The core–shell-structured Co–Z@TiO2(N2+O2) catalyst, which was prepared by subsequent pyrolysis and calcination from precursor ZIF-67 coated by amorphous TiO2, was applied in Fischer–Tropsch synthesis (FTS). Compared with Co–Z@TiO2 catalyst, which was directly calcinated in air (Co–Z@TiO2(O2)) or pyrolyzed in N2 (Co–Z@TiO2(N2)), the Co–Z@TiO2(N2+O2) catalyst showed better dispersion, easier reducibility, and optimal metal cobalt particle size (8.4 nm) due to the intermediate pyrolysis treatment and core–shell structure. The Co–Z@TiO2(N2+O2) catalyst exhibited high cobalt time yield (14.84 μmolCO·gCo–1·s–1), high selectivity to C5+ (81.5%), and low selectivity to low carbon hydrocarbon (CH4 (12.7%) and C2–C4 (5.8%)). The core–shell structure could enhance diffusion limitations to transform intermediate products into heavier hydrocarbons. After 110 h of evaluation, the Co–Z@TiO2(N2+O2) catalyst still maintained good catalytic performance and cobalt particle size distribution.
Optimizing metal nanoparticle size, dispersion, accessibility, and metal-support interaction has proven impactful for Fischer-Tropsch synthesis (FTS) activity, selectivity of long-chain hydrocarbons and stability. Herein, the Co/Al 2 O 3 -CAI catalyst was successfully prepared by a coordination-assisted impregnation strategy. Compared with Co/Al 2 O 3 -EWI catalyst prepared by traditional impregnation method, the Co/Al 2 O 3 -CAI catalyst displayed superior FTS performance with a low methane selectivity (3.2 %) and surprisingly high C 5+ hydrocarbons selectivity (94.0 %) within 200 h reaction time. The catalyst remained excellent stability with ca. 40 % CO conversion even after 1600 h on stream. It revealed that the high dispersion of cobalt species as well as reduced CoAl 2 O 4 spinel could be achieved via a coordination-assisted impregnation strategy, which provide the increased number of surface-exposed Co sites. Meanwhile, the relatively strong metal-support interaction facilitated surface confinement of cobalt species and electron transfer, guarantying catalyst stability under long-term FTS process. This work provides a new insight into the design of highly efficient and stable catalysts for FTS reaction.
For supported heterogeneous catalyst, metal-support interaction (MSI) is very important factors for catalytic performance. Commercial γ-alumina was reduced with hydrogen in advance, providing strong anchoring sites for metal (metal oxide) species. This research demonstrates the use of pre-reduced alumina as catalyst carrier to anchor metal Co species in FTS compared with unreduced one. The defective alumina supported catalyst displayed a supeior performance. The Co/RAl2O3-550 catalyst showed surprisingly high CO conversion of 56.0%, C5+ hydrocarbons selectivity of 93.2%, and a low methane selectivity of 2.7% at a remarkable high activity (CTY = 1.1 × 10-5 molCO gCo-1 s−1). It revealed the strong reduction of alumina generated more defective sites, which was strongly anchored with metal cobalt species under MSI. Besides, the reduction of alumina also boosted the number of surface L-acidity, promoting the CO absorption rate through CO dissociation. These results reveal the unique property of defective Al2O3 supported cobalt catalysts, and provide a practical strategy to explore stable and efficient FTS catalysts.
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