3 Catalysts via Atomic Layer Deposition
89
TiO 2 at 120 °C [97]. TiO 2 is utilized as catalytic promoters in hydrogenation reaction,
CO oxidation, carbon dioxide reforming of methane, photoelectrochemical catalysis,
and 1-propanol reforming reaction [79, 86, 93, 97–107].
CoO x , FeO x , NiO x
The most commonly used precursors for CoO x , FeO x , and NiO x ALD are Co(Cp) 2 ,
Fe(Cp) 2 , and Ni(Cp) 2 with O 3 or O 2 . The CoO x film’s thickness and growth rate
as functions of deposition temperature are monitored in the range of 100–300 °C.
The growth rate is relatively low when the deposition temperature is below 150 °C,
due to the lack of thermal activation energy. Then, it reaches a steady growth rate
of 0.37 Å per cycle in the temperature range from 150 °C to 250 °C. The growth
rate increases abruptly when the temperature goes beyond 250 °C, partially due to
the thermal decomposition of precursors [108]. CoO x prepared by ALD has shown
potential in the epoxidation reaction of styrene, photoelectrochemical catalysis,
CO oxidation, and MMP (1-methoxy-2-methyl-2-propanol) decomposition reaction
[108–115]. FeO x prepared by ALD has been investigated in hydrogenation and dehydrogenation reaction, reductive coupling reaction, and photoelectrochemical water
splitting [116–120]. NiO x prepared by ALD is investigated in CO oxidation reaction
[121–123].
Other metal oxides
There are still a large number of oxides prepared by ALD as shown in Table 3.2
that we have not covered in the above discussion. MgO [124], In 2 O 3 [125], MnO x
[126], CeO x [106, 127], La 2 O 3 [128], ZrO 2 [129, 130], VO x [131, 132], WO 3 [133,
134], NbO x [135, 87], SiO 2 [136, 137], CrO x [138, 139], etc., were used as catalysts in several reactions, such as furfural hydrogenation, electrochemistry, syngas
conversion to higher oxygenates, 1-propanol reforming, CO oxidation, photoelectrochemical water oxidation, methane oxidation, electrochemical capacitance, oxidative
dehydrogenation of cyclohexane, propane dehydrogenation, 2-butanol dehydration,
water splitting, 2-propanol dehydration, cyclohexanol dehydration. For example, Liu
et al. fabricated photoelectrodes with WO 3 coated on a Mn catalyst via ALD. The
soaking of WO 3 occurs in water with pH of 7, where the oxygen is generated through
the water splitting under illumination. This is the first time demonstrating the stable
WO 3 photoelectrodes in neutral solution [126].
3.3.2 Porous Oxide Coating Catalysts Structures
Besides oxides acting as support in catalysts, the ultrathin oxide overcoating layer
fabricated with ALD can also act as decoration layer to modify NPs to improve
catalytic activity and selectivity. Meanwhile, the coating layer could also anchor the
NPs and enhance the thermal stability. One method to create porous coating layer
fabricated via ALD involves calcination post-treatment after the oxide coating. The
residual organic groups in the oxide layer will be oxidized, and nanotunnels will be
89
TiO 2 at 120 °C [97]. TiO 2 is utilized as catalytic promoters in hydrogenation reaction,
CO oxidation, carbon dioxide reforming of methane, photoelectrochemical catalysis,
and 1-propanol reforming reaction [79, 86, 93, 97–107].
CoO x , FeO x , NiO x
The most commonly used precursors for CoO x , FeO x , and NiO x ALD are Co(Cp) 2 ,
Fe(Cp) 2 , and Ni(Cp) 2 with O 3 or O 2 . The CoO x film’s thickness and growth rate
as functions of deposition temperature are monitored in the range of 100–300 °C.
The growth rate is relatively low when the deposition temperature is below 150 °C,
due to the lack of thermal activation energy. Then, it reaches a steady growth rate
of 0.37 Å per cycle in the temperature range from 150 °C to 250 °C. The growth
rate increases abruptly when the temperature goes beyond 250 °C, partially due to
the thermal decomposition of precursors [108]. CoO x prepared by ALD has shown
potential in the epoxidation reaction of styrene, photoelectrochemical catalysis,
CO oxidation, and MMP (1-methoxy-2-methyl-2-propanol) decomposition reaction
[108–115]. FeO x prepared by ALD has been investigated in hydrogenation and dehydrogenation reaction, reductive coupling reaction, and photoelectrochemical water
splitting [116–120]. NiO x prepared by ALD is investigated in CO oxidation reaction
[121–123].
Other metal oxides
There are still a large number of oxides prepared by ALD as shown in Table 3.2
that we have not covered in the above discussion. MgO [124], In 2 O 3 [125], MnO x
[126], CeO x [106, 127], La 2 O 3 [128], ZrO 2 [129, 130], VO x [131, 132], WO 3 [133,
134], NbO x [135, 87], SiO 2 [136, 137], CrO x [138, 139], etc., were used as catalysts in several reactions, such as furfural hydrogenation, electrochemistry, syngas
conversion to higher oxygenates, 1-propanol reforming, CO oxidation, photoelectrochemical water oxidation, methane oxidation, electrochemical capacitance, oxidative
dehydrogenation of cyclohexane, propane dehydrogenation, 2-butanol dehydration,
water splitting, 2-propanol dehydration, cyclohexanol dehydration. For example, Liu
et al. fabricated photoelectrodes with WO 3 coated on a Mn catalyst via ALD. The
soaking of WO 3 occurs in water with pH of 7, where the oxygen is generated through
the water splitting under illumination. This is the first time demonstrating the stable
WO 3 photoelectrodes in neutral solution [126].
3.3.2 Porous Oxide Coating Catalysts Structures
Besides oxides acting as support in catalysts, the ultrathin oxide overcoating layer
fabricated with ALD can also act as decoration layer to modify NPs to improve
catalytic activity and selectivity. Meanwhile, the coating layer could also anchor the
NPs and enhance the thermal stability. One method to create porous coating layer
fabricated via ALD involves calcination post-treatment after the oxide coating. The
residual organic groups in the oxide layer will be oxidized, and nanotunnels will be