Browsing by Subject "Synthesis gas"

Now showing 1 - 4 of 4

Open Access
Dry reforming of glycerol over Rh-based ceria and zirconia catalysts: New insights on catalyst activity and stability
(Elsevier B.V., 2018) Bulutoğlu, P. S.; Say, Zafer; Bac, S.; Özensoy, Emrah; Avcı, A. K.
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 CO2 on Rh/ZrO2 and Rh/CeO2 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/ZrO2 and Rh/CeO2, respectively. In accordance with thermodynamic predictions, CO2 transformation occurred only above 700 °C. Syngas was obtained at H2/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, CO2 conversion remained constant upon increasing CO2/glycerol ratio (CO2/G) from 1 to 4. In alignment with the slightly higher specific surface area of and smaller average Rh-particle size on ZrO2, Rh/ZrO2 exhibited higher conversions and syngas yields than that of Rh/CeO2. Current characterization studies indicated that Rh/CeO2 revealed strong metal-support interaction, through which CeO2 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/CeO2, rendering its activity loss to stay below that of Rh/ZrO2 after 72 h time-on-stream testing at 750 °C and for CO2/G = 4. Enhanced stability in the presence of CeO2 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/ZrO2 was attributed to the sintering of Rh nanoparticles and carbon formation.
Open Access
The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2
(Elsevier, 2009-12) Özkara-Aydınoğlu, Ş.; Özensoy, E.; Aksoylu, A. E.
Dry reforming of methane has been studied over Pt/ZrO2 catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO2 catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce-1 wt.%Pt/ZrO2 catalyst prepared by sequential impregnation displayed inferior CH4 and CO2 conversion performances with lowest H-2/CO production ratios. 1 wt.%Ce-1 wt.%Pt/ZrO2 catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH4/CO2 ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt-Ce surface interaction results in an increase in the number of Ce3+ sites and enhances the dispersion of Pt.
Open Access
Exceptionally active and stable catalysts for CO2 reforming of glycerol to syngas
(Elsevier, 2019) Bac, S.; Say, Zafer; Koçak, Yusuf; Ercan, Kerem E.; Harfouche, M.; Özensoy, Emrah; Avcı, A. K.
CO2 reforming of glycerol to syngas was studied on Al2O3-ZrO2-TiO2 (AZT) supported Rh, Ni and Co catalysts within 600–750 °C and a molar inlet CO2/glycerol ratio (CO2/G) of 1–4. Glycerol and CO2 conversions decreased in the following order: Rh/AZT > Ni/AZT > Co/AZT. Reactant conversions on Rh/AZT exceeded 90% of their thermodynamic counterparts at 750 °C and CO2/G = 2–4 at which the activity of Ni/AZT was boosted to ˜95% of the thermodynamic CO2 conversion upon increasing the residence time. The loss in CO2 conversions was below 13% during the 72 h longevity tests confirming the exceptional stability of Rh/AZT and Ni/AZT. However, Co/ AZT suffered from sintering, carbon deposition and oxidation of Co sites, demonstrated via TEM-EDX, XPS, XANES and in-situ FTIR experiments. Characterization of Rh/AZT revealed no significant signs of deactivation. Ni/AZT preserved most of its original metallic pattern and gasified carbonaceous deposits during earlier stages of the reaction
Open Access
A highly active and stable Ru catalyst for syngas production via glycerol dry reforming: Unraveling the interplay between support material and the active sites
(Elsevier, 2022-04-25) Ozden, M.; Say, Zafer; Kocak, Yusuf; Ercan, Kerem Emre; Jalal, Ahsan; Ozensoy, Emrah; Avci, A. K.
Glycerol dry reforming (GDR) was studied on Ru/La2O3, Ru/ZrO2, and Ru/La2O3–ZrO2 catalysts. Impacts of the support on morphological, electronic and surface chemical properties of the catalysts were comprehensively characterized by TEM, in–situ DRIFTS, XPS, ATR–IR and XRD. Initial (5 h) CO2 conversion at 750 °C and CO2–to–glycerol ratio of 1–4 was ordered as Ru/La2O3 < Ru/ZrO2 < Ru/La2O3–ZrO2. During 72 h stability tests, Ru/ZrO2 deactivated by ~33% due to Ru sintering, structural deformation of the monoclinic zirconia support, and strong metal–support interaction. Under identical conditions, CO2 conversion on Ru/La2O3 decreased by 27% mainly due to dehydroxylation/carbonation of lanthana and severe coking. Lanthana–stabilized tetragonal zirconia phase of Ru/La2O3–ZrO2 led to finely dispersed small oxidic Ru clusters which deactivated by 15% after 72 h and demonstrated unusually high catalytic performance that was on par with the significantly more expensive Rh–based catalysts, which are known with their exceptional activity and stability in GDR.