Amine functionalized silica catalyst for preparation of organic carbonate and other applications thereof

Abstract

The present invention relates to mesoporous amine-functionalized silica catalysts with worm-hole or channel-like morphology, prepared using 3-aminopropyl trimethoxysilane (3- APTMS) or 3-aminopropyltriethoxysilane (APTES). The catalysts exhibit average pore diameters of 1-100 nm and specific surface areas of 100-1,000 m2 / g. The preparation process involves mixing Pluronic P123 with hydrochloric acid at 30-40°C, followed by addition of a mixture of 3-APTMS or 3-APTES with tetraethyl orthosilicate (TEOS), and subsequent hydrothermal treatment. The choice of precursor determines morphology: 3- APTMS yields worm-hole structures, while 3-APTES produces channel-like structures. These catalysts efficiently convert epoxides and carbon dioxide into cyclic organic carbonates with excellent yield. Additionally, the invention discloses a process for preparing styrene carbonate-coated zinc anodes and assembling full cells incorporating these anodes, significantly enhancing the durability of aqueous rechargeable zinc-metal batteries (ARZMBs).

Description

[0001] AMINE FUNCTIONALIZED SILICA CATALYST FOR PREPARATION OF ORGANIC CARBONATE AND OTHER APPLICATIONS THEREOF

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to an amine functionalized silica catalyst and a process for preparation of amine functionalized silica catalyst with characteristic features of broad pore size distribution, large pore volume and tunable basic sites. The process for preparation of the catalyst employs Pluronic P123 as a template and involves the co-condensation of tetraethyl orthosilicate (TEOS) with either 3-aminopropyltrimethoxysilane (3-APTMS) or 3 -aminoprop yltriethoxysilane (3-APTES), resulting in worm-hole-like or channel-like pore structure respectively. The present invention further relates to a process for preparation of styrene carbonate using the amine functionalized silica catalyst of the present invention which, achieves 90% conversion with nearly complete selectivity towards styrene carbonate (SC) under solvent free condition and atmospheric pressure of CO2. Moreover, the catalyst demonstrates versatility with various epoxide substrates for preparation of cyclic organic carbonates. The present invention also relates to the value addition of carbonate prepared by the catalyst of the present invention in aqueous rechargeable zinc metal batteries (ARZMBs).

[0004] BACKGROUND AND PRIOR ART OF THE INVENTION

[0005] The abrupt escalation in global temperature, coupled with erratic seasonal variations, constitutes compelling evidence of the disruption of nature's homeostasis equilibrium, with anthropogenic carbon dioxide (CO2) emissions being a purported causal factor. Carbon Capture and Storage (CCS) and Carbon Capture and Utilization (CCU) are deemed as effective measures to mitigate CO2 concentration in the atmosphere. CCU, involving the conversion of CO2 into fuels, and chemicals, is more industrially viable and acceptable than CCS because CCS requires large capital investment in capturing, transporting and storage of CO2. The hydrogenated products of CO2 into fuels such as methanol, methane, dimethyl ether and higher hydrocarbons may open up a potentially profitable market with the availability of cheaper sources of green hydrogen. But the conversion of CO2 into the feedstock of industrially valuable chemicals like carbonates, polycarbonates, salicylic acids, epoxide, etc., refrains CO2 utilization from the additional cost of hydrogen leading CCU to a more profitable and sustainable technique. Trapping CO2 as a cyclic organic carbonate (COC) using epoxides is one of the promising ways in CCU due to the diverse applications of COC. Among the COCs, ethylene carbonate, and propylene carbonate have a wide commercial market due to their applications like organic electrolytes in lithium-ion batteries, intermediates for biomedical and pharmaceutical fine chemical synthesis, herbicides and disinfectants in the agriculture industry, raw materials for polymer production, organic insulator, in paint industry and as polar aprotic solvents in heck reaction etc. Based on the industrial importance, the global market size for COC is expected to be valued at over US$7.1 billion in 2030 at 7.2% CAGR respectively. However, the available synthesis method of COC includes utilizing highly toxic phosgene gas, which is not an environmentally friendly route and results in toxic hydrochloric acid formation.

[0006] COC derived from anthropogenic CO2 involves the main catalytic challenge in activating a thermodynamically stable and kinetically inert CO2 molecule. In this regard, many homogeneous catalysts like metal complexes, metal salts, and ionic liquids have been explored for this particular reaction but, the low yield of the product, challenge in product separation, non-recyclability, low thermal stability, and the use of toxic transition metals open up the need for heterogeneous catalyst. Among the heterogeneous catalysts metalorganic frameworks (MOFs), thin films of MOFs, zeolite, and metal oxides have been explored for this transformation but, the utilization of toxic metal ions, low thermal stability, and low yield leads to the requirement of an efficient heterogeneous catalytic system. According to the researchers, materials containing Lewis basic and acidic sites like amine / sulfonic acid / carboxylic acid and various other functional groups grafted onto silica materials nicely interact with the 7t* LUMO and non-bonding HOMO of CO2 respectively facilitating the high catalytic conversion at ambient reaction conditions. It is known that amine-functionalized silica catalysts are well-recognized as CO2 absorbents. Transition / noble metal-free heterogeneous catalysts with targeted catalytic sites for CO2 activation, such as primary / secondary / tertiary amine-functionalized silica spheres / SBA- 15 / MCM-41, sulfonic acid, carboxylic acid grafted onto silica materials, adenine functionalized dendritic fibrous nanosilica demonstrates moderate to good conversion under high-pressure and atmospheric pressure conditions. However, the synthesis procedures involve tedious post-grafting or mechano-chemical synthetic routes. Recently, Bhanage et al. synthesized primary amine grafted dendritic fibrous nano-silica (N-DFNS), demonstrating the efficient conversion of styrene oxide (SO) to styrene carbonate (SC) under ambient pressure of CO2. Here, the catalyst was synthesized via ammonolysis process at 500-700 °C.

[0007] Hence, there remains a need for development of an improved amine functionalized silica catalyst and an efficient method for synthesis of amine functionalized silica catalyst with characteristic features of broad pore size distribution, large pore volume and tunable basic sites which when further used, is capable of synthesizing a cyclic carbonate in a cost- effective manner.

[0008] Further, among the COCs the utility of ethylene carbonate and propylene carbonate are well explored especially, in the field of nonflammable organic electrolytes in lithium-ion batteries. Aqueous rechargeable Zinc metal batteries (ARZMBs) occupy a critical position among post lithium-ion batteries owing to good battery performance, high abundance of zinc (Zn) metal, and lower risk towards fire because of the aqueous electrolytes employed for the fabrication of ARZMBs. Despite the advantages offered, ARZMBs are susceptible to limited lifetime arising from the irreversible side effects associated with zinc metal anode such as rapid and uncontrollable zinc dendrite growth accompanied by hydrogen evolution reaction (HER) / oxygen evolution reaction (OER) leading to electrolyte decomposition, zinc metal corrosion, and by-product formation etc. Thus, there is a need to overcome these drawbacks associated with ARZMBs. The present invention demonstrates styrene carbonate (SC) synthesized via the catalyst of the present invention as an artificial interface coating for achieving a stable Zn anode. A thin layer of SC coating over Zn anode enhances the cycling life by many folds of ARZMBs as compared to bare zinc batteries by ensuring uniform zinc plating-stripping along with the reduction of interfacial charge transfer resistance, suppression of Oxygen Evolution Reaction (OER) and zinc corrosion.

[0009] OBJECTIVESS OF THE INVENTION

[0010] Objectives of the present disclosure is to provide a catalyst with characteristic features of broad pore size distribution, large pore volume and tunable basic sites.

[0011] An objective of the present disclosure is to provide a process for preparation of amine functionalized silica catalyst.

[0012] Another objective of the present invention is to provide convenient environment friendly tunable amine and silanol functional catalyst synthesis for CO2 valorization.

[0013] Another objective of the present disclosure is to synthesize channel morphology and wormhole morphology of the amine functionalized silica material by varying the organo-amine silane precursors 3-APTES and 3-APTMS respectively in the co-condensation synthesis route.

[0014] Another objective of the present disclosure is to provide a one-pot green synthesis route for a cost-effective amine functionalized silica catalyst, which when further used, is capable of synthesizing a cyclic carbonate in a cost-effective manner.

[0015] Another objective of the present disclosure is to provide a catalyst having an excellent catalytic activity driven by widespread mesopores with optimum amine sites and being capable of synthesizing a cyclic carbonate in a high conversion rate and a high yield, produced at a low cost and at atmospheric pressure of CO2.

[0016] Yet another objective of the present disclosure is to provide a method of synthesizing a cyclic carbonate by reacting an epoxide with carbon dioxide using the catalyst of the present disclosure.

[0017] Another objective of this present disclosure is depositing styrene carbonate prepared using the catalyst of the present invention as a protective layer on zinc anode thereby enhancing the aqueous reversible zinc metal batteries durability.

[0018] Yet another objective of this present disclosure is utilizing atmospheric greenhouse CO2 gas in the form of styrene carbonate synthesized via a cost-effective porous tunable amine functionalized silica catalyst obtained through a one pot green co-condensation synthesis route of the present invention, as a protective layer on zinc anode in enhancing the aqueous reversible zinc metal battery’s durability manifold via suppressing dendrite growth, zinc corrosion and HER reaction.

[0019] SUMMARY OF THE INVENTION

[0020] Aspects of the present invention relate to an amine functionalized silica catalyst with characteristic features of broad pore size distribution, large pore volume and tunable basic sites. The sponge-like interior of the catalyst provides wide range of mesopores with catalytically active silanol and amine sites enabling CO2 activation at ambient reaction conditions to form styrene carbonate (SC) from styrene oxide (SO). The present invention also relates to a one- step greener co-condensation synthesis method of the catalyst.

[0021] In an aspect, the present invention relates to a worm-hole like or channel like amine functionalized silica catalyst comprising 3-aminopropyl trimethoxysilane (3-APTMS) or 3-ami- nopropyl triethoxy silane (3-APTES) having average pore diameter in a range from 1 to 100 nm and specific surface area in a range from 100 to 1,000 m2 / g. In another aspect, the present invention relates to a process for preparation of an amine functionalized silica catalyst, the process comprising:

[0022] (a) mixing poly(ethylene glycol) -block-poly(propylene glycol) -block-poly (ethylene glycol) (Pluronic Pl 23) with hydrochloric acid (HC1) at a temperature in a range from 30°C to 40 °C to obtain a solution;

[0023] (b) adding a mixture of 3-aminopropyl trimethoxysilane (APTMS) or 3-aminopropyl triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) to the solution of step (a) and treating under hydrothermal conditions.

[0024] In another aspect, the present disclosure relates to a method for converting epoxide and carbon dioxide (CO2) to carbonate, the process comprising:

[0025] (a) reacting epoxide, tetrabutylammonium bromide (TBAB) and the amine functionalized silica catalyst to obtain a mixture; and

[0026] (b) flushing the mixture with CO2, followed by heating at 10° C to 120° C to obtain the carbonate.

[0027] In another aspect, the present invention relates to a process for preparation of styrene carbonate coated zinc anode by depositing a slurry on styrene carbonate, binder and solvent on zinc.

[0028] In another aspect, the present invention relates to a full cell comprising:

[0029] (a) styrene carbonate coated zinc anode;

[0030] (b) a manganese oxide (P- MnCh) cathode;

[0031] (c) an electrolyte; and

[0032] (d) a separator.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Fig.l depicts TEM images of (a) AMS-20, (b) AES-20 of Example 1 and (c) solvent extracted SBA-15, FESEM images of (d) AMS-20, (e) AES-20 catalyst of Example 1 and (f) solvent extracted SBA-15 (Comparative Example A).

[0035] Fig.2 depicts surface area of (a) SBA-15 (Comparative Example A), AMS- 15, AMS-20, AMS-25 and AMS-30 catalyst of Example 1; and (b) depicts the type IV isotherm of SBA- 15 (Comparative Example A), and AES- 15, AES-20, AES-25 and AES-30 catalyst of Example 1. Fig.3 depicts the pore size distribution plots of AMS -20, AES-20 catalyst of Example 1 and SBA-15 (Comparative Example A).

[0036] Fig.4 depicts the Nls XPS spectrum of the SBA-15 (Comparative Example A), AMS-20 and AES-20 catalysts of Example 1.

[0037] Fig.5 depicts XPS of the catalysts (a) AMS- 15, AMS-20, AMS-25 and AMS-30 catalyst of Example 1, and (b) AES-15, AES-20, AES-25 and AES-30 catalyst prepared according to Example 1.

[0038] Fig.6 depicts the full XPS scan of AMS -20 catalyst ofExample 1 and SBA-15 (Comparative Example A).

[0039] Fig.7 depicts the TEM images of AES-20 of Example 1 at magnified scale at 50 nm (Left) and 100 nm (Right) respectively.

[0040] Fig.8 depicts the CO2-TPD of the SBA-15 (Comparative Example A), AMS-20 and AES- 20 catalysts of Example 1.

[0041] Fig.9 depicts the CO2TPD of AMS-15, AMS-20, AMS-25 and AMS-30 catalysts of Example 1.

[0042] Fig.10 depicts FTIR finger print region(a) and full spectra (b) of SBA-15 (Comparative Example A), AMS-20, AES-20 of Example 1, and solvent extracted SBA-15 (Comparative Example B).

[0043] Fig.ll depicts the TGA analysis data of solvent extracted SBA-15 (Comparative Example B) and AMS-20 of Example 1.

[0044] Fig.12 depicts the29Si and15N solid state NMR of AMS-20 of Example 1 and SBA-15 (Comparative Example A),

[0045] Fig.13 depicts the CO2 absorption capacity of SBA-15 (Comparative Example A), AMS- 20 and AES-20 of Example 1 at room temperature.

[0046] Fig.14 depicts the (a) Temperature variation study; (b) Time variation study; (c) Catalyst amount variation study; and (d) Recyclability test of AMS-20 of Example 1.

[0047] Fig.15 depicts (a) Linear Polarization Resistance (LPR) of Zn-SC||Zn-SC symmetric cell prepared according to Example 5 vs Zn||Zn symmetric cells, (b) Cyclic voltammograms of Zn||SS (zinc against stainless steel) and SC@Zn||SS (SC@Zn anode prepared according to Example 5 against stainless steel) cells, (c) Chronoamperometric plots of Zn-SC||Zn-SC and Zn||Zn symmetric cells, (d) Linear Sweep Voltametric plot (LSV) of Zn-SC||SS vs Zn||SS, (e) Electrochemical Impedance Spectra (EIS) of Zn-SC||Zn-SC and Zn||Zn symmetric cells, and (f) Platting stripping (cyclic stability) data of Zn-SC||Zn-SC vs Zn||Zn symmetric cells. Fig.16 depicts contact angle studies bare Zinc foil (left) and SC@Zn (right). Fig.17 depicts (a) Cyclic voltammogram of full cell SC@Zn||P-MnO2 comprising SC@Zn anode prepared according to Example 5 vs Zn||P-Mn()2, (b) Galvanostatic charge-discharge curves of Bare Zn||Mn()2, vs SC@Zn||Mn()2, (c) rate performance of SC@Zn||P-Mn()2 vs Zn||P-Mn()2, (d) cycling stability of full cell SC@Zn||P-MnO2 vs bare Zn||P-Mn()2.

[0048] Fig.18 depicts catalyst synthesis.

[0049] DETAILED DESCRPITION OF THE INVENTION

[0050] Embodiments of the present invention relate to an amine functionalized silica catalyst and a process for preparation of a mesoporous worm hole like amine functionalized silica catalyst with characteristic features of broad pore size distribution, large pore volume and tunable Lewis basic sites. The present invention also relates to a one-step greener co-condensa- tion synthesis method of channel like 3-aminopropyl triethoxysilane (3-AES) catalyst analogous to SBA-15 synthesis route. The worm-hole like (mesoporous / spongy) interior of the catalyst provides a wide range of mesopores with catalytically active silanol and amine sites enabling CO2 activation at ambient reaction conditions to form styrene carbonate (SC) from styrene oxide (SO). The present invention also relates to a process for preparation of a SC coated zinc anode by depositing the SC prepared via the catalyst of the present invention on zinc foil (as shown in Fig. 18).

[0051] In an embodiment, the present invention provides a mesoporous worm-hole like or channel like amine functionalized silica catalyst comprising of 3-aminopropyl trimethoxysilane (3- APTMS) or 3-aminopropyl triethoxysilane (3-APTES) having average pore diameter in a range from 1 to 100 nm and specific surface area in a range from 100 to 1,000 m2 / g. Preferably, the present invention provides a mesoporous worm hole like amine functionalized silica catalyst. Preferably, the amine functionalized silica catalyst is prepared by the process of the present invention as described below.

[0052] The amine functionalized silica catalyst is a heterogeneous catalyst (solid catalyst) having the average pore diameter preferably in a range from 5 nm to 50 nm. In some embodiments, the average pore diameter is more preferably, in a range from 5 mn to 20 nm, further preferably in a range from 10 nm to 20 nm, and even more preferably in a range from 10 nm to 15 nm.

[0053] In an embodiment of the present disclosure, the specific surface area of the amine functionalized silica catalyst is in a range from 100 to 1,000 m2 / g. For example, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 m2 / g. Preferably in a range from 400 to 1,000 m2 / g, or more preferably in a range from 400 to 550 m2 / g.

[0054] In another embodiment, the present disclosure provides a process for preparation of an amine functionalized silica catalyst, the process comprising:

[0055] (c) mixing poly(ethylene glycol) -block-poly(propylene glycol) -block-poly (ethylene glycol) (Pluronic Pl 23) with hydrochloric acid (HC1) at a temperature in a range from 30°C to 40°C to obtain a solution; and

[0056] (d) adding a mixture of 3-aminopropyl trimethoxysilane (3-APTMS) or 3- aminopropyl triethoxysilane (3-APTES) and tetraethyl orthosilicate (TEOS) to the solution of step (a) and treating under hydrothermal conditions.

[0057] In step (a) the Pluronic P123 having weight in a range from 1.5 g to 2.5 g is mixed with 70 mL to 80 mL of HC1 (35%) having concentration in a range from 1.6 M to 1.8 M. The Pluronic 123 in step (a) may be replaced with another surfactant selected from but not limited to poly(ethylene oxide)-block-poly(propylene oxide) -block-poly (ethylene oxide) (P104), polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide (PEO) based block copolymer (P105), poly(oxyethylene-co-oxypropylene) block copolymer (F127), or combination thereof. The mixing in step (a) is carried out for 2 hours to 4 hours at a speed of 500 rotations per minute (rpm) to 700 rpm. Preferably, the mixing is carried out at a temperature of 40°C for 4 hours.

[0058] Then, in step (b) the 3-APTMS or 3-APTES and TEOS are mixed in a volume ratio in a range from 1: 15 to 1:30. Preferably, the 3-APTMS or 3-APTES and TEOS are mixed in the said ratio in a total volume of 4.4 mL of silane precursors (TEOS and 3-APTMS or TEOS and 3-APTES. Preferably, prior to hydrothermal treatment, the mixture obtained in step (b) is stirred at a speed of 500 rpm to 700 rpm at 40°C to 50 °C for 24 hours to 36 hours. Preferably, the stirring is carried out at a speed of 700 rpm at 40°C for 24 hours. Then, the mixture is hydrothermally treated at a temperature in a range from 90°C to 110°C for 48 hours to 60 hours. Preferably, the mixture is hydrothermally treated at a temperature of 100°C for 48 hours.

[0059] The process of the present invention provides a facile co-condensation synthesis route for preparation of amine functionalized silica catalyst with two different morphologies like channel or mesoporous worm-hole like, arising from two different organo-amine silica precursors 3-APTES or 3-APTMS respectively. The worm-hole morphology of the amine functionalized silica catalyst exhibits a wide range distribution of pores with pore size ranging from 13 to 15 nm with almost the same pore size density, whereas, the channel morphology of the amine functionalized silica catalyst contains the maximum density of the pore size in a range from 4 to 7 nm. The widespread pores are attributed to the in-contrast functional group interaction (methoxy vs ethoxy) of amino silica precursor 3-APTMS and the main silane precursor, TEOS by channel deformation which is absent in 3-aminopropyl triethoxysilane (3-APTES). Thus, the channel-distorted catalyst of the present invention is more active due to the widespread pores obtained by the process of the present invention which results in high catalytic conversion by providing sufficient space for the large reactant molecules to participate in reaction.

[0060] Further, the process of the present invention results in a noble / transition metal free amine grafted / functionalized silica material / catalyst with tunable Lewis basic sites. The process of the present invention not only offers a greener grafting of the functional groups on the catalyst surface but also by introducing a wide range of mesopores acts like a catalytic micro factory, which when employed catalyzes / promotes an excellent conversion of carbon dioxide (CO2) and epoxide into carbonates at ambient pressure and temperature with accelerated rate, thereby resulting in high selectivity and high conversion rate. Additionally, the catalyst of the present invention helps in adsorption of CO2, hence, the amine functionalized silica material / catalyst of the present invention acts as CO2 adsorbate.

[0061] Further, the process of the present invention is a one pot, scalable and cost-effective green co-condensation synthesis route which provides a highly porous tunable amine / silanol functionalized amine silica catalyst.

[0062] In a preferred embodiment, the present disclosure provides a process for preparation of a mesoporous worm-hole like amine functionalized silica (AMS) catalyst, the process comprising: b) mixing of 2 g of Pluronic P123 in 77 mL of 1.6 M HCL, followed by stirring at 40°C at 700 rpm for 4 hours to get a clear solution; c) adding a total volume of 4.4 mL of a mixture of tetraethyl orthosilicate (TEOS) and 3-aminopropyl trimethoxysilane (3-APTMS) with a ratio of (1: 15 to 1:30) to obtain a mixture; d) stirring the mixture at 700 rpm at 40° C for 24 h, followed by transferring the same into a Teflon autoclave and hydrothermally treating the mixture by heating at 100° C for 48 hours followed by extracting the same with ethanol at 70° C for 6 h; and e) centrifuging the extracted solution at 10000 rpm for 10 minutes, followed by repeating the steps c) and d) for 3-4 times to obtain a solid product of AMS, which is dried for further use.

[0063] The process of the present invention is scalable and may synthesize from 1 g to 20 g of amine silica catalyst (AMS).

[0064] In another embodiment, the present disclosure provides a method of synthesizing a channel like amine silica (AES) catalyst comprising: a) mixing of 2 g of Pluronic P123 in a 77 mL of 1.6 M HCL, followed by stirring at a temperature in the range of 30-40°C at 500- 700 rpm for 4 hours to get a clear solution; b) adding a total volume of 4.4 mL of a mixture of tetraethyl orthosilicate (TEOS) and 3-aminopropyl triethoxysilane (3-APTES) with a ratio of (1: 15 to 1:30) to obtain a mixture; c) stirring the mixture at 700 rpm at 40°C for 24 h, followed by transferring the same into a Teflon autoclave and heating at 100°C for 48 hours to obtain a solid product; d) cooling down the solid product, followed by extracting the same with ethanol at 70°C for 6 h; and e) centrifuging the extracted solution 10000 rpm for 10 minutes, followed by repeating the steps d) and e) for 4-4 times to obtain a solid product of AES, which is dried for further use.

[0065] The process of the present invention by employing 3-aminopropyl triethoxysilane (3- APTES) instead of 3-aminopropyl triethoxysilane (3-APTMS) results in channel like morphology in the co-condensation synthesis route with TEOS.

[0066] In another embodiment, the present invention provides a process for converting epoxide and carbon dioxide (CO2) to carbonate, the process comprising:

[0067] (a) reacting epoxide, a co-catalyst and the amine functionalized silica catalyst to obtain a mixture; and

[0068] (b) flushing the mixture with carbon dioxide (CO2), followed by heating at 30° C to 120° C.

[0069] Preferably, the cyclic organic carbonate prepared by the process of the present invention employs the amine functionalized silica catalyst of the present invention. In step (a), the epoxide is reacted in a concentration ranging from 15 mmol to 25 mmol, the amount of co-catalyst may be appropriately adjusted based on the amount of the epoxide used. In an embodiment, the co-catalyst is used in a concentration ranging from 0.1 mmol to 0.5 mmol, preferably from 0.1 mmol to 0.5 mmol, more preferably from 20 mmol to 100 mmol of the epoxide. The catalyst is used in a concentration ranging from 25 mg to 150 mg, preferably from 50 mg to 100 mg, more preferably from 1 mmol to 20 mmol of the epoxide. The epoxide is selected from but not limited to styrene oxide, 4- fluorostyrene oxide, 4- chlorostyrene oxide, 4-bromostyrene oxide, cyclopentane oxide, cyclohexane oxide or combination thereof. Preferably, the epoxide is styrene oxide. The co-catalyst is selected from the group consisting of tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB) and tetrabutylammonium iodide (TBAI) or any other halide salts. Preferably, the co-catalyst is tetrabutylammonium bromide. The step (a) is carried out at a temperature in a range from 30 to 120° C for 6 hours to 12 hours. Preferably, the reaction of step (a) is carried out in a round-bottom flask (RB) connected to an open-head condenser attached to a gas connector.

[0070] Then, in step (b), the CO2 having concentration in a range from 90 % to 99.8 % is flushed at a pressure in a range from 1 atm to 2 atm. Preferably, the CO2 is flushed through a gas connector and is captured from industrial exhaust thus providing global warming mitigation. The step (b) is carried out for 6 hours to 12 hours. Preferably, the carbonate formed in styrene carbonate.

[0071] The process of the present invention is carried out at a temperature in a range from 20 to 170° C, preferably in a range from 50 to 140° C., more preferably in a range from 80 to 130° C., from the viewpoint of reaction efficiency. Further, the process of the present invention is carried out for a time period in a range from 1 to 12 hours, preferably in a range from 5 to 10 hours, more preferably in a range from 6 to 8 hours, from the viewpoint of reaction efficiency.

[0072] The process further comprises optionally recovering the amine functionalized silica catalyst of the present invention by dissolving the carbonate obtained, in solvent selected from chloroform / dichloromethane then centrifuging the dissolved carbonate to obtain / recover the spent catalyst, washing the catalyst with chloroform / dichloromethane to remove the trace amount of reactant / product. Advantageously, the catalyst recovered can be recycled, by employing in subsequent processes of the present invention.

[0073] The process of the present invention for preparing a carbonate preferably a cyclic carbonate using the amine functionalized silica catalyst of the present invention can adopt a method / process that is universally used as a reaction mode, such as a stirring system or a parr reactor system. The process may be carried out by any method selected from but not limited to batch type process, a semi-batch type process, a continuous flow type process, and the like. In an embodiment of the present disclosure, the method for synthesizing the cyclic carbonate using the catalyst of the present disclosure comprises the step of mixing an epoxide, co-catalyst and carbon dioxide together, followed by heating the same in a reactor filled with a catalyst, and reacting continuously or batch- wise therein.

[0074] In a preferred embodiment, the AMS catalyst employed in the process of the present invention includes the participation of both surface silanol and amines groups in CO2 activation in the form of bicarbonate and carbamate species respectively. Thus, the process of the present invention by employing the AMS catalyst of the present invention achieves a 70-95% conversion of epoxide with 80-99% selectivity of carbonate at ambient reaction condition, under solvent free condition with 100% atom economy. Preferably, a 90% conversion of epoxide with 99 % selectivity of carbonate is achieved by the process of the present invention. This is attributed to the excellent catalytic activity of the AMS catalyst of the present invention comprising balanced Lewis base functionality, wide pore size distribution and larger pore volume. In an embodiment of the present disclosure, the AMS catalyst exhibits catalytic activity up to five cycles. Additionally, the catalysts of the present invention provides valorization of the CO2, thereby providing a way of Carbon Capture and Utilization (CCU). Moreover, various substrate scopes of aromatic and aliphatic epoxides can be employed in the process of the present invention for preparation of versatile carbonates.

[0075] In a preferred embodiment, the process for converting epoxide and CO2 to carbonate using the catalyst of the present invention comprises:

[0076] (a) providing a 20 mmol epoxide selected from but not limited to styrene oxide, 4- fluorostyrene oxide, 4 -chloro styrene oxide, 4 -bromo styrene oxide, cyclopentane oxide, cyclohexane oxide or combination thereof and a co-catalyst and 50 mg of the amine functionalized silica catalyst obtained by the process of the present invention in a reaction set-up connected to an open-head condenser attached with a gas connecter with CO2 (1 atm) balloon;

[0077] (b) flushing the reaction set-up with CO2, followed by heating at 30 to 120° C;

[0078] (c) cooling the reaction set-up to room temperature and obtaining the reaction mixture; (d) adding chloroform and centrifuging the reaction mixture to remove the spent AMS catalyst;

[0079] (e) optionally, washing the spent AMS catalyst with chloroform thrice to remove any trace amount of reactant and / or product; and

[0080] (f) re-using the AMS catalyst.

[0081] In another embodiment, the present invention provides a process for preparation of styrene carbonate coated zinc anode by depositing a slurry of styrene carbonate prepared via the amine functionalized silica catalyst of the present invention, binder and solvent on zinc.

[0082] The binder is selected from polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE) or combination thereof. The solvent is selected from N-methyl-2-pyrrolidone (NMP), isopropyl alcohol (IPA), dimethylformamide (DMF) or mixture thereof.

[0083] The styrene carbonate prepared via the amine functionalized silica catalyst of the present invention is used as a protective layer on Zn anode in aqueous rechargeable zinc metal / ion battery (ARZMBs). The layer provides a protective layer against dendrite formation, corrosion and suppresses the hydrogen evolution reaction (HER) / oxygen evolution reaction (OER), electrolyte decomposition, zinc metal corrosion, and other side product formation which enhances the battery durability many folds as compared to the bare zinc batteries.

[0084] In an embodiment, the present invention provides a full cell comprising:

[0085] (a) styrene carbonate coated zinc anode;

[0086] (b) a manganese oxide (P- MnCh) cathode;

[0087] (c) an electrolyte; and

[0088] (d) a separator.

[0089] Preferably, the styrene carbonate coated zinc anode is prepared by the process of the present invention.

[0090] The P- Mn02 cathode is prepared by processes known in the art. Preferably, the P- MnCh cathode is prepared by (i) dissolving 0.6 g of MnCh EEO in 20 mL of DI water, followed by adding 0.3 g of KMnCU and stirring for 30 minutes to obtain a solution, and (ii) transferring the solution to a Teflon-lined autoclave and treating hydrothermally at 160 °C for 20hours to obtain raw P- MnCh, washing the raw P- MnChwith ethanol and DI water, followed by filtration , and drying at 60 °C for 24hours.

[0091] The electrolyte is selected from zinc trifluoromethane sulfonate (Zn(OTf)2), zinc sulfate (ZnSCU), zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)2), zinc chloride (ZnCh), zinc nitrate (Zn(N0s)2), and zinc acetate (Zn(OAc)i), or mixture thereof. The separator is selected from Nafion membrane, Glass fiber, Celgard, or combination thereof.

[0092] The process of the present invention is illustrated by non-limiting examples.

[0093] EXAMPLES

[0094] The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0095] Experimental Section

[0096] Materials: Chemicals, Materials, and Method

[0097] Catalyst synthesis: Pluronic P123 (average Mn~5800), tetraethyl orthosilicate (98%), aminopropyltrimethoxy silane (97%), and aminopropyltriethoxy silane (99%) were procured from Sigma Aldrich. Absolute ethanol (99.4%) and 35% hydrochloric acid were purchased from Merck.

[0098] Catalytic reactions: Styrene oxide (Sigma- Aldrich, 97%), tetrabutylammonium halides (Thomas Baker) and other substituted epoxides purchased from Sigma Aldrich were used without further purification. Chloroform (Molychem, 99.5%) was used as a solvent for chromatography sample preparation.

[0099] SC@Zn half Cell / full cell fabrication: zinc trifluoromethane sulfonate (Zn(CF3SO3)2 / Zn(OTf)2), polyvinylidene fluoride (PVDF), N-methyl-2-pyrrolidone, manganese chloride (MnCh- FbO), potassium permanganate (KMnC ) were procured from Sigma- Aldrich and Nafion 212 membrane from Du Pont, USA.

[0100] Example 1: Process for preparation of amine functionalized silica catalyst

[0101] The amino methoxy silica (AMS) catalyst was synthesized similarly to the method Zhao et al reported with few modifications. First, 2 g P123 was stirred with 77 mL of 1.6 (M) aq. HC1 at 40°C in a 250 mL round-bottom flask (RB). After 4 h of stirring at a speed of 500 rpm to 700 rpm at 30 °C to 50 °C, a total of 4.4 mL of 3 -aminopropyltrimethoxy silane (3- APTMS) and (tetraethyl orthosilicate) TEOS mixture with 1:20 ratio of 3-APTMS and TEOS, respectively, were added drop-wise into the acidic P123 solution. The mixture was then allowed to stir at 40°C for 24 h and then hydrothermally treated at 100°C for 48 h. The hydrothermal treatment of the catalyst was carried out in a 100 mL stainless steel hydrothermal autoclave with a Glass Filled liner made of PTFE (GFT-Liner). The suspension was refluxed with ethanol at 70°C for 6 h to remove the surfactant. This step was repeated thrice, and the material was dried for 24 h. The synthesized catalyst was named AMS-20. Similarly, three more sets of catalysts AMS-30, AMS-25 and AMS- 15 with 1:30, 1:25 and 1: 15 ratios of 3-APTMS: TEOS of a total volume of 4.4 mL respectively were synthesized with the same procedure. Next, amino ethoxy silica (AES) series catalysts were synthesized using (3-aminopropyltriethoxy silane) 3-APTES as an organic amine silica precursor, keeping the number of moles of 3-APTES the same as 3-APTMS in AMS- 15, AMS-20, AMS-25 and AMS-30 and named as AES-15, AES-20, AES-25 and AES-30 respectively. The functional group interaction of the APTMS / APTES with the TEOS in the AMS / AES catalyst respectively, prepared by the process of the present invention is depicted in Scheme 1 below:

[0102] Scheme 1:

[0103] The synthesis of SBA-15 was carried out using the method reported by Stucky et al with minor modification. 2 g of P-123 was dissolved in 77 mL of 1.6 M HCL under stirring at a temperature of 40° C in a 250 mL RB. After 4 h, 4.4 mL TEOS was added dropwise and magnetically stirred at 40° C for 24 h. The solution was then transferred to a 100 mL stainless steel hydrothermal autoclave with a Glass Filled liner made of PTFE (GFT-Liner) and heated at 100° C for 48 h. After that, the product was washed with water until the foam formation disappeared. The solid was then dried and calcined at 550°C for 6 h. Similarly, a solvent extracted SBA-15 catalyst was prepared according to the process described above, except that instead of calcination, the product was extracted by solvent extraction process using ethanol at 70°C, the product obtained was labelled as Comparative Example B.

[0104] Example 2: Characterization of AMS catalyst prepared according to Example 1 FESEM and SEM analysis

[0105] The transmission electron microscopy (TEM) images reveal the morphological diversity of the amine functionalized / grafted silica material upon changing the organo-amine silane precursor from 3-APTES to 3-APTMS in the co-condensation synthesis route (Example 1). 3- APTMS (Figure la) leads to the deformation of channels which appear like a wormhole structure, whereas 3-APTES (Figure lb) mediated synthesis leads to the formation of chan- nels like SBA-15. The template removal process of solvent extraction is as effective as calcination process revealed by the clear channel occurrence in the TEM image of solvent extracted SBA-15 (Figure 1c). The field emission scanning electron microscopy (FESEM) images of AMS-20 (Figure Id) and AES-20 (Figure le) indicates porous surfaces formed from the incomplete formation of long silicate chains. The FESEM image of solvent extracted SBA-15 (Figure If) (Comparative Example B) showed uniform cylindrical silicate chain formation.

[0106] Surface area analysis

[0107] In the N2 adsorption / desorption experiment, the surface area of SBA-15 (Comparative Example A) showed a Barrett-Joyner-Halenda (BET) Type IV isotherm, indicating the meso- porous structure. The Hl hysteresis loop characterized a narrow pore size distribution of cylindrical pores in which both ends were open, with capillary condensation occurring in the middle of the relative pressure. Upon functionalization with organo-amine moiety, the BET Type IV isotherm becomes an H2 hysteresis loop, indicating ink-bottle- shaped pores with poor connectivity and uneven pore structure (Figure 2a, 2b). As observed from the said figures, the surface area of the functionalized catalyst of the present invention is in a range from 435-663 m2 / g, which is less than that of SBA-15 (741 m2 / g) because of the surface coverage by the organo-amine moiety. Though the catalysts of the present invention showed reduced surface area, the enlarged pore size and pore volume of the catalysts of the present invention provides a superior catalytic conversion in comparison to SBA-15 as described below. The surface area, pore volume and average pore width of all the catalysts of Example 1 and Comparative Examples A and B are given in Table- 1 below.

[0108] Table 1:

[0109] The pore size distribution graph depicted in (Figure 3) shows a wide range distribution in pore size in a range from 13-15 nm with almost the same pore size density in AMS-20 catalyst of the present invention, whereas, in SBA-15 and AES-20, the maximum density of the pore size is in the range of 4-7 nm. The channel deformation in AMS-20 may introduce a wide pore size distribution. From the electron microscopy and N2 physiosorption analysis, it is clear that adding 3-APTMS in the co-condensation synthesis method leads to the channel-deformed worm-hole like structure with multi-modal porosity, unlike 3-APTES. It may be inferred that the ethoxy group in APTES and TEOS provides not only a similar rate of hydrolysis of the silanes but also a favourable interaction with the hydrophilic corona of poly(ethylene oxide) (PEO) in the surfactant Pl 23, leading to the formation of channels in AES catalyst. During the synthesis of AMS, contrast functional group interaction between the methoxy and ethoxy moieties of the silane precursors and the hydrophilic corona of the surfactant leads to channel deformation, as depicted in Scheme 1 above. In addition, it has been observed that the change in the pH during the addition of the organo-amine precursor also leads to pore enlargement.

[0110] XPS Analysis

[0111] Further, X-ray photoelectron spectroscopy (XPS) was utilized to examine the presence of amine groups on the surface of the catalysts. In the Nls XPS spectrum of various catalysts (Figure 4), peaks at 399.8 eV and 402 eV correspond to the presence of the amine (-NH2) and ammonium (-NH3+) groups on the surface of the catalyst. The absence of such peaks in the case of SBA-15 (Comparative Example A) indicated the successful grafting of organo- amine moieties in the catalyst of the present invention. Further, among the catalyst of the present invention, the quantitative analysis showed a higher amount of ammonium groups in the case of the AMS-20 catalyst as compared to the AES-20 catalyst, which is correlated with the channel deformation of the catalyst. The in-situ addition of 3-APTMS in hydrochloric acid medium causes instant protonation of the amine group, which further crosslinks with the silanol groups to form zwitterionic (NH3+OSi) like species which not only disturbs the formation of the long silicate chains but also prevents the direct interaction of the surfactant Pl 23, which thereby result in the channel deformation in AMS-20. With the increase in the 3-APTMS molar ratio, there is an increase in the peak intensity of the ammonium group, which may relate to the structure deformation in the AMS series as depicted in Figure 5a. In the AES catalysts of the present invention, though the ammonium group increases with an increase in the molar ratio of 3-APTES, predominantly amines are present, which correlate to the channel resembling morphology as observed from Figure 5b. The presence of all the relevant elements has been confirmed by the XPS wide area scan of AMS-20 (Figure 6a) and SBA-15 (Figure 6b).

[0112] TEM

[0113] The increase in 3-APTES molar ratio can also, in part, lead to channel deformation of the catalyst as revealed in the Transmission Electron Microscopy (TEM) image of AES-20 (Figure 7). Figure 7 depicts the TEM images of AES-20 of Example 1 at magnified scale at 50 nm (Left) and 100 nm (Right) respectively exhibiting channel formation with channel distortion at some areas.

[0114] CO2 temperature programmed desorption (TPD) analysis:

[0115] The tuneability of the basic site density on the catalyst surface was investigated with the help of CO2 temperature programmed desorption (TPD) technique (Figure 8). As per the literature in CO2-TPD, the desorption temperature range of 100-170 °C corresponds to the weak basic sites, followed by the moderate- strong basic sites within the 170-320 °C range. The desorbed CO2 beyond 320 °C is attached to the strong basic sites. Amongst the catalyst of the present invention, the concentration of medium basic sites is higher in AMS-20 catalyst as compared to AES-20. SBA-15 only has weak basic sites, which means that the silanol groups in SBA-15 weakly bind to CO2 compared to amines in AMS / AES catalyst of the present invention. The medium basic sites play an essential role in the catalysis as these can easily adsorb and desorb CO2 at ambient temperature conditions. With the increase in the organo-amine loading (3-APTMS), the moderate-strong basic sites gradually increase, as observed from Figure 9 and Table 1 above.

[0116] FTIR analysis

[0117] Fourier transform infrared (FTIR) spectroscopy was utilized to confirm the presence of the amines and silanol groups in the silicate (Figure 10a). The C~N stretching vibration of the organic-amine moiety is usually observed in the 1000-1200 cm-1 range. However, this peak was not resolved due to the overlay with the IR adsorption of Si-O-Si in the range 1130- 1000 cm1and of Si-CH2~R in the range 1250-1200 cm1. Due to the protonation of some of the amines, the stretching frequency of the C-N bond shifts to a slightly higher frequency at 1305 cm1, which is absent in SBA-15 (Comparative Example A) and solvent-extracted SBA-15 (Comparative Example B). This suggests the presence of both the amine and ammonium groups in the functionalized material. In addition, the peak at 750 cm1corresponding to the N-H wagging, which generally appears within the range 665-910 cm1, is present in the functionalized material / catalyst of the present invention. The absence of this peak in SBA-15 and solvent-extracted SBA-15 suggests the successful incorporation of the amine functionality in a silicate framework in the catalyst of the present invention. The IR adsorption at 3500 cm1is due to symmetric stretching of the silanol groups' (Figure 10b). The broadness of the peak in AMS-20 and AES-20 is inferred due to the merging of the symmetric stretching of the N-H group, which appears in the 3300-3350 cm1range. The scissoring frequency of the water molecule appeared at 1635 cm1, indicating the hygroscopic nature of the catalyst. The additional adsorption frequencies appeared in solvent-extracted SBA-15, AES-20 and AMS-20 but were absent in calcined SBA-15, corresponding to the leftover P123 template during the solvent extraction process for template removal. The adsorption bands at 1700 cm1and 1375 cm1corresponded to the ‘C=O’ stretching and ‘C-O- C’ stretching, respectively. As per literature, when P123 is used as a template similar peaks have been observed in the material. So, these peaks probably correspond to leftover P123 in the material.

[0118] TGA analysis

[0119] To understand the thermal stability of the grafted material, i.e., AMS-20 catalyst of the present invention in comparison with solvent-extracted SBA-15, TGA analysis was carried out as depicted in Figure 11 and presented in Table 2 below. The TGA data showed mainly four weight loss peaks at 35-100 °C, 130-280 °C, 280-550 °C and above 550 °C. The weight loss in the temperature range 35-100 °C (13-16%) is mainly due to the loss of the physisorbed water molecules. The weight loss in the 130-280 °C (5-8%) corresponds to the loss of the chemisorbed water molecules and other surface impurities. At 280-550 °C, more or less the same percentage of weight loss (8-9%) was observed in both solvent-extracted SBA-15 and AMS-20, which is mainly due to the removal of the leftover surfactant P123. Above 550 °C, a considerable difference in weight loss is observed in AMS-20 as compared to solvent- extracted SBA-15. The weight loss in solvent-extracted SBA-15 (3.16%) is observed above 550 °C due to the dehydroxylation of the silicate networks. In addition, the removal of or- gano-amine functionality happens in AMS-20 at high temperatures, contributing to the higher weight loss (7.24%) in AMS-20.

[0120] Table 2

[0121] Solid State NMR

[0122] To understand the structural framework around the Si and N atoms, 29Si and 15N solid- state NMR are carried out, and the corresponding results are presented in (Figure 12). In the29Si NMR, the three peaks assigned as Q4 (-110 ppm), Q3 (-102 ppm), and Q2 (-92 ppm) are observed. The Q4 peak is due to the silicate (SiO44) units, whereas the Q3 and Q2 peaks are due to the replacement of the one and two (-OSi) units with the hydroxyl (- OH) units. The highest intensity of the Q3 peak indicateed the presence of the silanol groups with high concentrations in AMS-20. The T2 (-58 ppm) and T3 (-67 ppm) states represented the abundance of the organic silicates in the material. Also, the observed low-intensity DO and DI peaks were assigned to the methyl hydrosiloxane groups from the degradation of a certain extent of 3-APTMS. The low sensitivity of15N nuclei combined with the small quantity of organo-amine silane present in AMS-20 placeed it below the detectable range for both amine and ammonium groups in15N solid-state NMR. However, the singlet observed at 41.5 ppm may correspond to an ammonium group. This is because ammonium (NH4+) groups typically display sharp peaks due to their high symmetry and mobility in the solid state, in contrast to amine (NH2, NH, etc.) groups, which often exhibit broader peaks owing to their lower symmetry and restricted mobility.

[0123] Example 3: Process for preparation of styrene carbonate (SC) from styrene epoxide (SO) using the amine functionalized silica catalyst of Example 1.

[0124] A mixture of epoxides (20 mmol), TBAB (0.1 mmol), and a specific amount of catalyst (100 mg) were taken in a 50 mL RB (Round-bottom flask), which was then connected to an openhead condenser attached to a gas connector with a CO2 (1 atm) balloon. The reaction mixture was flushed with CO2 before the reaction and heated to the desired temperature. After the completion of the reaction, the RB was cooled to room temperature. The quantitative and qualitative analyses of the products were done using gas chromatography and NMR techniques. For gas chromatography sample preparation, a 10 pL reaction mixture was dissolved in 1 mL chloroform and centrifuged to remove the catalyst. After that, the reaction mixture was analysed in an Agilent 7890B-gas chromatography instrument equipped with an FID detector and a HP-5 30 m * 0.32 mm x 0.25 pm (19091 J-413) capillary column. The conversion and selectivity were derived by comparing them with standard calibration curves. The conversion of the reactant and selectivity of the products was calculated considering the Adj. R-Square value. The products were characterised by 1H and 13C NMR using CDCI3 as a solvent in an AV 400 MHZ (Bruker) NMR instrument. The spent catalyst was collected after centrifugation and washed with chloroform three times to remove the trace amount of the reactant / product. After drying, the spent catalyst was further tested for recyclability.

[0125] Example 4: Catalytic activity of AMS catalyst

[0126] Cycloaddition of CO2 into the epoxide ring was carried out in a single pot as described in example 3 above. SO was taken as a model substrate for the epoxide family, and the catalysis was performed under solvent-free conditions. In the controlled experiments, SO activation with CO2 was not observed without a catalyst and a co-catalyst (Table 3, Entry 1). The nonfunctionalized catalyst, i.e., SBA-15, gave 68% conversion with 85% selectivity towards SC in the presence of TBAB (Table 3, Entry 2). Besides having a high surface area, the surface silanol groups of SBA-15 played a crucial role in enhancing the conversion, as these silanol groups bind the epoxide molecules through hydrogen bonding and bring them in close proximity to the surface. The major side product is styrene glycol, which is supposed to be formed from the physiosorbed water molecules. Tetrabutylammonium bromide (TBAB), i.e., the co-catalyst alone, gives 40% conversion with 99% selectivity towards SC (Table 3, Entry 3). The TBAB has previously been utilised for this conversion, but the high- pressure reaction condition makes this process unfriendly. The role of TBAB is to help open the epoxide ring and favour the cycloaddition reaction with CO2. The amine functionalized silica catalysts of the present invention and the co-catalyst TBAB enabled the CO2 insertion reaction at atmospheric pressure at 120 °C with good conversion and selectivity. Further, among the catalysts, the optimum basic sites and the enlarged pore width resulting from the channel distortion make AMS-20 an efficient catalyst compared to SBA-15 / AES, as reflected in the presented data in Table 3 below.

[0127] Table 3

[0128]

[0129] Reaction conditions: 20 mmol SO, 0.1 mmol TBAB, CO2-balloon, 120° C, 7 h, 50 mg catalyst. aIn the absence of the catalyst and co-catalyst (TBAB),bIn the absence of the catalyst but in the presence of TBAB,cIn the presence of the catalyst only.

[0130] Further, as observed from Table 3 above, with the increase in the amine content in the AMS catalysts, the conversion of SO gradually increases from AMS-30 to AMS-20. The amine moieties in the catalyst surface enhances CO2 adsorption, resulting in more CO2 molecules in the close vicinity of SO, favouring accelerated SC formation. However, a further increase in the amine content in the (AMS -15) catalyst of the present invention showed a decrease in the conversion of SO. This may be due to the decrease in pore volume with an increase in surface coverage of the organic-amine content in AMS-15 (Table 3, Entry 7). The effect of suitable pore size / pore volume in accelerating catalytic conversion of the reactions deriving from the mesoporous materials is well explained in the literature. To further prove the effect of the pore volume / pore size on the catalytic activity, the set of AES catalysts (AES- 30 to AES- 15) of Example 1 was tested for catalytic activity, and the catalytic results are tabulated in Table 3 above. The AES series has a similar pore volume / pore size, which may be due to the channel structure with variable amine content, as presented in Table 1. This is reflected in the similar percentage of conversion of SO in AES series catalyst (Table 3, Entries 8 to 11). The fixation of CO2 into styrene oxide to form styrene carbonate is a kinetically controlled reaction. So, the role of the catalyst in the catalytic conversion is more significant at the initial reaction time. AES -20 has the same amine content as AMS-20, but the narrower pore size distribution decreases the conversion of SO. The AMS-20 catalyst is more active among all the amine functionalized silica catalysts due to the enlarged pores resulting from the channel distortion, besides having optimum basic sites. Without the cocatalyst, AMS-20 converts only 15% of SO, which means TBAB plays an important role in this reaction (Table 3, Entry 12). As explained earlier, the large surface area, pore volume, and pore sizes of the catalyst material plays an important role in making it a suitable CO2 absorbent. Depending on the pressure at which the CO2 capture is carried out, the pores of different diameters contribute the most, as explained by Gogotsi et al. At 1 bar, the pores smaller than 0.80 nm contribute the most to the CO2 uptake, and at 0.10 bar, the pores smaller than or equal to 0.50 nm are preferred. The CO2 adsorption capacity was experimentally analyzed by CO2 adsorption isotherm at room temperature with an increase in pressure up to 1 bar, as depicted in Figure 13. SBA-15 (Comparative Example A) has the highest CO2 adsorption capacity 13.6 cc / g followed by AES-20 (11.8 cc / g) and AMS-20 (9.5 cc / g). Though the CO2 adsorption capacity is highest for SBA-15 but, the larger hysteresis loop in AMS-20 indicates more retention of CO2 within the pores. Here, both the CO2 uptake and the retention of CO2 during the activation of SO are to be considered for effective cycloaddition of CO2. The larger pores provide sufficient space to accommodate bigger reactant molecules like SO, co-catalyst, and CO2, facilitating a high catalytic conversion.

[0131] Further, to investigate the scalability scope, a catalytic reaction was performed with a large quantity of SO and the data are presented in Table 4 below. AMS-20 shows 50% conversion and 30% conversion with 40 mmol and 60 mmol of SO within 6h of reaction time. To explore the role of co-catalysts, the reaction was performed with the tetrabutylammonium halides (Table 5). TBAB is the most efficient co-catalyst, giving the best conversion of 78% with 99% selectivity within 6 h of reaction time, followed by TBAI and TBAC. The effectiveness of the bromide is likely to be a good balance between nucleophilicity and leaving ability to facilitate the ring-opening and ring-closing steps during the cycloaddition reaction. Though iodide ion is the best nucleophile and leaving group among the other halides, the large size creates steric hindrance while attaching the styrene oxide molecule, leading to a lower conversion rate than TBAB.

[0132] Table 4

[0133] Reaction condition: O.lmmol TBAB, 7h, 120° C, CO Balloon

[0134] Table 5

[0135] Reaction condition: 20 mmol SO, O.lmmol Co-catalyst, 6h, 120° C, CO2 Balloon

[0136] Further, the reaction parameters like time, temperature and catalyst loading were varied with AMS -20 catalyst of the present invention and the results are depicted in Figure 17. With time, the conversion of SO gradually increases, reaching a maximum at 7 h with 90% conversion of SO (Figure 14a). When the temperature was increased from 60 °C to 120 °C, the catalytic activity increased. However, after 120 °C, due to the formation of many side products, the selectivity of SC decreased (Figure 14b). With the increase in the catalyst loading, the conversion of SO gradually increases, compromising the selectivity of SC (Figure 14c) because of the formation of styrene diol SDO as byproduct from the physisorbed water molecules. Recyclability of up to 4 cycles confirms the stability of the catalytic material (Figure 14d). The catalysis results showed the optimum parameters as 50 mg of the catalyst of the present invention gave 90% conversion, with 99% selectivity of SC at 120 °C, with a 7 h reaction time at atmospheric pressure of CO2.

[0137] Substrate Scope

[0138] AMS-20 showed excellent catalytic conversion of SO to SC at ambient reaction conditions with minimal TBAB as depicted in Table 3 to 5 above. The basic functionality, wide pore size distribution, and larger pore volume of the catalysts are responsible for this excellent catalytic conversion. Further, the catalyst was explored for substrate scope at the optimised reaction condition, and the results are presented in Table 6 below. Various substituted aromatic epoxides, including 4-fluorostyrene oxide, 4-chlorostyrene oxide, and 4-bromosty- rene oxide, were tested for the catalytic conversion at atmospheric pressure of CO2 (Table 6, Entries 1 to 3). Aliphatic cyclic epoxides, such as cyclopentene oxide and cyclohexene oxide, were also included in this test and found to have a good catalytic response regarding conversion and selectivity. The1H and13C NMR spectra of the products were matched with the previously reported1H and13C NMR data and given in Table 7 below.

[0139] Table 6:

[0140] Reaction condition: 20 mmol substrate, 0.1 mmol TBAB, CO2 (Balloon), 120 °C, 7 h.

[0141] Table 7:

[0142] Example 5: Process for preparation of styrene carbonate (SC)-coated zinc (SC@Zn) anode from the styrene carbonate prepared according to Example 3.

[0143] For the fabrication of styrene carbonate-coated zinc foil / anode, 110 mg of SC prepared according to Example 3 and 11 mg of Polyvinylidene fluoride (PVDF) binder were dispersed in 100 pL of N-methyl-2-pyrrolidone (NMP) and sonicated for 1 hour. After the complete dissolution of SC and PVDF, 20 pF of the solution is drop-cast over 1 cm2of Zn foil and dried in an oven at 70 °C for 24h to obtain a uniform coating of SC over Zn foil.

[0144] Example 6: Evaluation of SC@Zn anode of Example 5

[0145] SC was investigated as a protective coating for Zn anode in aqueous rechargeable zinc metal batteries (ARZMBs) for the first time. It was observed that SC acts as an excellent protective layer on the Zn anode and enhances the ARZMB's durability many folds as compared to the bare aqueous Zn batteries. As a protective layer SC was found to suppress the Zn dendrite growth, oxygen evolution reactions (OER) and electrolyte decomposition, and zinc metal corrosion which reflects in the enhanced battery durability. Bare zinc foil exhibits uniform and smooth surface morphology whereas after SC coating, the Zn foil (SC@Zn) anode of Example 5 has a rough texture which confirmed the uniform coating of SC over the zinc foil as analysed by Field emission scanning electron microscopy (FESEM). FESEM images also revealed the uniform Zn deposition in the anode of Zn-SC||Zn-SC symmetric cell as compared to bare Zinc cell after 100 cycles. The impact of the SC coating on the corrosion properties of the Zn anode in ARZMBs was analysed using Linear Polarization Resistance (LPR) as shown in Figure 15a. Zn-SC||Zn-SC symmetric cell comprising the styrene carbonate coated zinc anode of Example 5 showed a decreased corrosion current density and slightly higher corrosion potential than Zn||Zn symmetric cells indicating that the SC@Zn electrode of the present invention comprising SC coating successfully decreases self-corro- sion of Zn anode. Achieving a stable and lower corrosion current density indicates that the zinc anode is less prone to rapid deterioration, thus potentially extending the longevity of the battery.

[0146] Cyclic voltammograms of Zn||SS (zinc against stainless steel) and Zn-SC||SS (styrene carbonate coated zinc of Example 5 against stainless steel) cells were performed from -0.5V to 2V at a scan rate of 1 mV s’1. The CV plots in (Figure 15b) illustrated a lower nucleation of Zn-SC||SS (98 mV) compared to bare zinc (Zn||SS) (126 mV). Uniformly distributed zincophilic groups in the SC coating layer helps in enhanced interaction between these functional groups thus enhancing the Zn deposition kinetics, reduced nucleation overpotential, and uniform Zn deposition of the Zn-SC||SS comprising the anode of the present invention as compared to bare Zn foil. The evaluation of the mechanism of Zn deposition was confirmed by recording chronoamperometric plots of Zn-SC||Zn-SC and Zn||Zn symmetric cells at -150 mV (Figure 15c). When a constant voltage was applied, the rapid increase in the current density of Zn||Zn symmetric cells resulted in the uncontrolled random 2D diffusion process caused by dendrite formation over Zn foil. Whereas, after an initial increase in current density as a result of Zn nucleation, there was a stable 3D diffusion process occurring in the Zn-SC||Zn-SC cell of the present invention indicating a uniform Zn deposition process enabled by SC coating prepared by the catalyst of the present invention over the Zn anode. To have a battery operating at high potential it is essential to suppress water decomposition. The Linear Sweep Voltametric plot of Zn-SC||SS cells (Fig. 15d) exhibited an increased over potential for oxygen evolution reaction indicating the increased stability of electrolyte against water oxidation compared to Zn||SS. Significant information on the electrochemical behaviour and performance of SC coatings on zinc substrates was gathered from the Electrochemical Impedance Spectra (EIS) (Figure 15e). Lower charge transfer resistance values exhibited by Zn-SC||Zn-SC symmetric cell comprising the SC@Zn electrode of the present invention in EIS indicated that hydrophilic SC coatings can stabilize the zinc- electrolyte interface by facilitating uniform wetting and reducing interfacial resistance. Also, the zincophilic functional groups of SC coatings plays a pivotal role in accelerating and facilitating uniform zinc deposition. The cycling stability of Zn||Zn and Zn-SC||Zn-SC symmetric cells were recorded at 1 mA cm-2with a capacity of 1 mAh cm-2to analyze the stability of bare Zn anode compared to Zn-SC as depicted in Figure 15f. The Zn-SC||Zn-SC cell exhibited a plating- stripping stability for over 1000 cycles compared to 80 cycles of the Zn||Zn cell. This excellent stability of zinc anode coated with SC is the result of suppressed electrolyte decomposition and dendrite formation aided by the zincophilicity and hydrophilicity offered by SC prepared via the amine functionalized silica catalyst of the present invention. Further, the contact angle studies as shown in Figure 16, suggested SC coated Zn surface was more hydrophilic as compared to bare Zn. More hydrophilic surface facilitates improved interaction between the electrolyte and the zinc surface, resulting in an uniform dispersion of zinc ions and easy Zn ion transport by lowering the ionic transport resistance at the electrode / electrolyte interface throughout the cycle which improves the life of the battery.

[0147] Example 7: Synthesis of MnCh cathode

[0148] The synthesis of P- MnC was carried out by following the literature. To 0.6 g MnCFAHiO dissolved in 20 mL DI water, 0.3 g KMnC was added and allowed to stir for 30 minutes. The above solution was transferred to a Teflon-lined autoclave and treated hydrothermally at 160 °C for 20h. The resulting product is washed with ethanol and DI water, filtered, and then dried at 60 °C for 24h.

[0149] Example 8: Electrochemical performance of the SC@Zn anode of Example 5 in full cell configuration.

[0150] The practical application of SC@Zn anode of Example 5 was evaluated through a full cell (SC@Zn||P-MnO2 cells) investigation as depicted in Figure 17. A P-MnCh cathode prepared according to Example 7 was used against bare Zn and SC@Zn anode of Example 5, with a 1 M aqueous Zinc trifluoromethane sulfonate (Zn(OTf)2) electrolyte and a Nafion membrane as the separator.

[0151] The cyclic voltammetry (CV) (Figure 17a) and galvanostatic charge-discharge (GCD) (Figure 17b) curves indicated superior performance of SC@Zn||P-MnO2 cells compared to Zn||P-MnO2. Specifically, SC@Zn||P-MnO2 cells exhibited a discharge capacity of 198 mAh g1versus 167 mAh g1for Zn||P-MnO2 cells. Additionally, the rate performance of SC@Zn||P-MnO2 cells demonstrated higher specific capacities at 0.1 A g’1, 0.25 A g’1, 0.5 A g-1and 1 A g-1than Zn||P-MnO2 cells (Figure 17c). The cycling stability of SC@Zn||P- Mn02 cells (Figure 17d) showed better capacity retention (60%) compared to Zn||P-MnO2 cells (51%). These findings demonstrate that the SC prepared via the amine functionalized silica catalyst of the present invention coated on zinc foil enhances the overall performance of full cells by stabilizing the SC coated zinc anode against corrosion and improving zinc ion transport (Figures 15 to 17).

[0152] ADVANTAGES OF THE INVENTION

[0153] • An amine functionalized silica catalyst having broad pore size distribution, large pore volume and tunable Lewis basic sites thereby providing a high catalytic conversion.

[0154] • Hustle free one-pot green co-condensation synthesis route of tunable amine functionalized silica catalyst.

[0155] • Channel and worm-hole morphology both can be synthesized by the process of the present invention by changing the organo amine precursor from 3-APTES to 3-APTMS.

[0156] • Method for scalable catalyst synthesis is provided.

[0157] • Catalysis of CO2 fixation into cyclic carbonates at ambient temperature and atmospheric pressure under solvent free and metal free catalyst.

[0158] • Amine functionalized silica catalyst of the present invention may be employed for synthesis of carbonates from various epoxide substrates.

[0159] • The amine functionalized silica catalyst of the present invention demonstrates high conversion and selectivity.

[0160] • Value addition of CO2 is demonstrated by using CO2 derived product i.e. styrene carbonate as a protective layer on Zn anode in ARZMBs.

Claims

AMENDED CLAIMS received by the International Bureau on 20 April 2026 (20.04.2026)We Claim:

1. A mesoporous worm-hole like amine functionalized silica catalyst comprising of 3- aminopropyl trimethoxy silane (3-APTMS) having average pore diameter in a range from 1 to 100 nm and specific surface area in a range from 100 to 1,000 m2 / g.

2. The mesoporous worm-hole like amine functionalized silica catalyst as claimed in claim 1, having pore diameter in a range from 5 nm to 50 nm and specific surface area in a range from 400 to 1,000 m2 / g.

3. A process for preparation of the amine functionalized silica catalyst, the process comprising:(a) mixing poly(ethylene glycol) -block-poly(propylene glycol) -block-poly (ethylene glycol) (Pluronic Pl 23) with hydrochloric acid (HC1) at a temperature in a range from 30° C to 40° C to obtain a solution; and(b) adding a mixture of 3 -aminopropyl trimethoxy silane (3-APTMS) and tetraethyl orthosilicate (TEOS) to the solution of step (a) and treating under hydrothermal conditions.

4. The process as claimed in claim 3, wherein the Pluronic P123 having weight in a range from 1.5 g to 2.5 g is mixed with 70 mL to 80 mL of HC1 (35%) having concentration in a range from 1.6 M to 1.8 M.

5. The process as claimed in claim 3, wherein the 3-APTMS and TEOS are mixed at a volume ratio in a range from 1: 15 to 1:30.

6. The process as claimed in claim 3, wherein the mixture is hydrothermally treated at a temperature in a range from 90°C to 110°C for 48 hours to 60 hours.

7. A process for converting epoxide and carbon dioxide (CO2) to carbonate, the process comprising:(a) reacting epoxide, a co-catalyst and the amine functionalized silica catalyst as claimed in claim 1 to obtain a mixture; and(b) flushing the mixture with carbon dioxide (CO2), followed by heating at 10° C to 120° C.

8. The process as claimed in claim 7, wherein the epoxide is selected from styrene oxide, 4-fluorostyrene oxide, 4 -chloro styrene oxide, 4 -bromo styrene oxide, cyclopentane oxide, cyclohexane oxide or combination thereof.

9. A process for preparation of styrene carbonate coated zinc anode by depositing a slurry of styrene carbonate prepared by the process as claimed in claim 7, binder and solvent on zinc.

10. A full cell comprising:(a) a styrene carbonate coated zinc anode obtained by a process as claimed in claim 9;(b) a manganese oxide (P- MnCh) cathode; (c) an electrolyte; and(d) a separator.

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