Effect of Oxide Support on Catalytic Performance of FeNi‐based Catalysts for CO 2 ‐assisted Oxidative Dehydrogenation of Ethane

Bimetallic Exsolved Heterostructures of Controlled Composition with Tunable Catalytic Properties

In this paper, we show how the composition of bimetallic Fe-Ni exsolution can be controlled by the nature and concentration of oxygen vacancies in the parental matrix and how this is used to modify the performance of CO₂-assisted ethane conversion. Mesoporous A-site-deficient La_0.4Sr_0.6-αTi_0.6Fe_0.35Ni_0.05O_3±δ (0 ≤ α ≤ 0.2) perovskites with substantial specific surface area (>40 m²/g) enabled fast exsolution kinetics (T < 500 °C, t < 1 h) of bimetallic Fe-Ni nanoparticles of increasing size (3-10 nm). Through the application of a multitechnique approach we found that the A-site deficiency determined the concentration of oxygen vacancies associated with iron, which controlled the Fe reduction. Instead of homogeneous bimetallic nanoparticles, the increasing Fe fraction from 37 to 57% led to the emergence of bimodal Fe/Ni₃Fe systems. Catalytic tests showed superior stability of our catalysts with respect to commercial Ni/Al₂O₃. Ethane reforming was found to be the favored pathway, but an increase in selectivity toward ethane dehydrogenation occurred for the systems with a low metallic Fe fraction. The chance to control the reduction and growth processes of bimetallic exsolution offers interesting prospects for the design of advanced catalysts based on bimodal nanoparticle heterostructures.

Supported FexNiy catalysts for the co-activation of CO2 and small alkanes

The effect of both the Fe : Ni ratio (5 to 1 : 1) and the relative Lewis acidity of a metal oxide support on catalytic activity, selectivity and stability was investigated in the CO₂ mediated oxidative dehydrogenation of ethane (CO₂-ODH). To avoid effects of varying pore sizes, shapes and volumes of the supports, chromia and zirconia overlayers were coated onto a common γ-Al₂O₃ carrier (CrO_x@Al₂O₃ and ZrO_x@Al₂O₃). Separately, oxidic Fe_xNi_y alloy precursor nanoparticles were prepared using a nonaqueous surfactant-free method and deposited by sonication onto the carrier. In comparison to previous studies in the field, this synthesis technique yields closely associated iron and nickel increasing the chances for alloy formation. During reduction, a mixture of a bcc and a fcc alloy phase was formed, with the content of bcc increasing with increasing iron content as predicted by the bulk phase diagram. Upon exposure to carbon dioxide at elevated temperatures, the bcc metallic phase is selectively oxidised to an inverse spinel structure via the dissociation of CO₂. When exposed to CO₂-ODH conditions, the bare ZrO_x@Al₂O₃ support shows no activity. The presence of FeNi phases increases the conversion of ethane and CO₂ marginally (<2%) but forms ethylene at high selectivity (S_C2H4 > 80%). The CrO_x@Al₂O₃ support shows some initial activity (X_C2H6 < 5%) at very high ethylene selectivity (S_C2H4 > 90%) but deactivates with time on stream. Comparison of the ethane and carbon dioxide conversions suggests that direct dehydrogenation rather than the oxidative pathway is taking place. When FeNi particles with the highest Fe content are added, the ethane conversion behavior hardly changes, but the CO₂ conversion is increased now supporting the stoichiometric CO₂-ODH reaction (S_C2H4 > 95%). It is therefore evident that a tandem catalyst system between a reducible oxide carrier and the FeNi species is required. Increasing the Ni content results in an increase in activity and stability while changing the dominant reaction pathway to a combination of dry reforming, CO₂-ODH and possibly the reverse Boudouard reaction, with the latter countering catalyst deactivation through carbon deposition.

Synthesizing High-Volume Chemicals from CO2 without Direct H2 Input

Decarbonizing the chemical industry will eventually entail using CO₂ as a feedstock for chemical synthesis. However, many chemical syntheses involve CO₂ reduction using inputs such as renewable hydrogen. In this review, chemical processes are discussed that use CO₂ as an oxidant for upgrading hydrocarbon feedstocks. The captured CO₂ is inherently reduced by the hydrocarbon co-reactants without consuming molecular hydrogen or renewable electricity. This CO₂ utilization approach can be potentially applied to synthesize eight emission-intensive molecules, including olefins and epoxides. Catalytic systems and reactor concepts are discussed that can overcome practical challenges, such as thermodynamic limitations, over-oxidation, coking, and heat management. Under the best-case scenario, these hydrogen-free CO₂ reduction processes have a combined CO₂ abatement potential of approximately 1 gigatons per year and avoid the consumption of 1.24 PWh renewable electricity, based on current market demand and supply.

Catalytic conversion of ethane to valuable products through non-oxidative dehydrogenation and dehydroaromatization

Chemical utilization of ethane to produce valuable chemicals has become especially attractive since the expanded utilization of shale gas in the United States and associated petroleum gas in the Middle East. Catalytic conversion to ethylene and aromatic hydrocarbons through non-oxidative dehydrogenation and dehydroaromatization of ethane (EDH and EDA) are potentially beneficial technologies because of their high selectivity to products. The former represents an attractive alternative to conventional thermal cracking of ethane. The latter can produce valuable aromatic hydrocarbons from a cheap feedstock. Nevertheless, further progress in catalytic science and technology is indispensable to implement these processes beneficially. This review summarizes progress that has been achieved with non-oxidative EDH and EDA in terms of the nature of active sites and reaction mechanisms. Briefly, platinum-, chromium- and gallium-based catalysts have been introduced mainly for EDH, including effects of carbon dioxide co-feeding. Efforts to use EDA have emphasized zinc-modified MFI zeolite catalysts. Finally, some avenues for development of catalytic science and technology for ethane conversion are summarized.

Catalytic performance and stability of Fe-doped CeO2 in propane oxidative dehydrogenation using carbon dioxide as an oxidant

Propane oxidative dehydrogenation (ODH) in the presence of CO₂ was investigated over a series of Fe-doped CeO₂ catalysts.