Dynamic Evolution of Fe and Carbon Species over Different ZrO₂ Supports during CO Prereduction and Their Effects on CO₂ Hydrogenation to Light Olefins

Abstract

The dynamic evolution of active Fe species and carbon species during CO prereduction was revealed for Fe–Zr catalysts with different (monoclinic and tetragonal) zirconia supports (m-ZrO2 and t-ZrO2) on CO2 hydrogenation to light olefins. As the Fe loading reached 15 wt %, the corresponding Fe–K/m-ZrO2 catalyst presented a remarkable CO2 conversion (38.8%) and a high selectivity to light olefins in the hydrocarbon (C–H) products (42.8%). Using in situ characterization techniques including in situ X-ray diffraction (XRD), Raman, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the dynamic evolution (reduction and carburization) of iron oxides and the generation of diverse carbon species during CO prereduction on different ZrO2 supports were probed. The detected intermediate FeO species in the Fe–K/m-ZrO2 catalyst indicates a mild and sufficient reduction of Fe2O3 on m-ZrO2, promoting the carburization leading to smaller and more active iron species (Fe3O4 and χ-Fe5C2). More oxygen vacancies (Ov) on the surface of m-ZrO2 and the electron-donating ability of iron elements boosted the charge transfer between Fe and the ZrO2 support, forming a more active Fe species. For the Fe–K/t-ZrO2 catalyst, the low selectivity of C x H y implied its weak capacity to produce light olefins through CO2 hydrogenation. By comparison, the m-ZrO2 support provided relatively more strong basic sites, reducing the physically deposited carbon species and coke generation. The formation of more χ-Fe5C2 species contributed to the high yield of light olefins in products. Tuning the physicochemical properties and base microenvironment of supports could be an effective means to boost the iron catalyst activity for CO2 hydrogenation to olefins.

Effect of the Zr promoter on precipitated iron-based catalysts for high-temperature Fischer–Tropsch synthesis of light olefins

“…The introduction of zirconium and sodium can increase the FT activity and optimizes the selectivity to C 2 = –C 4 = in the hydrocarbon distribution on the FeMn x Zr2Na catalysts. 19,47 The carbonization of catalysts is promoted by the Na promoter, which prevents the hydrogenation of olefins and hindered the formation of CH 4 . 20,21 At a CO conversion of 96.3%, the FeMn5Zr2Na catalyst exhibits the highest C 2 = –C 4 = selectivity of 34.4% and the lowest selectivity of 17.8% for CH 4 .…”

Direct Synthesis of Ethylene and Hydrogen from CO2 and Ethane over a Bifunctional Structured CaO/Cr2O3-V2O5/ZSM-5 Adsorbent/Catalyst Monolith

“…This novel technique can minimize the need to store and transport CO 2 , thus making the process of combining CO 2 capture and utilization an attractive route from economic and industrial perspectives. 18,20 In that regard, utilizing materials comprising of adsorptive and catalytic phases (i.e., bifunctional materials (BFMs)) offers a promissing approach to perform CO 2 adsorption−reaction steps in a single bed, thereby lowering the thermal gradient requirements. It has been theorized that BFMs can reduce the thermal energy penalties compared to segregated systems of adsorption and reaction, which require higher energy for heating two columns as opposed to heating one column.…”

“…The adsorption step typically takes place at temperatures below the reaction step, resulting in a large temperature swing between the two steps. , This situation leads to long cycle times due to additional cooling and heating steps. − Such issues can be resolved by operating both adsorption and reaction steps isothermally or close to isothermal conditions. This novel technique can minimize the need to store and transport CO 2 , thus making the process of combining CO 2 capture and utilization an attractive route from economic and industrial perspectives. , …”

Insights into Coke Formation and Removal under Operating Conditions with a Quantum Nanoreactor Approach

“…C atalyst deactivation due to coke formation through in situ carbon deposition is a critical problem in several industrial processes such as Fischer−Tropsch synthesis (FTS), 1−3 CO 2 hydrogenation, 4,5 steam reforming, 6,7 methanation, 6,8 dehydrogenation, 9 and many other catalytic processes. 10,11 It is economically beneficial to regenerate deactivated catalysts and recover catalytic activity.…”

“…Catalyst deactivation due to coke formation through in situ carbon deposition is a critical problem in several industrial processes such as Fischer–Tropsch synthesis (FTS), − CO 2 hydrogenation, , steam reforming, , methanation, , dehydrogenation, and many other catalytic processes. , It is economically beneficial to regenerate deactivated catalysts and recover catalytic activity . The regeneration of deactivated catalysts by H 2 is often recommended for coke removal which can be realized by hydrocracking treatments removal. ,, Methane formation (C + 2H 2 → CH 4 ) from the deposited coke is the primary reaction in regeneration.…”