A scalable microwave-assisted continuous flow method for synthesis of platinum on carbon catalyst and a system thereof

Abstract

A SCALABLE MICROWAVE-ASSISTED CONTINUOUS FLOW METHOD FOR SYNTHESIS OF PLATINUM ON CARBON CATALYST AND A SYSTEM THEREOF The present invention relates to a microwave-assisted continuous flow process for synthesis of platinum on carbon catalyst with shorter residence times and providing a high throughput. Further, the present invention relates to a microwave-assisted continuous flow system comprising two or more continuous stirred tank reactors (2 and 3) connected in series and placed in a microwave oven (6) for synthesizing platinum on carbon (Pt / C). Ref. Figure 1

Description

[0001] PT / 2025 / 16001

[0002] A SCALABLE MICROWAVE-ASSISTED CONTINUOUS FLOW METHOD FOR SYNTHESIS OF PLATINUM ON CARBON CATALYST AND A SYSTEM THEREOF

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] The present invention relates to a process for synthesis of platinum on carbon (Pt / C) catalyst and a system thereof. Particularly, the present invention discloses a micro wave-assisted continuous flow process employing continuous-flow microwave reactors for synthesizing Pt / C in shorter reaction times (a few minutes) with high throughput.

[0005] BACKGROUND OF THE INVENTION

[0006] Platinum supported on carbon (Pt / C) has emerged as a fundamental component in a multitude of industrial processes and scientific investigations, owing to its exceptional catalytic activity, stability, and adaptability. Its pivotal role in green and sustainable energy generation, particularly in proton exchange membrane (PEM) fuel cells and electrolysers, underscores its significance in advancing clean energy technologies. Pt / C functions as a catalyst at the cathode electrode and expedites the oxygen reduction reaction (ORR), thereby enhancing fuel cell efficiency, crucial for enhancing their performance and viability in various applications.

[0007] Pt / C catalysts exhibit remarkable electrochemical corrosion resistance, however, practical application reveals a decline in electrochemical activity over time in fuel cell operations, thereby compromising durability and increasing operational costs. This diminishment in activity is attributed to the corrosion of carbon support in an alkaline environment, Pt metal dissolution, and particle enlargement via the Ostwald ripening mechanism. Functionalizing the carbon support proves effective in enhancing the durability of the catalyst employed in PEM fuel cells.

[0008] Platinum on carbon catalyst is conventionally synthesized in batch reactors and require several hours for the complete conversion of the metal precursor.

[0009] Typically, Pt / C is synthesized using the wet chemical polyol method, which facilitates large- scale production. Chloroplatinic acid serves as the metal precursor, while various types of carbon, including acetylene black, Ketjen black, Black Pearl, Vulcan XC-72, Denka black, and Shawinigan black, are utilized as supports. Polyols such as ethylene glycol, water, ethanol, and PT / 2025 / 16001 methanol function as solvents and reducing agents. However, the polyol method requires reaction temperatures > 120 °C for the synthesis of Pt / C.

[0010] Micro wave heating is a commonly employed method for nanoparticle synthesis, offering several advantages. This includes a notable reduction in reaction time facilitated by the dielectric heating mechanism, which results in a rapid and efficient energy transfer to the reaction mixture. The uniform heating characteristic of microwaves promotes the formation of nanoparticles with monodisperse particle sizes. Moreover, this method is scalable and contributes to reduced energy consumption, as energy is directly absorbed by the precursor molecules rather than being transferred from the surrounding environment.

[0011] Sharma et al. reported the efficacy of pretreating carbon support with micro wave irradiation to facilitate functionalization and subsequent durability enhancement of catalysts. Microwave treatment induces the creation of functional groups and defects on the carbon surface, thereby augmenting nucleation sites.

[0012] Conventional processes for synthesizing Pt / C catalysts yield low quantities, are timeconsuming, and exhibit batch-to-batch variations. In contrast, the microwave method has the potential to produce Pt / C in a short reaction time with higher throughput. However, a significant drawback of batch microwave-assisted synthesis is the challenge of scaling up due to the limited penetration depth of microwave irradiation. This constraint affects the energy efficiency of the microwave process and may lead to a wide particle size distribution and variations in product yield due to large temperature gradients within the reaction volume. The limited penetration depth of microwaves thus inhibits the scalability of batch reactors.

[0013] The current synthesis of Pt / C using batch reactors is insufficient to meet the growing demand for various applications such as fuel cells. This limitation can be addressed by utilizing a continuous flow reactor, which offers enhanced mass and heat transfer. Continuous flow reactors hold the potential to overcome the limitations associated with microwave batch reactors. These systems enable real-time analysis and control of reaction conditions, thereby improving the repeatability and precision of the synthesis process. Continuous flow reactors provide high throughput and yield in the synthesis of both organic and inorganic materials under microwave conditions. To prevent channel congestion caused by the continuous deposition of nanomaterials on the reactor walls, it is essential to maintain a superficial velocity that exceeds the particle sedimentation velocity. PT / 2025 / 16001

[0014] Micro wave heating reduces reaction time significantly due to the influence of ‘microwave dielectric’ heating. Employing a tubular reactor in a microwave oven for continuous flow synthesis can result in carbon deposition on the reactor's surface and flushing of the reaction mixture due to superheating, leading to unsteady state operation, uneven platinum deposition on the carbon support, and heterogeneity in particle size.

[0015] CN116314873A discloses a horizontally positioned polytetrafluoroethylene (PTFE)- constructed spiral reactor employed within a microwave apparatus. Sodium hydroxide (NaOH) was utilized to modulate the pH level within the reaction mixture, maintaining it within the range of 9 to 13. Various mechanical components were integrated into the experimental setup, including a speed-regulated screw pump, a pressure regulating valve, and a magnetic filter designed to eliminate the magnetic material brought in after passing through the screw pump. The use of a PTFE spiral reactor raises concerns regarding the potential for sparking within the microwave oven attributable to material deposition on the reactor's surface.

[0016] KR102580903B1 discloses synthesizing platinum nanomaterials with particle sizes ranging from 2 to 5 nanometers using a batch processing mode.

[0017] The publication titled ‘Batch synthesis of high activity and durability carbon-supported platinum catalysts for oxygen reduction reaction using a new facile continuous microwave pipeline technology’ by Cheng et al. (Colloids and Surfaces A: Physicochemical and Engineering Aspects 687(2024)133548) disclosed a microwave-assisted synthesis of Pt / C catalyst using pipeline technology for methanol oxidation reaction. In this process, the pH of the solution was maintained by NaOH solutions. The total residence time of the process was 20 minutes, utilizing a reactor volume of 1 E within the microwave oven. The average particle size of the synthesized Pt / C catalyst ranged from 2.9 to 3.6 nm. Higher residence time (20 min) may result in material deposition on the reactor surface, potentially causing sparking within the oven, which poses safety concerns. Moreover, the steady-state operation of the process was not addressed, limiting the evaluation of its potential.

[0018] Therefore, there is an unmet need in the art to solve the aforementioned limitations or disadvantages in terms of batch process, higher reactions time (4 hours or more), poor scalability, sparking in the reactor, deposition of reactants / products formed onto wall of the reactors making yield and reactivity lesser and settling of reactants / products as slurry rendering wastage. PT / 2025 / 16001

[0019] OBJECTS OF THE INVENTION

[0020] The object of the present invention is to provide a scalable manufacturing process for platinum on carbon (Pt / C) support, where the process is continuous.

[0021] Another object of the present invention is to provide a scalable continuous process of synthesizing platinum on carbon, where the process provides a uniform deposition of platinum on the carbon support with an average particle size in a range from 2 nm to 3 nm.

[0022] Another object of the present invention is to provide a micro wave-assisted continuous flow system for synthesizing Pt / C catalysts.

[0023] SUMMARY OF THE INVENTION

[0024] In an aspect, the present invention relates to a microwave-assisted continuous flow process for the synthesis of platinum on carbon (Pt / C) catalyst. The process comprises a. preparing a mixture comprising a solvent- 1 selected from ethylene glycol, dimethyl sulfoxide, dimethyl formamide, or polyalcohols, and a solvent-2 selected from tap water or demineralized water, b. preparing a carbon mixture by mixing a carbon support and 50 % to 70% of the solvent mixture of step (a), c. preparing a solution of platinum metal precursor in the remaining 30% to 50% of the solvent mixture of step (a), d. adding the platinum metal precursor solution of step (c) into the carbon mixture of step (b) to obtain a reaction mixture, e. continuously feeding the reaction mixture of step (d) into two or more continuously stirring tank reactors (CSTRs) connected in series and placed inside a microwave oven, f. applying a microwave power in a range of 150W to 750W to the microwave oven to heat the CSTR’s at a temperature in a range from 100°C to 180°C.

[0025] In another aspect, the present invention relates to a microwave-assisted continuous flow system for synthesis of Pt / C catalyst. The system comprises, a microwave oven (6) containing two or more continuously stirred tank reactors (CSTR’s) (2 and 3) arranged inside the microwave oven (6), each CSTR (2 and 3) having an inlet and outlet, PT / 2025 / 16001 the inlet of CSTR (2) is connected to a peristaltic pump (1) for feeding a reaction mixture comprising the carbon mixture and platinum metal precursor solution into the CSTR (2), the outlet of CSTR (2) is connected with the inlet of CSTR (3) by means of a peristaltic pump (4) such that the CSTR’s (2 and 3) are connected in a series, and the outlet of CSTR (3) is connected to a peristaltic pump (5) facilitating removal of the product in a collector (9).

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 illustrates a micro wave-assisted continuous flow system comprising two continuous stirred tank reactors as per an embodiment of the present invention.

[0028] Figure 2 illustrates the real-time temperature progression of the reaction mixture at various applied microwave powers.

[0029] Figure 3 illustrates the effect of microwave power on the percent conversion and reaction time of platinum on carbon catalyst synthesis.

[0030] Figure 4 illustrates the HRTEM images and corresponding particle size distribution of platinum on carbon catalyst synthesized using two-CSTR in series.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

[0033] In an aspect, the present invention relates to a microwave-assisted continuous flow process for synthesis of platinum on carbon (Pt / C) catalyst, the process comprising, a. preparing a mixture comprising a solvent- 1 selected from ethylene glycol, dimethyl sulfoxide, dimethyl formamide, or polyalcohols, and a solvent-2 selected from tap water or demineralized water, b. preparing a carbon mixture by mixing a carbon support and 50 % to 70% of the solvent mixture of step (a), c. preparing a solution of platinum metal precursor in the remaining 30% to 50% of the solvent mixture of step (a), PT / 2025 / 16001 d. adding the platinum metal precursor solution of step (c) into the carbon mixture of step (b) to obtain a reaction mixture, e. continuously feeding the reaction mixture of step (d) into two or more continuously stirring tank reactors (CSTRs) connected in series and placed inside a microwave oven, f. applying a microwave power in a range of 150W to 750W to the microwave oven to heat the CSTR’s at a temperature in a range from 100°C to 180°C.

[0034] The ‘polyalcohols’ refer to polyol compounds other than ethylene glycol such as but not limited to propylene glycol, glycerol, and diethylene glycol. The solvent mixture in step (a) comprises solvent -1 and solvent-2 in a volume ratio ranging from 1: 1 to 3:3. Preferably, the solvent mixture comprises ethylene glycol and water in a ratio ranging from 1: 1 to 3:3.

[0035] The carbon support in step (b) is conductive carbon black, which is commercially available under the tradenames Vulcan carbon XC-72, Ketjen Black EC600JD and Ketjen Black EC300J. Preferably, the carbon support is Vulcan carbon XC-72.

[0036] In an embodiment, the carbon mixture in step (b) is prepared by mixing 1 ml of solvent mixture for each 1 mg of the carbon support.

[0037] In another embodiment, the process further comprises a step of ultrasonication of the carbon mixture prepared in step (b) for a duration ranging from 30 to 40 minutes. Ultrasonication provides uniform dispersion of the carbon support in the carbon mixture. In another embodiment, ultrasonication of the carbon mixture of step (b) is performed at room temperature.

[0038] The solution of step (c) comprises platinum metal precursor in a concentration in a range from 0.003 M to 0.015 and the platinum metal precursor is selected from chloroplatinic acid, ammonium chloroplatinate, or platinum acetylacetonate. Preferably, the solution of step (c) comprises platinum metal precursor in a concentration of 0.00408 M and the platinum metal precursor is chloroplatinic acid.

[0039] In an embodiment, in step (d) the platinum metal precursor solution is added dropwise to the carbon mixture with continuous stirring to form the reaction mixture. Preferably, the dropwise addition is carried out using a burette. Stirring is carried out at a speed in a range from 700 revolutions per minute (RPM) for 1 hour. PT / 2025 / 16001

[0040] In another embodiment, in step (d), the addition of the platinum metal precursor solution to the carbon mixture is carried out at 20°C to 80°C.

[0041] In step (e), the reaction mixture of step (d) is fed to the CSTR’s at a flow rate in a range from 8ml / min to 25 ml / min.

[0042] In an embodiment of step (e), the reaction mixture is passed through CSTR’s placed inside a microwave at a temperature in a range from 100°C to 120°C for a residence time of 2 to 6 minutes to continuously obtain the Pt / C catalyst. The residence time is understood to refer to the reaction time.

[0043] The process results in reduction of the platinum metal precursor in the solvent mixture and subsequent heterogenous nucleation on the carbon support. The process of the present invention provides Pt / C catalyst having uniform particle size with average particle size (particle diameter) in a range from 2 nm to 3 nm, preferably the particle size is in the range from 2.2 nm to 3 nm. Preferably, the catalyst particles are spherical in shape.

[0044] The process is an advancement over the traditional batch process by providing a continuous process for Pt / C catalyst synthesis using a series of CSTR’s in a reliable and reproducible manner. Further, the process is scalable and provides 100% conversion of metal precursor within a short residence time of 2 to 6 minutes with uniform deposition of platinum on the carbon support under steady-state operation. The short residence time boosts throughput and reduces operational costs. Additionally, the short residence time results in a reduced consumption of energy making the process sustainable and cost-effective. Furthermore, the process prevents deposition or settling on the reactor walls and thereby prevents clogging of the reactor which are common issues in traditional batch or poorly controlled flow systems. The process of present invention, unlike known processes, eliminates the need for initial addition of sodium hydroxide (NaOH) followed by addition of nitric acid (HNO3) to quench the reaction.

[0045] In another aspect, the present invention relates to a microwave-assisted continuous flow system for synthesis of platinum on carbon (Pt / C) catalyst, the system comprising, a microwave oven (6) containing two or more continuously stirred tank reactors (CSTR’s) (2 and 3) arranged inside the micro wave oven (6), PT / 2025 / 16001 each CSTR (2 and 3) having an inlet and outlet, the inlet of CSTR (2) is connected to a peristaltic pump (1) for feeding a reaction mixture comprising the carbon mixture and platinum metal precursor solution into the CSTR (2), the outlet of CSTR (2) is connected with the inlet of CSTR (3) by means of a peristaltic pump (4) such that the CSTR’s (2 and 3) are connected in a series, and the outlet of CSTR (3) is connected to a peristaltic pump (5) facilitating removal of the product in a collector (9).

[0046] The CSTR’s (2 and 3) are jacket-less and each CSTR (2 and 3) is coupled with a reflux condenser (7 and 8). The system comprises up to four CSTR’s connected in series.

[0047] The microwave oven (6) has a power in a range from 150 to 750 W. Preferably, the microwave oven (6) is equipped with two magnetrons.

[0048] A microwave-assisted continuous flow system with two CSTR’s is illustrated in Figure 1.

[0049] The system of the present invention provides a continuous, safe and scalable synthesis of Pt / C catalyst suitable for industrial applications.

[0050] EXAMPLES

[0051] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0052] Procurement Details: Chloroplatinic acid was purchased from Hindustan Platinum Ltd. (India) and other chemicals were purchased from Merck GmBh and used without any further purification.

[0053] Comparative Example 1: Batch synthesis (45 mg Pt / C)

[0054] For the synthesis of Pt / C with 60% loading, a mixture comprising 20 mg of Vulcan carbon (VC) and 28 ml of ethylene glycol / DI water (3:2 v / v) was ultrasonicated for 30 min at a temperature of 27-50 °C to achieve a homogeneous dispersion of VC. Subsequently, a chemisorption process was initiated by dropwise addition of 13.73 mM of chloroplatinic acid (12 ml) into the VC solution, with stirring maintained at 700 rpm for 1 hour. The reaction mixture was transferred into a micro wave oven (Ragatech Pvt. Ltd., Pune, India), equipped PT / 2025 / 16001 with two magnetrons operating at 2.45 GHz, employing varying output powers (150 to 750 W). A condenser was attached to the round bottom flask containing the reaction mixture for reflux. Teflon tubing was inserted into the flask to extract a small amount of the sample at different time intervals to monitor the reaction progress. The real-time temperature of the reaction mixture at different microwave power was monitored by an infrared (IR) sensor within the microwave oven, as shown in Figure 2. The heating rate exhibits a substantial escalation, rising from 6.5 to 97.5 as the microwave (MW) power is increased from 150 to 750 W, as depicted in Figure 2. This increased heating rate results in a reduction in reaction time significantly, achieving over 90% conversion of the Pt precursor, as illustrated in Figure 3. The set temperature was rapidly reached within a minute at higher MW power, triggering the cessation of microwave irradiation by the PID (proportional-integral-derivative) controller. Consequently, a lower conversion was achieved at higher microwave power. The augmented heating rate facilitates accelerated nucleation and growth rates, promoting the formation of smaller-sized Pt particles.

[0055] Comparative Example 2: Large-scale synthesis (1000 mg Pt / C)

[0056] For the gram- scale synthesis of the Pt / C catalyst, the reaction volume was increased by a factor of 15. Subsequently, a reaction was conducted in a 1 -liter round bottom flask. The synthesis involved a 40 wt.% platinum on carbon reaction. Initially, a homogeneous dispersion of 600 mg of Vulcan carbon in 420 ml of ethylene glycol / DI water (3:2 v / v) was attained via ultrasonicated for 30 minutes at temperature of 27-50°C. Subsequently, a chemisorption process was performed by dropwise addition of 13.73 mM chloroplatinic acid (180 ml) into the VC solution while stirring at 700 rpm for 1 hour. The optimization of the heating rate at an expanded scale was conducted by subjecting a mixture of ethylene glycol and water (3:2 v / v) to varying microwave power. Consequently, the reaction was performed at 750 W. HRTEM images confirm the average particle size of 2.342 ± 0.036 nm (Figure 4).

[0057] Comparative Example 3: Continuous flow synthesis using a tubular reactor

[0058] The experimental setup involved utilizing a 1 / 8 inch tubular reactor with a 32 ml volume placed inside the microwave oven operating at 1200 W. The reaction mixture comprised a stoichiometry of ethylene glycol (EG) to water in a ratio of 3:2, with a concentration of chloroplatinic acid at 0.0048 M, and Pt ion to Vulcan Carbon weight ratio of 1.498, the temperature ranged from 100 to 120 °C and microwave power varied from 150 to 750 W. The PT / 2025 / 16001 total residence time was maintained at 4 minutes. Initially, carbon was dispersed into the solvent using sonication followed by stirring to ensure uniform dispersion. The atomic absorbance spectroscopy (AAS) analysis confirms that 70% conversion of metal precursors. However, lesser conversion was attributed to the flushing of the reaction caused by localized temperature increases. Nevertheless, carbon particles adhere to the reactor surface, resulting in sparking within the oven.

[0059] Comparative Example 4: Two-phase flow

[0060] A single-phase flow resulted in carbon deposition on the reactor surface while employing a two-phase flow configuration mitigated this issue. Thus, experiments were conducted utilizing air as a dispersed phase. The stoichiometry of the reaction mixture remained unchanged, with the sole modification being the introduction of air to facilitate air-water slug formation. The air injection was felicitated by a peristaltic pump operating at a flow rate equivalent to 50-60% of the total flow rate. Sparking occurred at the reactor inlet, where the lower temperature facilitates carbon deposition on the reactor surface. Additionally, backflow phenomena were observed, inducing reverse flow within the air tubing, thereby impeding slug generation.

[0061] Comparative Example 5: Single CSTR

[0062] A two-neck 50 ml continuous stirred tank reactor (CSTR) equipped with a reflux condenser was employed for the experiment. The inlet stoichiometry of reactants was kept the same as illustrated in Example-2, while residence time and microwave power were maintained constant at 3 minutes and 525 W, respectively. Notably, no occurrences of sparking or deposition were observed during the experimental procedure. Time-dependent samples were collected to monitor the steady-state operation of the process. AAS analysis confirmed the attainment of a steady state concerning the conversion of the metal precursor after the second residence time (RT) cycle. Remarkably, an approximately 85 % conversion of the metal precursor was achieved within 4 minutes of residence time. The HRTEM image revealed the non-uniform deposition of platinum nanoparticles onto the carbon support, characterized by relatively larger particle sizes averaging 3.2 nm.

[0063] Example 6: Two CSTRs in a series

[0064] Two separate two-necked CSTR (2 and 3), each with a volume of 50 ml and equipped with individual reflux condensers (7 and 8), were configured for the experiments. The inlet PT / 2025 / 16001 stoichiometry of reactants was kept the same as illustrated in Example 2, while total residence time and microwave power were maintained constant at 2, 4, 5, and 6 minutes and 450-750 W, respectively. To facilitate continuous flow between the reactors, a peristaltic pump (4) was positioned between them, while another peristaltic pump (5) was employed at the outlet of the second reactor (3) for outflow, as depicted in Figure 1. AAS analysis confirmed the complete conversion of the metal precursor and steady-state operation of the process. Additionally, the HRTEM image shows the uniform deposition of platinum on a carbon support, characterized by an average particle size of 2.5 nm. The thermogravimetric analysis (TGA) confirms that 40% platinum loading obtained on the carbon support.

[0065] To facilitate the uniform deposition of platinum on the carbon support, chloroplatinic acid was introduced into the second reactor independently. In the first reactor, a solution containing Vulcan carbon solution was introduced, where micro wave treatment enhanced the active sites on the carbon support. Hence, nucleation and growth of platinum nanoparticles occurred within the second reactor. TEM analysis confirms the uneven distribution of platinum nanoparticles on the carbon support, exhibiting an average particle size of 2.3 nm.

[0066] In view of the above, the process and system for synthesis of Pt / C provides complete conversion of metal precursor with shorter residence time. Further the process and system PT / 2025 / 16001 provides a uniform deposition of platinum particles within the desired size range on the carbon support.

[0067] ADVANTAGES OF THE PRESENT INVENTION

[0068] • Continuous flow process • High throughput

[0069] • Shorter reaction time

[0070] • Narrow particle size distribution

[0071] • Easy to operate, since there are no moving parts

[0072] • Controllable particle size

Claims

PT / 2025 / 16001WE CLAIM:

1. A microwave-assisted continuous flow process for synthesis of platinum on carbon (Pt / C) catalyst, the process comprising, a. preparing a mixture comprising a solvent- 1 selected from ethylene glycol, dimethyl sulfoxide, dimethyl formamide, or polyalcohols, and a solvent-2 selected from tap water or demineralized water, b. preparing a carbon mixture by mixing a carbon support and 50 % to 70% of the solvent mixture of step (a), c. preparing a solution of platinum metal precursor in the remaining 30% to 50% of the solvent mixture of step (a), d. adding the platinum metal precursor solution of step (c) into the carbon mixture of step (b) to obtain a reaction mixture, e. continuously feeding the reaction mixture of step (d) into two or more continuously stirring tank reactors (CSTRs) connected in series and placed inside a microwave oven, f. applying a microwave power in a range of 150W to 750W to the microwave oven to heat the C STR’s at a temperature in a range from 100°C to 180°C.

2. The process as claimed in claim 1, wherein the mixture of step (a) comprises solvent 1 and solvent 2 in a volume ratio value ranging from 1: 1 to 3:3 and the polyalcohols are selected from one or more of propylene glycol, glycerol, or diethylene glycol, the carbon support in step (b) is conductive carbon black, the platinum metal precursor in the solution of step (c) is present in a concentration in a range from 0.003 M to 0.015 M and is selected from chloroplatinic acid, ammonium chloroplatinate or platinum acetylacetonate, and the addition of the platinum metal precursor solution to the carbon mixture in step (d) is dropwise.PT / 2025 / 160013. The process as claimed in claim 1 or 2, wherein in step (d) addition of the platinum metal precursor solution to the carbon mixture is carried out at a temperature ranging from 20°C to80°C.

4. The process as claimed in claim 1, wherein the feeding at step (e) of the reaction mixture to the CSTR is at a flow rate in a range from 8ml / min to 25 ml / min.

5. The process as claimed in claim 1, wherein the carbon mixture after preparation in step (b) is ultrasonicated for a duration in a range from 30 to 40 minutes.

6. The process as claimed in claim 1, wherein CSTR’s are heated to a temperature in a range from 100°C to 120°C and the residence time of the reaction mixture in the CSTR’s is in a range from 2 to 6 minutes.

7. The process as claimed in claim 1, wherein the Pt / C catalyst has a particle size of 2 nm to 3 nm.

8. A microwave-assisted continuous flow system for synthesis of platinum on carbon (Pt / C) catalyst, the system comprising, a microwave oven (6) containing two or more continuously stirred tank reactors (CSTR’s) (2 and 3) arranged inside the microwave oven (6), each CSTR (2 and 3) having an inlet and outlet, the inlet of CSTR (2) is connected to a peristaltic pump (1) for feeding a reaction mixture comprising the carbon mixture and platinum metal precursor solution into the CSTR (2), the outlet of CSTR (2) is connected with the inlet of CSTR (3) by means of a peristaltic pump (4) such that the CSTR’s (2 and 3) are connected in a series, and the outlet of CSTR (3) is connected to a peristaltic pump (5) facilitating removal of the product in a collector (9).

9. The system as claimed in claim 8, wherein the two or more CSTR are jacket-less and each CSTR (2 and 3) is coupled with a reflux condenser (7 and 8).PT / 2025 / 1600110. The system as claimed in claim 8, wherein the system comprises up to four CSTR’s and the microwave (6) has a power in a range from 150 to 750 W.

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