Nondegradable polyolefin plastics pose severe environmental threats and thus demand efficient upcycling technologies. In this work, we discovered that low-loading (≤0.25 wt %) Ru/CeO2 exhibits remarkable catalytic performance in the hydrogenolysis of polypropylene (PP), polyethylene (PE), and n-C16H34 that is superior to high-loading (≥0.5 wt %) Ru/CeO2. They possess high PP conversion efficiency (sevenfold increase over current literature reports), low selectivity toward undesired CH4, and good isomerization ability. In the low-loading range, the intrinsic activity of Ru in PP hydrogenolysis increases as the particle size decreases, opposite of the trend in the high-loading range. Detailed characterization revealed that the abrupt changes in catalytic behaviors coincide with Ru species transitioning from well-defined to highly disordered structures in the low-loading domain. The disordered Ru species were shown to be sub-nanometer in size and cationic. Mechanistically, the regioselectivity and the rate dependence on hydrogen pressure of C–C bond cleavage are different on low- and high-loading Ru/CeO2, both explained by the higher coverage of adsorbed hydrogen (*H) on low-loading Ru/CeO2. This work reveals the remarkable catalytic performance of highly disordered, sub-nanometer, cationic Ru species in polyolefin hydrogenolysis, opening immense opportunities to develop effective, selective, and versatile catalysts for plastic upcycling.

Oxidation of glucose to gluconic and glucaric acid using molecular O 2 in aqueous solution is an environmentally friendlier alternative to the conventional method, which uses nitric acid as the oxidant. However, obtaining a satisfactory yield of the desirable product, glucaric acid, especially under base-free conditions, is still a challenge. In this paper, optimization of Ptbased mono-and bimetallic catalysts is reported by tuning four factors: support type, synthesis method, reductant used in the synthesis, and choice of the second metal. All four of these factors influence the glucaric acid selectivity. Among the tested combinations, the Pt−Cu/TiO 2 bimetallic catalyst showed ∼60% glucaric acid selectivity in one-step glucose oxidation under base-free conditions at 90 °C and 15 bar O 2 . The catalyst consists of Pt metal particles (∼2.8 nm diameter on average) with a dominant presence of the alloyed Pt−Cu phase, as confirmed by X-ray diffraction and transmission electron microscopy analyses. These results provide valuable insights for the rational design of glucose oxidation catalysts.

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A highly active and selective Pt−Fe alloy catalyst on CeO 2 support is reported in this work for aqueous phase oxidation of ethylene glycol (EG) to glycolic acid. The Pt−Fe nanoparticles are highly alloyed with a face-centered cubic (fcc) type of crystal structure and a chemical state of Pt 0 /Fe 0 , as confirmed from X-ray diffraction and extended X-ray absorption fine structure characterizations, respectively. Compared to the monometallic Pt catalyst, the Pt−Fe catalyst shows more than a 17-fold higher initial TOF, while achieving complete EG conversion in 4 h at 70°C and ambient O 2 pressure under alkaline conditions. The synergistic bimetallic effect occurs due to significantly changing the O 2 adsorption-dissociation characteristics on the catalyst surface. The addition of a base shows a promotional effect on both Pt and Pt−Fe catalysts at low NaOH concentrations but an inhibition effect is observed for both catalysts at sufficiently high NaOH concentrations. Furthermore, the base enhances the synergistic effect observed with Pt−Fe catalyst.

Research interest in single-atom catalysts (SACs) has been continuously increasing. However, the lack of understanding of the dynamic behaviors of SACs during applications hinders catalyst development and mechanistic understanding. Herein, we report on the evolution of active sites over Pd/TiO2-anatase SAC (Pd1/TiO2) in the reverse water–gas shift (rWGS) reaction. Combining kinetics, in situ characterization, and theory, we show that at T ≥ 350 °C, the reduction of TiO2 by H2 alters the coordination environment of Pd, creating Pd sites with partially cleaved Pd–O interfacial bonds and a unique electronic structure that exhibit high intrinsic rWGS activity through the carboxyl pathway. The activation by H2 is accompanied by the partial sintering of single Pd atoms (Pd1) into disordered, flat, ∼1 nm diameter clusters (Pd n ). The highly active Pd sites in the new coordination environment under H2 are eliminated by oxidation, which, when performed at a high temperature, also redisperses Pd n and facilitates the reduction of TiO2. In contrast, Pd1 sinters into crystalline, ∼5 nm particles (PdNP) during CO treatment, deactivating Pd1/TiO2. During the rWGS reaction, the two Pd evolution pathways coexist. The activation by H2 dominates, leading to the increasing rate with time-on-stream, and steady-state Pd active sites similar to the ones formed under H2. This work demonstrates how the coordination environment and nuclearity of metal sites on a SAC evolve during catalysis and pretreatments and how their activity is modulated by these behaviors. These insights on SAC dynamics and the structure–function relationship are valuable to mechanistic understanding and catalyst design.