General negative pressure annealing approach for creating ultra-high-loading single atom catalyst libraries.

Catalyst systems populated by high-density single atoms are crucial for improving catalytic activity and selectivity, which can potentially maximize the industrial prospects of heterogeneous single-atom catalysts (SACs). However, achieving high-loading SACs with metal contents above 10 wt% remains challenging. Here we describe a general negative pressure annealing strategy to fabricate ultrahigh-loading SACs with metal contents up to 27.3-44.8 wt% for 13 different metals on a typical carbon nitride matrix. Furthermore, our approach enables the synthesis of high-entropy single-atom catalysts (HESACs) that exhibit the coexistence of multiple metal single atoms with high metal contents. In-situ aberration-corrected HAADF-STEM (AC-STEM) combined with ex-situ X-ray absorption fine structure (XAFS) demonstrate that the negative pressure annealing treatment accelerates the removal of anionic ligand in metal precursors and boosts the bonding of metal species with N defective sites, enabling the formation of dense N-coordinated metal sites. Increasing metal loading on a platinum (Pt) SAC to 41.8 wt% significantly enhances the activity of propane oxidation towards liquid products, including acetone, methanol, and acetic acid et al. This work presents a straightforward and universal approach for achieving many low-cost and high-density SACs for efficient catalytic transformations.

High-Performance Styrene Epoxidation with Vacancy-Defect Cobalt Single-Atom Catalysts.

Exploring highly active and cost-effective catalysts for styrene epoxidation is of great significance, but it remains challenging to simultaneously achieve excellent conversion and selectivity toward styrene oxide. In this work, the structures and performance of Co, Fe, and Cu single-atom catalysts (SACs) in styrene epoxidation with tert-butyl hydroperoxide (TBHP) are predicted using density functional theory (DFT) calculations. The results reveal that the Co-N structure prefers that of styrene oxide over Fe-N and Cu-N structures. This predicted result is verified via catalytic evaluations, where the Co SACs displayed significantly higher styrene oxide selectivity than Fe and Cu SACs. Moreover, the activity of Co SAC can be further improved by the construction of unsaturated vacancy-defect cobalt single sites. As a result, excellent performance with styrene conversion of 99.9% and styrene oxide selectivity of 71% is achieved after a reaction time of 8 h on the optimal Co SAC.