84
3.4.2 Hydrogenation of Carbon Dioxide Using Metal Organic
Frameworks
The first published trial to investigate the catalytic activities of MOFs towards the
hydrogenation of carbon dioxide was released in 2016 (Trickett et al. 2017). In this
work, Rungtaweevoranit et al. (2016) studied the catalytic activity of UiO-66 MOF
as a promoter for the conventional copper nanocatalyst. They found that the promoted catalyst achieved high selectivity and high yield towards the production of
methanol. This catalytic affinity was attributed to the presence of different oxidation
states of copper and the high interfacial contact area between the Zn-MOF and the
copper nanoparticles.
On the other hand, the functionalized UiO-67 MOF could be considered as the
first trial to evaluate the catalytic activity of the MOF itself. In this study, the authors
found that the catalytic hydrogenation activity of carbon dioxide by using the functionalized UiO-67 MOF was initiated via heterolytic dissociation of the hydrogen
molecules to generate hydridic and protic hydrogen atoms bound to Lewis acid and
base sites, respectively. This step facilitated a series of simultaneous transfer of two
hydrogen species with the adsorbed carbon dioxide to produce methanol (Ye and
Johnson 2016).
Also, the activity of Pd/ZnO catalyst prepared by the pyrolysis of Pd/ZIF-8 was
investigated. Although the investigated catalyst should be considered as conventional
one, the MOF parent strongly affected its catalytic features, whereas, due to the high
porosity of the parent ZIF-8, the dispersed palladium nanoparticles were confined in
the pore framework, which facilitated the transformation to a conventional catalyst
having strong metal-support interaction after the pyrolysis step (Yin et al. 2018).
3.5 Conclusions
The reduction of carbon dioxide into methanol by using MOF catalysts is a new area
of research. To the extent of our knowledge, the published works in this field are still
few numbers with respect to the conventional materials. In this chapter, we mentioned these few works. However, based on the upper mentioned publications, one
may conclude the following points:
• The photocatalytic efficiency, of any MOF, is based on the type of metal ion and
the organic ligands.
• The metal centers of MOFs should be selected within the transition metals having d orbitals that can overlap with the lowest unoccupied molecular orbital of
the organic linker.
• The hybrid catalysts such as nanocomposites of MOF could enhance the catalytic production of methanol, due to the synergistic effect arising from the photoexcitation properties of the inorganic nanomaterials acting as semiconductors
and the high adsorption power of MOFs towards carbon dioxide.
T. Zaki
3.4.2 Hydrogenation of Carbon Dioxide Using Metal Organic
Frameworks
The first published trial to investigate the catalytic activities of MOFs towards the
hydrogenation of carbon dioxide was released in 2016 (Trickett et al. 2017). In this
work, Rungtaweevoranit et al. (2016) studied the catalytic activity of UiO-66 MOF
as a promoter for the conventional copper nanocatalyst. They found that the promoted catalyst achieved high selectivity and high yield towards the production of
methanol. This catalytic affinity was attributed to the presence of different oxidation
states of copper and the high interfacial contact area between the Zn-MOF and the
copper nanoparticles.
On the other hand, the functionalized UiO-67 MOF could be considered as the
first trial to evaluate the catalytic activity of the MOF itself. In this study, the authors
found that the catalytic hydrogenation activity of carbon dioxide by using the functionalized UiO-67 MOF was initiated via heterolytic dissociation of the hydrogen
molecules to generate hydridic and protic hydrogen atoms bound to Lewis acid and
base sites, respectively. This step facilitated a series of simultaneous transfer of two
hydrogen species with the adsorbed carbon dioxide to produce methanol (Ye and
Johnson 2016).
Also, the activity of Pd/ZnO catalyst prepared by the pyrolysis of Pd/ZIF-8 was
investigated. Although the investigated catalyst should be considered as conventional
one, the MOF parent strongly affected its catalytic features, whereas, due to the high
porosity of the parent ZIF-8, the dispersed palladium nanoparticles were confined in
the pore framework, which facilitated the transformation to a conventional catalyst
having strong metal-support interaction after the pyrolysis step (Yin et al. 2018).
3.5 Conclusions
The reduction of carbon dioxide into methanol by using MOF catalysts is a new area
of research. To the extent of our knowledge, the published works in this field are still
few numbers with respect to the conventional materials. In this chapter, we mentioned these few works. However, based on the upper mentioned publications, one
may conclude the following points:
• The photocatalytic efficiency, of any MOF, is based on the type of metal ion and
the organic ligands.
• The metal centers of MOFs should be selected within the transition metals having d orbitals that can overlap with the lowest unoccupied molecular orbital of
the organic linker.
• The hybrid catalysts such as nanocomposites of MOF could enhance the catalytic production of methanol, due to the synergistic effect arising from the photoexcitation properties of the inorganic nanomaterials acting as semiconductors
and the high adsorption power of MOFs towards carbon dioxide.
T. Zaki