Harnessing Multi-Element Perovskites as Catalysts for Selective Oxidation of Light Alkanes

A promising new catalyst could transform selective oxidation processes for light alkanes, as reported by scientists at Science Tokyo. In a recent study, they developed an iron-oxide-based perovskite that can turn isobutane into valuable products like tert-butyl alcohol under mild conditions. This catalyst, with the formula La_0.8Sr_0.2FeO_3−δ, achieves high selectivity, yield, and stability simultaneously, surpassing previous catalysts. Their efforts could lead to more efficient and sustainable synthesis of essential chemicals across various industries.

Light alkanes are relatively simple molecules made entirely of carbon and hydrogen, arranged in linear or branching structures. Their oxidized counterparts, which include alcohols, epoxides, ketones, and aldehydes, are ubiquitous in the chemical industry, as they serve as essential starting materials in the synthesis of commodity substances, fine chemicals, agrochemicals, and pharmaceuticals. However, the selective oxidation of light alkanes remains a significant challenge.

To date, scientists have explored various types of catalysts for this task. Although some offer decent performance in gas-phase reactions, there are inherent advantages to developing catalysts applicable to liquid-phase selective oxidation. However, such catalysts often suffer from poor reusability, require extreme reaction conditions, or can only operate in the presence of heavy oxidants or photoirradiation.

Fortunately, a research team from the Institute of Science Tokyo, Japan, is on track to find a solution to these problems. Led by Professor Keigo Kamata, they have been investigating various iron-oxide-based perovskites as catalysts for years. In a recent study published in ACS Applied Materials & Interfaces on November 1, 2024, the team successfully developed a promising catalyst that could revolutionize the selective oxidation of alkanes.

The researchers focused on the oxidation of isobutane, a simple four-carbon alkane, into tert-butyl alcohol as a representative reaction with multiple applications. "In our preliminary examinations of the oxidation of isobutane, we found that high-valent iron-based perovskite oxides like BaFe_3−δ and SrFeO_3−δ, on the one hand, and LaFeO₃, on the other, have drawbacks in terms of reusability and C−H bond activation," explains Kamata. "In this work, we focused on the partial substitution of La³⁺ in LaFeO₃ with Sr²⁺ to achieve both stability and reactivity simultaneously."

In this way, seeking to obtain the best of both worlds through a multi-element approach, the team synthesized La_1-xSr_xFeO_3−δnanoparticles of various compositions and tested them. Through a series of experiments, they observed that La_0.8Sr_0.2FeO_3−δ was the composition with the best performance in terms of yield. With this catalyst, tert-butyl alcohol could be obtained as the main product with high selectivity under an oxygen atmosphere, with small quantities of byproducts.

Notably, this perovskite functioned properly under mild reaction conditions, as Kamata remarks: "La_0.8Sr_0.2FeO_3−δ efficiently catalyzed the oxidation of isobutane even at 60 °C with good selectivity for tert-butyl alcohol. In contrast, high reaction temperatures of about 130 °C, excess amounts of specific additives or oxidants, and high oxygen pressures of 3.5 MPa were typically required for previously reported homogeneously catalyzed systems."

These features, coupled with its outstanding stability and reusability, make La_0.8Sr_0.2FeO_3−δ an important achievement in perovskite catalyst design. The research team also conducted mechanistic studies to understand the origin of the material’s notable properties. The insights obtained in this work will hopefully guide and inspire the development of solid perovskite catalysts made from earth-abundant elements. Ultimately, this could pave the way for more efficient and less costly synthesis of various useful chemicals, supporting worldwide sustainability goals.

Authors:

Masanao Yamamoto^1,2, Takeshi Aihara^1,2, Keiju Wachi^1,2, Michikazu Hara^1,2, and Keigo Kamata^1,2*

Title:

La_1–xSr_xFeO_3–δ Perovskite Oxide Nanoparticles for Low-Temperature Aerobic Oxidation of Isobutane to tert-Butyl Alcohol

Journal:

ACS Applied Materials & Interfaces

Affiliations:

¹Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, Japan
²Materials and Structures Laboratory, Institute of Integrated Research, Institute of Science Tokyo, Japan

DOI:

10.1021/acsami.4c15585

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