Ni/KIT-6 catalysts were synthesized using ordered mesoporous silica-based KIT-6 molecular sieves as a support in conjunction with an impregnation method. These catalysts were characterized using transmission electron microscopy, X-ray diffraction, N 2 -Brunauer–Emmett–Teller surface area analysis and hydrogen temperature-programmed reduction. The results showed good dispersion of metallic nickel (Ni) on the surface of the KIT-6 and strong interactions between the metal and carrier. The surface areas of the catalysts were in the range of 387–788 m 2 /g and the average pore diameters were in the range of 5.5–8.6 nm. Following H 2 reduction, these materials were applied to the catalytic cracking of a waste cooking oil model compound to produce hydrogen and carbon nanotubes in a laboratory-scale fixed bed reactor. A catalyst with a Ni loading of 10 wt% showed optimal catalytic activity. Reaction trials using an oil flow rate of 0.04 mL/min at 750 °C provided an instantaneous H 2 volume-based proportion of 44.2% with a maximum H 2 concentration in the gaseous products of 59.0% after 25 min. Analyses by thermogravimetry and Raman spectroscopy indicated that carbon nanotubes deposited on the spent catalyst had good oxidative stability and a high degree of graphitization.
During steam reforming, the performance of a catalyst and amount/property of coke are closely related to reaction intermediates reaching surface of a catalyst. Herein, modification of reaction intermediates by placing Mg-Al-hydrotalcite above Ni/KIT-6 catalyst in steam reforming of glycerol was conducted at 300 to 600 °C. The results revealed that the catalytic activity of Ni/KIT-6 in the lower bed was enhanced with either Mg 1 -Al 5 -hydrotalcite (containing more acidic sites) or Mg 5 -Al 1 -hydrotalcite (containing more alkaline sites) as upper-layer catalyst. The in situ infrared characterization of steam reforming demonstrated that Mg-Al-hydrotalcite catalyzed the deoxygenation of glycerol, facilitating the reforming of the partially deoxygenated intermediates over Ni/KIT-6. Mg-Al-hydrotalcite as protective catalyst, however, did not protect the Ni/KIT-6 from formation of more coke. Nonetheless, this did not lead to further deactivation of Ni/KIT-6 while Mg 5 -Al 1 -hydrotalcite even substantially enhanced the catalytic stability, even though the coke was much more significant than that in the use of single Ni/KIT-6 (52.7% vs. 28.6%). The reason beneath this was change of the property of coke from more aliphatic to more aromatic. Mg 5 -Al 1 -hydrotalcite catalyzed dehydration of glycerol, producing dominantly reaction intermediates bearing C=C, which formed the catalytic coke of with carbon nanotube as the main form with smooth outer walls as well as higher aromaticity, C/H ratio, crystallinity, crystal carbon size, thermal stability, and resistivity toward oxidation on Ni/KIT-6 in the lower bed. In comparison, the abundance of acidic sites on Mg 1 -Al 5 -hydrotalcite catalyzed the formation of more oxygen-containing species, leading to the formation of carbon nanotubes of rough surface on Ni/KIT-6.
Sarmad Soomro,Zhenkun Sun,Dennis Y. Lu,Zhihao Zhou,Lin Li,Lunbo Duan
Catalyst deactivation due to carbon deposition and sintering poses a significant challenge to the efficient dry reforming of CH 4 and CO 2 into syngas, particularly at high Ni loadings. To tackle this difficulty, ordered mesoporous silicas with varied pore symmetries were employed as supports in this study to synthesize the Ni-based catalysts using hydrothermal treatment. The 10% Ni/MCM-41 catalyst exhibited the highest conversion rates for CO 2 (81%) and CH 4 (77%), with favourable H 2 /CO (0.92) ratios indicating efficient syngas production Higher Ni concentrations increase active sites and catalytic performance, they also increase carbon deposition, reducing catalyst durability. At lower Ni loadings (4% Ni), catalysts with a 3D pore structure showed improved activity and stability, effectively reducing carbon deposition. This study demonstrates that optimized mesopore symmetries and Ni loadings can enhance catalyst efficiency and durability for syngas production.
危险品化学品经营许可证（带存储）