Effects of reaction temperature and feed composition on reactant conversion, product distribution and catalytic stability were investigated on syngas production by reforming of glycerol, a renewable waste, with CO 2 on Rh/ ZrO 2 and Rh/CeO 2 catalysts. For the first time in the literature, fresh and spent catalysts were characterized by in-situ FTIR, Raman spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis techniques in order to unravel novel insights regarding the molecular-level origins of catalytic deactivation and aging under the conditions of glycerol dry reforming. Both catalysts revealed increased glycerol conversions with increasing temperature, where the magnitude of response became particularly notable above 650 and 700°C on Rh/ZrO 2 and Rh/CeO 2 , respectively. In accordance with thermodynamic predictions, CO 2 transformation occurred only above 700°C. Syngas was obtained at H 2 /CO ∼0.8, very close to the ideal composition for Fischer-Tropsch synthesis, and carbon formation was minimized with increasing temperature. Glycerol conversion decreased monotonically, whereas, after an initial increase, CO 2 conversion remained constant upon increasing CO 2 /glycerol ratio (CO 2 /G) from 1 to 4. In alignment with the slightly higher specific surface area of and smaller average Rh-particle size on ZrO 2 , Rh/ZrO 2 exhibited higher conversions and syngas yields than that of Rh/CeO 2. Current characterization studies indicated that Rh/CeO 2 revealed strong metal-support interaction, through which CeO 2 seemed to encapsulate Rh nanoparticles and partially suppressed the catalytic activity of Rh sites. However, such interactions also seemed to improve the stability of Rh/CeO 2 , rendering its activity loss to stay below that of Rh/ZrO 2 after 72 h time-on-stream testing at 750°C and for CO 2 /G = 4. Enhanced stability in the presence of CeO 2 was associated with the inhibition of coking of the catalyst surface by the mobile oxygen species and creation of oxygen vacancies on ceria domains. Deactivation of Rh/ZrO 2 was attributed to the sintering of Rh nanoparticles and carbon formation.
Being able to control polymorphism of a crystal is of great importance to many industries, including the pharmaceutical industry, since the crystal’s structure determines significant physical properties of a material. While there are many conventional methods used to control the final crystal structure that comes out of a crystallization unit, these methods fail to go beyond a few known structures that are kinetically accessible. Recent studies have shown that externally applied fields have the potential to effectively control polymorphism and to extend the set of observable polymorphs that are not accessible through conventional methods. This computational study focuses on the application of high-intensity dc electric fields (e-fields) to induce solid-state transformation of glycine crystals to obtain new polymorphs that have not been observed via experiments. Through molecular dynamics simulations of solid-state α -, β -, and γ -glycine crystals, it has been shown that the new polymorphs sustain their structures within 125 ns after the electric field has been turned off. It was also demonstrated that strength and direction of the electric field and the initial structure of the crystal are parameters that affect the resulting polymorph. Our results showed that application of high-intensity dc electric fields on solid-state crystals can be an effective crystal structure control method for the exploration of new crystal structures of known materials and to extend the range of physical properties a material can have.
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