WO2024075136A1

WO2024075136A1 - A catalyst for partial oxidation of substrate to value-added products under ambient conditions

Info

Publication number: WO2024075136A1
Application number: PCT/IN2023/050903
Authority: WO
Inventors: Chathakudath Prabhakaran VINOD; Anuradha Vijay JAGTAP; Pawan Kumar; Sharad Gupta
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2022-10-04
Filing date: 2023-10-04
Publication date: 2024-04-11

Abstract

The present invention relates to a modified silica-supported bimetallic catalyst (M₁M₂- mod-SiO₂) for partial oxidation of the substrate(s) to values added products such as alcohols or acids under ambient conditions using H₂O₂ solution or in-situ H₂O₂ as oxidant.

Description

A CATALYST FOR PARTIAL OXIDATION OF SUBSTRATE TO VALUE- ADDED PRODUCTS UNDER AMBIENT CONDITIONS

FIELD OF THE INVENTION

The present invention relates to a catalyst for partial oxidation of substrate to value-added products under ambient conditions. More particularly, the present invention relates to a modified silica- supported bimetallic catalyst (MiMi-mod-SiOi) for partial oxidation of substrates (e.g., alkanes such as methane, ethane, propane etc.) to value-added products under ambient conditions where the value-added products are alcohols (methanol, ethanol, propanol, etc.), and acids (acetic acid, etc.). More particularly, the present invention relates to a catalyst for partial oxidation of substrates to value-added products under ambient conditions using hydrogen peroxide (H2O2) solution or in-situ formed H2O2 using H2 and O2 gases.

BACKGROUND AND PRIOR ART OF THE INVENTION

Methane is the simplest organic molecule in nature, consisting of one carbon atom bonded with four hydrogen atoms. Methanol is only one atom change away, with one of the hydrogen atoms replaced by a hydroxyl (OH) group. Methanol, the initial product of methane oxidation, is a desirable product of conversion because it retains much of the original methane energy in a room temperature transportable, storable liquid that can be used directly as a fuel or converted to other valuable products. Studies in this area are rapidly increasing, with the desire to find a stable, active, and selective catalyst for CH4 conversion into methanol. Several catalysts have been proposed and studied to perform methanol synthesis from CH4 and H2O2.

The current commercial production of H2O2 by 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 presence of the same catalysts employed for its formation. To avoid this problem, a promising strategy could be the utilization of in-situ synthesized H2O2 from H2 and O2 in a subsequent reaction in same vessel (one -pot oxidation reaction), which would contribute to savings of both energy and time by avoiding isolation and purification steps as well as minimize risks involved in transportation of concentrated H2O2. Methanol is feedstock for making many commercially important commodity chemicals like dimethyl ether, acetic acid etc.

Thus, there is still a need to produce methanol, ethanol, acetic acid and other value-added products from cheap hydrocarbon sources with easy and facile methods for the reaction process using intelligent catalyst synthesis.

OBJECTIVES OF THE INVENTION

The main objective of the present invention is to provide a modified silica- supported bimetallic catalyst (MiM2-mod-SiO2) for partial oxidation of substrate to value-added product(s) under ambient conditions.

Another objective of the present invention is to provide a process for the preparation of said modified silica- supported bimetallic catalyst (MiM2-mod-SiO2) for partial oxidation of substrate to value-added product(s) under ambient conditions.

Another objective of the present invention is to provide a process for preparing in-situ H2O2 from H2 and O2 at ambient pressure conditions.

Another objective of the present invention is to provide a process for preparing methanol or ethanol by reacting methane or ethane with H2O2 solution or in-situ H2O2 from H2 and O2 and said catalyst.

Another objective of the present invention is to provide a process for preparing acids by reacting CO with methane and oxidant using the same process above and said catalyst.

Another objective of the present invention is to provide a process for preparing acetic acid by reacting CO with methane produced herein above and said catalyst.

Another objective of the present invention is to demonstrate the scope of the present invention for the production of higher alcohols from higher alkanes using said catalyst.

Another objective of the present invention is to demonstrate the scope of the present invention for the production of higher acids by reacting higher alkanes with CO using the said catalyst using the same processes. SUMMARY OF THE INVENTION

Accordingly, to accomplish the objectives, the present invention provides a modified silica- supported bimetallic catalyst (MiM2-mod-SiO2) for partial oxidation of alkanes to values added products under ambient conditions.

In an aspect, the present invention relates to a catalyst system, comprising: a) a modified silica- support (mod-SiO2), and b) a bimetallic catalysts (M1M2), wherein the modified silica-support comprises silicon dioxide or modified silicon dioxide in the form of hydrophobic S i O 2, wherein the bimetallic catalysts comprise transition metal (Mi) and noble metal (M2), and wherein the bimetallic catalysts are deposited onto said modified silica-support with amount is in the range of 0.1 to 10.0 wt. % of the total weight of the catalyst system.

In another aspect, the catalyst system disclosed herein is a calcined catalyst system with amorphous in nature.

In another aspect, the catalyst system has a surface area in the range of about 400 m² g ¹ to about 600 m² g^-1.

In another aspect, the modified silica-support (mod-SiC ) is in an amount in the range of 90 to 99 wt. % based on the total weight of the catalyst system.

In another aspect, the modified silica-support (mod-SiC ) is in an amount in the range of 98 to 99.9 wt. % based on the total weight of the catalyst system.

In another aspect, the transition metal (Mi) is selected from copper, nickel, iron and cobalt.

In another aspect, the noble metal (M2) is selected from palladium, gold, platinum and silver. In another aspect, an average particle size of transition metal (Ml) and noble metal (M2), respectively, is in range of 1 to 10 nm.

In a preferred aspect, the present invention provides a modified silica-supported bimetallic catalyst (MiM2-mod-SiO2) for the synthesis of value-added products, wherein the supported catalyst comprises modified silicon oxide in the form of hydrophobic SiCh, one transition metal (Mi) selected from Cu, Ni, Fe, or Co and one noble metal (M2) selected from Pd, Au, Pt, or Ag, wherein both metals are deposited on a support in the range from 0.1 to 10.0 wt. % of the total weight of the supported catalyst.

In another aspect, the present invention relates to a process of preparation of said catalyst system comprising steps of: a) preparing a modified silica- support (mod-SiO2) by reacting P123 as templating agent with TEOS and PMHS as silica precursors in the presence of 1.6 mol/L of HC1 solution at a temperature in the range of 35-40°C for a time period in the range of 22- 26 h to obtain a reaction mixture, followed by aging the reaction mixture at a temperature in the range of 90-1 KFC for a period of 42-48 h to afford the modified silica-support powder; b) calcining the modified silica-support powder at temperature in the range of 300-400 °C for time period in the range of 8-12 h at 1-5 degree/min ramp rate to obtain calcined modified silica-support; c) fabricating the transition metal (Ml) over the modified silica support of step a) or calcined modified silica support of step b) by dissolving a solution of transition metal precursor in said modified silica support of step a) or calcined modified silica support of step b) in water under controlled pH in the range of 9-10 using base solution to afford transition metal (Ml) loaded onto modified silica support, which after calcination at temperature in the range of 340 to 360 °C for time period of 3.5 to 4.5 h afford calcined Ml metal supported onto modified silica support in powder form (Mi-mod-SiCh); and d) loading noble metal (M2) on the M 1 -mod-SiCh of step c) by treating it with a solution of a noble metal precursor by using a modifier under controlled pH of 9-10 using base solution to afford the MiMi-mod-SiCh catalyst system, which after calcination at temperature in the range of 340 to 360 °C for time period of 3.5 to 4.5 h to obtain the calcined Ml -M2 metals supported onto modified silica support catalyst system in powder form.

In another aspect, the process disclosed herein is carried out in a continuous manner of steps a), b), c) and then finally d), or in an interchangeable manner of steps a), b), d) and then finally b). In another aspect, the transition metal precursor is selected from transition metal nitrate, transition metal sulphate and transition metal chloride.

In another aspect, the noble metal precursor is selected from noble metal nitrate, noble metal sulphate and noble metal chloride.

In another aspect, the base solution comprises 0.1M of NaOH, KOH or ammonia solution.

In another aspect, the modifier is ammonium chloride.

In yet another aspect, the present invention relates to a process of preparation of value added products comprises: reacting a substrate with an oxidizing agent and carbon monoxide as optional additive, in presence of said catalyst system (M i Mi-mod-SiOj) as claimed in claim 1, maintained at one or more reaction conditions; wherein the oxidizing agent is H2O2 solution or in-situ generated H2O2, and wherein said in-situ generated H2O2 is produced in said reaction by using H2 and O2 gases.

In yet another aspect, the process of preparation of value added products is carried out in a gaseous phase in a continuous flow reactor or in a liquid phase in a batch reactor.

In yet another aspect, the one or more reaction conditions in said process of preparation of value added products comprise(s): i) a pressure is in the range of 1-10 atm., ii) a temperature is in range of 40-100°C, iii) a reaction time period in the range of 1-24 hrs, iv) a feed stream in contact with the modified silica-supported catalyst (MiM2-mod- SiCh) is at a weight hourly space velocity in the range of 2000-30000 cm³ STP gcai h’¹, and/or v) a molar ratio of H2O2 to said substrate in the feed stream is in the range of 1 : 1 to 1:10.

In yet another aspect, the value-added products are selected from C1-C10 alcohols and Cl- C10 acids; and wherein the substrate is selected from Cl -CIO alkane or Cl -CIO alcohol. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 represents TEM images of mod-SiOi support (a, b, c), Mi-mod-SiOi supported catalyst (d, e, f).

Fig. 2 represents the TEM images of the MiM2-mod-SiO2 supported catalyst.

Fig. 3 represents the elemental mapping of the MiM2-mod-SiO2 supported catalyst.

Fig. 4 represents the XRD pattern of mod-SiO2 and supported catalysts.

Fig. 5 represents the methanol yield (mrnol/gmetai) obtained during the time on stream of reaction over MiM2-mod-SiO catalyst. Reaction Conditions: Catalyst = 100 mg, Methane flow = 50 mmol/h, H2:O2:N2:CH4 = 1.25:0.25:8.50:20 mL/min , Temperature =80 °C, Pressure = 1 atm.

Fig. 6 represents the NMR data to confirm methanol and acetic acid formation (sample collected from a batch reactor where acetic acid is formed using methane, H2O2 and CO).

Fig. 7 represents the Gas chromatogram of formed methanol and acetic acid (sample collected from a batch reactor where acetic acid is formed using methane, H2O2 and CO).

Fig. 8 represents the catalytic activity of different Mi-mod. silica, M2-mod. silica and M1M2- mod. silica at the reaction temperature of 60°C and total pressure of 20 bar having the composition of 5 bar diluted O2 (25 % O2 + 75 % CO2 or N2)+ 5 bar diluted H2 (5 % H2 + 95 % CO2 or N2) + 10 bar CH₄ (99.99 % pure),

Fig. 9 represents catalytic activity of MiM2-mod.silica catalyst at different pressures [Reaction temperature - 60°C, Total pressure - 10 bar (3 bar diluted O2 (25 % O2 + 75 % CO₂ or N₂)+ + 3 bar diluted H₂ (5 % H₂ + 95 % CO₂ or N₂) + 4 bar CH₄ (99.99 % pure)), 20 bar ( 5 bar diluted O2 + 5 bar diluted H2+ 10 bar CH₄), and 30 bar (7 bar diluted O2 + 7 bar diluted H2 + 14 bar CH₄ ).

Fig. 10 represents the catalytic activity of AuFeHS by varying the reaction pressure in the batch process, confirming the 10 bar as the optimized reaction pressure for effective methane conversion. Reaction conditions: 25 mg of catalyst, time period of 30 min, 5-30 bar of methane, 0.5 mL of H2O2 (30% w/v), and 20 mL H2O, at 60G. Fig. 11 represents the catalytic activity analysis in the batch process of AuFeHS at various temperatures, confirming 60X2 as the optimized temperature. Reaction conditions: 25 mg catalyst, time period of 30 min, 10 bar of methane, 0.5 mb of H2O2 (30 % w/v), and 20 mL H2O, temp, in the range of 30-80X2.

Fig. 12 represents the catalytic activity analysis in the batch process of various catalysts, confirming AuFeHS as the best active catalyst among all tested catalysts. This analysis further confirms that hydrophobicity plays a key role in the effective conversion of methane to methanol. Reaction conditions: 25 mg catalyst, time period of 30 min, 10 bar methane, 0.5 mL H2O2 (30% w/v), and 20 mL H₂O, at 60X2.

Fig. 13 represents the catalytic activity analysis in the batch process of AuFeHS at various temperatures confirming 50 °C as optimized temperature of efficient acetic acid production. Reaction conditions: 50 mg catalyst, time period of 30 min, 20 bar methane, 5 bar CO, 0.5 mL H2O2 (30 % w/v), and 20 mL H2O, temp, in the range of 50-70X2.

Fig. 14 represents the catalytic activity of various catalysts under the batch process for acetic acid production: Reaction conditions: 50 mg catalyst, time period of 30 min, 20 bar methane, 5 bar CO, 0.5 mL H2O2 (30 % w/v), and 20 mL H2O, at 50C.

Fig. 15 represent the catalytic activity of various catalysts in continuous flow reactor: Reaction conditions: 100 mg catalyst, temp, of 80 C, 2 mL/h H2O2 (15 % w/v) flow, and methane flow 20 mL/min, for 4 h.

Fig. 16 represents the catalytic activity of AuFeHS in a continuous flow reactor, confirming the stability of the catalyst. Reaction conditions: 100 mg catalyst, temp, of 80X2, 2 mL/h H2O2 (15% w/v) flow, and methane flow 20 mL/min, for 1-7 h.

Fig. 17 represent the catalytic activity of AuFeHS, at various pressure in the batch reactor: Reaction conditions: 50 mg catalyst (AuFeHS), time period of 30 min, temp, of 60X2, 20 mL H2O, and 10-30 bar (methane+d-H2+d-O2)

Fig. 18 represent the Catalytic activity of various catalysts in batch reactor, Reaction conditions: 50 mg catalyst, time period of 30 min, temp, of 60X2, 20 mL H2O, 10 bar methane, 5 bar d-H2, and 5 bar d-CL Fig. 19 represents the titration plot for quantitative analysis of produced H2O2, confirming the in- situ peroxide production during the reaction.

ACRONYMS USED TO DESCRIBE THE INVENTION

Pl 23 or Pluronic Pl 23 is a symmetric triblock copolymer comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) in an alternating linear fashion, PEO-PPO-PEO.

Tetraethoxysilane (TEOS)

Polymethylhydrosiloxane (PMHS)

Carbon Monoxide (CO)

DETAILED DESCRIPTION OF THE INVENTION

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.

The term “value-added products” provided herein may be defined as oxidized products such as alcohols (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.

The term “substrate” provided herein may be 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.

The term “ambient conditions” or “specific reaction conditions” provided herein may be 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.

The terms “catalyst system”, “modified silica-supported catalyst”, “modified silica- supported bimetallic catalyst”, “supported catalyst(s)” or “calcined supported catalyst(s)” provided and used herein throughout the specification possess or have the same meaning or nearly the same meaning covering the claimed metal catalyst(s) supported onto modified silica. The present invention provides a modified silica-supported bimetallic catalyst (M i N -mod- SiCh) for partial oxidation of substrate to value-added product(s) under ambient conditions.

In an embodiment, the present invention provides a modified silica-supported bimetallic catalyst (MiMi-mod-SiOz) for the synthesis of value-added products, wherein the supported catalyst comprises silicon dioxide or modified silicon dioxide in the form of hydrophobic SiOi. one transition metal (Mi) selected from Cu, Ni, Fe, or Co and one noble metal (M2) selected from Pd, Au, Pt, or Ag, wherein both the metals are deposited on a support in the range from 0.1 to 10.0 wt. % of the total weight of the supported catalyst.

In another embodiment, the metals M1M2 deposited overall onto the silica or modified silica surface may be done by deposition precipitation method.

In a preferred embodiment, the modified silica-supported catalyst (MiMi-mod-SiOi) is a calcined supported catalyst and the organosilica content in the form of -(CH3)_n- ranges from 10 to 60% by weight, preferably from 40 to 50 wt % based on the total weight of the modified supported catalyst.

In another preferred embodiment, the supported catalyst (MiMi-mod-SiCh) is a calcined supported catalyst, wherein the support comprises modified silicon dioxide (SiCh) in an amount of at least 95 wt% and even more preferably at least 99 wt% based on the total weight of the calcined modified supported catalyst.

In another preferred embodiment, the modified silica-supported catalyst (M 1 Mi-inod-SiOz.) comprises at least one noble metal (M2) from 0.1 to 2.0 wt% based on the total weight of the calcined catalyst, more preferably from 0.2 to 1.0 wt %.

In another preferred embodiment, the modified silica-supported catalyst (MiM2-mod-SiO2) comprises at least one transition metal (Mi) from 0.1 to 2.0 wt% based on the total weight of the calcined catalyst, more preferably from 0.2 to 1.0 wt %.

In another preferred embodiment, the supported catalyst (MiM2-mod-SiO2) is a calcined supported catalyst, wherein the support comprises modified silicon dioxide (SiCh) in an amount in the range of 90 to 99 wt. % or 95 to 96 wt. % and even more preferably in the range of 95-98 wt.% based on the total weight of the calcined modified supported catalyst system. In another preferred embodiment, the supported catalyst (MiM -mod-SiCh) is a calcined supported catalyst, wherein the amount of bimetals Mi and M2 together in said catalyst system is in range of 0.1 to 10 wt% or 0.1 to 4 wt. % or 0.1 to 2 wt. %.

The modified silica- supported catalyst (MiMi-mod-SiCh) is calcined and shows an amorphous structure as determined by XRD (as shown in Fig. 4).

The average particle size of the transition metal (Mi) is less than 10 nm, preferably less than 4 nm, more preferably less than 1 nm as determined by HRTEM. (As shown in Fig. 2)

The average particle size of noble metal (M2) is less than 10 nm, as determined by HRTEM, preferably less than 10 nm, more preferably less than 5 nm, and even more preferably less than 2 nm. (as shown in Fig. 2 and 3).

So, in another embodiment, the average particle size of transition metal (Mi) is in range of 1 to 10 nm or 1 to 2 nm or 1 to 4 nm. Also, in another embodiment, the average particle size of noble metal (M2) is in range of 1 to 10 nm or 1 to 2 nm or 1 to 5 nm.

In another preferred embodiment, the modified silica- supported catalyst is a calcined supported catalyst and has preferably a surface area in the range of about 400 m² g ¹ to about 600 m² g^-1 as determined according to N2 sorption method.

In specific embodiment, the support present in said catalyst system is hydrophobically modified silica by an organic group (methyl/methoxy).

Another embodiment of the present invention provides a process for the preparation of the said modified silica-supported bimetallic catalyst, wherein said process comprises the steps: a) preparing modified SiC by reacting Pl 23 with an equal amount of TEOS and PMHS in the presence of 1.6 mol/L HC1 solution at a temperature in the range of 35-40°C for a period in the range of 22-24 h followed by aging the reaction mixture at a temperature in the range of 105-110 °C for a period of 42-48 h to afford modified SiCF; calcined the modified silica-support powder at temperature in the range of 300-400 °C for time period in the range of 8-12 h at 1-5 degree/min ramp rate to obtain calcined modified modified support. b) fabricating the transition metal (Mi) over the modified silica support obtained at step a) by treating the solution of transition metal precursor with modified silica support dissolved in DI water by controlling the pH of the reaction mixture (9-10) with 0.1M NaOH solution to afford loading of transition metal on a modified silica support, after calcination of powder sample at 350 °C catalyst labeled as (Mi-mod- SiO₂). c) loading noble metal (M₂) on the Mi-mod-SiO₂ product obtained at step b) by treating the compound with a solution of the noble metal precursor by using NH4CI as a modifier and controlling pH at 9-10 using 0.1M NaOH to afford the MIM₂- mod-SiO₂ catalyst. After the calcination of the resulting material at 350 °C, the powder sample was used as final catalyst.

In another embodiment, the process of preparation of the modified silica- supported bimetallic catalyst is carried out in a continuous manner [steps a) to b) to c)] or interchangeable fashion [steps a) to c) to b) or steps a) to b) to c)].

Another embodiment of the present invention provides a process for the preparation of unmodified silica, wherein said process comprises using only TEOS as a silica precursor for the synthesis of unmodified SiO₂.

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 a modified silica- supported catalyst (MIM₂- mod-SiO₂) at specific reaction conditions, wherein the in-situ H₂O₂ is produced in said reaction by using H₂ and O₂ gases.

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 H₂O₂ solution or in-situ generated H₂O₂, optionally CO, and said modified silica- supported catalyst (MiM₂-mod-SiO₂) at specific reaction conditions, wherein the in-situ H₂O₂ is produced in said reaction by using H₂ and O₂ gases.

In a specific embodiment, the specific reaction conditions comprise one or more of the: i) a pressure is of 1 atm, ii) a temperature is at least 40- 100°C, iii) a feed stream in contact with the modified silica- supported catalyst (M1M2- mod-SiCh), or silica- supported catalyst (MiNfe-SiCh), or modified silica (mod-SiOi) at a weight hourly space velocity of 12000 cm³ STP g_cai h ¹, iv) the molar ratio of H2O2 to substrate in the feed stream is in the range of 1:1 to 1: 10.

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

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 described above.

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

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 H2O2 keeping at said one or more reaction conditions.

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 modified silica-supported catalyst (MiM2-mod- SiC ) at one or more of said specific reaction conditions, wherein in-situ H2O2 is produced in said reaction by treating H2 and O2 gases.

In preferred embodiment, the present invention provides a process for the preparation of value-added products such as acid, acetic acid, etc. or mixtures thereof, from a substrate such as methane, ethane or propane in the presence of oxidizing agent such as H2O2 solution or in-situ H2O2, CO and said modified silica-supported catalyst (MiM2-mod-SiO2) at one or more of said specific reaction conditions, wherein the in-situ H2O2 is produced in said reaction by treating H2 and O2 gases. In a specific embodiment, the present invention provides that the presence of noble metal, in a transition metal supported modified silica catalyst allows increasing the methanol productivity as compared to a transition metal supported modified silica catalyst that is not noble metal promoted. It is also seen that supported catalyst prepared by modification of silica allows for increasing the methanol productivity compared to non-modified silica supported catalyst. Several experiments have been conducted by using different concentrations of metals.

Table 1 below thus summarises the results obtained with the activity of catalysts having different concentrations of metals Mi and M2.

Table-1

Reaction Condition: Catalyst = 100 mg, Methane flow = 50 mmol/h, H2O2 flow =20 mmol/h, Temperature =80 °C, Pressure = 1 atm, and Time = 3h.

Table-2 and Table-3 below summarize the results obtained using gas flow (methane and nitrogen) and pressure/process, respectively.

Table-2

Table 4 below thus summarises the results obtained with MiM2-Mod-SiO2 for acetic acid formation with in-situ generated H2O2.

Table-4

Reaction Conditions:

Batch reactor process: Catalyst = 50mg, Methane 10 bar, CO = 2 bar, Hydrogen (5 % H2 + 95 % N2 or CO2) = 5 bar, Oxygen (25 % O2 + 75 % N2 or CO2) = 5 bar, Temperature = 60

°C, Time = 0.5 h

Continuous flow process: Catalyst = 100 mg, Methane flow = 20 mL/min, CO = 5 mL/min, Diluted H2 and O2 = 30 mL/min, Temperature =80 °C, Pressure = 1 atm,

Table 5. Catalytic activity of various catalyst in continuous process.

Reaction conditions: 100 mg catalyst, atmospheric pressure (1 atm), methane flow 20 mL/min, H2O2 flow 2 mL/min, 4 h reaction data.

Table 6. Catalytic activity of various catalyst in batch process.

Reaction conditions 25 mg catalyst, 30 min, 10 bar methane, 0.5 mL H2O2 (30% w/v), 20 mL H₂0, 60 C

Table 7. Catalytic activity of various catalyst in continuous process.

Reaction conditions: 100 mg catalyst, atmospheric pressure (1 atm), methane flow

20 mL/min, 4 h reaction data

GENERAL INFORMATION: Product analysis. The gaseous products analysis was performed on a Nucon GC-5760 gas chromatography system equipped with a methanizer unit and flame ionization detector using a carbosieve packed column. The liquid products were quantified by GC analysis on a Nucon 5760 gas chromatography system equipped with a flame ionization detector using a 30 m length DB-624 capillary column. Liquid products were also quantified by solvent- suppressed 1H NMR on a Bruker 400 MHz spectrometer. The measurement was calibrated using an external standard method with a series of methanol solutions with known concentrations. Typically, 0.9 ml liquor after the reaction was mixed with 0.1 ml D2O to prepare a solution for NMR measurement.

EXAMPLES

Tetraethoxysilane (TEOS) was used as a silica precursor, and Polymethylhydro siloxane (PMHS) was used as a modifier organic silica precursor. Non-ionic triblock copolymer P123 was used as a templating agent to generate mesoporosity in silica. All these materials/chemicals are obtained from OMKAR TRADERS, Pune, MH, India.

Example 1: Synthesis of modified SiCh

In synthesis, the required amount of P123 was completely dissolved in 300 mb of a 1.6 M HC1 solution at 40°C. After 3-5 h, an equal amount of TEOS and PMHS were added together to the above solution under vigorous stirring. After 22-26 h of stirring at 40°C, the reaction mixture was allowed to age at 90-110°C for another 42-54 h under static conditions. Then, the white precipitate was recovered by filtration, washed with deionized water, and dried at 80°C. Finally, the template inside the as-synthesized powder material was removed by calcination at 300-400°C for 8-12 h. Only TEOS was used as a silica precursor for the synthesis of unmodified SiOi-

Example 2: Synthesis of i-mod-SiOi catalyst

Fabrication of the transition metal nanoparticles over the modified silica support was performed by deposition precipitation method. Typically, 0.5 g of inod-SiCF support was dispersed in deionized water. Solution of a transition metal precursor of different concentrations (0.01, 0.025, and 0.05 M) was added to the support solution. The pH of the mixture was subsequently controlled by the dropwise addition of a 0.1 M NaOH aqueous solution between 9-10. The solution was stirred for another 1 hr at the same pH. The precipitate was centrifuged, washed with deionized water, and dried at 80°C overnight. The dried powder was calcined in static air at 340-360°C for 3.5-4.5 h. The weight loading of transition metal on modified silica ranges from 0.1 to 2%.

Example 3: Synthesis of MiM -mod-SiOz catalyst

Noble metal was supported over Mi-mod-SiCh by a modified deposition precipitation method. Typically, 0.5 g of M i-mod-SiOi was dispersed in 30 mL water under sonication for 20 min, and an appropriate amount of NH4CI was added as a modifier. Then the pH of the solution was maintained at around 9-10 using 0.1 M NaOH solution. The required amount of noble metal precursor solution of different concentrations was added to the solution dropwise for 20-30 minutes while maintaining the pH. The solution was stirred for another 1 hr at the same pH. The as-synthesized Mi F-mod-SiO? catalyst was obtained after centrifugation and drying in a hot air oven at 80°C. The as -synthesized MiMi-mod- SiC>2 catalyst was calcined in air at 340 -360 °C for 3.5-4.5 h.

Example 4: Process for methanol synthesis in continuous flow reactor using H2O2 as oxidant

Providing a feed stream comprising methane (99.9% pure) and 15 % diluted H2O2 putting in contact with the said catalyst at a reaction temperature of at least 80 °C under a pressure of 1 atm and collecting the methanol from the effluents by an ice-cold condensation process below 10 °C to avoid the loss of volatile products. Catalyst performance was measured in continuous flow cotton plugged quartz reactor. An aqueous feed containing hydrogen peroxide (Thermo-Fischer, typically 15 V/V%) was controlled by a syringe pump and methane flow was controlled by a mass flow controller (Alicat). Both were fed down through the catalyst bed which was composed of layers of pelleted catalyst. The quartz reactor had a total length of 50 cm and an internal diameter of 8 mm. Liquid and gaseous products were separated in a coiled gas condenser and collected periodically for analysis over a time period.

Example 5: Process for methanol synthesis in a batch reactor using H2O2 solution as oxidant-

The partial oxidation of methane was performed in a stainless-steel autoclave with a total volume of 50 mL. The catalyst (25 mg) was dispersed in 20 mL of 0.50 M H2O2 aqueous solutions. The charged autoclave was sealed and purging for three times with CH4 gas at 5 bar pressure. It was then pressurized to the desired pressure (typically 10 bar) with CH4 gas. The solution was heated to desired reaction temperature (typically 60 °C), and a thermocouple was used to measure the temperature. Once the temperature reached the set value, the solution was vigorously stirred at ca. 950 rpm for a certain time (typically 30 min). After the reaction, the autoclave was cooled to below 10 °C in an ice -water mixture in order to minimize the loss of volatile products. The gaseous products of the reaction were collected in a gas bag when the temperature was below 10 °C.

Example 6: Process for methanol synthesis in continuous flow reactor using in-situ generated H2O2 as oxidant

Methane (CH4) cylinder (99.99 %), O2 cylinder in which 25% O2 diluted with CO2 or N2 and H2 Cylinder in which 5% H2 diluted with CO2 or N2 was used.

Providing a feed stream comprising methane (99.99% pure) with H2 and O2 gases, the feed stream is in contact with the catalyst at a reaction temperature of 80 °C (or in the range of 40-100 deg C) and under a pressure of 1 atm and collecting the methanol from the effluents by an ice-cold condensation process below 10 °C to avoid the loss of volatile products. Catalyst performance was measured in continuous flow cotton plugged quartz reactor. A feed containing water only was controlled by a syringe pump and methane flow was controlled by a mass flow controller (Alicat). Both were fed down through the catalyst bed which was composed of layers of pelleted catalyst. The quartz reactor had a total length of 50 cm and an internal diameter of 8 mm. Liquid and gaseous products were separated in a coiled gas condenser and collected periodically for analysis.

Example 7: Process for methanol synthesis in a batch reactor using in-situ generated H2O2.

Direct oxidation of CH4 with H2 and O2 gases with all catalysts was evaluated in a 50 mL stainless-steel fixed bed reactor. 50 mg of catalyst was dispersed in 20 mL of millipore water. Then the autoclave was sealed and purged three times with diluted O2 gas. It was then pressurized to the desired pressure (20 bar) of feed gas with CL/f /CChor N2/CH4 with a ratio of 1.25/0.25/8.5/10 used for the reaction. To achieve this ratio, the reactor was pressurized using 5 bar pressure from the cylinder of diluted O2 in which 25% O2 and the remaining 75% balanced with CO2 or N2, 5 bar H2 gas from the cylinder, which contains 5% H2 and 95% CO2 or N2 and 10 bar of methane cylinder (99.99 % pure). The solution was heated to desired reaction temperature (60°C). Once the temperature reached the set value, the solution was vigorously stirred at 950 rpm. The reaction was carried out for 30 min at 60 °C, and ice-cold water was constantly circulated during the reaction. The gas sample was collected in a gas bag after cooling the products. Liquid samples were collected after centrifugation and analyzed by gas chromatography.

Example 8: Process for acetic acid synthesis in a continuous flow reactor from methane, H2O2 and CO.

Catalyst performance was measured in continuous flow cotton plugged quartz reactor. Providing a feed stream comprising methane (99.99 % pure), carbon monoxide (99.99 % pure) and diluted H2O2 as feed stream putting in contact with the catalyst at a reaction temperature in the range of 40-100 °C and under a pressure of 1 atm and recovering the methanol from the effluents by an ice-cold condensation process below 10°C. An aqueous feed containing hydrogen peroxide was controlled by a syringe pump, and methane and carbon monoxide flow was controlled by a mass flow controller (Alicat). Both were fed down through the catalyst bed which was composed of layers of pelleted catalyst. Liquid and gaseous products were separated in a coiled gas condenser and collected periodically for analysis.

Example 9: Process for acetic acid synthesis in a batch reactor from methane, H2O2 and CO

The reaction was tested in a high-pressure Amar reactor using methane (99.99% pure), carbon monoxide (99.99% pure) and 30% hydrogen peroxide as feed. Initially, a fixed amount of catalyst was dispersed in 20 mL of water in the autoclave and 50 uL of H2O2 was added to the solution. The autoclave was sealed and the reactor was flushed out with CO to remove the air content followed by 5 bar of CO filling in the reactor; after that, 15 bar of methane was introduced to the reactor achieving a total pressure of 20 bar. Then the reaction was carried out at 50 °C for Ih. After cooling the reaction mixture below 10 °C, the liquid and gaseous samples were collected for analysis. The liquid and gaseous products were analyzed using gas chromatography with FID as a detector (Fig. 7). The product confirmation was also done using the NMR technique (Fig. 6).

Example 10: Process for acetic acid synthesis in continuous flow reactor using methane, CO and in-situ generated H2O2 as oxidant

Methane (CH4) cylinder (99.99 % pure), Carbon monoxide (CO) cylinder (99.99 %), O2 cylinder in which 25% O2 was diluted with N2 or CO2 and H2 Cylinder in which 5% H2 diluted with N2 or CO2 was used. Providing a feed stream comprising methane (99.9% pure), CO with H2 and O2 gases, the feed stream is in contact with the catalyst at a reaction temperature of in the range of 40- 100 °C and under a pressure of 1 atm and collecting the products from the effluents by an ice-cold condensation process below 10 °C to avoid the loss of volatile products. Catalyst performance was measured in continuous flow cotton plugged quartz reactor. Water flow was controlled by a syringe pump and gas flow was controlled by a mass flow controller (Alicat). Both were fed down through the catalyst bed which was composed of layers of pelleted catalyst. The quartz reactor had a total length of 50 cm and an internal diameter of 8 mm. Liquid and gaseous products were separated in a coiled gas condenser and collected periodically for analysis.

ADVANTAGES OF THE INVENTION

• Highest yield of methanol from partial oxidation of methane using H2O2 as an oxidizing agent in continuous flow and atmospheric pressure conditions is provided

• Partial oxidation of methane to methanol using H2O2 as an oxidant at atmospheric pressure conditions and in continuous mode is not reported so far

• Catalyst with novel composition for the partial oxidation of methane using H2O2 as an oxidizing agent in continuous flow and atmospheric pressure conditions is provided

• Active catalyst composition contains only less than 1% of metal content

• More than 90% selectivity for methanol at atmospheric pressure conditions with H2O as a side product

• Catalyst with novel composition for the production of acetic acid from methane, H2O2 and CO in batch and continuous reactor

• Onsite production of H2O2 from H2 and O2 on the same catalyst

• Onsite production and utilization of the produced H2O2 for methane to methanol formation.

• Production of acetic acid using CO, methane and in-situ generated H2O2

Claims

We Claim:

1. A catalyst system, comprising: a) a modified silica- support (mod-SiO2), and b) a bimetallic catalysts (M1M2), wherein the modified silica-support comprises silicon dioxide or modified silicon dioxide in the form of hydrophobic SiC , wherein the bimetallic catalysts comprise a transition metal (Mi) and a noble metal (M2), and wherein the bimetallic catalysts are deposited onto said modified silica-support with amount in the range of 0.1 to 10.0 wt. % of the total weight of the catalyst system.

2. The catalyst system as claimed in claim 1, wherein the catalyst system is calcined catalyst system having amorphous nature; and wherein the catalyst system has a surface area in the range of about 400 m² g ¹ to about 600 m² g ¹.

3. The catalyst system as claimed in claim 1 or 2, wherein the modified silica-support (mod- SiCh) is in an amount in the range of 90 to 99 wt. % based on the total weight of the catalyst system.

4. The catalyst system as claimed in claim 1, wherein the transition metal (Mi) is selected from copper, nickel, iron and cobalt.

5. The catalyst system as claimed in claim 1, wherein the noble metal (M2) is selected from palladium, gold, platinum and silver.

6. The catalyst system as claimed in claim 1, wherein an average particle size of transition metal (Mi) and noble metal (M2) is in range of 1 to 10 nm.

7. A process of preparation of catalyst system as claimed in claim 1, the process comprising steps of: a) preparing a modified silica-support (mod-SiO2) by reacting P123 as templating agent with tetraethoxysilane (TEOS) and polymethylhydrosiloxane (PMHS) as silica precursors in the presence of HC1 solution at a temperature in the range of 35-40 °C for a time period in the range of 22-26 h to obtain a reaction mixture, followed by aging the reaction mixture at a temperature in the range of 90-110 °C for a period of 42-48 h to afford the modified silica-support powder; b) calcining the modified silica-support powder of step a) at a temperature in the range of 300-400 °C for a time period in the range of 8-12 h at 1-5 degree/min ramp rate to obtain a calcined modified silica-support; c) fabricating a transition metal (Mi) over the modified silica support of step a) or calcined modified silica support of step b) by dissolving a solution of transition metal precursor in said modified silica support of step a) or calcined modified silica support of step b) in water under pH in the range of 9-10 using a base solution to afford a transition metal (Mi) loaded onto modified silica support, which after calcination at a temperature in the range of 340 to 360 °C for a time period of 3.5 to 4.5 h afford a calcined Mi metal supported onto modified silica support in powder form (Mi-mod-SiCh); and d) loading a noble metal (M2) on the Mi-mod-SiC of step c) by treating it with a solution of a noble metal precursor by using a modifier under pH of 9-10 using a base solution to afford a MiM2-mod-SiO2 catalyst system, which after calcination at a temperature in the range of 340 to 360 °C for a time period of 3.5 to 4.5 h provide a calcined M1-M2 metals supported onto modified silica support catalyst system in powder form.

8. The process as claimed in claim 7, wherein the process is carried out in a continuous manner of steps a), b), c) and then finally d), or in an interchangeable manner of steps a), b), d) and then finally b).

9. The process as claimed in claim 7, wherein the transition metal precursor is selected from the group consisting of transition metal nitrate, transition metal sulphate and transition metal chloride.

10. The process as claimed in claim 7, wherein the noble metal precursor is selected from the group consisting of noble metal nitrate, noble metal sulphate and noble metal chloride.

11. The process as claimed in claim 7, wherein the base solution comprises 0.1M NaOH, KOH or ammonia solution.

12. The process as claimed in claim 7, wherein the modifier is ammonium chloride.

13. A process of preparation of a value added product comprises reacting a substrate with an oxidizing agent and carbon monoxide as optional additive, in the presence of catalyst system (MiMi-mod-SiOi) as claimed in claim 1, maintained at one or more reaction conditions; wherein the oxidizing agent is H2O2 solution or in- situ generated H2O2, and wherein said in-situ generated H2O2 is produced in said reaction by using H2 and O2 gases.

14. The process as claimed in claim 13, wherein the process is carried out in a gaseous phase in a continuous flow reactor or in a liquid phase in a batch reactor.

15. The process as claimed in claim 13, wherein said one or more reaction conditions comprise(s): i) a pressure is in the range of 1-10 atm., ii) a temperature is in range of 40-100 °C, iii) a reaction time period in the range of 1-24 h, iv) a feed stream in contact with the modified silica-supported catalyst (MiM2-mod- SiC ) is at a weight hourly space velocity in the range of 2000-30000 cm³ STP g_cai h ¹, and/or v) a molar ratio of H2O2 to said substrate in the feed stream is in the range of 1:1 to 1:10.

16. The process as claimed in claim 13, wherein the value-added product is selected from C1-C10 alcohol or C1-C10 acid.

17. The process as claimed in claim 13, wherein the substrate is selected from C1-C10 alkane or Cl -CIO alcohol.