Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).

Recent advances in catalytic hydrogenation of carbon dioxide

8.4.5. Nitromercuration Reactions 3878 9. Hydroamination of Alkenes and Alkynes under Microwave Irradiation 3878 * To whom correspondence should be addressed. Phone: +49 241 8

Hydroamination: direct addition of amines to alkenes and alkynes.

Conversion of Biomass into Chemicals over Metal Catalysts

This review highlights recent developments and future perspectives in carbon dioxide usage for the sustainable production of energy and chemicals and to reduce global warming. We discuss the heterogeneously catalysed hydrogenation, as well as the photocatalytic and electrocatalytic conversion of CO2 to hydrocarbons or oxygenates. Various sources of hydrogen are also reviewed in terms of their CO2 neutrality. Technologies have been developed for large-scale CO2 hydrogenation to methanol or methane. Their industrial application is, however, limited by the high price of renewable hydrogen and the availability of large-volume sources of pure CO2. With regard to the direct electrocatalytic reduction of CO2 to value-added chemicals, substantial advances in electrodes, electrolyte, and reactor design are still required to permit the development of commercial processes. Therefore, in this review particular attention is paid to (i) the design of metal electrodes to improve their performance and (ii) recent developments of alternative approaches such as the application of ionic liquids as electrolytes and of microorganisms as co-catalysts. The most significant improvements both in catalyst and reactor design are needed for the photocatalytic functionalisation of CO2 to become a viable technology that can help in the usage of CO2 as a feedstock for the production of energy and chemicals. Apart from technological aspects and catalytic performance, we also discuss fundamental strategies for the rational design of materials for effective transformations of CO2 to value-added chemicals with the help of H2, electricity and/or light.

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Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes

Iron Catalysis in Organic Synthesis

Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO2 at various pressures (1–2 MPa) and temperatures (573–673 K). Potassium, as an important promoter, enhanced the CO2 uptake and selectivity towards olefins and long-chain hydrocarbons. Al2O3, when added as a structural promoter during co-precipitation, increased CO2 conversion as well as selectivity to C2+ hydrocarbons. Among V, Cr, Mn and Zn promoters, Zn offered the highest selectivity to C2–C4 alkenes. The different episodes involved in the transformation of the catalyst before it reached steady-state were identified, on the co-precipitated catalyst. Using a biomass derived syngas (CO/CO2/H2), CO alone took part in hydrogenation. When enriched with H2, CO2 was also converted to hydrocarbons. The deactivation of impregnated Fe–K/Al2O3 catalyst was found to be due to carbon deposition, whereas that for the precipitated catalyst was due to increase in crystallinity of iron species. The suitability of SiO2, TiO2, Al2O3, HY and ion exchanged NaY as supports was examined for obtaining high activity and selectivity towards light olefins and C2+ hydrocarbons and found Al2O3 to be the best support. A comparative study with Co catalysts revealed the advantages of Fe catalysts for hydrocarbon production by F–T synthesis.

Fischer-Tropsch Synthesis by Carbon Dioxide Hydrogenation on Fe-Based Catalysts

Glycerol hydrogenolysis to propane diols was carried out over Ru/C catalysts using different solid acids as co-catalysts. Solid acids such as niobia, 12-tungstophosphoric acid (TPA) supported on zirconia, cesium salt of TPA and cesium salt of TPA supported on zirconia were used. The acidities of the solid acid catalysts were measured by temperature programmed desorption of ammonia. The conversion of glycerol depends on the total acidity of the catalysts and there exists a linear correlation between conversion and acidity. The selectivity towards 1,2-propanediol and the glycerol conversion varied with the change in the concentrations of both Ru/C and solid acid catalysts, suggesting a synergetic effect of the reaction. This reaction requires minimum amount of both acid and metal sites to obtain reasonable activity. Different reaction parameters were studied and optimized reaction conditions were established.

Influence of solid acids as co-catalysts on glycerol hydrogenolysis to propylene glycol over Ru/C catalysts

A series of Cu–ZnO catalysts with varying Cu to Zn weight ratio are prepared by co-precipitation method. The catalysts were characterized by surface area, XRD, TPR and N2O chemisorption to measure Cu metal area. These catalysts were evaluated for hydrogenolysis of glycerol. The catalyst with Cu to Zn ratio of 50:50 is highly active under relatively low H2 pressure. The catalysts are highly selective towards 1,2 propanediol (>93%). The glycerol conversion depends upon the bifunctional nature of catalyst where it requires both acidic sites and metal surface. The presence of sufficient amount with small particle size of ZnO and Cu are required for high conversion of glycerol and selectivity to 1,2 propanediol. Different reaction parameters are studied in order to optimize the reaction conditions.

Selective Hydrogenolysis of Glycerol to 1, 2 Propanediol Over Cu–ZnO Catalysts

Glycerol carbonate was synthesized by transesterification of glycerol with dimethyl carbonate using Mg/Al/Zr mixed oxide base catalysts. A series of Mg/Al/Zr catalysts were prepared with different molar ratios by using co-precipitation method and calcining at different temperatures. The catalysts were characterized by FT-infrared spectroscopy, X-ray diffraction and temperature-programmed desorption of CO2. The transesterification activity depends on the Mg/Al/Zr molar ratio and the catalyst with Mg/Al/Zr molar ratio of 3:1:1 showed excellent activity. The catalyst activity depends on the pretreatment temperature, structure and basicity of the catalysts. The transesterification activity of catalysts was correlated with the structural aspects and the amount of basicity. Various parameters such as reaction temperature, catalyst concentration and molar ratio of dimethyl carbonate to glycerol were studied to optimize the reaction conditions.

Synthesis of glycerol carbonate by transesterification of glycerol with dimethyl carbonate over Mg/Al/Zr catalysts

Esterification of palmitic acid with methanol was studied on zirconia supported tungsten oxide solid acid catalysts prepared by both impregnation and co-precipitation methods; the tungsten loading and calcination temperature were varied. These catalysts were characterized by X-ray diffraction for structural elucidation and by temperature-programmed desorption of ammonia for their surface acidity. Whereas the impregnated catalysts exhibited both tetragonal and monoclinic phases of zirconia, at calcination temperatures beyond 500 °C their co-precipitated analogues showed stability towards the tetragonal phase. The formation of monoclinic phases of zirconia and crystalline tungsten oxide decreased the esterification activity, as a consequence of decreased surface acidity. Coexistence of tetragonal zirconia with the amorphous tungsten oxide offered maximum esterification activity.

Esterification of palmitic acid with methanol over tungsten oxide supported on zirconia solid acid catalysts: effect of method of preparation of the catalyst on its structural stability and reactivity ☆

P.S. Sai Prasad

Papers

Fischer-Tropsch Synthesis by Carbon Dioxide Hydrogenation on Fe-Based Catalysts

Influence of solid acids as co-catalysts on glycerol hydrogenolysis to propylene glycol over Ru/C catalysts

Selective Hydrogenolysis of Glycerol to 1, 2 Propanediol Over Cu–ZnO Catalysts

Synthesis of glycerol carbonate by transesterification of glycerol with dimethyl carbonate over Mg/Al/Zr catalysts

Esterification of palmitic acid with methanol over tungsten oxide supported on zirconia solid acid catalysts: effect of method of preparation of the catalyst on its structural stability and reactivity ☆