Tailoring the synergistic dual-decoration of (Cu–Co) transition metal auxiliaries in Fe-oxide/zeolite composite catalyst for the direct conversion of syngas to aromatics

Abstract

Tailoring the crystal lattice and multiple phase interfaces via the feasible accommodation of Cu–Co into the host (Fe) structure, expedited the surface oxygen vacancies that modulated the reduction/chemisorption behavior of active Fe species.

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

“…It is a fact that the aromatics fraction in the liquid phase is generally dependent on the strong acidic strength and morphology of the HZSM-5 molecular sieve . However, different metals loaded on a Fe-based catalyst can adjust the olefin/paraffin ratio (Figure c) that can lead to the higher aromatic fractions and better product distribution, in response to the enhanced aromatization activity on the HZSM-5 surface. , Similarly, the CO conversion rate of the composite catalyst after the addition of HZSM-5 is higher than that of the other catalyst, indicating that the introduction of a molecular sieve promotes the syngas to aromatics (STA) reaction by pushing the balance of FTS to the right …”

“…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) . However, the IP method simply loads the promoters on the surface of Fe, the binding is not strong, and it is easily detaches during the reaction process which led to a decrease in the catalytic effect. , Therefore, the SP method is more suitable for the preparation of the FeZnMg catalyst system for FTS, and it can be seen that choosing a suitable preparation method can improve the catalytic performance of the catalyst.…”

“…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. , …”

“…However, the excessive addition of both elements inhibits their frequent use in bifunctional catalysts, causing the rapid catalyst deactivation . While the synthesis methods of different Fe-based catalysts also need to be regulated with different parametric influence, where the precipitation technique has been generally considered to provide a larger specific surface area and a higher catalytic activity being suitable for a wide product distribution. ,, …”