Support engineering enables sulfur-tolerant pt single atoms for nitroarene hydrogenation
An optimized nitrogen environment around individual platinum atoms boosts selective hydrogenation while weakening the sulfur binding that poisons catalysts.
image: Catalytic tests link the nitrogen content of the carbon support to platinum single-atom activity. The panels show reaction progress, turnover frequency, five-cycle reuse, performance with and without sulfur species, apparent activation energies, and hydrogen-deuterium exchange. The catalyst obtained after a 60-minute ammonia treatment delivered the highest turnover frequency in the series.
Credit: ©Science China Press
Sulfur can bring a useful catalyst to a halt. By binding tightly to metal sites, it blocks the hydrogen activation needed to produce valuable chemical building blocks. Researchers at Sun Yat-sen University have now shown that engineering the carbon support around individual platinum atoms can keep these sites active even in sulfur-containing reactions.
The study, led by Xiaohui He and published in SCIENCE CHINA Chemistry, focuses on converting sulfur-containing nitroarenes into aromatic amines, which are important intermediates for pharmaceuticals and agrochemicals. The challenge lies in reducing the nitro group selectively while preserving the sulfur-containing moiety and avoiding catalyst poisoning.
The team first treated carbon supports with ammonia for different durations, then introduced isolated platinum atoms via a precursor-atomization strategy. Varying the treatment changed the amount and chemical forms of nitrogen in the support, as well as its porous structure. Aberration-corrected HAADF-STEM and spectroscopy confirmed the presence of atomically dispersed platinum, with the best-performing sample showing a local environment resembling platinum coordinated to four nitrogen atoms.
More nitrogen did not always mean better performance: activity rose and then fell as nitrogen content increased. In the hydrogenation of 4-nitrothioanisole, the catalyst prepared using a 60-minute ammonia treatment reached a turnover frequency (TOF) of 1,166 h-1, measured below 30% substrate conversion — about 12 times that of the least active catalyst in the series. TOF measures how rapidly catalytic sites convert reactant molecules.
The optimized catalyst showed 100% product selectivity in the reaction-time study. Across five reuse cycles, its turnover frequency remained nearly unchanged and selectivity stayed above 99%. Post-reaction measurements showed no detectable platinum aggregation or change in oxidation state. The catalyst also retained high activity in tests involving sulfur-containing substrates and added sulfur species, whereas a carbon-supported platinum single-atom catalyst prepared without ammonia treatment lost activity sharply in sulfur-rich environments.
Experiments and calculations help explain this behavior. Hydrogen-deuterium exchange measurements showed that the optimized catalyst activated hydrogen most effectively within the series. Density functional theory calculations indicated that nitrogen coordination weakened the binding of sulfur-containing groups while favoring reaction at the nitro group. Together, these findings suggest that the local environment helps platinum activate the desired reactant while resisting deactivation by sulfur.
The results identify support engineering as a route to balance hydrogenation activity, selectivity, and sulfur tolerance. They also show why isolating metal atoms is only part of the design challenge: the atoms surrounding each catalytic site matter. These findings provide a basis for developing more robust catalysts for the synthesis of sulfur-containing fine chemicals.