Mechanistic understanding of tautomer, a new class of modifiers, that affects crystal shape and growth kinetics is crucial to tailoring the property of tautomeric crystalline materials but remains elusive. Herein, we investigated this effect through a combination of kinetics modeling and experimental validation. Accounting for both tautomeric thermodynamics and inter-conversion kinetics, we developed mechanistic expressions that consider the tautomerism-induced growth self-inhibition process. Our approach enables us to calculate the influence of various operational conditions on growth kinetics and to predict the dominant factors of growth self-inhibition by tautomers. Tautomers were found primarily to suppress crystal growth by reducing the driving force under mass-transfer growth regime. However, the inhibitory effect shifts to a more complex synergistic action of step pinning and kink blocking mechanisms with interfacial tautomer inter-conversions under surface-integration limited growth regime. Finally, the effectiveness of our developed kinetics model was further experimentally validated using two urate salts as model systems.
Boron nitride (BN) has a two-dimensional covalent structure and offers a catalytic platform for highly selective oxidative dehydrogenation of propane (ODHP). However, the limited structural tunability of pristine BN restricts its activity and stability under harsh conditions. Here, we demonstrate that highly curved BN surfaces in small-diameter multiwalled BN nanotubes promote ODHP activity via B-O sites at nitrogen vacancies, achieving over 20% propane conversion at 520°C. These nanotubes are synthesized via a metal-free millisecond carbon thermal shock method, avoiding oxidative degradation. The resulting catalyst withstands temperatures up to 600°C, and the local B-O/H environment impedes oxygen and water intrusion, ensuring stability over 100 h through multiple reaction cycles.
Rh-metal clusters, characterized by an ultrahigh surface-to-volume ratio approaching 100%, serve as pivotal active centers in hydroformylation. However, such Rh clusters containing numerous Rh–Rh metallic bonds typically exhibit limited selectivity for oxygenated products. Herein, we report the architectural engineering of high-entropy-alloy Rh nanoclusters (Rh-HEACs) confined within MCM-41 mesopores, achieving a remarkable styrene turnover frequency (TOF) of 7377.0 h−1, 3-fold over that of RhMg@MCM-41 (2675.0 h−1). The Rh-HEA architecture not only reduces the surface density of Rh–Rh assemblies but also modifies adsorption behavior through its distinctive electronic configuration. Specifically, the interfacial coupling among Rh, Cu, Co, Zn, and Mg induces electron transfer from the transition metals to Rh centers. This unique electronic structure weakens CO binding while preserving styrene affinity, optimizing reaction pathways. Our findings convincingly demonstrate that HEA nanoclusters bridge the critical performance gap between heterogeneous and homogeneous Rh-based catalytic systems in hydroformylation applications.
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