Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

July 19, 2018

Researchers at Tokyo Tech have developed a ruthenium-based perovskite catalyst¹ that shows strong activity even at low temperatures (down to 313 K). The reusable catalyst does not require additives, meaning that it can prevent the formation of toxic by-products. The oxidation of sulfides is a commercially important process with broad applications ranging from chemicals production to environmental management.

Schematic representations of the face-sharing unit in rhombohedral BaRuO3 and corner-sharing unit in tetragonal RuO2, cubic SrRuO3, and orthorhombic CaRuO3.

Scanning electron microscope (SEM) image of BaRuO3.

Figure 1. Structure and image of the BaRuO₃ catalyst

Left: Schematic representations of the face-sharing unit in rhombohedral BaRuO₃ and corner-sharing unit in tetragonal RuO₂, cubic SrRuO₃, and orthorhombic CaRuO₃.

Right: Scanning electron microscope (SEM) image of BaRuO₃.

A research group led by Keigo Kamata and Michikazu Hara of Tokyo Institute of Technology (Tokyo Tech) has succeeded in developing a barium ruthenate (BaRuO₃) perovskite — the first catalyst of its kind shown to be capable of the selective oxidation of sulfides under mild conditions, with molecular oxygen (O₂) as the only oxidant and without the need for additives.

Reporting their findings in ACS Applied Materials & Interfaces, the researchers state that BaRuO₃ has three advantages over conventional catalysts.

Firstly, it exhibits high performance even at 313 K, a temperature much lower than the 373–423 K range reported in previous systems including other ruthenium- and manganese-based catalysts. Secondly, its high rate of oxygen transfer indicates that it has many potential uses; for example, it is applicable to the oxidative desulfurization² of dibenzothiophene, which can produce a 99% yield of pure sulfone. Thirdly, the new catalyst is recyclable — the present study showed that BaRuO₃ could be reused at least three times without loss of performance.

The achievement overcomes several classic limitations, such as the need for additives, toxic reagents and high reaction temperatures to achieve good catalytic performance.

The catalyst has a rhombohedral structure (see Figure 1). While other ruthenium-based catalysts investigated to date such as SrRuO₃, CaRuO₃ and RuO₂ can all be described as having corner-sharing octahedral units, BaRuO₃ has face-sharing octahedra. This configuration is thought to be one of the main reasons behind the catalyst’s higher oxygen transfer capability.

The way in which BaRuO₃ was synthesized — based on the sol–gel method³ using malic acid — was also important. The researchers say: "The catalytic activity and specific surface area of BaRuO₃ synthesized by the malic acid-aided method were higher than those of BaRuO₃ synthesized by the polymerized complex method."

The study highlights the importance of subtle changes in the nanoscale structure of perovskite catalysts, and could provide promising leads for further research on a wide range of perovskite-based functional materials.

1 Perovskite catalyst

Referring to a family of catalysts with the general formula ABO₃, which are of great interest due to their structural simplicity, flexibility, good stability and controllable physicochemical properties.

2 Oxidative desulfurization

An important reaction process for sulfur removal — this is particularly relevant to the fuel industry and efforts to curb sulfur emissions.

3 Sol–gel method

A process widely used to prepare novel materials by converting monomers in a colloidal solution (sol) to a network of polymers (gel).

Reference

Authors :	Keigo Kamata^1,2,* , Kosei Sugahara¹, Yuuki Kato¹, Satoshi Muratsugu^2,3, Yu Kumagai^2,4, Fumiyasu Oba¹ and Michikazu Hara^1,5
Title of original paper :	Heterogeneously Catalyzed Aerobic Oxidation of Sulfides with a BaRuO3 Nanoperovskite
Journal :	ACS Applied Materials & Interfaces
DOI :	10.1021/acsami.8b05343
Affiliations :	¹ Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology ² Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology (PRESTO) ³ Department of Chemistry, Graduate School of Science, Nagoya University ⁴ Materials Research Center for Element Strategy, Tokyo Institute of Technology ⁵ JST, Advanced Low Carbon Technology Research and Development Program (ALCA)