Effect of the synthesis conditions of Ni/Al2O3 catalysts on the biogas decomposition to produce H2-rich gas and carbon nanofibers
Abstract The utilization of biogas as carbon source for the co-production of filamentous-like materials and syngas is proposed. Catalysts with different Ni:Al molar ratios, Al 2 O 3 supports and preparation methods were synthesized. The suitability of the catalysts was analyzed considering activity, stability and carbon yield. Catalysts showed a good performance and similar results according to syngas compositions were obtained. However, some differences related to stability over time and carbon yields were detected. TPR analysis and TEM micrographs of the fresh catalysts revealed the presence of two different Ni particles: large Ni particles with low metal support interaction (MSI) that favoured the formation of encapsulating carbon and small Ni particles inserted in the Al 2 O 3 structure with a greater MSI that lead to nanofilamentous carbons formation. Generally both kinds of Ni particles were observed in all catalysts, however their relative abundance was dramatically affected by the Al 2 O 3 employed, the preparation method and the Ni:Al molar ratio.
The Properties of Individual Carbon Residuals and Their Influence on The Deactivation of Ni–CaO–ZrO2 Catalysts in CH4 Dry Reforming
Ni–CaO–ZrO2 catalysts with different properties were prepared and tested for CO2 reforming of methane. The catalysts were characterized by means of transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction to reveal their distinct properties and carbon deposition behaviors in the reforming reaction. It was found that the catalyst prepared by a coprecipitation method and ageing by heating to reflux exhibited a nanocrystalline structure with strong metal–support interaction, which was responsible for both high activity and stability, but it also exhibited the highest carbon formation rate among the tested catalysts. This result suggests that catalyst deactivation might not necessarily correlate with the amount of formed carbon, and the individual properties of carbon residuals could play a more decisive role. Carbon residuals on different catalysts were identified as amorphous carbon, encapsulating carbon, whisker carbon, and graphite, which had different influence on the deactivation. On the surface of the most active and stable catalyst, the carbon species mainly consisted of amorphous and whisker carbon, suggesting that the formation of such carbon species does not necessarily lead to catalyst deactivation. In contrast, the deactivation was found to be closely related to the formation of encapsulating carbon and graphite, which could coat the catalyst surface. The accumulation of different carbon residuals was proven to follow a formation–diffusion/elimination scenario, which was significantly influenced by the Ni particle size and Ni–ZrO2 interactions.
Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols.
Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.