Supported Iron Fischer–Tropsch Catalyst: Superior Activity and Stability Using a Thermally Stable Silica-Doped Alumina Support

Abstract

Fischer−Tropsch synthesis (FTS) is a technically proven and economically viable route for the conversion of coal, biomass, and natural gas to hydrocarbon fuels. Although unsupported Fe catalysts are proven for FTS, they lack the physical strength and durability that would make them more viable for large-scale commercial reactors, and their activity is still significantly less than that of Co FT catalysts. In this work, we report on a very active and stable supported Fe FT catalyst that is more active than any supported Fe FT catalyst previously reported and competitive with the best unsupported catalysts. In addition, its productivity, which takes into account selectivity to desired hydrocarbon products, is also very competitive. More importantly, the catalyst is extremely stable, as evidenced by the fact that after 700 h on stream, its activity and productivity are still increasing. These catalyst properties result from using a novel γ-alumina support material doped with silica and pretreated at 1100 °C. This unique support has high pore volume, large pore diameter, and unusually high thermal stability. The ability to pretreat this support at 1100 °C enables preparation of a material having a low number of acid sites and weak metal oxide−support interactions, all desirable properties for an FT catalyst. These results demonstrate that the surface chemistry of the support material plays a crucial role in the design of an active and stable supported Fe FT catalyst.

Highly active and stable supported iron Fischer–Tropsch catalysts: Effects of support properties and SiO2 stabilizer on catalyst performance

“…This and other previous studies provide evidence that cation vacancies in alumina are occupied by Si atoms, which suppress surface diffusion of Al atoms at elevated temperatures. Our previous work [18] on MAS 27 Al NMR and 29 Si NMR reveals that the percentage of tetrahedral Al in alumina does not change as 5 wt% silica is added to the pure alumina; this observation provides further evidence that Si enters tetrahedral vacancies in a defect spinel structure of alumina thereby forming a Si-Al spinel phase of high porosity and structural stability. The inherent structural stability of this Si-doped alumina spinel accounts for the enhanced support porosity and thermal/hydrothermal stability of the c-Al 2 O 3 phase at high temperatures, i.e.…”

“…To increase the thermal stability of the supports, 3 wt% La was added to AlG, AlA, and AlC, while AlSi consisted of alumina doped with 5% SiO 2 as described previously [18]. The supports were first sieved to 30-60 mesh and calcined at 700°C in air for 4 h prior to impregnation, except AlSi, which was calcined at 1100°C.…”

The effect of Fe2O3 crystal phases on CO2 hydrogenation

“…There is only α-Fe 2 O 3 (PDF: 33–0664) detected in P-1, and only γ-Fe 2 O 3 (PDF: 39–1346) in P-3, while P-2 contains α-Fe 2 O 3 and γ-Fe 2 O 3 phases simultaneously. Calculated with Scherer equation [33] based on 35.6° peak, the particle size is 32.2 nm (P-1), 17.7 nm (P-2) and 16.3 nm (P-3), respectively. The data indicates that the particle size in the precursor built by γ-Fe 2 O 3 is small.…”

Effects of Weak Surface Modification on Co/SiO2 Catalyst for Fischer-Tropsch Reaction

“…Besides the SiO 2 peak in CS, PCS and CPS, other peaks are assigned to Co 3 O 4 species (PDF: 80–1532). Calculated with Scherer equation [7,8,18,19] based on 36.8° peak, the crystal particle size of Co 3 O 4 is 21 nm, 25 nm and 15 nm in CS, PCS and CPS, respectively. The hydrothermal condition to prepare PCS may induce the growth of Co 3 O 4 particles by the decomposition of cobalt nitrate remained in CS.…”