Redispersion strategy for high-loading carbon-supported metal catalysts with controlled nuclearity

Tracking life and death of carbon nitride supports in platinum-catalyzed vinyl chloride synthesis

Deactivation of metal-based catalysts for vinyl chloride synthesis via acetylene hydrochlorination is often dictated by indispensable, catalytically-active carbon supports, but underlying mechanisms remain unclear. Carbon nitrides offer an attractive platform for studying them thanks to ordered structure and high N-content, which facilitates coking. Herein, we monitor the life and death of carbon nitride supports for Pt single atoms in acetylene hydrochlorination, demonstrating that specific N-functionalities and their restructuring cause distinct deactivation mechanisms. Varying polymerization and exfoliation degrees in pristine carbon nitrides (i.e., -NHx termination and N-vacancy concentrations), we establish graphitic and pyridinic N-atoms as C2H2 adsorption sites and pyridinic N-vacancies as coking sites through kinetic and spectroscopic analyses. Uniquely suited for probing point defects, operando electron paramagnetic spectroscopy, coupled to simulations, reveals that HCl drives depolymerization, by protonating heptazine-linking graphitic N-atoms, and generates graphitic N-vacancies, forming NH3. These reduce C2H2 adsorption and promote radical polymerization into coke, respectively, without altering Pt atoms. Design guidelines to mitigate deactivation are discussed, highlighting the importance of tracking active functionalities in carbons.

Structural evolution of metal single-atoms and clusters in catalysis: Which are the active sites under operative conditions?

The structural evolution of metal single-atoms and clusters has been recognized as the new frontier in catalytic reactions under operative conditions, playing a crucial role in key aspects of catalytic behavior, including activity, selectivity, stability, and atomic efficiency as well as precise tunability in heterogeneous catalysis. Accurately identifying the structural evolution of metal single-atoms and clusters during real reactions is essential for addressing fundamental issues such as active sites, metal-support interactions, deactivation mechanisms, and thereby guiding the design and fabrication of high-performance single-atom and cluster catalysts. However, how to evaluate the dynamic structural evolution of metal species during catalytic reactions is still lacking, hindering their industrial applications. In this review, we discuss the behaviors of dynamic structural evolution between metal single-atoms and clusters, explore the driving force and major factors, highlight the challenges and inherent limitations encountered, and present relevant future research trends. Overall, this review provides valuable insights that can inspire researchers to develop novel and efficient strategies for accurately identifying the structural transformations of metal single-atoms and clusters.

Layered Na2Ti3O7-supported Ru catalyst for ambient CO2 methanation

The methanation of CO2 offers a practical solution for storing renewable energy and mitigating global climate risks. However, the primary challenge lies in achieving efficient CH4 production at lower temperatures. Here, we report a layered Na2Ti3O7-supported Ru catalyst as a stabilizer of low-valence Ru that enables CO2 activation at low temperatures. This catalyst leads to a CH4 production rate of 33.6 and 139.1 mmol gcat-1 h-1 at 140 and 180 °C, respectively, with a gas hourly space velocity of 24,000 mL g-1 h-1 at ambient pressure (1 bar), significantly surpassing state-of-the-art catalysts performance. Moreover, the catalyst demonstrates robustness to on-off intermittency and 220-hour long-term stability tests, indicating its reliability under challenging conditions. The catalyst is also successfully synthesized at the gram scale and on a 3D-printed metal self-catalytic reactor by a facile ion-exchange method, confirming its excellent scalability. This study marks a significant step forward in the design of catalysts for the low temperature CO2 hydrogenation.

Understanding the Dynamic Evolution of Active Sites among Single Atoms, Clusters, and Nanoparticles

Catalysis remains a cornerstone of chemical research, with the active sites of catalysts being crucial for their functionality. Identifying active sites, particularly during the reaction process, is crucial for elucidating the relationship between a catalyst's structure and its catalytic property. However, the dynamic evolution of active sites within heterogeneous metal catalysts presents a substantial challenge for accurately pinpointing the real active sites. The advent of in situ and operando characterization techniques has illuminated the path toward understanding the dynamic changes of active sites, offering robust scientific evidence to support the rational design of catalysts. There is a pressing need for a comprehensive review that systematically explores the dynamic evolution among single atoms, clusters, and nanoparticles as active sites during the reaction process, utilizing in situ and operando characterization techniques. This review aims to delineate the effects of various reaction factors on dynamic evolution of active sites among single atoms, clusters, and nanoparticles. Moreover, several in situ and operando techniques are elaborated with emphases on tracking the dynamic evolution of active sites, linking them to catalytic properties. Finally, it discusses challenges and future perspectives in identifying active sites during the reaction process and advancing in situ and operando characterization techniques.

Substance migration in the synthesis of single-atom catalysts

Substance migration is universal and crucial in the synthesis of catalysts, which directly affects their existing form and the micro-structure of their active sites. Realizing migration during the synthesis of single-atom catalysts (SACs) is beneficial for not only increasing their metal loading capacity but also manipulating the electronic structures (coordination structure, long-range interactions, etc.) of their metal sites. This review summarizes the thermodynamics and kinetic processes involved in the synthesis of SACs to unveil the fundamental principles involved in their synthesis. For a better understanding of the effect of migration, the migration of both metal (including ions, atoms, and molecules) and nonmetal species is outlined. Moreover, we propose the research directions to guide the rational design of SACs in the future and deepen the fundamental understanding in the formation of catalysts.

Asymmetric Ru-In atomic pairs promote highly active and stable acetylene hydrochlorination

Ru single-atom catalysts have great potential to replace toxic mercuric chloride in acetylene hydrochlorination. However, long-term catalytic stability remains a grand challenge due to the aggregation of Ru atoms caused by over-chlorination. Herein, we synthesize an asymmetric Ru-In atomic pair with vinyl chloride monomer yield (>99.5%) and stability (>600 h) at a gas hourly space velocity of 180 h-1, far surpassing those of the Ru single-atom counterparts. A combination of experimental and theoretical techniques reveals that there is a strong d-p orbital interaction between Ru and In atoms, which not only enables the selective adsorption of acetylene and hydrogen chloride at different atomic sites but also optimizes the electron configuration of Ru. As a result, the intrinsic energy barrier for vinyl chloride generation is lowered, and the thermodynamics of the chlorination process at the Ru site is switched from exothermal to endothermal due to the change of orbital couplings. This work provides a strategy to prevent the deactivation and depletion of active Ru centers during acetylene hydrochlorination.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

The Progress and Outlook of Metal Single-Atom-Site Catalysis

Single-atom-site catalysts (SASCs) featuring maximized atom utilization and isolated active sites have progressed tremendously in recent years as a highly prosperous branch of catalysis research. Varieties of SASCs have been developed that show excellent performance in many catalytic applications. The major goal of SASC research is to establish feasible synthetic strategies for the preparation of high-performance catalysts, to achieve an in-depth understanding of the active-site structures and catalytic mechanisms, and to develop practical catalysts with industrial value. This Perspective describes the up-to-date development of SASCs and related catalysts, such as dual-atom-site catalysts (DASCs) and nano-single-atom-site catalysts (NSASCs), analyzes the current challenges encountered by these catalysts for industrial applications, and proposes their possible future development path.