127
atmospheric pressure and only carbon monoxide and methane were detected as
products (Edelmannová et al. 2018).
During the last years, new applications of layered double hydroxides with high
carbon dioxide adsorption capacity at room temperature have attracted the interest
as eco-friendly photocatalysts. The magnesium–aluminum-layered double hydroxide samples were evaluated in the carbon dioxide photoreduction for methanol generation in both liquid and gas phases. According to the results of Flores-Flores and
co-workers (2018), the magnesium–aluminum-layered double hydroxides could
photocatalytically generate some methanol in liquid phase, e.g., the best methanol
productivity being 0.009 mmol MeOH .g cat
−1
.h
−1
. The methanol productivity in this case
is influenced by such parameters as the carbon dioxide adsorption and the charge
transfer from the material surface to the adsorbed carbon dioxide. No methanol was
observed in the gas phase photocatalytic experiments at atmospheric pressure supposing that a deoxidation occurs and allows the production of carbon monoxide and
methane by the reduction of carbon species with electrons.
Different promoters as palladium, rhodium, platinum, or ruthenium for photocatalytic hydrogenation of carbon dioxide were studied. In all cases, no methanol
was observed in the gas phase reaction (Ishitani et al. 1993). Other materials of
interest reported to date are indium-based photothermal catalysts, e.g., In 2 O 3−x (OH) y
with methanol productivity in liquid phase of 0.06 mmol MeOH g cat
−1
h
−1
(Wang et al.
2018).
Apart from the photocatalytic materials development, the main difficulty and
limiting step of the photochemical conversion of carbon dioxide into methanol in
the gas phase are the reactor design and optimization allowing the performance of
the photocatalytic materials under higher pressures (Chen et al. 2017).
Even though it is highly desirable to produce methanol in a sustainable way and
use carbon dioxide as feedstock and solar energy to drive the synthesis, there is still
a way to go. Based on the discussion regarding the activities in carbon dioxide
hydrogenation to methanol via photocatalytic route, it can be concluded that the
game-changing rates are not yet achieved. The use of high pressures for the gas
phase photocatalytic hydrogenation of carbon dioxide is required. The development
of the photocatalytic reactors will open the strategies to a potentially clean solar
methanol process using carbon dioxide and renewable hydrogen as feedstocks.
5.3.5 Kinetic Study of the Hydrogenation of Carbon Dioxide
to Methanol in the Gas Phase
The state-of-the-art methanol production is based on syngas conversion. So, using
carbon dioxide as feedstock poses new challenges, such as development of new
catalysts and optimization of reaction parameters to ensure high carbon dioxide
conversion as well as high selectivity to methanol. Kinetic studies of methanol production from carbon dioxide hydrogenation are also required for designing highly
5 Selective Hydrogenation of Carbon Dioxide into Methanol
atmospheric pressure and only carbon monoxide and methane were detected as
products (Edelmannová et al. 2018).
During the last years, new applications of layered double hydroxides with high
carbon dioxide adsorption capacity at room temperature have attracted the interest
as eco-friendly photocatalysts. The magnesium–aluminum-layered double hydroxide samples were evaluated in the carbon dioxide photoreduction for methanol generation in both liquid and gas phases. According to the results of Flores-Flores and
co-workers (2018), the magnesium–aluminum-layered double hydroxides could
photocatalytically generate some methanol in liquid phase, e.g., the best methanol
productivity being 0.009 mmol MeOH .g cat
−1
.h
−1
. The methanol productivity in this case
is influenced by such parameters as the carbon dioxide adsorption and the charge
transfer from the material surface to the adsorbed carbon dioxide. No methanol was
observed in the gas phase photocatalytic experiments at atmospheric pressure supposing that a deoxidation occurs and allows the production of carbon monoxide and
methane by the reduction of carbon species with electrons.
Different promoters as palladium, rhodium, platinum, or ruthenium for photocatalytic hydrogenation of carbon dioxide were studied. In all cases, no methanol
was observed in the gas phase reaction (Ishitani et al. 1993). Other materials of
interest reported to date are indium-based photothermal catalysts, e.g., In 2 O 3−x (OH) y
with methanol productivity in liquid phase of 0.06 mmol MeOH g cat
−1
h
−1
(Wang et al.
2018).
Apart from the photocatalytic materials development, the main difficulty and
limiting step of the photochemical conversion of carbon dioxide into methanol in
the gas phase are the reactor design and optimization allowing the performance of
the photocatalytic materials under higher pressures (Chen et al. 2017).
Even though it is highly desirable to produce methanol in a sustainable way and
use carbon dioxide as feedstock and solar energy to drive the synthesis, there is still
a way to go. Based on the discussion regarding the activities in carbon dioxide
hydrogenation to methanol via photocatalytic route, it can be concluded that the
game-changing rates are not yet achieved. The use of high pressures for the gas
phase photocatalytic hydrogenation of carbon dioxide is required. The development
of the photocatalytic reactors will open the strategies to a potentially clean solar
methanol process using carbon dioxide and renewable hydrogen as feedstocks.
5.3.5 Kinetic Study of the Hydrogenation of Carbon Dioxide
to Methanol in the Gas Phase
The state-of-the-art methanol production is based on syngas conversion. So, using
carbon dioxide as feedstock poses new challenges, such as development of new
catalysts and optimization of reaction parameters to ensure high carbon dioxide
conversion as well as high selectivity to methanol. Kinetic studies of methanol production from carbon dioxide hydrogenation are also required for designing highly
5 Selective Hydrogenation of Carbon Dioxide into Methanol