In situ tuning of the electronic structure of active sites is a long-standing challenge. Herein, we propose a strategy by controlling the hydrogen spillover distance to in situ tune the electronic structure. The strategy is demonstrated to be feasible with the assistance of CoO_x/Al₂O₃/Pt catalysts prepared by atomic layer deposition in which CoO_x and Pt nanoparticles are separated by hollow Al₂O₃ nanotubes. The strength of hydrogen spillover from Pt to CoO_x can be precisely tailored by varying the Al₂O₃ thickness. Using CoO_x/Al₂O₃ catalyzed styrene epoxidation as an example, the CoO_x/Al₂O₃/Pt with 7 nm Al₂O₃ layer exhibits greatly enhanced selectivity (from 74.3% to 94.8%) when H₂ is added. The enhanced selectivity is attributed to the introduction of controllable hydrogen spillover, resulting in the reduction of CoO_x during the reaction. Our method is also effective for the epoxidation of styrene derivatives. We anticipate this method is a general strategy for other reactions.

Sustainable production of fuels and olefins from syngas (carbon monoxide and hydrogen) through the Fischer-Tropsch synthesis process requires catalysts that deliver high selectivity, industrial productivity, and minimal carbon dioxide (CO ₂ ) emissions. Current industrial iron catalysts form substantial CO ₂ by-product that limits carbon efficiency. We report that introducing trace amounts [parts per million (ppm) level] of halogen-containing compounds into the feed gas can suppress CO ₂ formation using iron-based catalysts and boost olefin selectivity over paraffin and olefin productivity. Cofeeding 20 ppm bromomethane over an iron carbide catalyst decreased CO ₂ selectivity to <1% and increased olefin selectivity to ~85% among all carbon-containing products. Surface-bound halogens modulated the catalyst surface structure and selectively inhibited pathways responsible for CO ₂ generation and olefin hydrogenation. This strategy provides a simple, scalable, and broadly applicable route for carbon-efficient syngas conversion.

Accurately controlling the product selectivity in syngas conversion, especially increasing the olefin selectivity while minimizing C1 byproducts, remains a significant challenge. Epsilon Fe₂C is deemed a promising candidate catalyst due to its inherently low CO₂ selectivity, but its use is hindered by its poor high-temperature stability. Herein, we report the successful synthesis of highly stable ε-Fe₂C through a N-induced strategy utilizing pyrolysis of Prussian blue analogs (PBAs). This catalyst, with precisely controlled Mn promoter, not only achieved an olefin selectivity of up to 70.2% but also minimized the selectivity of C1 byproducts to 19.0%, including 11.9% CO₂ and 7.1% CH₄. The superior performance of our ε-Fe₂C-xMn catalysts, particularly in minimizing CO₂ formation, is largely attributed to the interface of dispersed MnO cluster and ε-Fe₂C, which crucially limits CO to CO₂ conversion. Here, we enhance the carbon efficiency and economic viability of the olefin production process while maintaining high catalytic activity.