromo methane (DBM) as an external standard. The GC is confirming the analysis and formation of methanol and other gaseous products; refer figures 4-9.

[0124] Table 3 shows the catalytic activity of the bimetallic combination using the in- situ generated H2O2, confirming the production of the liquid oxygenates in the batch process. Table 3 Sr. No. Catalyst Reaction feed Products (µmol) 1 0.1Au0.1FeNZ CH4 + dH2 + dO2 23 2. NZ CH4 + dH2 + dO2 0 ADVANTAGES OF THE INVENTION

[0125] The various advantages of the present invention are as follows: · Lower alkane activation under mild conditions is efficiently achieved using the disclosed heterogeneous catalyst · Active catalyst synthesis using easy precipitation deposition route. · High catalytic activity and selectivity of the value-added products · Highest yield of methanol from partial oxidation of methane using H2O2 as an oxidizing agent in batch process or continuous flow process with atmospheric pressure conditions is provided. · Partial oxidation of methane to methanol using H2O2as an oxidant at atmospheric pressure conditions and in continuous mode is not reported so far. · Active catalyst composition contains only less than 2% of metal content. · Provides more than 90% selectivity for alcohol-based value-added products at atmospheric pressure conditions with H2O as a side product. · Provides heterogeneous catalyst for the production of acetic acid from methane or ethane, H2O2and CO in batch and continuous reactor.· Onsite production of H2O2from H2and O2on the same catalyst. · Production of acetic acid using CO, methane and in-situ generated H2O2.

Claims

CLAIMS:

1. A heterogeneous catalyst for partial oxidation of hydrocarbon substrate to value- added product(s), the catalyst comprises: bimetallic catalysts (M1M2) supported onto a sodium-based zeolite support, wherein the amount of metals M1 and M2 deposited onto said Na based support is in the range from 0.1 to 5.0 wt. % of the total weight of the catalyst; and the amount of sodium in said sodium-based zeolite support is in range of 0.1 wt. % to 3 wt. %.

2. The heterogeneous catalyst as claimed in claim 1, wherein the M1 metal is transition metal or noble metal; and wherein the M2 metal is noble metal or transition metal; and wherein the sodium-based zeolite support is selected from Na-ZSM5, Na-LSX, Na-β zeolite, Na-SSZ-13, and Na-ZSM35.

3. The heterogeneous catalyst as claimed in claim 1, wherein M1 metal is selected from Cu, Ni, Fe and Co and M2 metal is selected from Pd, Au, Pt and Ag, and wherein the amount of M1 metal in said bimetallic catalysts (M1M2) is in the range of 0.1 to 5 wt. %, and the amount of M2 metal in the said bimetallic catalysts (M1M2) is in the range of 0.1 to 5 wt. %.

4. The heterogeneous catalyst as claimed in claim 1, wherein a particle size of M1 metal is in range of 1 to 10 nm; and wherein a particle size of M2 metal is in range of 1 to 5 nm.

5. A process for the preparation of the heterogeneous catalyst system as claimed in claim 1, wherein the process comprises the steps of: a) reacting alkaline aqueous solution of Na based support with aqueous solution of M1-metal precursor by drop wise addition of said M1-metal precursor solution into alkaline solution of Na based support for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation and drying to obtain powder of M1 metal catalyst supported onto Na based support;b) preparing modified aqueous solution of M1 metal catalyst supported onto Na based support as obtained in step a) with water and a modifier; and c) reacting the modified aqueous solution of step b) with aqueous solution of M2- metal precursor by drop wise addition of said M2-metal precursor solution into the modified solution of step b) for time period of 20-30 minutes under pH of 9-10 and at temperature in the range of 25-35 °C to obtain precipitate, followed by centrifugation, washing and drying to obtain powder of the heterogeneous catalyst system comprising bimetallic catalysts (M1M2) supported onto sodium-based zeolite support.

6. The process as claimed in claim 5, wherein M1 metal precursor is Iron (III) nitrate nonahydrate and M2 metal precursor is hydrogen tetrachloroaurate (III) trihydrate, and wherein the modifier is ammonium chloride.

7. A process for the preparation of value-added products, comprising: reacting a hydrocarbon in the presence of oxidizing agent, optionally CO, and the heterogeneous catalyst as claimed in claim 1, at one or more specific reaction conditions to obtain the value added products.

8. The process as claimed in claim 7, wherein the one or more specific reaction conditions is / are selected from: i) a pressure is of 1 atm or 10 to 30 bar, ii) a temperature is at least 25-120 °C, iii) a feed stream in contact with the heterogeneous catalyst system at a weight hourly space velocity of 12000 cm3STP gcal h-1, iv) stirring the reaction mixture containing substrate, catalyst and oxidant at 900-1100 rpm, v) the H2O2 molarity of aqueous solution in a batch process is in the range of 0.1-5M, and / orvi) the molar ratio of H2O2solution to substrate in the continuous flow feed stream is in the range of 1:1 to 1:

10.

9. The process as claimed in claim 7, wherein the hydrocarbon is selected from methane, ethane, propane and butane; wherein the process is done in a batch mode or continuous flow mode; and wherein the oxidizing agent is H2O2solution or in- situ generated H2O2.

10. The process as claimed in claim 7, wherein the value-added products are selected from methanol, ethanol, and formic acid with 90% selectivity; wherein the value- added products are selected from carboxylic acids, esters and aldehydes when the process is conducted in the presence of CO, wherein the carboxylic acid is selected from acetic acid and ethanoic acid.

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