573
• Addition of metal oxide in the form spinel or doping it with other non-refractory
oxide can permit the catalyst to get operated at higher pressures without compromising its activity for a longer duration of time.
• Use of hydrophobic oxide promoters so that the accumulation of water at the
catalyst surface can be avoided.
2 Novel Catalyst Approaches for CO 2 Hydrogenation
After the discovery of Cu/ZnO/Al 2 O 3 catalyst, low-pressure methanol synthesis
units are established all around the globe as the operating cost was significantly
reduced by low-pressure process. The research paradigm shifted to development of
Cu-based catalyst with suitable metal oxide (ZnO, ZrO 2 , CeO 2 , MgO) and structural
promoters (ternary metal oxide) like Al 2 O 3 , ZrO 2 , and CeO 2 . The novel catalyst
synthesis approaches and parameters like pH, temperature, and composition are the
prime focus for catalyst development. Jadhav et al. [81] and Álvarez et al. [82] complied literature on Cu-based catalytic system. Besides, Pd is the second most
reported metal for methanol synthesis via CO 2 hydrogenation. The bimetallic sites
of Pd with Ga, In, and Zn formed on catalyst reduction were explored for the reaction. Li et al. [83] complied the literature reports on bimetallic catalyst used for the
reaction system. Here we elaborate application of In 2 O 3 -based catalyst, metal carbides, and MOF for the hydrogenation of CO 2 .
The DFT calculations on defective [84] and non-defective [85] In 2 O 3 (110)
revealed that oxygen vacancy on the In 2 O 3 surface is helpful for methanol synthesis.
The methanol synthesis mechanism over In 2 O 3 comprises of cyclic creation and
annihilation of oxygen vacancies. The main challenge for methanol synthesis from
CO 2 hydrogenation is selective dissociation one of the C=O bonds. The C=O bonds
in reported Cu-based catalytic systems break only by dissociation of intermediates
formed during reaction [84], whereas, for In 2 O 3 , one oxygen atom of the intermediate fills the vacancy on the surface, and cleavage of C=O occurs. The DFT results
were experimentally verified with application of commercial In 2 O 3 as catalyst.
Methanol selectivity of 54.9% with methanol production rate 3.69 mol h
−1
kgcat
−1
at 330 °C and 4 MPa [86]. Martin et al. [87] reported 99.8% methanol selectivity at
573 K and 50 bar over ZrO 2 supported In 2 O 3 catalyst. The interaction ZrO 2 with
In 2 O 3 increased number of the active sites on the surface. The supported In 2 O 3 /
ZrO 2 catalyst was stable for run time of 1000 h [87]. The existence of ZrO 2 under the
In 2 O 3 overlayer obstructs CO 2 dissociation to CO and improved the concentration of
oxygen vacancies on In 2 O 3 catalytic surface [88]. Moreover, incorporation of Ga
ions into the lattice of In 2 O 3 improved the physicochemical properties and desorption temperature of CO 2 for Ga x /In x O n-2 catalyst. However, strong adsorption of CO 2
results to CH 4 synthesis, and significant reduction in CO yield was noticed over Ga x /
In x O n-2 catalyst [89]. Additionally, Chou [90] et al. reported lanthanum and yttrium
promoted In 2 O 3 catalyst by wet impregnation method. Improved CO 2 adsorption
sites and methanol selectivity were witnessed for La, and Y promoted In 2 O 3 catalyst
Perspectives in Carbon Oxides Conversion to Methanol/Dimethyl Ether: Distinctive…
• Addition of metal oxide in the form spinel or doping it with other non-refractory
oxide can permit the catalyst to get operated at higher pressures without compromising its activity for a longer duration of time.
• Use of hydrophobic oxide promoters so that the accumulation of water at the
catalyst surface can be avoided.
2 Novel Catalyst Approaches for CO 2 Hydrogenation
After the discovery of Cu/ZnO/Al 2 O 3 catalyst, low-pressure methanol synthesis
units are established all around the globe as the operating cost was significantly
reduced by low-pressure process. The research paradigm shifted to development of
Cu-based catalyst with suitable metal oxide (ZnO, ZrO 2 , CeO 2 , MgO) and structural
promoters (ternary metal oxide) like Al 2 O 3 , ZrO 2 , and CeO 2 . The novel catalyst
synthesis approaches and parameters like pH, temperature, and composition are the
prime focus for catalyst development. Jadhav et al. [81] and Álvarez et al. [82] complied literature on Cu-based catalytic system. Besides, Pd is the second most
reported metal for methanol synthesis via CO 2 hydrogenation. The bimetallic sites
of Pd with Ga, In, and Zn formed on catalyst reduction were explored for the reaction. Li et al. [83] complied the literature reports on bimetallic catalyst used for the
reaction system. Here we elaborate application of In 2 O 3 -based catalyst, metal carbides, and MOF for the hydrogenation of CO 2 .
The DFT calculations on defective [84] and non-defective [85] In 2 O 3 (110)
revealed that oxygen vacancy on the In 2 O 3 surface is helpful for methanol synthesis.
The methanol synthesis mechanism over In 2 O 3 comprises of cyclic creation and
annihilation of oxygen vacancies. The main challenge for methanol synthesis from
CO 2 hydrogenation is selective dissociation one of the C=O bonds. The C=O bonds
in reported Cu-based catalytic systems break only by dissociation of intermediates
formed during reaction [84], whereas, for In 2 O 3 , one oxygen atom of the intermediate fills the vacancy on the surface, and cleavage of C=O occurs. The DFT results
were experimentally verified with application of commercial In 2 O 3 as catalyst.
Methanol selectivity of 54.9% with methanol production rate 3.69 mol h
−1
kgcat
−1
at 330 °C and 4 MPa [86]. Martin et al. [87] reported 99.8% methanol selectivity at
573 K and 50 bar over ZrO 2 supported In 2 O 3 catalyst. The interaction ZrO 2 with
In 2 O 3 increased number of the active sites on the surface. The supported In 2 O 3 /
ZrO 2 catalyst was stable for run time of 1000 h [87]. The existence of ZrO 2 under the
In 2 O 3 overlayer obstructs CO 2 dissociation to CO and improved the concentration of
oxygen vacancies on In 2 O 3 catalytic surface [88]. Moreover, incorporation of Ga
ions into the lattice of In 2 O 3 improved the physicochemical properties and desorption temperature of CO 2 for Ga x /In x O n-2 catalyst. However, strong adsorption of CO 2
results to CH 4 synthesis, and significant reduction in CO yield was noticed over Ga x /
In x O n-2 catalyst [89]. Additionally, Chou [90] et al. reported lanthanum and yttrium
promoted In 2 O 3 catalyst by wet impregnation method. Improved CO 2 adsorption
sites and methanol selectivity were witnessed for La, and Y promoted In 2 O 3 catalyst
Perspectives in Carbon Oxides Conversion to Methanol/Dimethyl Ether: Distinctive…