WO2021234717A1

WO2021234717A1 - Magnesium nanoparticles to capture and convert co2 to methane, methanol or formic acid or other fuels or chemicals

Info

Publication number: WO2021234717A1
Application number: PCT/IN2020/050458
Authority: WO
Inventors: Vivek Polshettiwar; Sushma RAWOOL; Rajesh Belgamwar
Original assignee: Tata Institute Of Fundamental Research
Priority date: 2020-05-21
Filing date: 2020-05-21
Publication date: 2021-11-25

Abstract

This invention discloses a process of conversion of Carbon Dioxide (CO₂) into methane, methanol, formic acids or other fuels or chemicals, characterized by the use of Magnesium (Mg) nanoparticles (NPs) or bulk Mg for the conversion process, wherein Magnesium (Mg) chemisorbs and then activates the Carbon Dioxide (CO₂) molecules by electron transfer to facilitate the reduction, using water as a hydrogen source. This conversion of Carbon Dioxide (CO₂) is carried out at atmospheric pressure and at room temperature, and without any external energy source, such as thermal, light or electric energy source, or any sacrificial reagent or any co-catalysts. The reaction also facilitates in the production of high yield of Hydrogen.

Description

TITLE

Magnesium Nanoparticles to Capture and Convert CO₂ to Methane, Methanol or Formic Acid or Other Fuels or Chemicals.

FIELD OF THE INVENTION

The present invention relates to the development of CO₂ conversion process that works at atmospheric pressure and temperature without any external energy source, and with water as a hydrogen source. This invention will have a significant scientific and technological impact to achieve the dream of “Net-zero emissions energy systems”.

PRIOR ART

Climate change hits a giant weak spot in human history. Disproportionate use of natural resources, including fossil fuels, has created an extreme imbalance on planet earth and first- priority of all of us is to take on this challenge. An excessive amount of CO₂ is the main cause of climate change, and hence, its reduction from the Earth’s atmosphere is key to stop further degradation of the environment. The best approach is not only the capture of CO₂ but also its conversion to fuel, where CO₂ can act as a carbon feedstock with zero cost. The catalytic conversion of CO₂ to, for example, methane and methanol using pure water as a hydrogen source can provide a direct solution to the problems of excessive CO₂ levels.

Given the vital importance of energy and environmental challenges, several research groups are working in this field of CO₂ conversion worldwide. Catalysts stability, the requirement of high pressure/temperature and need of external hydrogen gas, are some of the main concerns of the current protocols for CO₂ conversion.

Magnesium is known as a powerful reducing agent in chemistry, although mostly in the form of Grignard reagents. Magnesium-based catalysts were used in the reduction of ketones and for Pinacol reactions, assisted with a magnesium halide, hydride, and HgCF etc. Organometallic Mg- complexes are also extensively used in various organic transformations. Magnesium is also known for generation of hydrogen, as well as thermal and electric energy. There are several reports on the generation of hydrogen using Mg metal with the aid of catalyst or additives from water. During the year 1986-88, Robert and Ryder et al. studied the interaction of CO2 with Mg surface and mentioned the possibility of formation of formate type species.

DISADVANTAGES OF PRIOR ART

No report was found where Mg metal (bulk as well as nanoparticles) was used to convert CO2 (pure as well as directly from the air) into methane, methanol or formic acid or other fuels or chemicals until today.

AIMS AND OBJECTIVES

It is, thus, the basic object of this invention to disclose a process for conversion of C02 (pure as well as directly from the air) that works at atmospheric pressure and temperature without any external energy source and water as a hydrogen source.

SUMMARY OF THE INVENTION

In this invention, an unexpected behavior of magnesium (Mg) towards carbon dioxide was observed. Mg nanoparticles (NPs) as well as bulk Mg convert CO2 to methane, methanol and formic acid by simply using water as a hydrogen source. This conversion took place at atmospheric pressure within a few minutes. Notably, no external energy (thermal, light or electric) was required, and reaction took place at room temperature. There was also no need of sacrificial reagent or co-catalysts for this conversion to proceed. Magnesium chemisorbed and then activated CO2 molecules by electron transfer to facilitate the reduction. Mechanistic studies indicate a unique cooperative act of magnesium, basic magnesium carbonate, CO2 and water, to convert CO2 to methane, methanol and formic acid. In the absence of any one of these, no CO2 conversion takes place. Isotopic labeled ¹³C0₂ experiment, PXRD, NMR, and FTIR studies allowed identification of reaction intermediates and overall reaction pathway. Magnesium is the eighth most common element and the sixth most abundant metal. Reusability of Mg nanoparticles which were converted to magnesium carbonates during CO2 conversion is possible by a commercially available solar energy pumped laser process. Thus, use of magnesium (nano and bulk), which are air-stable and can be used in open environment, although non-catalytic and stoichiometric could serve as the basis of an economical and sustainable CO2 utilization strategy, which could be a step towards magnesium civilization.

Magnesium nanoparticles converted carbon dioxide to methane, methanol, and formic acid, using water as a hydrogen source. No external energy, like light, heat or electricity was required for this conversion, and it took place at room temperature and atmospheric pressure. There was also no need of sacrificial reagent or co-catalysts for this conversion to proceed. The reaction was very fast with a maximum yield of products was achieved in less than 15 minutes.

It was observed that the unique property of Mg is not only to chemisorb and activate CO2 but also transfer an electron to facilitate the reduction of CO2 using water as a hydrogen source. Mechanistic studies showed a distinctive cooperative act of magnesium, basic magnesium carbonate, CO2 and water, to convert CO2 to methane, methanol and formic acid. Isotopic labeled CO2 experiment, PXRD, NMR and FTIR studies allowed the identification of reaction intermediates and overall reaction pathway.

Reusability of Mg nanoparticles which were converted to magnesium carbonates during CO2 conversion is possible by a commercially available solar energy pumped laser processes. Thus, although this is a non-catalytic stoichiometric reaction, regeneration of Mg by solar laser in just 1 USD for 1 Kg of Mg, makes this protocol economical and sustainable. Using this protocol, 1 kg of magnesium on reaction with water and CO2, at ambient conditions, in a simple and safer way, produces 2.24 liters of methane, 0.57 liters of methanol, 0.59 liters of formic acid and 3.9 kg of basic magnesium carbonate, in just 15 minutes. This protocol can even be used for hydrogen production (940 mL g-1), which is nearly 420 times more than hydrogen produced by the reaction of Mg with water alone (2.24 mL g-1). Thus, Mg (nano and bulk), which is air-stable and can be used in open environment, assisted CO2 conversion protocol may open up a novel way to tackle COi’s environmental challenge to our climate. It will also have a significant scientific and technological impact on “Magnesium Civilization” 49 for an alternative energy source to conventional fuel. The low- temperature experiments also indicate the future prospect of the use of this CO2 to fuel the process at Mars surface where CO2, water (ice), and magnesium are abundant.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. (a), (b) TEM, (c) PXRD and (d) N2 sorption isotherm of Mg nanoparticles.

Figure 2. Methane yield with reaction time by reduction of C02 using water at room temperature and atmospheric pressure, using (a) magnesium nanoparticles, (b) various metals and Mg-metal alloy. Error bars are not shown in b to avoid crowding and was less than 10%.

Figure 3. Methanol, formic acid, methane and hydrogen yield by reduction of C02 using water at room temperature and atmospheric pressure using magnesium nanoparticles, micro powder and bulk, and Mg- metal alloy.

Figure 4. (a) Methane yield with reaction time, by reduction of 13C02 using water at room temperature and atmospheric pressure, using magnesium nanoparticles, (b) 13C NMR spectrum of the reaction mixture carried out using labeled 13C02 gas after 1 h of reaction.

Figure 5. Hydrogen yield with reaction time by reduction of C02 using water at room temperature and atmospheric pressure, using (a) magnesium nanoparticles, (b) various metals and Mg-metal alloy. Error bars are not shown in b to avoid crowding and was less than 5%.

Figure 6. (a) Methane, methanol and formic acid yield at 1, 5 and 15 minutes by reduction of C02 using water at room temperature and atmospheric pressure using magnesium nanoparticles and their respective, (b) FTIR spectra, and (c) PXRD patterns. SEM images of the solid products are in figure S4. Figure 7. (a) methane yield with reaction time, by reduction of C02 at room temperature and atmospheric pressure, using magnesium nanoparticles, where initial products formed were flushed out at 5, 10 and 15 minutes (b) PXRD of the solid product after 0, 5, 10 and 15 minutes of the reaction.

Figure 8. Plausible reaction mechanism of C02 conversion to methane, methanol and formic acid by magnesium using water.

Figure 9. Experimental set up for C02 conversion. Gaseous product of the reaction was identified and quantified using micro GC and liquid product by 1H NMR.

Figure 10. (a) Hydrogen and (b) methane yield, during control experiments where water was replaced by hydrogen gas, and in another case no C02 was used.

Figure 11. The 13C NMR spectrum of the reaction mixture after 1 h of reaction using unlabeled C02, under exactly same NMR pulse sequence and the total number of scans (that of the 13C02 experiment).

Figure 12. SEM images of solid product formed after reduction of C02 using magnesium nanoparticles and water, at (a) 1, (b) 5 and (c) 15 minutes.

Figure 13. (a) Hydrogen and (b) methane yield with reaction time, by reduction of C02 at room temperature and atmospheric pressure, using magnesium nanoparticles, in various solvents.

Figure 14. (a) Hydrogen and (b) methane yield with reaction time, by reduction of C02 using water at room temperature and atmospheric pressure, using magnesium nanoparticles, exposed to air for 1, 3 and 11 days (c) PXRD of 1, 3 and 11 days exposed Mg nanoparticles.

DETAILED DESCRIPTION OF THE INVENTION

First magnesium nanoparticles were synthesized by the reported protocol using MgCF and dibutyl magnesium as Mg precursor⁴² and carried out preliminary CO2 conversion experiments. Subsequently, we directly purchased the commercially available Mg nanoparticles and conducted further experiments. Transmission electron microscopy (TEM) images indicate that the nanoparticles are aggregates of nanocrystals with sizes between 20 to 100 nm (Figure la, b). Powder X-ray diffraction (PXRD) analysis confirms the crystalline phase of Mg nanoparticles (JCPDS No.:01-089-7195) (Figure lc). N2 sorption studies indicate the surface area of 13 m² g ¹ (Figure Id).

These Mg NPs were evaluated for CO2 reduction reaction in the water at room temperature, and atmospheric pressure in a batch reactor made up of glass (as shown in Figure 9). Product identification and quantification were conducted by on-line micro-gas chromatography (GC) with a thermal conductivity detector (TCD). These results were also re-confirmed by using another off-line GC-TCD- FID system. Formation of a good amount of methane (~ 100 pmol g-1) (Figure 2) was observed. The CO2 conversion took place at room temperature and 1 bar pressure. Kinetics of the reaction was very fast, with around 100 pmol g-1 of methane was produced in just 15 minutes (Figure 2a). Mg-assisted CO2 conversion, directly from the air, yielded 3.5 pmol g ¹ methane in just 10 minutes at room temperature.

The Mg-metal (Al, Ni, Ca) alloy and bulk Mg powders were then studied for this process. No significant improvement in the reactivity of Mg for methane production was observed (Figure 2b, Table SI for Mg content normalized yield). Notably, even bulk (granules) and micron sized (powder) Mg converted CO2 to methane in good yield, but with a slower rate as compared to nanoparticles. This indicates that due to nano-size of the Mg and their high external surface area, efficient chemisorption of CO2 on Mg surface took place, which accelerated the rate of methane formation (Figure 2b). Thus, both nano, as well as bulk, were able to activate the CO2 and transfer the electron to yield methane, albeit at different reaction rates. Magnesium hydride did not produce any methane (Figure 2b). This indicates that the bare surface of Mg(0) was necessary for adsorption and activation of CO2 on its surface. Calcium yielded no methane (Figure 2b). This could be due to either low residence time of proton to reduce carbonates or poor electron transfer efficiency of calcium.

Notably, when the liquid reaction mixture was analyzed by 1H nuclear magnetic resonance (NMR) spectroscopy, the formation of methanol and formic acid as well was observed (Figure 3). Mg nanoparticles yielded 25.6 pmol g-1 of methanol and 26.2 pmol g-1 of formic acid. Other Mg-alloy also yielded a moderate amount of methanol and formic acid (Figure 3). MgH2 and calcium metal yielded a very small amount of methanol and formic acid, confirming their poor ability to adsorb and activate CO2 on their surface.

To prove that carbon source is indeed CO2, a blank reaction without CO2 was conducted and no methane yield was observed (Figure 10). To further confirm CO2 as the carbon source, isotopically labeled ¹³C0₂ was used and the products by GC (Figure 4a) and ¹³C NMR (Figure 4b) were analyzed. ¹³C NMR spectrum clearly shows the signal for methanol and formic acid. However, when unlabeled CO2 was used, although the formation of methanol and formic acid was confirmed by 1H NMR, no 13C signal was observed under exactly same NMR pulse sequence and the total number of scans (that of the ¹³C0₂ experiment) (Figure 11). This was due to low abundance ¹³C in unlabeled CO2 (Figure 4b). This confirms CO2 as a carbon source. ¹³C NMR also indicates the formation of basic carbonates of Mg (Figure 4b).

Notably, a large amount of hydrogen production in the process was observed when Mg (nano, bulk, and its alloy) reacted with water and CO2 (Figure 5). In the absence of CO2, Mg does not react efficiently with water and hydrogen yield was extremely low, 100 pmol g-1 as compared to 42000 pmol g-1 in the presence of CO2. This was due to poor solubility of magnesium hydroxide formed by the reaction of Mg with water, forming shell around Mg. This restricted the internal Mg surface to react further with water, reducing hydrogen yield. However, in the presence of CO2, magnesium hydroxide was converted to carbonates and basic carbonates, which are more soluble in water than magnesium hydroxide and hence peeled off from Mg. This exposed fresh Mg surface to react with water, accelerating the hydrogen production rate. Thus, this protocol, using air stable magnesium (nano and bulk), can even be used for hydrogen production (940 mL g-1) with faster kinetics, which is nearly 420 times more than hydrogen produced by the reaction of Mg with water alone (2.24 mL g- 1).

To understand the mechanism of the CO2 conversion, a diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, 1H NMR and PXRD studies were carried out. First, Mg nanopowder was purged with C02 gas for 30 min, and then 5 mL water was added to it. Reactions was stopped at various time intervals to capture the reaction intermediates and Mg containing surface species, and solid product was analysed by DRIFT and PXRD (Figure 6). The gaseous and liquid products at each time intervals of the reaction were analyzed by GC and 1H NMR analysis respectively (Figure 6a). The increase in methane, methanol and formic acid yield was observed with an increase in reaction time (Figure 6a). The FTIR spectra of the magnesium nanoparticles after purging with C02 gas shows a broad absorption band at 1259-1621 cm-1, which corresponds to the adsorbed carbonate species.45 The sample collected just after the addition of water also shows broad absorption in the region of 1259- 1621 cm-1 and a sharp band at 3691 cm-1 which corresponds to the asymmetric stretching vibration of OH group.46 FTIR spectra of samples collected after 1 and 5 minutes matches with a characteristic spectrum of MgC0₃.3H₂0, whereas the spectrum of the sample collected after 15 minutes matches to the basic magnesium carbonate, Mg₅(C0₃)₄(0H)₂.4H₂0^46,47 Weak PXRD signal of magnesium hydroxide was also observed after 1 minute, which vanished in 5 minutes sample (Figure 6c), indicating the reaction of CO2 with magnesium hydroxide to yield basic magnesium carbonate.

The presence of bands at 880 (D2 mode), 1077 (D 1 mode), 1485 and 1427 (D3 mode) cm ¹ were attributed to the carbonate species of MgC0₃.3H₂0⁴⁶ A band at 1645 cm ¹ corresponds to the O-H bending mode of water, 46 while a sharp band at 3699 cm-1 observed corresponds to the asymmetric stretching vibration of OH group 45 . The FTIR spectra of 15 min sample showed bands corresponds to carbonate species at 1481, 1425, 1114 cm ¹. The bands appeared at 801, 850 and 880 cm ¹ corresponds to the carbonate bending vibrations. These absorption bands are the characteristic peaks of the Mgs(C0₃)₄(0H)₂.4H₂0⁴⁷ Thus, FTIR analysis shows the formation of magnesium carbonate after 1 and 5 minutes and basic magnesium carbonate after 15 minutes of reaction, confirming their formation during the CO2 conversion. PXRD (Figure 6c) of these samples also confirm the formation of magnesium carbonate (JCPDS No.00-001-0130) at 1 and 5 minutes, and basic carbonate (JCPDS No.Ol- 070-0361) after 15 minutes. The formation of basic carbonate was also confirmed from ¹³C NMR (Figure 4b).

In order to confirm that basic carbonate (I) and carbonate (II) species are reaction intermediates and getting converted to various products, once these species are formed at a various reaction time interval (5, 10 and 15 minutes), all the gases (CO2, hydrogen and methane) from the reactor by inert argon gas were flushed out. The reaction progress was then further monitored with time (Figure 7a). Notably, even after flushing out all the CO2 gas, the formation of methane (Figure 7a) was still observed. This confirms that basic magnesium carbonates are the reaction intermediate.

Methane yield was highest for 10 minutes flushed reaction and lowest for 15 minutes flushed reaction, while the moderate yield for 5 minutes flushed reaction was observed (Figure 7a). Lowest yield of 15 minutes flushed reaction was due to the transformation of most of the Mg to basic carbonate, and a negligible amount of Mg remained (as can be seen from PXRD, Figure 7b), which was not sufficient to provide a required electron to split water as well as convert a proton to hydrogen radical. 10 minutes flushed reaction showed the highest methane yield, as it has the optimum amount of basic magnesium carbonate and magnesium metal (based on PXRD, Figure 7b). At 5 minutes flushed reaction, not enough amount of basic magnesium carbonate was formed (based on PXRD, Figure 7b) and hence moderate methane yield was observed. These experiments confirm the proton assisted electron mediated reduction of CO² via basic magnesium carbonate species.

Role of solvent was studied, and it was observed that water is the important for this conversion (Figure 13). Since MgO is known for CO2 adsorption, the role of MgO on Mg surface by oxidizing Mg surface by exposing them to air at 80 °C for 1 day, 3 days and 11 days was studied and then evaluated for CO2 conversion (Figure 14). No significant effect on methane yield was observed, indicating that MgO is not playing any role in this process of C02 conversion, although a thin layer of MgO on Mg surface may be aiding during the CO2 adsorption step. Pure MgO was also evaluated under these conditions, and no CO2 conversion was observed.

Based on these studies, a plausible mechanism (Figure 8) was proposed. First, the CO2 molecules get adsorbed and activated by magnesium in the presence of water forming magnesium carbonate hydroxide (basic carbonate). Then, the reduction proceeds through a series of elementary steps which involve the transfer of an electron (from Mg) and a proton (from water splitting), as well as breaking C-0 bonds and creating new C-H bonds. Formation of several of the intermediates (radical anion species) formed at different stages accounts for the various products (formic acid, methanol, and methane) formation. CO2 molecule first physically adsorbed and held at the Mg surface. This is followed by the formation of chemisorbed bent surface anionic species CO2- by bonding between magnesium and one of the CO2 oxygen atom. The monodentate binding of the CO2 via oxygen atoms to one Mg atom and reaction with water yields basic hydroxide, which leads to the formation of a formate anion bound in a bidentate mode (not shown in figure 5). It is known that O removal is easy from such a species of CO2.⁴³ Such a CO2- species is found to be unstable, and hence it reacts with water molecules producing basic magnesium carbonate species (I) (Figure 5).

Then, the formation of second Mg-0 bond takes place forming a four-member ring (II).43 This step is similar to the CO2 reaction by the magnesium-containing enzyme RuBisCo.⁴⁴ Robert and Ryder et al. predicted that Mg-CC - species due to instability could readily add hydrogen to yield formate type species. On a similar line, since this four-membered ring species (II) is also unstable, it readily adds hydrogen to produce formaldehyde intermediate species. The electron from magnesium and proton from water splitting converts this cyclic species (II) to carboxyl radical species IV (via species III). The free hydrogen atom (radical) that originates from the reduction of a proton by a magnesium electron, then converts carboxyl radical to formic acid surface intermediate (V), which on hydrolysis yields formic acid.

In the next step, the formic acid surface species (V) accepts further H. to form a dihydroxymethyl radical intermediates (VI), which upon attachment of another H. leads to methanol surface intermediate (VII), which yields methanol. Species VII on further reduction forms a methyl radical intermediates (VIII), which then reduced by H. to yield methane and magnesium hydroxide. Magnesium hydroxide (X) then reacts with CO2 to form basic carbonate (I), and ideally, the reaction cycle continues. However, product yields saturated after around 15 minutes and no further reaction was observed. This was due to complete conversion of Mg to basic carbonate and hence non-availability of electron donor Mg(0) metal.

To confirm that it is the proton from water splitting that is reducing to radical species by an electron from Mg, the reaction using external hydrogen (Figure 10) was conducted. No methane formation was observed in the absence of water using hydrogen gas, ratifying the proposed mechanism. However, if Mg reacts with water and get oxidized, it is no more available for reduction of CO2. The answer came from the experiment where Mg was reacted with water in the absence of CO2. Notably, in the absence of CO2, Mg does not react efficiently with water and hydrogen yield was extremely low, 100 pmol g ¹ as compared to 42000 pmol g ¹ in the presence of CO2 (Figure 10). This was due to poor solubility of magnesium hydroxide formed by the reaction of Mg with water, which formed the shell around Mg, restricting the internal Mg surface to further react with water. This unreacted Mg was then interacting with CO2 and acting as a reducing agent, as proposed in the mechanism. These Mg phases were seen in PXRD studies while their interactions with CO2 were seen in FTIR and NMR studies.

Reusability of Magnesium. Reusability of Mg nanoparticles, which gets converted to magnesium carbonates during the CO2 conversion process is possible. The product basic magnesium carbonate can be treated with HC1 to convert them instantaneously to MgCk which can be converted to Mg nanoparticles by a commercially available process. Recently Yabe et al. reported regeneration of Mg by solar energy pumped laser. They needed only ~ 1 USD to produce 1 kg of magnesium. Thus, although this is a non-catalytic stoichiometric reaction, regeneration of Mg by solar laser in just 1 USD for 1 Kg of Mg, makes this protocol economical and sustainable.

Also, magnesium is the eighth most common element and the sixth most abundant metal, (2.5% of Earth's surface and 0.14% in seawater) and costs about US$ 1 per kg. Product basic magnesium carbonates also have high demand in the industry, including self-cementing application. Using this protocol, 1 kg of magnesium by simply reaction with water and CO2 produces 2.24 liters of methane, 0.57 liters of methanol, 0.59 liters of formic acid and 3.9 kg of basic magnesium carbonate. Notably, this entire production can happen in just 15 minutes, at room temperature and atmospheric pressure, in the exceptionally simple and safer protocol. Unlike other metal nanoparticles, nano-Mg powder is extremely stable and can be handled in the open air without any loss in activity (Figure 14).

To gain insight about the sustainability of the protocol, Mg was compared with some of the best reported metal catalysts which converted CO2 to methane at room temperature and atmospheric pressures (Table 1). Methane yield per gm of catalysts as well as per US$, is dramatically high in case of Mg NPs as compare some of the best reported catalysts recently.

Table 1. Comparison of metal catalysts that converted CO2 to methane at room temperature and atmospheric pressure.

Magnesium Assisted CO2 to Fuel at Mars Surface. Planet Mars environment has 95.32 % of CO2, while its surface has water in the ice form. Recently, the presence of magnesium on Mars in abundant amounts was also reported. Therefore, to explore the possibility of the use of this Mg-assisted CO2 conversion process on Mars, the Mg-assisted CO2 conversion was carried out at - 1 to +1 °C temperature. Notably, methane was produced in a reasonable amount (35 pmol g ¹) in just 20 minutes, although at a slower rate as compare to room temperature reaction, due to low reaction temperature. Good amount of methanol (28 pmol g ¹ ) and formic acid (37 pmol g ¹) formation was also observed. These results indicate the potential of this Mg-process to be used in Mars environment.

Examples

Mg nanopowder, its alloy and other metals were purchased from Nanoshel Inc. with purity > 99.9%. Electron microscopy imaging was performed on a ZEISS ULTRA scanning electron microscope and FEI tecnai transmission electron microscope. Samples were prepared by drop casting diluted ethanolic suspension of the powder onto the aluminum stub (for SEM) and on the copper grid (for TEM). Powder X-ray diffraction patterns were recorded using Panalytical X’Pert Propowder X-ray diffractometer using Cu-Ka radiation. FTIR spectra were recorded using JASCO FT/IR-4700. The NMR study was carried out by Bruker AVANCE II spectrometer BO = 9.4 T (VO = 800 MHz for ¹ H). Methanol and formic acid was identified by 1H NMR and quantified by the external calibration method. ¹³C NMR was used to identify the products of the ¹³C02 labeled experiment.

CO2 conversion reaction was carried out by taking 50 mg of magnesium (or other metal/alloy) in a 350 ml round bottom (RB) flask as a batch reactor (as shown in Figure 9). To protect the oxidation of magnesium surface, Mg nanoparticles were stored in a glove box with inert (argon) atmosphere and loaded in RB flask in the glove box. The RB flask was purged with CO2 gas (99.995 % pure) for 30 min with a flow rate of 250 mL min-1 using a mass flow controller. After that 5 ml of DI water was added in ~20 seconds. Reaction progress was monitored with time, and gas sampling was done after every 5 min. Methane and hydrogen were quantified by on-line Agilent Technologies 490 micro GC, with molecular sieve column and TCD detector. Methanol and formic acid were identified and quantified by 1H NMR. C02 conversion by Mg nanoparticles was reproduced for more than 15 times.

Table SI. Methanol, formic acid, methane, and hydrogen yield (normalized by Mg contents) by reduction of CO2 using water at room temperature and atmospheric pressure using magnesium nanoparticles, and Mg-metal alloy.

Table S2. Methanol, formic acid, methane, and hydrogen yield by reduction of CC using water at room temperature and atmospheric pressure using magnesium

The foregoing description of the embodiments will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt, for various applications, such embodiments without further research and without parting from the invention, and it is, therefore, to be understood that such adaptations and modifications will have to be considered as equivalent to these embodiments. The means and the materials to realize the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not for limitation. It will also be apparent to those skilled in the art that other embodiments, improvements, details and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this invention.

Claims

CLAIMS I/we claim:

1. A process of conversion of Carbon Dioxide (CO2) into methane, methanol, formic acids or other fuels or chemicals, characterized by the use of Magnesium (Mg) for the conversion process.

2. A process, as claimed in claim 1, wherein Magnesium (Mg) chemisorbs and then activates the Carbon Dioxide (CO2) molecules by electron transfer to facilitate the reduction, using water as a hydrogen source.

3. A process, as claimed in claim 1, wherein this conversion of Carbon Dioxide (CO2) is carried out at low to atmospheric pressure and at -100 °C to room temperature.

4. A process, as claimed in claim 1, wherein this conversion Carbon Dioxide (CO2) is carried out without any external energy source, such as thermal, light or electric energy source, or any sacrificial reagent or any co-catalysts.

5. A process, as claimed in claim 1, wherein Magnesium (Mg) nanoparticles (NPs) or bulk Mg is used to carry out this conversion of Carbon Dioxide (CO2).

6. A process, as claimed in claim 1, wherein the conversion of Carbon Dioxide (CO2) into around 100 pmol g-1 of methane using Magnesium (Mg) nanoparticles (NPs) takes place in a time range of less than 15 minutes.

7. A process, as claimed in claim 1, which can also be used to produce high yield of Hydrogen.