Effect of surface acidity modulation on Pt/Al2O3 single atom catalyst for carbon monoxide oxidation and methanol decomposition

Solar-Driven Hydrogen Production from Methanol Decomposition Catalyzed by High-Entropy Spinel Oxides

To address safety and economic issues in hydrogen storage and transportation, developing liquid organic hydrogen carriers to deliver hydrogen to where it can be utilized for in situ hydrogen production is an attractive approach. Herein, a spinel phase high-entropy oxide (HEO) (FeCrCoNiCu)3O4 comprising of non-noble metals is synthesized via the PVP (Polyvinyl Pyrrolidone)-templated method as a catalyst for solar-driven hydrogen production through methanol decomposition. Benefiting from the synergistic effects of various components in high-entropy materials, (FeCrCoNiCu)3O4 HEO achieves an optimized hydrogen production rate of 49.4 mmol g-1 min-1, with a surface temperature of 279 °C under full-spectrum illumination of 2.68 W cm-2. The performance is significantly higher than that under thermocatalytic conditions at the same temperature and surpasses the activity of the state-of-the-art catalysts. The catalyst exhibits long-term stability over 80 h through in situ removing deposited carbon, and thus HEOs show great promise for efficient hydrogen production from methanol decomposition under mild conditions.

Fine-Tuning of Pt Dispersion on Al2O3 and Understanding the Nature of Active Pt Sites for Efficient CO and NH3 Oxidation Reactions

Fine-tuning the dispersion of active metal species on widely used supports is a research hotspot in the catalysis community, which is vital for achieving a balance between the atomic utilization efficiency and the intrinsic activity of active sites. In this work, using bayerite Al(OH)3 as support directly or after precalcination at 200 or 550 °C, Pt/Al2O3 catalysts with distinct Pt dispersions from single atoms to clusters (ca. 2 nm) were prepared and evaluated for CO and NH3 removal. Richer surface hydroxyl groups on AlOx(OH)y support were proved to better facilitate the dispersion of Pt. However, Pt/Al2O3 with relatively lower Pt dispersion could exhibit better activity in CO/NH3 oxidation reactions. Further reaction mechanism study revealed that the Pt sites on Pt/Al2O3 with lower Pt dispersion could be activated to Pt0 species much easier under the CO oxidation condition, on which a higher CO adsorption capacity and more efficient O2 activation were achieved simultaneously. Compared to Pt single atoms, PtOx clusters could also better activate NH3 into -NH2 and -HNO species. The higher CO adsorption capacity and the more efficient NH3/O2 activation ability on Pt/Al2O3 with relatively lower Pt dispersion well explained its higher CO/NH3 oxidation activity. This study emphasizes the importance of avoiding a singular pursuit of single-atom catalyst synthesis and instead focusing on achieving the most effective Pt species on Al2O3 support for targeted reactions. This approach avoids unnecessary limitations and enables a more practical and efficient strategy for Pt catalyst fabrication in emission control applications.

Scalable Synthesis of Flexible Single-Atom Monolithic Catalysts for High-Efficiency, Durable CO Oxidation at Low Temperature

The creation of single-atom catalysts in a large-size, high-yield, and stable form represents an important direction for high-efficiency industrial catalysis in the future. Herein, we report a strategy to synthesize flexible single-atom monolithic catalysts (SAMCs) based on the hierarchical 3D assembly of single-atom-loaded oxide ceramic nanofibers. The nanofibers, which can be produced in a continuous and scalable manner, serve as an ideal support for single atoms spontaneously and almost completely exposed at the surface through the Kirkendall effect-enabled in situ ion migration during the spinning process, resulting in both high yield and large loading quantity. Moreover, the hierarchical 3D assembly of these nanofibers into a porous, flexible structure endows the SAMCs with the advantages of sufficient infiltration and oscillation tolerance when faced with high-throughput gaseous media, leading to both high catalytic efficiency and excellent durability. As a proof-of-concept demonstration, a Pt SAMC is synthesized, which exhibits 100% CO oxidation at low temperature (∼170 °C), excellent invariance toward high-frequency (10 Hz) oscillation, and high structural stability from 25 to 300 °C. This work is beneficial for the large-scale production of SAMCs in broad industrial applications.

Single-atom site catalysts for environmental remediation: Recent advances

Single-atom site catalysts (SACs) can maximize the utilization of active metal species and provide an attractive way to regulate the activity and selectivity of catalytic reactions. The adjustable coordination configuration and atomic structure of SACs enable them to be an ideal candidate for revealing reaction mechanisms in various catalytic processes. The minimum use of metals and relatively tight anchoring of the metal atoms significantly reduce leaching and environmental risks. Additionally, the unique physicochemical properties of single atom sites endow SACs with superior activity in various catalytic processes for environmental remediation (ER). Generally, SACs are burgeoning and promising materials in the application of ER. However, a systematic and critical review on the mechanism and broad application of SACs-based ER is lacking. Herein, we review emerging studies applying SACs for different ERs, such as eliminating organic pollutants in water, removing volatile organic compounds, purifying automobile exhaust, and others (hydrodefluorination and disinfection). We have summarized the synthesis, characterization, reaction mechanism and structural-function relationship of SACs in ER. In addition, the perspectives and challenges of SACs for ER are also analyzed. We expect that this review can provide constructive inspiration for discoveries and applications of SACs in environmental catalysis in the future.