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Dalian, China-Sulfur, long feared as a “poison” that shuts down precious metal catalysts, can actually help them work better when used in just the right way, according to new research published in Chinese Journal of Catalysis.
A team led by Prof. Yunjie Ding at Dalian Institute of Chemical Physics, Chinese Academy of Sciences andProf. Xueqing Gong at Shanghai Jiao Tong University, has shown that a tiny, carefully tuned amount of sulfur can boost the speed and robustness of a key industrial reaction by up to twofold.
The reaction, called hydroformylation, adds carbon monoxide and hydrogen to simple molecules known as olefins (alkenes) to make aldehydes. These aldehydes are essential building blocks for alcohols, plasticizers, surfactants, lubricants and many other bulk and specialty chemicals. Worldwide, more than 25 million tons of aldehydes and alcohols are made each year by hydroformylation, mostly using rhodium-based catalysts dissolved in liquid.
“Hydroformylation is one of the workhorses of modern chemical industry,” the authors note in the paper. “Designing catalysts that are both highly active and tolerant to real-world, sulfur-containing feedstocks is crucial for greener production.”
Traditionally, sulfur compounds in feed gases or liquids are seen as a serious problem. They bind very strongly to precious metals like rhodium, blocking the active sites and deactivating the catalyst. As a result, major effort is spent on deep desulfurization-removing sulfur as completely as possible before the reaction.
The new study takes a very different approach: instead of fighting sulfur at all costs, the researchers ask whether sulfur can be harnessed and controlled.
Tuning the catalyst’s “microenvironment”
The team builds on an earlier heterogeneous (“solid”) rhodium catalyst, known as Rh₁/POPs-PPh₃, in which isolated rhodium atoms are anchored to a porous organic polymer (POPs-PPh3) through frame-phosphine (frame-P) ligands. That system has already been demonstrated at industrial scale for hydroformylation.
In the new work, the researchers designed a related material where the porous polymer framework contains both phosphine and sulfur sites. When rhodium is introduced, each single rhodium center can be coordinated by a mixture of phosphorus and sulfur atoms, creating a sulfur–phosphine co-coordinated microenvironment (Rh₁/POPs-PPh₃&S).
By varying the ratio of sulfur to phosphine in the polymer, they discovered a “sweet spot”:
At about 10% sulfur in the framework, the new catalyst hydroformylates propylene and C₅–C₈ olefins 1.5–2.0 times faster than the phosphine-only benchmark,
while maintaining high selectivity to the desired linear aldehydes and showing excellent stability in long-term tests.
In contrast, when sulfur dominates the coordination, the catalyst indeed suffers severe sulfur poisoning and its performance drops sharply, confirming that dosage and microenvironment are critical.
Seeing how sulfur helps instead of “hurts”
To understand why a small amount of sulfur promotes rather than harms, the team combined advanced characterization and computer modelling.
Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption spectroscopy, they confirmed that rhodium remains atomically dispersed — as single “mononuclear” centers — in both the original and the sulfur-modified catalysts. Solid-state NMR and X-ray photoelectron spectroscopy showed that adding sulfur partly replaces phosphine around rhodium slightly lowers the electron density on the metal.
In simple terms:
Phosphine ligands are strong electron donors. They tend to make rhodium more electron-rich and highly reactive.
Sulfur ligands are more electron-withdrawing and occupy one coordination site, which can moderate rhodium’s reactivity.
Using in-situ infrared spectroscopy under reaction conditions and temperature-programmed surface reaction experiments, the researchers observed that the sulfur–phosphine catalyst forms key aldehyde-forming intermediates faster, while suppressing unwanted hydrogenation and isomerization by-products.
Density functional theory (DFT) calculations then revealed that the rate-determining step in hydroformylation — the insertion of the olefin into a rhodium–hydrogen bond — has a lower energy barrier on the sulfur–phosphine co-coordinated catalyst than on the phosphine-only one. The calculations also showed how the combination of electron-donating phosphine and electron-withdrawing sulfur tunes the charge and bond lengths around rhodium into an optimal window for reactivity and selectivity.
Rethinking “sulfur poison” for real-world feedstocks
The work provides a unified picture of when sulfur behaves as a poison and when it can act as a promoter:
Too little sulfur, and the catalyst behaves like the original phosphine system.
Too much sulfur, and rhodium sites are blocked, leading to classic sulfur poisoning and poor performance.
At an intermediate sulfur level, the microenvironment around single rhodium atoms is ideally tuned, giving higher activity, better regioselectivity and robust stability.
This insight could be particularly important for processing sulfur-containing feedstocks, such as coal-based chemicals, biomass-derived oils, or low-grade olefin streams, where completely removing sulfur is costly or impractical.
“Our results suggest that, instead of treating sulfur as an absolute enemy, we can sometimes design catalysts that tolerate and even use sulfur to their advantage,” the authors write. The concept of microenvironment engineering around single-atom active sites may also be applied to other catalytic reactions beyond hydroformylation.
Article details
The research article, “Regulating microenvironment of heterogeneous Rh mononuclear complex via sulfur-phosphine co-coordination to enhance the performance of hydroformylation of olefins,” by Siquan Feng, Cunyao Li, Yuxuan Zhou, Xiangen Song, Yunjie Ding and co-workers, appears in Chinese Journal of Catalysis (Vol. 78, 2025, pp. 156–169).
DOI: 10.1016/S1872-2067(25)64795-4
Corresponding authors:
Prof. Yunjie Ding, Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Email: dyj@dicp.ac.cn
About the Journal
Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.
At Elsevier http://www.journals.elsevier.com/chinese-journal-of-catalysis
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