For sustainable sulfur-tolerant catalysts, alloy the precious metals with phosphorus!

Osaka, Japan – Catalysts play crucial roles in chemical processes. However, many conventional catalysts have suffered from deactivation caused by sulfur-containing molecules which are strongly absorbed onto catalyst surfaces and suppress catalytic reactions. Osaka University researchers have developed a highly active and durable metal-phosphide catalyst for the deoxygenation of sulfoxides. The developed catalyst has a high durability against sulfur-poisoning in contrast with the conventional metal catalysts. Their findings are published in JACS Au.

Transformation of sulfur-containing molecules is a fundamental and significant reaction in organic and pharmaceutical chemistry. However, the sulfur atom strongly coordinates with the active sites of metal catalysts, significantly decreasing the catalytic performance. Sulfur impurities contained in chemical feedstocks also cause catalyst deactivation. Therefore, the development of a new sulfur-tolerant and highly active catalyst is desired.

The researchers prepared precious metal phosphide nanoparticle catalysts for the deoxygenation of sulfoxides into sulfides. The integration of phosphorus into the metal framework—a method called “phosphorus-alloying”— greatly improved the catalytic performance of precious metal nanoparticles. In particular, the ruthenium phosphide nanoparticles (Ru−P/SiO₂) exhibited excellent catalytic activity and durability against sulfur-poisoning.

“Integration of phosphorus into ruthenium nanoparticles drastically enhanced catalytic activity and durability (Fig. 1a),” study first author Hiroya Ishikawa explains.

Ru−P/SiO₂ achieved the highest turnover number (12,500) reported to date (Fig. 1b). This catalyst shows wide substrate applicability and can deoxygenate structurally complex drug intermediates to produce bioactive sulfides such as sulindac sulfide (anti-inflammatory drug), ufiprazole (anti-ulcer drug), and fenbendazole (anthelmintic) in high yields (Fig. 1c). Moreover, Ru−P/SiO₂ can promote sulfoxide deoxygenation even in the presence of a lot of sulfur-containing molecules; even in the presence of 200 equiv. of sulfide per ruthenium, Ru−P/SiO₂ quantitatively promoted the deoxygenation of sulfoxide, while the conventional ruthenium nanoparticle catalyst (Ru/SiO₂) was completely deactivated (Fig. 2).

“We expect that our metal phosphide catalyst will make a significant contribution to a lot of chemical processes, which suffered from catalyst deactivation caused by sulfur,” says study corresponding author Takato Mitsudome. “But beyond this, we believe phosphorus-alloying can be a powerful method for designing highly active and durable metal nanoparticle catalysts for a variety of organic syntheses.” 

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The article, “Phosphorus-Alloying as a Powerful Method for Designing Highly Active and Durable Metal Nanoparticle Catalysts for the Deoxygenation of Sulfoxides: Ligand and Ensemble Effects of Phosphorus” was published in JACS Au at DOI: https://pubs.acs.org/doi/10.1021/jacsau.1c00461 (open access)

About Osaka University

Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.

Website: https://resou.osaka-u.ac.jp/en