Fischer-Tropsch synthesis (FTS) is a classical topic of great significance because of the approach of post-petroleum times. Recently we found that, taking the advantage of the anchoring effect and intrinsic basicity of nitrogen-doped carbon nanotubes (NCNTs), iron nanoparticles could be conveniently immobilized on the NCNTs without surface pre-modification. The so-constructed Fe/NCNTs catalyst presents the superb catalytic performance in FTS with high selectivity as well as high catalytic activity and stability. In this study, three Fe/NCNTs catalysts were prepared by incipient wetness impregnation method, colloidal method and deposition-precipitation method, denoted as Fe/NCNTs-IWP, Fe/NCNTs-C, and Fe/NCNTs-DP, respectively. The influence of preparation methods on the particle size distribution and morphology, reduction and carbonization of the active species, as well as the FTS catalytic performance were systematically examined. The results indicate that the incipient impregnation method could achieve high dispersion, smaller particles and narrower size distribution [(8±4) nm], leading to the easier reduction and carbonization of the iron nanoparticles compared with those prepared by the other two methods. The FTS catalytic performance of the Fe/NCNTs-IWP catalyst is much better than those of the Fe/NCNTs-C and the Fe/NCNTs-DP catalysts in terms of the high lower olefins selectivity, high catalytic activity and stability. Colloid method got the different morphologies of iron particles with the average size of (13±7) nm. The active iron species was susceptible to oxidation during the reaction, which cause poor catalytic activity and stability. The deposition-precipitation method got the largest particles of (19±11) nm which were difficult to be reduced and carbonized, leading to the sharp decline of the catalytic activity and stability after 15 h reaction. The size-dependence of the catalytic performance for the Fe/NCNTs catalysts in this study are generally in consistent with those in literatures for the iron catalysts supported on carbon nanotubes. These results should be suggestive for exploring the advanced FTS catalysts with the abundant N-doped carbon nanostructures.
The adoption of plant-derived natural products to synthesize metal nanoparticles and their complexes has the advantages of mild reaction conditions, environmental protection, sustainability and simple operation compared with traditional physical or chemical synthesis methods. Herein, silver nanoparticles (AgNPs) were in situ synthesized on the surface of graphene oxide (GO) by a “one-pot reaction” to prepare graphene oxide-silver nanoparticles composite (GO-AgNPs) based on using AgNO3 as the precursor of AgNPs and gallic acid (GA) as the reducing agent and stabilizer. The size and morphology of GO-AgNPs were characterized by ultraviolet-visible spectrophotometer (Uv-vis), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), X-ray diffractometer (XRD) and dynamic light scattering (DLS). The effects of pH, temperature, time and material ratio on the synthesis of GO-AgNPs were investigated experimentally. The results showed that ideal GO-AgNPs could be prepared under the conditions of pH = 9, 45°C, 2 h and the 2:1 of molar ratio of AgNO3 to GA. The AgNPs within GO-AgNPs are highly crystalline spherical particles with moderate density on the surface of GO, and the size of AgNPs is relatively uniform and determined to be about 8.19 ± 4.21 nm. The research results will provide new ideas and references for the green synthesis of metal nanoparticles and their complexes using plant-derived natural products as the reducing agent and stabilizer.
The water–gas shift (WGS) reaction is an important process in the hydrogen industry, and its catalysts are of vital importance for this process. However, it is still a great challenge to develop catalysts with both high activity and high stability. Herein, a series of high-purity Cu-Mn-Al hydrotalcites with high Cu content have been prepared, and the WGS performance of the Cu-Mn-Al catalysts derived from these hydrotalcites have been studied. The results show that the Cu-Mn-Al catalysts have both outstanding catalytic activity and excellent stability. The optimized Cu-Mn-Al catalyst has displayed a superior reaction rate of 42.6 μmol−1 CO·g−1 cat·s−1, while the CO conversion was as high as 96.1% simultaneously. The outstanding catalytic activities of the Cu-Mn-Al catalysts could be ascribed to the enriched interfaces between Cu-containing particles and manganese oxide particles, and/or abundant oxygen vacancies. The excellent catalytic stability of the Cu-Mn-Al catalysts may be benefitting from the low valence state of the manganese of manganese oxides, because the low valence manganese oxides have good anti-sintering properties and can stabilize oxygen vacancies. This study provides an example for the construction of high-performance catalysts by using two-dimensional hydrotalcite materials as precursors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.