541
(precipitating solution) for a fixed time. Ageing impacts the final morphology of the
catalyst as agglomeration and structural changes occur. The precipitate/gel is filtered to separate it from its precipitating solution and typically washed with deionized water to remove unwanted occluded ions. Subsequently it is dried and formed
by processes such as palletisation, extrusion or spray drying. And finally, the catalyst is calcined by relatively high temperature treatment. The calcination step
improves the physical properties of the catalyst and may impact phase transitions to
desirable catalytic phase.
3.1.2 Catalyst Synthesis by Aerosol Synthesis Methods
In general, the wet synthesis method leads to the synthesis of different types of catalytic materials with desirable properties. However, wet synthesis methods are typically multi-step, batch processes with significant waste treatment requirements and
present scale-up challenges for continuous catalyst production at industrial scales.
The novel catalyst synthesis technique by aerosol processes is an easily scalable,
continuous, one-step synthesis method for catalyst synthesis [49–51]. Another
advantage of flame synthesis is the manufacture of nano-sized particles with highpurity, well-controlled crystallinity and narrow size distribution [52]. High-purity
catalysts obtained from flame synthesis technique may minimize waste generation
in reactors from side reactions. The flame synthesis technique has been shown to
produce catalysts with well-controlled size, morphology, high dispersion, surface
area, strong metal support interaction and therefore good catalytic properties [53–
56]. In some cases, flame-made catalysts have been shown to have better catalytic
performance compared to conventionally synthesized catalysts by wet methods
[57–60].
The aerosol synthesis method describes synthesis methods to produce solid catalyst particles from droplets of liquid precursor solution. Aerosol synthesis methods
for catalyst production include flame synthesis and spray pyrolysis. In flame synthesis, the precursor is introduced into a flame while in spray pyrolysis, the precursor
is introduced as droplets into a controlled high-temperature tubular reactor.
In aerosol synthesis processes catalyst particle formation mechanism can be
either gas to particle conversion mechanism or droplet to particle conversion mechanism. In the gas to particle conversion mechanism, the active component (metal
oxide) is first formed in the gaseous phase; and subsequently by nucleation, condensation, coagulation and agglomeration, a solid catalyst material is produced. In the
droplet to particle conversion (intraparticle reaction) mechanism, catalyst particles
are formed by solvent evaporation, precipitation and thermal decomposition of the
precursor to form the active component in the solid phase with subsequent coagulation and agglomeration [52]. A schematic diagram showing the particle formation
process in aerosol processes is shown in Fig. 3.
Flame synthesis is further divided based on the method of introduction of the
precursor into the flame into vapour-fed flame synthesis and liquid-fed flame synthesis. In vapour-fed flame synthesis, gaseous precursors are fed into typically
Synthesis of Novel Catalysts for Carbon Dioxide Conversion to Products of Value
(precipitating solution) for a fixed time. Ageing impacts the final morphology of the
catalyst as agglomeration and structural changes occur. The precipitate/gel is filtered to separate it from its precipitating solution and typically washed with deionized water to remove unwanted occluded ions. Subsequently it is dried and formed
by processes such as palletisation, extrusion or spray drying. And finally, the catalyst is calcined by relatively high temperature treatment. The calcination step
improves the physical properties of the catalyst and may impact phase transitions to
desirable catalytic phase.
3.1.2 Catalyst Synthesis by Aerosol Synthesis Methods
In general, the wet synthesis method leads to the synthesis of different types of catalytic materials with desirable properties. However, wet synthesis methods are typically multi-step, batch processes with significant waste treatment requirements and
present scale-up challenges for continuous catalyst production at industrial scales.
The novel catalyst synthesis technique by aerosol processes is an easily scalable,
continuous, one-step synthesis method for catalyst synthesis [49–51]. Another
advantage of flame synthesis is the manufacture of nano-sized particles with highpurity, well-controlled crystallinity and narrow size distribution [52]. High-purity
catalysts obtained from flame synthesis technique may minimize waste generation
in reactors from side reactions. The flame synthesis technique has been shown to
produce catalysts with well-controlled size, morphology, high dispersion, surface
area, strong metal support interaction and therefore good catalytic properties [53–
56]. In some cases, flame-made catalysts have been shown to have better catalytic
performance compared to conventionally synthesized catalysts by wet methods
[57–60].
The aerosol synthesis method describes synthesis methods to produce solid catalyst particles from droplets of liquid precursor solution. Aerosol synthesis methods
for catalyst production include flame synthesis and spray pyrolysis. In flame synthesis, the precursor is introduced into a flame while in spray pyrolysis, the precursor
is introduced as droplets into a controlled high-temperature tubular reactor.
In aerosol synthesis processes catalyst particle formation mechanism can be
either gas to particle conversion mechanism or droplet to particle conversion mechanism. In the gas to particle conversion mechanism, the active component (metal
oxide) is first formed in the gaseous phase; and subsequently by nucleation, condensation, coagulation and agglomeration, a solid catalyst material is produced. In the
droplet to particle conversion (intraparticle reaction) mechanism, catalyst particles
are formed by solvent evaporation, precipitation and thermal decomposition of the
precursor to form the active component in the solid phase with subsequent coagulation and agglomeration [52]. A schematic diagram showing the particle formation
process in aerosol processes is shown in Fig. 3.
Flame synthesis is further divided based on the method of introduction of the
precursor into the flame into vapour-fed flame synthesis and liquid-fed flame synthesis. In vapour-fed flame synthesis, gaseous precursors are fed into typically
Synthesis of Novel Catalysts for Carbon Dioxide Conversion to Products of Value