Harnessing the Synergistic Interplay of Fischer‐Tropsch Synthesis (Fe‐Co) Bimetallic Oxides in Na‐FeMnCo/HZSM‐5 Composite Catalyst for Syngas Conversion to Aromatic Hydrocarbons

Abstract

The efficient conversion of syngas to aromatic hydrocarbons (STA) has attracted attention in recent years for its extensive utilization in the energy and defense sectors. In current study, the alloying of two active FT synthesis metal components (FeÀ Co) was employed in Na-FeMnCo/HZSM-5 composite catalyst for STA process. Different calcination temperatures and Fe/Mn/Co molar ratios were modulated for harnessing the different Fe 2 O 3 /CoFe 2 O 4 /MnCo 2 O 4 structures that possessed divergent structural, reduction, carburization and catalytic behaviors to give Fe 3 O 4 /Fe x C/Co x C reactive species. Herein, the effective inclusion of Co and Mn into Fe brought about the expedient geometric and electronic modulations for providing the homogenously distributed CoFe 2 O 4 nanocrystals. This particular substitution of Fe played a vital role for tuning the density of oxygen vacancies, tailoring the reduction behavior of Fe-O x , giving the FeÀ Co alloy structure, and adjusting the adsorption capabilities of catalytic surface that mainly dictate the concentration of active Fe 5 C 2 phase. An escalated selectivity to olefinic intermediates and subsequent higher aromatics fractions (~55 %) thus was imparted with an inhibited CO 2 (21 %) generation by meliorating the different Fischer-Tropsch/ Aromatization reactions in stable CO conversion of~98 %.

Advances in Selectivity Control for Fischer–Tropsch Synthesis to Fuels and Chemicals with High Carbon Efficiency

“…Theoretically, aromatics can be produced after coupling FTO catalysts and H-ZSM-5 using various catalyst integrated configurations including the dual-bed model, physical mixture model, and core–shell structure or zeolite supported model. , Moreover, the light aromatics components could be effectively tuned by neutralizing and/or sealing the exposed external acidic sites of HZSM-5 through silica deposition or impregnation of oxides of some metals. , Another effective approach is to tune the size of H-ZSM-5 crystallites Table S2 summarizes the typical catalysts for direct syngas conversion to aromatics, which are mainly obtained through a physical mixture or core–shell-structured model. − …”

“…Many studies select Fe-based catalysts for the FTO reaction due to their broad operation temperature (200–400 °C), which will match the working temperature of the olefins to aromatics reaction over zeolite (300–400 °C). ,,, A reaction rate match between each step is required for the tandem reaction. Therefore, the fine design of highly efficient FTO catalyst and HZSM-5 zeolites with a suitable pore structure (i.e., hierarchical- or hollow-structured) and moderate acidity as well as their synergism play a crucial role for direct syngas conversion to aromatics.…”

Effective Inclusion of ZnMg in a Fe-Based/HZSM-5-Integrated Catalyst for the Direct Synthesis of Aromatics from Syngas

“…Generally, the synthesis methods of the Fe-based catalyst include CP, IWI, and SP methods; therefore, in order to compare the catalytic activity of different schemes, Fe-based catalysts with the same Mg and Zn contents were evaluated by CP and IWI methods, respectively. , Figure d shows that compared with CP and IWI, the catalyst made by the SP method shows a better catalytic effect of (97%) CO conversion, while the CO conversion rate of the catalyst prepared by the former two methods is similar, and the selectivity of the byproducts (CO 2 and CH 4 ) produced therewith is lower for CP. It could be interpreted that the SP method contributes to the formation of metal colloids, which makes the combination of Fe, Zn, and Mg stronger and more stable (to be discussed) .…”

“…The Na–FeZnMg catalyst was synthesized by the sol precipitation (SP) method with different Fe (NO 3 ) 3 ·9H 2 O, Mg (NO 3 ) 2 ·6H 2 O, and Zn (NO 3 ) 2 ·3H 2 O weight ratios dissolved into a beaker of 200 mL of water. , Then, slowly drop-by-drop pre-configured 1.5 mol/1000 mL NaOH precipitant was added into the beaker through a separatory funnel until the final pH reached 9, while being continuously stirred at a temperature of 70 °C. After the titration process, the mixture was allowed to stand for an aging time of 1 h at 70 °C.…”

“…The usage of a metal oxide/zeolite composite catalyst to directly convert syngas into aromatics in a single step has substituted the former method with its characteristics of fewer reaction steps, simple operation, and high economic efficiency . A vast range of methanol synthesis catalysts composited with HZSM-5 have been successfully investigated for the synthesis of aromatics from syngas, illustrating the higher aromatics selectivity; however, it shows a lower CO conversion rate with considerable byproducts and usually is prone to earlier catalyst deactivation. − As such, Fe-based metal oxides with high-temperature resistance and a broad range of (C 1 –C 60 ) hydrocarbon streams have become the focus of interest in recent years to be integrated with ZSM-5 for breaking the Anderson–Schulz–Flory distribution law of the Fischer–Tropsch synthesis (FTS) product and obtaining higher aromatics selectivity. − However, the poor chain growth ability, being prone to coke formation, and poisonous nature of these metallic systems at higher reaction temperatures direly need the addition of appropriate auxiliary components to play a vital role in adjusting the catalytic activity, selectivity, and stability. , Alkali metal promoters are famous electron donors that can greatly improve the dissociation ability of the C–O bond and promote the reduction and carbonization of iron oxides, leading to the active FeC x species. , Nevertheless, the competitive adsorption of CO and H 2 on the catalyst surface and the alkali migration phenomenon in the composite catalyst need the careful optimization of the added metal amount and other catalytic/process parameters. , …”