124
Another interesting nickel-based catalysts worth mentioning are the bimetallic
nickel–indium catalysts (Dang et al. 2018). Richard and Fan (2017) have developed
Ni–In–Al/SiO 2 catalysts that achieve twice the methanol productivity than the traditional CuO–ZnO–Al 2 O 3 catalyst in the low-pressure carbon dioxide hydrogenation
to methanol; still some tests at high pressure are needed for confirmation of these
results in realistic conditions.
The indium-based materials have previously demonstrated high activity and
selectivity in multiple catalytic transformations involving carbon dioxide (Detweiler
et al. 2014). Martin and co-workers (2016) studied In 2 O 3 -based catalysts with the
zirconia carrier. It was found that those materials could be very promising catalysts
for carbon dioxide hydrogenation to methanol with 100% selectivity to methanol
and complete suppression of undesirable reverse water-gas shift reaction.
5.3.3 Noble Metal-Based Catalysts for Carbon Dioxide
Hydrogenation in the Gas Phase
Palladium, one of the noble metals, was studied in the form supported over different oxides such as cerium oxide, zinc oxide, titanium oxide, zirconium oxide, and
others (Saito 1998). Fujitani and co-workers (1995) have shown that the Pd/Ga 2 O 3
catalysts allow better carbon dioxide conversions and better yields of methanol
compared to other palladium-based catalysts and to Cu–ZnO catalysts. This high
activity is explained by the stabilization of palladium in the intermediate oxidative
state (Pd
n+
, n between 0 and 2) due to the presence of gallium oxide. An infrared
study of the intermediates of methanol synthesis from carbon dioxide over Pd/βGa 2 O 3 and Ga 2 O 3 –Pd/silica catalysts has been performed (Collins et al. 2004;
Chivassa et al. 2009). It was determined that hydrogen dissociates over palladium
and then migrates rapidly to gallium oxide to form formate species and confirms
thus the high activity of Pd/Ga 2 O 3 catalysts. One of the highest methanol selectivities (>90%) was observed using palladium supported over cerium oxide by Fan and
Fujimoto (1995), through low carbon dioxide conversion, and probably partial
reduction of ceria is at the origin of such increase in activity. Nevertheless,
palladium- based catalytic materials are far from their potential industrial application due to the high loading 2–10 wt.% of palladium.
Another noble metal worthy of attention used in the catalysis of carbon dioxide
hydrogenation to methanol is silver. Sugawa and co-workers (1995) studied catalysts based on silver that was supported over zinc oxide. These showed good selectivity to methanol compared to the copper-based and other noble metal-based
(rhodium, ruthenium, and others) catalysts. Addition of aluminum to the zinc support (Ag/ZnO–Al 2 O 3 ) had a beneficial effect on the dispersion of metallic silver
active site, and addition of gallium oxide (Ag/ZnO–Ga 2 O 3 ) allowed increasing the
yield of methanol that was explained by slightly oxidative character of the silver
surface in the presence of gallium(III) oxide.
D. P. Minh et al.
Another interesting nickel-based catalysts worth mentioning are the bimetallic
nickel–indium catalysts (Dang et al. 2018). Richard and Fan (2017) have developed
Ni–In–Al/SiO 2 catalysts that achieve twice the methanol productivity than the traditional CuO–ZnO–Al 2 O 3 catalyst in the low-pressure carbon dioxide hydrogenation
to methanol; still some tests at high pressure are needed for confirmation of these
results in realistic conditions.
The indium-based materials have previously demonstrated high activity and
selectivity in multiple catalytic transformations involving carbon dioxide (Detweiler
et al. 2014). Martin and co-workers (2016) studied In 2 O 3 -based catalysts with the
zirconia carrier. It was found that those materials could be very promising catalysts
for carbon dioxide hydrogenation to methanol with 100% selectivity to methanol
and complete suppression of undesirable reverse water-gas shift reaction.
5.3.3 Noble Metal-Based Catalysts for Carbon Dioxide
Hydrogenation in the Gas Phase
Palladium, one of the noble metals, was studied in the form supported over different oxides such as cerium oxide, zinc oxide, titanium oxide, zirconium oxide, and
others (Saito 1998). Fujitani and co-workers (1995) have shown that the Pd/Ga 2 O 3
catalysts allow better carbon dioxide conversions and better yields of methanol
compared to other palladium-based catalysts and to Cu–ZnO catalysts. This high
activity is explained by the stabilization of palladium in the intermediate oxidative
state (Pd
n+
, n between 0 and 2) due to the presence of gallium oxide. An infrared
study of the intermediates of methanol synthesis from carbon dioxide over Pd/βGa 2 O 3 and Ga 2 O 3 –Pd/silica catalysts has been performed (Collins et al. 2004;
Chivassa et al. 2009). It was determined that hydrogen dissociates over palladium
and then migrates rapidly to gallium oxide to form formate species and confirms
thus the high activity of Pd/Ga 2 O 3 catalysts. One of the highest methanol selectivities (>90%) was observed using palladium supported over cerium oxide by Fan and
Fujimoto (1995), through low carbon dioxide conversion, and probably partial
reduction of ceria is at the origin of such increase in activity. Nevertheless,
palladium- based catalytic materials are far from their potential industrial application due to the high loading 2–10 wt.% of palladium.
Another noble metal worthy of attention used in the catalysis of carbon dioxide
hydrogenation to methanol is silver. Sugawa and co-workers (1995) studied catalysts based on silver that was supported over zinc oxide. These showed good selectivity to methanol compared to the copper-based and other noble metal-based
(rhodium, ruthenium, and others) catalysts. Addition of aluminum to the zinc support (Ag/ZnO–Al 2 O 3 ) had a beneficial effect on the dispersion of metallic silver
active site, and addition of gallium oxide (Ag/ZnO–Ga 2 O 3 ) allowed increasing the
yield of methanol that was explained by slightly oxidative character of the silver
surface in the presence of gallium(III) oxide.
D. P. Minh et al.