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

Although being very challenging, utilization of carbon dioxide (CO2) originating from production processes and flue gases of CO2-intensive sectors has a great environmental and industrial potential due to improving the resource efficiency of industry as well as by contributing to the reduction of CO2 emissions. As a renewable and environmentally friendly source of carbon, catalytic approaches for CO2 fixation in the synthesis of chemicals offer the way to mitigate the increasing CO2 buildup. Among the catalytic reactions, methanation of CO2 is a particularly promising technique for producing energy carrier or chemical. This article focuses on recent developments in catalytic materials, novel reactors, and reaction mechanism for methanation of CO2.

Methanation of carbon dioxide: an overview

IR spectroscopy of probe molecules (pyridine, 2,6-dimethylpyridine, and CO) as well as high-resolution solid state NMR and especially double-resonance experiments give a new insight into the acidic sites of amorphous silica alumina (ASA). ASA samples are heterogeneous compounds that contain a silica alumina mixed phase as well as aluminum clusters and pure silica zones. The distribution of various forms depends both on the preparation method and on the Si/Al ratio. Formation of mixed phase leads to the creation of acidic hydroxyl groups of various strength, up to that present in dealuminated HY zeolite. Detailed spectroscopic analyses show that these acidic OH groups correspond to the silanol groups located in close vicinity to an Al atom in tetrahedral environment. The strength of the acidity of the OH species of ASA could be modified both by the location of the vicinal Al atom on the surface or in the bulk and by the number of aluminum atoms in the vicinity of silanol group. Cogelification of high silica-containing ASA appears as the best mean to prepare homogeneous amorphous aluminosilicate, which exhibits the strongest Bronsted acidity.

Nature, structure and strength of the acidic sites of amorphous silica alumina: an IR and NMR study.

Enhanced low-temperature activity of CO2 methanation over highly-dispersed Ni/TiO2 catalyst

Glucose hydrogenation on promoted raney-nickel catalysts

Raney metal catalysts: I. comparative properties of raney nickel proceeding from Ni-Ai intermetallic phases

The strength and number per unit surface area of acid sites on a series of silica—aluminas of composition ranging from 0 to 100 % in alumina have been investigated. The results of titration by n-butylamine in the presence of six different HR indicators and of activity and selectivity in the transformation of 4-methylpentan-2-ol are compared.An overall parallelism between the amount of acidity of different strengths and the activity in the different reactions (i.e., dehydration, cis-trans-isomerization, double-bond shift and isomerization of the hydrocarbon skeleton, which set in successively with increasing acidity of the catalyst) is observed.Acidity in all samples arises only from strongly acidic (HR⩽–13.3) and intermediate strength sites (–6.63 ⩽HR⩽+ 0.82).Comparison of the results with those of cation exchange capacity measurements is not satisfactory, because of the inherent limitations of the latter method. Results for strong acid sites agree perfectly with those reported in infrared studies using adsorbed pyridine and CD3CN. Results concerning intermediate strength sites suggest that i.r. studies, titration and catalytic acitivity measurements may complement each other.

Acidic properties of silica—alumina gels as a function of chemical composition. Titration and catalytic activity measurements

Catalytic hydrogenation on raney nickel catalyst modified by chromium hydroxide deposition

New approach to skeletal nickel catalysts catalytic properties of the nickel-chromium system

The surface acidity of series of solid catalysts have been studied using H, indicators and a catalytic test reaction: dehydration of 4-methyl-2-pentanol. In the presence of surfaces of increasing acid strengths, this alcohol undergoes the following transformations: selective dehydration to 1-olefin, dehydration to 1- and 2-olefin, double-bond cis-trans isomerization, double-bond shift and isomerization of the hydrocarbon skeleton. A perfect parallelism between the occurence of a given reaction and a given acid strength, as determined by Hr indicators, has been shown. This parallelism is supported by results on: (i) widely different catalysts, i.e., ThO2, AI2O3, AI2O3-SiO2, H3PO4-SiO2; and (ii) series of ThO2 and Al2O3 modified in a controlled manner by addition of F, Cl, or Na ions.

J.P. Damon

Papers

Raney metal catalysts: I. comparative properties of raney nickel proceeding from Ni-Ai intermetallic phases

Acidic properties of silica—alumina gels as a function of chemical composition. Titration and catalytic activity measurements

Catalytic hydrogenation on raney nickel catalyst modified by chromium hydroxide deposition

New approach to skeletal nickel catalysts catalytic properties of the nickel-chromium system

Contribution of catalytic selectivity measurements to the characterization of surface acidity