Abstract
This review emphasizes the importance of the catalytic conversion techniques in the production of clean liquid and hydrogen fuels (XTF) and chemicals (XTC) from the carbonaceous materials including coal, natural gas, biomass, organic wastes, biogas and CO2. Dependence of the performance of Fischer–Tropsch Synthesis (FTS), a key reaction of the XTF/XTC process, on catalyst structure (crystal and size) is comparatively examined and reviewed. The contribution illustrates the very complicated crystal structure effect, which indicates that not only the particle type, but also the particle shape, facets and orientation that have been evidenced recently, strongly influence the catalyst performance. In addition, the particle size effects over iron, cobalt and ruthenium catalysts were carefully compared and analyzed. For all Fe, Co and Ru catalysts, the metal turnover frequency (TOF) for CO hydrogenation increased with increasing metal particle size in the small size region i.e., less than the size threshold 7–8 nm, but was found to be independent of particle size for the catalysts with large particle sizes greater than the size threshold. There are some inconsistencies in the small particle size region for Fe and Ru catalysts, i.e., an opposite activity trend and an abnormal peak TOF value were observed on a Fe catalyst and a Ru catalyst (2 nm), respectively. Further study from the literature provides deeper insights into the catalyst behaviors. The intrinsic activity of Fe catalysts (10 nm) at 260–300 °C is estimated in the range of 0.046–0.20 s−1, while that of the Co and Ru catalysts (7–70 nm) at 220 °C are 0.1 s−1 and 0.4 s−1, respectively.
Highlights
To supply vast energy needs in the world while meeting more stringent environmental regulation to reduce the greenhouse gas emission, the global energy structure dominated by the fossil fuels such as oil, coal and natural gas is required to turn to low carbon system in the thirty years [1]
The trigonal prismatic (TP) carbides such as θ-Fe3 C, γ-Fe5 C2, and Fe7 C3 are reported to be more stable than the octahedral carbides (O) ε-Fe2 C and η-Fe2 C at lower μC
The hexagonal close packed cobaltand metal (Co-hcp) preferentially formed whensurthe face). These authors found that reaction energy and effective barrier of CH4 formation cobalt catalysts were treated by hydrogen at low temperature below 330 °C, or by syngas have a linear relationship with the charge of the surface C atom and the d-band center reduction or by carburation followed by hydrogenation i.e., H2-CO-H2 pretreatment steps of the surface (Figure 2e,f)
Summary
To supply vast energy needs in the world while meeting more stringent environmental regulation to reduce the greenhouse gas emission, the global energy structure dominated by the fossil fuels such as oil, coal and natural gas is required to turn to low carbon system in the thirty years [1]. Cleaner utilization of the fossil fuels; development of renewable energy primarily based on solar, wind and hydropower; CO2 utilization technologies; and increase in efficiency of chemical processes will play important role in reducing CO2 emission. Chemicals (XTC), continues to play important role in carbonclean utilization, over, the renewable technologies that are currently being developed, cannot achieve the neutrality and supplying clean energy. The renewable excludes the nuclear and only world This scenario becomes more prominent in the nationsbecomes having abundant carbonaprovide of energy required in the world. This scenario more prominent in ceous resources, such as China, India, South. It is expected that through better understanding the structure effects and the reaction performance of Fe, Co and Ru catalysts, deep insights into catalysis on the catalysts’ surface and catalysts’ potential activity can be provided, which should be helpful for the design of new generation of catalysts with super activity, stability and selectivity
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