Investigation of the effect of formulation on the microstructure an‎d physical properties of alumina support catalysts used in the partial oxidation of ethylene an‎d its conversion to ethylene oxide

10/22/2026 12:00:00 AM

Ethylene oxide is one of the most important chemicals in the petrochemical industry an‎d is typically produced by the reaction of ethylene an‎d oxygen over a silver/alumina catalyst. This catalyst is prepared by impregnating silver metal an‎d various promoters onto an alumina support that is shaped by the extrusion method. In this study, after the characterization of a commercial reference catalyst support, macroporous alumina supports were designed an‎d fabricated in order to investigate the effects of composition an‎d key processing parameters. Finally, the impregnation process was carried out on both the optimized sample an‎d the reference sample, an‎d the results were compared. To investigate the phase structure, chemical composition, microstructure, surface characteristics, an‎d physical an‎d mechanical properties of the synthesized alumina supports, XRD, XRF, FESEM, ICP, mercury intrusion porosimetry, nitrogen adsorption–desorption analysis, compressive strength testing, an‎d water absorption measurements were employed, respectively. The design, fabrication, an‎d eva‎luation of the alumina supports were conducted in three phases, while the impregnation process was performed in the fourth phase. In the first phase, the feasibility of extrusion shaping of samples with dimensions similar to the reference support was investigated using α-Al₂O₃, γ-Al₂O₃, boehmite, gibbsite, an‎d other additives. In the second phase, a classical experimental design was applied, in which α-Al₂O₃ an‎d γ-Al₂O₃ contents of 70–80 wt.% an‎d 20–30 wt.%, respectively, along with pore-forming agents including walnut shell, sawdust, corn starch, activated carbon type 1, an‎d activated carbon type 2 in the range of 10–30 wt.%, particle size of pore formers, an‎d heat treatment holding times of 2–6 h were investigated. In the third phase, based on an L9 Taguchi design of experiments, four main fabrication parameters—namely the γ-Al₂O₃/α-Al₂O₃ ratio, plast Zuzo content, pore-forming agent content, an‎d heat treatment temperature—were examined at three levels. The γ-Al₂O₃/α-Al₂O₃ ratios were set at 75/25, 80/20, an‎d 85/15; plast Zuzo contents at 1, 1.25, an‎d 1.5 wt.%; pore-forming agent contents at 30, 35, an‎d 40 wt.%; an‎d heat treatment temperatures at 1375, 1425, an‎d 1475 °C. In the fourth phase, the reference an‎d optimized samples were impregnated with a silver-containing solution. Based on the results of the first-phase samples an‎d comparison with the reference support, a sample with a BET surface area of 1.3 m²/g, compressive strength of 10 kgf, an‎d water absorption of 25% was selec‎ted. According to the second-phase results, a sample with a BET surface area of 2.6 m²/g, compressive strength of 9.4 kgf, an‎d water absorption of 35% was chosen as the base composition for further fabrication. In the third phase, the results of BET surface area, porosity percentage, pore size an‎d distribution, as well as physical an‎d mechanical properties of the nine Taguchi samples were analyzed using Design of Experiments software to identify the most influential parameters an‎d determine the optimal composition. The final optimized composition consisted of a γ-Al₂O₃/α-Al₂O₃ ratio of 85/15, plast Zuzo content of 1 wt.%, pore-forming agent content of 40 wt.%, an‎d a heat treatment temperature of 1425 °C. The optimized sample exhibited a BET surface area of 2.3 m²/g, compressive strength of 9.4 kgf, water absorption of 34.5%, pore volume of 0.316 cm³/g, an‎d an average pore size of 499 nm, making it the most similar to the reference sample among all fabricated supports. According to ICP analysis, the silver contents of the reference an‎d optimized samples after impregnation were 11.3 wt.% an‎d 6.3 wt.%, respectively. Furthermore, XRD analysis confirmed the presence of metallic silver alongside the corundum alumina phase. SEM images of both samples demonstrated the distribution of silver particles on their surfaces.

كاتاليزگر , پايه كاتاليزگر , اكستروژن , Al2O3 -α , ماكرومتخلخل , اكسيداتيلن

Catalyst , catalyst support , extrusion , α-Al2O3 , macroporous , ethylene oxide

Pourya Mehrasbi

Hajar Ghanbari, Mahdi Maleki