materials Review Methanol Synthesis from CO2: A Review of the Latest Developments in Heterogeneous Catalysis R. Guil-López *, N. Mota, J. Llorente, E. Millán , B. Pawelec , J.L.G. Fierro and R. M. Navarro * Instituto de Catálisis y Petroleoquímica, CSIC, C/Marie Curie 2, Cantoblanco, 28049 Madrid, Spain; noelia.mota@icp.csic.es (N.M.); jorge.llorente@csic.es (J.L.); elena.millan.ordonez@csic.es (E.M.); bgarcia@icp.csic.es (B.P.); jlgfierro@icp.csic.es (J.L.G.F.) * Correspondence: rut.guil@icp.csic.es (R.G.-L.); r.navarro@icp.csic.es (R.M.N.); Tel.: +349-1585-4759 (R.G.-L.); +349-1585-4773 (R.M.N.) Received: 30 October 2019; Accepted: 22 November 2019; Published: 26 November 2019 Abstract: Technological approaches which enable the effective utilization of CO2 for manufacturing value-added chemicals and fuels can help to solve environmental problems derived from large CO2 emissions associated with the use of fossil fuels. One of the most interesting products that can be synthesized from CO2 is methanol, since it is an industrial commodity used in several chemical products and also an efficient transportation fuel. In this review, we highlight the recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO2 to methanol. The main efforts focused on the improvement of conventional Cu/ZnO based catalysts and the development of new catalytic systems targeting the specific needs for CO2 to methanol reactions (unfavourable thermodynamics, production of high amount of water and high methanol selectivity under high or full CO2 conversion). Major studies on the development of active and selective catalysts based on thermodynamics, mechanisms, nano-synthesis and catalyst design (active phase, promoters, supports, etc.) are highlighted in this review. Finally, a summary concerning future perspectives on the research and development of efficient heterogeneous catalysts for methanol synthesis from CO2 will be presented. Keywords: CO2; catalysts; hydrogenation; methanol; review 1. Introduction The current world energy system is still mainly based on the use of fossil fuels and, although the use of renewable energy sources has increased, it will continue in the medium and short term [1]. This massive use of fossil fuels in industry and transport produce large amounts of CO2 emissions [2] that could reach 35.2 billion metric tons in 2020 [3]. Therefore, it is necessary to develop technological approaches to reduce these CO2 emissions associated with the use of fossil fuels which must include the capture and subsequent reutilization of the CO2 produced [2]. In this scenario, to meet a climate target of limiting warming by 2 ◦C, annual energy-related CO2 emissions still need to decline by 2050 from 35 Gt (in the current levels) to 9.7 Gt, a decrease of more than 70% [1]. To reach this objective, the reutilization of 7–32% of the CO2 produced in the generation of energy from fossil fuels will be necessary by 2050 [1]. As an illustrative example, this means that the CO2 emissions in the energy sector in the EU-28 are expected to be reduced to 1550 Mt (mega ton) by 2030 from the 3400 Mt emitted in 2013 [4]. Therefore, technologies which enable the effective re-utilization of CO2 for manufacturing value-added compounds or fuel products will play a major role in the objectives related with the reduction of CO2 in the future. Today, the main chemical products obtained at the industrial scale using CO2 as a raw material (pure or derived from CO by the Water Gas Shift reaction (WGS)) are urea, methanol, formaldehyde, methanol, Materials 2019, 12, 3902; doi:10.3390/ma12233902 www.mdpi.com/journal/materials Materials 2019, 12, x FOR PEER REVIEW 2 of 24 Materials 2019 12 MaterialsMaterials ,2019 2019,,, 3902 , 12 12,, , x xx FOR FORFOR PEER PEERPEER REVIEW REVIEWREVIEW 22 ofof 2424 2 of 24 MaterialsMaterials 20192019,, 1212,, xx FORFOR PEERPEER REVIEWREVIEW 22 ofof 2424 them, the synthesis of urea and methanol are the predominant consumers of CO2 in industry with an them,them,Materials thethe 2019 synthesissynthesis, 12, x FOR ofof PEER ureaurea REVIEW andand methanolmethanol areare thethe predominantpredominant consumersconsumers ofof COCO22 inin industryindustry withwith2 of anan 24 Materialsthem,annualthem, thethe 2019consumption synthesissynthesis, 12, x FOR of ofPEER of ureaurea CO REVIEW and2and of more methanolmethanol than are110are the theMt/year. predominantpredominant consumersconsumers ofof COCO22 inin industryindustry withwith2 of anan24 them,them, thethe synthesissynthesis ofof ureaurea andand methanolmethanol areare thethe predominantpredominant consumersconsumers ofof COCO22 inin industryindustry withwith anan them,annual the consumption synthesis of of urea CO 2and2 of moremethanol than are110 the Mt/year. predominant consumers of CO2 in industry with an formicannualannual acid, consumptionconsumption carbamates, ofof COpolymer-buildingCO22 ofof moremore thanthan 110110 blocks Mt/year.Mt/year. and fine chemicals (Table1)[ 5]. Among them, annualannualthem, the consumptionconsumption synthesis of ofof urea COCO 22and ofof moremore methanol thanthan 110are110 theMt/year.Mt/year. predominant consumers of CO2 in industry with an the synthesisthem, the ofsynthesis urea andTable of urea methanol 1. Main and methanolchemicals are the products are predominant the predominant industrially consumers produced consumers of from CO of CO2 COin2 [5].2 industry in industry with with an an annual 2 annual consumptionTable of CO1. Main of morechemicals than products 110 Mt/year. industrially produced from CO22 [5].[5]. TableTable 1.1. MainMain2 chemicalschemicals productsproducts industriallyindustrially producedproduced fromfrom COCO2 [5].[5]. consumptionannual consumption of CO2 of of more CO than of more 110 than Mt/ year.110 Mt/year. 2 TableTable 1.1. MainMain chemicalschemicals productsproducts industriallyindustrially producedproduced fromfrom COCO2 [5].[5]. ChemicalTable 1. Main chemicalsMolecular products Form ulaindustrially Production produced (t/year) from COCO [5].2 Consumption (t/year) ChemicalTable 1. Main chemicalsMolecular products Formula industrially Production produced (t/year) from COCO2 22[5]. ConsumptionConsumption (t/year)(t/year) ChemicalChemical MolecularMolecular FormFormulaula ProductionProduction (t/year) (t/year) COCO22 ConsumptionConsumption (t/year)(t/year) TableTable 1. Main1. Main chemicals chemicals productsproducts industrially industrially produced produced from from CO CO2 [5].2 [5]. ChemicalChemical MolecularMolecular FormFormulaula ProductionProduction (t/year)(t/year) COCO2 ConsumptionConsumption2 (t/year)(t/year) Urea 1.5 × 108 1.12 × 108 Chemical Molecular Formula Production (t/year) CO2 Consumption (t/year) 88 88 ChemicalChemicalUrea Molecular FormulaForm ula Production Production1.5 × 10 (t/year) (t8 / year) CO CO2 Consumption2 Consumption1.121.12 ×× 1010 8 (t/year) (t/year) Urea 1.5 × 108 1.12 × 108 UreaUrea 1.51.5 ×× 10108 1.121.12 ×× 10108 Urea 1.5 × 108 1.12 × 108 UreaUrea 1.5 × 108 8 1.12 × 108 8 1.5 108 1.12 6 10 Methanol 1.0 ×× 10 2 × 10× 88 66 Methanol 1.0 × 10 8 22 ×× 1010 6 Methanol 1.0 × 108 2 × 106 MethanolMethanol 1.01.0 ×× 10108 22 ×× 10106 Methanol 1.0 × 10 2 × 10 MethanolMethanol 1.01.0 × 101088 2 2× 10106 6 Methanol 1.0 ×× 108 2 × ×106 6 Formaldehyde 9.7 × 10 66 Formaldehyde 9.7 × 10 6 Formaldehyde 9.7 × 106 Formaldehyde 9.7 × 106 6 FormaldehydeFormaldehyde 9.79.7 × 1010 × 6 Formaldehyde 9.7 × 10 56 FormaldehydeFormic acid 9.77.0× × 10 55 Formic acid 7.0× 1055 Formic acid 7.0× 1055 FormicFormicFormic acid acidacid 7.0×7.0×7.0 1010105 × Formic acid 7.0× 105 Formic acid 7.0× 105 4 4 Salicylic acid 7.0 × 10 3.0 × 10 44 44 SalicylicSalicylic acid acid 7.07.0 × × 10 104 4 3.03.03.0 × ×× 10 10104 4 Salicylic acid 44 44 SalicylicSalicylic acidacid 7.07.07.0 ×× 1010104 3.03.03.0 ×× 1010104 × × Salicylic acid 7.0 × 104 3.0 × 104 Salicylic acid 7.0 × 104 3.0 × 104 Cyclic carbamate 8.0 × 104 4.0× 104 444 44 4 CyclicCyclic carbamate carbamate 8.08.0 × 101044 4.0×4.0×4.0 10104104 Cyclic carbamate 8.0 × 1044 4.0× 1044 CyclicCyclic carbamatecarbamate 8.08.0 ××× 10104 4.0×4.0× 1010× 4 4 4 Cyclic carbamate 8.0 × 10 4.0× 10 Cyclic carbamate 8.0 × 104 4.0× 104 Ethylene carbamate Ethylene carbamate EthyleneEthylene carbamate carbamate EthyleneEthylene carbamatecarbamate Ethylene carbamate Di-methyl carbamate 1.0 × 107 Ethylene carbamate 7 Di-methyl carbamate 1.0 1077 Di-methyl carbamate 1.0 × 1077 Di-methyl carbamate 1.0 × 107 Di-methylDi-methyl carbamatecarbamate 1.01.0 ×× 10107 Di-methyl carbamate 1.0 × 107 Di-methylCopolymers carbamate 1.0 × 107 Copolymers CopolymersCopolymers CopolymersCopolymers Polymer-building blocks Polymer-buildingCopolymers blocks Polymer-buildingPolymer-buildingCopolymers blocks blocks Polymer-buildingPolymer-building blocksblocks Polymer-building blocks FineFine chemical: Polymer-buildingchemical: for for example, example, blocks biotin biotin FineFine chemical: chemical: for for example, example, biotin biotin FineFine chemical:chemical: forfor example,example, biotinbiotin Fine chemical: for example, biotin Fine chemical: for example, biotin OneOne of the of most the interestingmost interesting products products that canthat be can synthesized be synthesized from COfrom2 is CO methanol2 is methanol [6]. Methanol [6]. is One of the most interesting products that can be synthesized from CO22 isis methanolmethanol [6].[6]. MethanolOneOne ofisof anthethe industrial mostmost interestinginteresting commodity productsproducts used as thatthat
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