Thermodynamic Analysis of Methanol Synthesis viaCO2 Hydrogenation ReactionSuresh Kanuri 

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad CampusSatyapaul A. Singh 

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad CampusSantanu P. Datta 

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad CampusChanchal Chakraborty 

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad CampusSounak Roy 

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad CampusSrikanta Dinda  ( srikantadinda@gmail.com )

BITS Hyderabad: Birla Institute of Technology and Science - Hyderabad Campushttps://orcid.org/0000-0001-5566-1891

Research Article

Keywords: CO2 hydrogenation, Methanol synthesis, Aspen simulation, Equilibrium analysis

Posted Date: August 6th, 2021

DOI: https://doi.org/10.21203/rs.3.rs-721475/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.  Read Full License

1

Thermodynamic Analysis of Methanol Synthesis via CO2 Hydrogenation Reaction 1

Suresh Kanuri1, Satyapaul A. Singh1, Santanu P. Datta2, Chanchal Chakraborty3, Sounak Roy3, and 2

Srikanta Dinda1* 3

1Department of Chemical Engineering, 2Department of Mechanical Engineering, 3Department of Chemistry, 4

Birla Institute of Technology and Science Pilani, Hyderabad Campus, Hyderabad, Telangana-500078, India. 5

6

*Corresponding Author: 7

Srikanta Dinda, Email: srikantadinda@gmail.com; Telephone: +91–4066303586; Fax: +91–4066303998 8

9

Abstract 10

The most inspiring opportunity to reduce greenhouse gas emissions is direct hydrogenation of CO2 into a 11

commodity of products, which is also an appealing choice for generating renewable energy. CO2 hydrogenation 12

can yield methanol which has a broad range of applications. In the present study, a thermodynamic feasibility 13

analysis of the CO2 hydrogenation reaction is carried out using the Aspen Plus tool. CO2 hydrogenation to 14

methanol, reverse-water-gas-shift (RWGS), and methanol decomposition reactions were considered in this 15

analysis. The effect of different parameters such as temperature (ranging from 50 to 500 °C), pressures (ranging 16

from 1 bar to 50 bar), and CO2:H2 molar ratio (ranging from 1:3 to 1:20) on methanol yield has been investigated. 17

The Aspen predicted data is compared with the fixed-bed reactor experimental data. High pressure and low-18

temperature conditions are found to be the favourable option for a higher value of methanol yield. The CO2 19

conversion and CH3OH selectivity are favourable when the H2/CO2 molar ratio is greater than 3. A substantial gap 20

between the Aspen predicted equilibrium conversion of CO2 and the experimental value of CO2 conversion is 21

observed in the study. 22

23

Keywords: CO2 hydrogenation, Methanol synthesis, Aspen simulation, Equilibrium analysis. 24

25

2

1. Introduction 26

The growing trend of global warming, the declining trend of fossil fuel reserves, and the need for an 27

alternative to fossil fuels are the most critical challenges of the twenty-first century. CO2 levels in the atmosphere 28

have already exceeded the pre-industrial era by about 280 ppm and now reached 410 ppm (Li et al. 2018; Chen et 29

al. 2021). In this context, scientists and researchers concentrated on two key technologies: carbon capture and 30

storage (CCS) (Atsonios et al. 2016) and carbon capture and utilization (CCU) (Han et al. 2021). For reducing 31

CO2 concentrations in the atmosphere, the CCU has begun to emerge as a more appealing alternative than CCS 32

(Sha et al. 2020). When considering CCU, CO2 hydrogenation pathways have become essential for producing 33

useful chemicals such as syngas (CO2, CO, and H2), methane (CH4), methanol (CH3OH), ethanol (C2H5OH), 34

dimethyl ether (CH3OCH3), and formic acid (CH2O2) (Leonzio et al. 2019; Sharma et al. 2021). Methanol 35

synthesis from CO2 hydrogenation receives increasing emphasis than other commodities due to its environmental 36

friendliness, lack of toxic emissions when burned, and other uses (Din et al. 2019; Salehi et al. 2021). Methanol is 37

used as a solvent and a raw material to produce a wide range of chemicals (Dalena et al. 2018; Cai et al. 2020; 38

Zhong et al. 2020). The mission is to minimize the CO2 concentration, reduce Carbon emissions, and fulfil the 39

requirement for the chemicals listed above. 40

The synthesis of methanol from CO2 using Cu, Ag, Au, and Pd-based heterogeneous catalysts has also 41

been studied by a group of scientists and experts. Witoon et al. (2013) studied the CO2 hydrogenation to methanol 42

using Cu/ZnO catalyst at 180 °C and 20 bar. Their results revealed that the CH3OH selectivity is 98%, whereas 43

CO2 conversion is only 5%. Rui et al. (2020) investigated the in-situ characterizations using time-resolved X-ray 44

diffraction, ambient-pressure X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy using 45

Au/In2O3 catalyst. Due to the gold-indium oxide strong metal-support interactions and the dispersion of gold, their 46

investigation demonstrated that methanol selectivity reaches 100% at 225 °C temperature and 50 bar pressure, but 47

CO2 conversion is only 1.3%. In another study, it is observed that Ce+3 ions increased the oxygen-vacant sites of 48

the PdZn/CeO2 catalyst, resulting in 100% methanol selectivity and 7.7% CO2 conversion at 220 °C and 30 bar 49

(Malik et al. 2018). Many scientists have performed experimental investigations on the hydrogenation of CO2 for 50

methanol synthesis using different catalysts for a wide range of pressure. Surprisingly, in many articles, nearly 51

100% methanol selectivity has been reported, but all of them experienced poor (<15%) CO2 conversion. 52

Therefore, the design of highly efficient, high-stability, and low-cost catalysts are immediately required to enable 53

the CO2 conversion for large-scale production. The thermodynamic analysis of any reactive system can anticipate 54

the feasibility of the maximum amount of desired products and the optimum conditions required to obtain the 55

desired yield. Therefore, understanding the thermodynamic aspects of the methanol synthesis reactions is essential 56

for the strategic development of the catalytic CO2 hydrogenation process. 57

In the present study, the thermodynamic feasibility of CO2 hydrogenation into CH3OH, RWGS, and 58

CH3OH decomposition reactions was investigated. The effects of various parameters such as temperature, 59

pressure, and feed composition on CO2 conversion and methanol selectivity have been examined. Furthermore, 60

the simulated data has been elaborated with figures and charts to understand the optimum operating conditions for 61

a specific conversion and selectivity. Also, the Aspen predicted data is compared with the experimental data 62

obtained from various literature. 63

3

2. Methodology 64

The Gibbs free energy minimization approach can precisely define the equilibrium composition of a 65

reaction system. The overall Gibbs free energy (G) of the system is minimum at equilibrium. The equilibrium 66

reactor model (REquil) in Aspen Plus software was used in the present work. The Peng-Robinson equation of 67

state (PENG-ROB EOS) model was considered to introduce non-ideal behaviour in the Gibbs energy values 68

(Miguel et al. 2015). In order to obtain a better understanding of the concept of hydrogenation of CO2 into 69

methanol, we focused on three possible reactions, namely methanol synthesis from CO2 hydrogenation (Eq. 1), 70

RWGS (Eq. 2), and CH3OH decomposition (Eq. 3). 71

CO2 + 3H2 ⇌ CH3OH + H2O ∆H298K = -49.5 kJ mol-1 (Eq. 1) 72

CO2 + H2 ⇌ CO + H2O ∆H298K = +41.1 kJ mol-1 (Eq. 2) 73

CH3OH ⇌ CO + H2 ∆H298K = +90.6 kJ mol-1 (Eq. 3) 74

The following expressions (Eq. 4-7) are used to define the CO2 conversion, methanol selectivity and yield, and 75

CO selectivity. 76

Conversion of CO2 (%)= [1-FCO2, out

FCO2, in]×100 (Eq. 4) 77

Selectivity of CH3OH (%)= [ FCH3OH, out

FCH3OH, out + FCO, out]×100 (Eq. 5) 78

Yield of CH3OH (%) = [FCH3OH, out

FCO2, in]×100 (Eq. 6) 79

Selectivity of CO (%)= [ FCO, outFCH3OH, out + FCO, out

]×100 (Eq. 7) 80

where Fi,in and Fi,out (i = CO2, CO, CH3OH) is the reactor inlet and outlet molar flowrates of species ‘i’, 81

respectively. All thermodynamic simulations are carried out under isothermal conditions. The results are shown in 82

terms of CO2 conversion, CH3OH yield, and selectivity of both CH3OH and CO for specific reaction conditions. 83

84

3. Results and Discussion 85

3.1. Effect of temperature on enthalpy, entropy, and Gibbs free energy change: 86

The shift in Gibbs free energy governs the spontaneity of a chemical reaction. Fig. 1(a-c) shows the 87

effect of temperature in enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) change of the CO2 88

hydrogenation, RWGS, and CH3OH decomposition reactions under 1 bar pressure. As observed in Fig. 1(a) and 89

Fig. 1(b), the ΔH and ΔS values for CO2 hydrogenation reaction are less than zero as the temperature rises from 90

25 °C to 500 °C. This signifies that the CO2 hydrogenation to methanol reaction is exothermic and decreases the 91

randomness. In contrast, the ΔH and ΔS values for both the RWGS and CH3OH decomposition reactions are 92

greater than zero with temperature. This implies that the RWGS and CH3OH decomposition reactions are 93

endothermic with increasing molecular disorder. As shown in Fig. 1(c), the ΔG for methanol synthesis reaction 94

has greater than zero and increases with temperature, which means this reaction is favourable at lower 95

4

temperatures. The ΔG for the RWGS reaction has positive values and decreases with temperature, implying this 96

reaction is favourable at higher temperatures. 97

On the other hand, the ΔG for methanol decomposition reaction has positive values with decreasing trend 98

up to 130 °C. This suggests that the methanol decomposition starts or favourable from 130 °C. Therefore, the CO2 99

hydrogenation to CH3OH reaction is exothermic and spontaneous at lower temperatures. In contrast, the RWGS 100

and methanol decomposition reactions are endothermic and spontaneous at higher temperatures. 101

50 100 150 200 250 300 350 400 450 500-100

-80

-60

-40

-20

0

20

40

60

80

100

50 100 150 200 250 300 350 400 450 500-80

-60

-40

-20

0

20

40

60

80

100

120

50 100 150 200 250 300 350 400 450 500

-0.2

-0.1

0.0

0.1

0.2

0.3∆G

(kJ/m

ol)

Temperature (°C)

(c)

CO2 + 3H2 CH3OH + H2O

CO2 + H2 CO + H2O

CH3OH CO + 2H2

∆H (k

J/mol

)

Temperature (°C)

(a)

CO2 + 3H2 CH3OH + H2O

CO2 + H2 CO + H2O

CH3OH CO + 2H2

∆S (k

J/mol

-K)

Temperature (°C)

CO2 + 3H2 CH3OH + H2O

CO2 + H2 CO + H2O

CH3OH CO + 2H2

(b)

102

Fig. 1: Effect of temperature on (a) ΔH, (b) ΔS, and (c) ΔG for CO2 hydrogenation, RWGS, and CH3OH 103

decomposition reactions under 1 bar pressure. 104

105

3.2. Influence of temperature and pressure on CO2 conversion and CH3OH selectivity: 106

According to Le Chatelier’s principle and thermodynamic feasibility, higher pressure and lower 107

temperature seem to be favourable conditions for higher methanol selectivity (Eq. 1). RWGS and methanol 108

decomposition reactions are also limited under these conditions due to their endothermic nature. Hence, high 109

pressures and low temperatures can be the optimum operating conditions to improve methanol selectivity and, at 110

the same time to reduce CO selectivity. The impact of temperature and pressure on CO2 conversion, CH3OH 111

selectivity, and CO selectivity was examined, and the outcomes are shown in Fig. 2(a-c). 112

The plots show that the equilibrium conversion of CO2 is regulated by both temperature and pressure. As 113

the temperature rises, the methanol formation reaction becomes less favoured, and the RWGS and methanol 114

decomposition reactions become more favoured, resulting in U-shaped curves in the CO2 conversion patterns. 115

Increased pressure enhances CO2 conversion in the low-temperature zone (e.g., 50 °C to 300 °C). However, at 116

high temperatures (between 300 °C and 500 °C), increasing pressure has almost no influence on CO2 conversion, 117

5

and this is why the CO2 conversion curves eventually converged at these temperatures. The methanol synthesis 118

reaction is improved by rising pressure, whereas the RWGS and methanol decomposition reactions are mostly 119

unchanged. This fact illustrates that, as pressure rises, both the CH3OH and CO selectivity curves shift to 120

extremely high temperatures. Several scientists have confirmed this phenomenon by employing various reaction 121

schemes and the Soave-Redlich-Kwong equation of state (Stangeland et al. 2018; Ahmad and Upadhyayula 2019). 122

50 100 150 200 250 300 350 400 450 5000

10

20

30

40

50

60

70

80

90

100

50 100 150 200 250 300 350 400 450 500

0

10

20

30

40

50

60

70

80

90

100

50 100 150 200 250 300 350 400 450 500

0

10

20

30

40

50

60

70

80

90

100

CO

2 C

onver

sion (

%)

Temperature (°C)

1 bar 20 bar

3 bar 30 bar

5 bar 40 bar

10 bar 50 bar

(a)

Temperature (°C)

1 bar 20 bar

3 bar 30 bar

5 bar 40 bar

10 bar 50 bar

CH

3O

H S

elec

tivit

y (

%) (b)

CO

Sel

ecti

vit

y %

Temperature (°C)

1 bar 20 bar

3 bar 30 bar

5 bar 40 bar

10 bar 50 bar

(c)

123

Fig. 2: Effect of pressure and temperature on (a) CO2 conversion, (b) CH3OH selectivity, and (c) CO selectivity, 124

for H2/CO2 mole value of 3. 125

126

The effect of pressure on the optimum value of operating temperature and CO2 conversion to achieve 127

99% CH3OH and 1% CO selectivity is concluded in Fig. 3. When the pressure rises from 1 bar to 50 bars, the CO2 128

conversion is noticeable, i.e., from 13% to 48%. Hence, the optimum value of operating parameters to obtain 99% 129

methanol selectivity and 48% CO2 conversion is about 172 °C and 50 bar for the H2/CO2 molar value of 3. 130

6

72

95

107

125

145

157

167172

13

2024

29

3640

4448

1 3 5 10 20 30 40 50 --

25

50

75

100

125

150

175

200

Temperature

CO2 Conversion

Pressure (bar)

Tem

per

ature

(°C

)

0

20

40

60

80

100

CO

2 C

onver

sion (

%)

131

Fig. 3: Effect of pressure on CO2 conversion and reactor temperature to achieve 99% CH3OH selectivity for 132

H2/CO2 molar value of 3. 133

134

3.3. Influence of feed gas composition on CO2 conversion and CH3OH selectivity: 135

To investigate the influence of feed composition on CH3OH selectivity, the CO2:H2 molar ratio was 136

varied between 1:3 to 1:20 for a fixed value of 50 bar pressure. The simulation was performed for a temperature 137

range between 150 °C to 400 °C, and the results are shown in Fig. 4(a-c). The plot shows that the increase of H2 138

partial pressure promotes both CO2 conversion and CH3OH selectivity. The methanol formation from CO2 139

decreased as the temperature increased, and consequently, the CO2 consumption diminishes. As a result, the 140

observed increase in CO2 conversion at higher temperatures suggests that extra H2 promotes the RWGS reaction. 141

As the CO2:H2 ratio was increased from 1:3 to 1:12, the most significant change in CO2 conversion occurs. 142

Further increase of CO2:H2 ratio from 1:13 to 1:17, there seems to be a lower improvement of CO2 conversions. 143

From 1:18 to 1:20, almost similar conversions were obtained. 144

Fig. 5 depicts the influence of feed gas composition on CO2 conversion and optimum temperature to 145

obtain 99% CH3OH and 1% CO selectivity under 50 bar reactor pressure. The simulation shows the CO2 146

conversion improved from 48% to 87% when the CO2:H2 molar ratio increased from 1:3 to 1:20. About 87% CO2 147

conversion and 99% methanol selectivity can be achievable at 187 °C under 50 bar pressure and a CO2:H2 ratio of 148

1:20. Though the boosting of H2 partial pressure in the feed promotes the conversion of CO2, it has a detrimental 149

impact on the process economics. 150

7

175 200 225 250 275 300 325 350 375 4000

20

40

60

80

100

175 200 225 250 275 300 325 350 375 4000

20

40

60

80

100

175 200 225 250 275 300 325 350 375 40020

30

40

50

60

70

80

90

100

CH

3O

H S

elec

tiv

ity

(%

)

Temperature (°C)

1:3 1:9 1:15

1:4 1:10 1:16

1:5 1:11 1:17

1:6 1:12 1:18

1:7 1:13 1:19

1:8 1:14 1:20

(b)

CO

Sel

ecti

vit

y (

%)

Temperature (°C)

1:3 1:9 1:15

1:4 1:10 1:16

1:5 1:11 1:17

1:6 1:12 1:18

1:7 1:13 1:19

1:8 1:14 1:20

(c)

CO

2 C

on

ver

sio

n (

%)

Temperature (°C)

1:3 1:9 1:15

1:4 1:10 1:16

1:5 1:11 1:17

1:6 1:12 1:18

1:7 1:13 1:19

1:8 1:14 1:20

(a)

151

Fig. 4: Effect of CO2:H2 molar ratio on (a) CO2 conversion, (b) CH3OH selectivity, and (c) CO selectivity at 152

50 bar reactor pressure. 153

154

172176

179181182183183184185185185186186186186186187187

48

55

6165

6972

75 77 78 80 81 82 83 84 85 86 86 87

1:4 1:6 1:8 1:10 1:12 1:14 1:16 1:18 1:20

100

110

120

130

140

150

160

170

180

190

200

210 Temperature (°C)

CO2 Conversion (%)

CO2:H2 molar ratio

Tem

per

ature

(°C

)

0

20

40

60

80

100

120C

O2 C

onver

sion (

%)

155

Fig. 5: Effect of CO2:H2 molar ratio on CO2 conversion and desired temperature to achieve 99% CH3OH 156

selectivity under 50 bar reactor pressure. 157

8

158

4. Comparison of CO2 conversion and CH3OH selectivity between simulation predicted and experimental 159

results 160

For a similar range of reactor temperature, pressure, and feed gas composition conditions, the simulation 161

predicted and experimental results for CO2 conversion are shown in Fig. 6. The experimental findings are reported 162

in the presence of Au/In2O3 (Rui et al. 2020) and Cu/ZnO/Al2O3 (Gaikwad et al. 2016) catalysts. The simulation 163

results obtained from the present investigation are comparable and match well with the simulation data reported 164

by Stangeland et al. (2018). However, a substantial gap between the theoretical and experimental values of CO2 165

conversion is noted. The equilibrium CO2 conversion and experimental CO2 conversions (over Au/In2O3 and 166

Cu/ZnO/Al2O3 catalysts) show more deviation at lower temperatures. However, the gap reduces gradually with the 167

increase of reactor temperature. The lower value of CO2 conversion in the presence of catalysts can be related to 168

the weak activity of the catalysts. 169

We further compared the equilibrium CH3OH selectivity data with experimental CH3OH selectivity 170

results, as shown in Fig.7. The Cu/ZnO/Al2O3 catalyst shows a significant deviation from the equilibrium CH3OH 171

selectivity, whereas the gap is much less for the Au/In2O3 catalyst. The methanol selectivity of the Au/In2O3 172

catalyst is greater than the equilibrium CH3OH selectivity and which may be due to the presence of Auδ+-In2O3-x 173

interfacial sites in the Au/In2O3 catalyst. A summary of literature data on CO2 conversion, CH3OH selectivity is 174

shown in Table 1, along with the present simulation results. 175

176

175 200 225 250 275 300 325

0

10

20

30

40

50

CO

2 C

on

ver

sio

n (

%)

Temperature (°C)

Present work (Theoretical study @ 50 bar)

Stangeland et al. (Theoretical study @ 50 bar)

Rui et al. (Au/In2O

3 study @ 50 bar)

Gaikwad et al. (Cu/ZnO/Al2O

3 study @ 46 bar)

177

Fig. 6: Comparison of theoretical and experimental CO2 conversion for CO2: H2 molar ratio of 1:3. 178

9

175 200 225 250 275 300 325

0

30

60

90

120

150

CH

3O

H S

elec

tivit

y (

%)

Temperature (°C)

Present work (Theoretical study@ 50 bar)

Stangeland et al. (Theoretical study @ 50 bar)

Rui et al. (Au/In2O3 study @ 50 bar)

Gaikwad et al. (Cu/ZnO/Al2O3 study @ 46 bar)

179

Fig. 7: Comparison of theoretical and experimental CH3OH selectivity for CO2: H2 molar ratio of 1:3. 180

181

182

Table 1: A comparison between the simulation and experimental findings on CO2 conversion and CH3OH

selectivity for the methanol synthesis via CO2 hydrogenation.

Catalyst CO2:H2

ratio

TR

(°C)

PR

(bar)

XCO2

(%)

SMeOH

(%)

Reference

PdZn/CeO2 1:3 220 30 7.7 100 (Malik et al. 2018)

Au/In2O3 1:3 225 50 1.3 100 (Rui et al. 2020)

Pd-Zn/CNTs 1:3 250 30 6.3 99 (Liang et al. 2009)

Cu/ZnO 1:3 180 20 5 98 (Witoon et al. 2013)

Cu/ZnO/Al2O3 1:3 240 46 20 40 (Gaikwad et al. 2016)

Cu/ZnO/Al2O3 1:3 170 50 25 73 (Liu et al. 2007)

- 1:3 200 50 39 98 Stangeland et al. (2018)

- 1:3 250 50 28 68 Stangeland et al. (2018)

- 1:3 172 50 48 99 Present work

- 1:3 250 50 28 72 Present work

- 1:10 184 50 77 99 Present work

- 1:10 250 50 51 80 Present work

- 1:20 187 50 87 99 Present work

where, TR = Reaction temperature; PR = Reaction pressure; XCO2 = CO2 conversion, SMeOH = Methanol

selectivity.

183

5. Conclusions 184

A comprehensive and detailed thermodynamic investigation of CO2 conversion to methanol is presented 185

in this study. Based on the thermodynamic feasibility findings, the methanol decomposition reaction has a higher 186

endothermicity than the RWGS reaction, while methanol production from CO2 is an exothermic reaction. The 187

methanol decomposition reaction has a greater entropy change with temperature than the methanol and RWGS 188

10

reactions. Due to more negative changes in Gibbs free energy, the methanol decomposition reaction is more 189

spontaneous at higher temperatures. In the methanol synthesis, the effect of various critical parameters such as 190

pressure, temperature, feed gas composition on CO2 conversion, and methanol selectivity is investigated. Low 191

temperature, high pressure, and a high CO2:H2 feed ratio are found to be favourable conditions to facilitate 192

methanol production from CO2 and H2. The CO2 conversion is prominent at a 1:3 CO2:H2 feed gas molar ratio if 193

the pressure builds up from 1 bar to 50 bar, i.e., from 13% to 48%. At 50 bar pressure, the CO2 conversion 194

improved from 48% to 87% with the increase of CO2:H2 mole ratio from 1:3 to 1:20. However, methanol 195

synthesis at higher (> H2:CO2 mole ratio of 5) H2 partial pressure may not be economically viable. The gap in CO2 196

conversion between the simulation predicted and experimental data may be due to the insufficient activity of the 197

catalyst. Therefore, to enhance the CO2 conversion and CH3OH selectivity, developing a highly efficient, 198

thermally and chemically stable, and low-cost catalyst is essential. 199

. 200

201

Declarations: 202

Ethics approval and consent to participate: ‘Not applicable’ 203

Consent for publication: ‘Not applicable’ 204

Availability of data and materials: very few data have been extracted from published articles for comparison 205

purpose, and same has been mentioned in the manuscript with proper reference. 206

Conflict of interest statement: The authors declare that they have no known competing financial interests or 207

personal relationships that could have appeared to influence the work reported in this paper. 208

Funding: This research did not receive any specific grant from funding agencies. 209

Authors' contributions: SK: Conceptualization, Investigation, Data generation, Writing-original draft; SAS: 210

Conceptualization, Methodology, Result validation; SPD: Resources, Data validation; CC: Project administration; 211

SR: Project administration, data validation; SD: Conceptualization, Supervision, result validation, Writing- review 212

and editing; ‘All authors read and approved the final manuscript." 213

214

215

Acknowledgment: The authors express their gratitude to BITS-Pilani Hyderabad Campus for providing the 216

necessary support for the present study. 217

218

References 219

Ahmad K, Upadhyayula S (2019) Greenhouse gas CO2 hydrogenation to fuels: A thermodynamic analysis. 220

Environ Prog Sustain Energy 38:98-111. 221

Atsonios K, Panopoulos KD, Kakaras E (2016) Investigation of technical and economic aspects for methanol 222

production through CO2 hydrogenation. Int J Hydrogen Energy 41:2202-2214. 223

Cai Z, Dai J, Li W, et al (2020) Pd Supported on MIL-68(In)-Derived In2O3 nanotubes as superior catalysts to 224

boost CO2 hydrogenation to methanol. ACS Catal 10:13275-13289. 225

11

Chen J, Dahlin MJ, Luuppala L, et al (2021) Air Pollution and Climate Change: Sustainability, Restoration, and 226

Ethical Implications. In: Raines C (ed) Air Pollution Sources, Statistics and Health Effects. Springer US, 227

New York, NY, 279-325. 228

Dalena F, Senatore A, Marino A, et al (2018) Methanol production and applications: An overview. In: Methanol. 229

Elsevier, 3-28. 230

Din IU, Shaharun MS, Alotaibi MA, et al (2019) Recent developments on heterogeneous catalytic CO2 reduction 231

to methanol. J CO2 Util 34:20-33. 232

Gaikwad R, Bansode A, Urakawa A (2016) High-pressure advantages in stoichiometric hydrogenation of carbon 233

dioxide to methanol. J Catal 343:127-132. 234

Han Z, Tang C, Wang J, et al (2021) Atomically dispersed Ptn+ species as highly active sites in Pt/In2O3 catalysts 235

for methanol synthesis from CO2 hydrogenation. J Catal 394:236-244. 236

Leonzio G, Zondervan E, Foscolo PU (2019) Methanol production by CO2 hydrogenation: Analysis and 237

simulation of reactor performance. Int J Hydrogen Energy 44:7915-7933. 238

Li W, Wang H, Jiang X, et al (2018) A short review of recent advances in CO2 hydrogenation to hydrocarbons 239

over heterogeneous catalysts. RSC Adv 8:7651-7669. 240

Liang XL, Dong X, Lin GD, Zhang H Bin (2009) Carbon nanotube-supported Pd-ZnO catalyst for hydrogenation 241

of CO2 to methanol. Appl Catal B Environ 88:315-322. 242

Liu Y, Zhang Y, Wang T, Tsubaki N (2007) Efficient conversion of carbon dioxide to methanol using copper 243

catalyst by a new low-temperature hydrogenation process. Chem Lett 36:1182-1183. 244

Malik AS, Zaman SF, Al-Zahrani AA, et al (2018) Development of highly selective PdZn/CeO2 and Ca-doped 245

PdZn/CeO2 catalysts for methanol synthesis from CO2 hydrogenation. Appl Catal A 560:42-53. 246

Miguel C V., Soria MA, Mendes A, Madeira LM (2015) Direct CO2 hydrogenation to methane or methanol from 247

post-combustion exhaust streams - A thermodynamic study. J Nat Gas Sci Eng 22:1-8. 248

Rui N, Zhang F, Sun K, et al (2020) Hydrogenation of CO2 to Methanol on a Auδ+-In2O3- x Catalyst. ACS Catal 249

10:11307-11317. 250

Salehi MS, Askarishahi M, Gallucci F, Godini HR (2021) Selective CO2-hydrogenation using a membrane 251

reactor. Chem Eng Process - Process Intensif 160:108264. 252

Sha F, Han Z, Tang S, et al (2020) Hydrogenation of carbon dioxide to methanol over non−Cu-based 253

heterogeneous catalysts. ChemSusChem 13:6160-6181. 254

Sharma SK, Khan TS, Singha RK, et al (2021) Design of highly stable MgO promoted Cu/ZnO catalyst for clean 255

methanol production through selective hydrogenation of CO2. Appl Catal A Gen 623:118239. 256

Stangeland K, Li H, Yu Z (2018) Thermodynamic analysis of chemical and phase equilibria in CO2 hydrogenation 257

to methanol, dimethyl ether, and higher alcohols. Ind Eng Chem Res 57:4081-4094. 258

Witoon T, Permsirivanich T, Donphai W, et al (2013) CO2 hydrogenation to methanol over Cu/ZnO nanocatalysts 259

prepared via a chitosan-assisted co-precipitation method. Fuel Process Technol 116:72-78. 260

Zhong J, Yang X, Wu Z, et al (2020) State of the art and perspectives in heterogeneous catalysis of CO2 261

hydrogenation to methanol. Chem Soc Rev 49:1385-1413. 262