Ceria (CeO2) supports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single‐atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The single‐atom Pt/CeO2 catalysts are stable during propane dehydrogenation, but are not selective for propylene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when tin (Sn) is added to CeO2, the single‐atom Pt catalyst undergoes an activation phase where it transforms into Pt–Sn clusters under reaction conditions. Formation of small Pt–Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO2‐supported Pt–Sn clusters are very stable, even during extended reaction at 680 °C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore, upon oxidation the Pt–Sn clusters readily revert to the atomically dispersed species on CeO2, making Pt–Sn/CeO2 a fully regenerable catalyst.

Ceria (CeO 2 )s upports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single-atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The singleatom Pt/CeO 2 catalysts are stable during propane dehydrogenation, but are not selective for propylene.D FT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions.Incontrast, when tin (Sn) is added to CeO 2 ,t he single-atom Pt catalyst undergoes an activation phase where it transforms into Pt-Sn clusters under reaction conditions.F ormation of small Pt-Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO 2 -supported Pt-Sn clusters are very stable,e ven during extended reaction at 680 8 8C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore,u pon oxidation the Pt-Sn clusters readily revert to the atomically dispersed species on CeO 2 ,m aking Pt-Sn/CeO 2 af ully regenerable catalyst.

The kinetics of 1-hexene polymerization using a family of five zirconium amine bis-phenolate catalysts, Zr[tBu-ON(X)O]Bn2 (where X = THF (1), pyridine (2), NMe2 (3), furan (4), and SMe (5)), has been investigated to uncover the mechanistic effect of varying the pendant ligand X. A model-based approach using a diverse set of data including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction specific rate constants involved in a given polymerization process. The mechanism of polymerization for 1-5 was similar and the necessary elementary reaction steps included initiation, normal propagation, misinsertion, recovery from misinsertion, and chain transfer. The latter reaction, chain transfer, featured monomer independent β-H elimination in 1-3 and monomer dependent β-H transfer in 4 and 5. Of all the rate constants, those for chain transfer showed the most variation, spanning 2 orders of magnitude (ca. (0.1-10) × 10(-3) s(-1) for vinylidene and (0.5-87) × 10(-4) s(-1) for vinylene). A quantitative structure-activity relationship was uncovered between the logarithm of the chain transfer rate constants and the Zr-X bond distance for catalysts 1-3. However, this trend is broken once the Zr-X bond distance elongates further, as is the case for catalysts 4 and 5, which operate primarily through a different mechanistic pathway. These findings underscore the importance of comprehensive kinetic modeling using a diverse set of multiresponse data, enabling the determination of robust kinetic constants and reaction mechanisms of catalytic olefin polymerization as part of the development of structure-activity relationships.

The physical properties and morphologies of polymers are pivotal for their manufacturing and processing at the industrial scale. Here, we present the formation of either fibers or micrometer-sized polyethylene beads by using the MIL-100(Cr) and MIL-101(Cr) zeotypes. The MOF structures have been used for ethylene polymerization with diethylaluminum chloride (DEA) as a cocatalyst, resulting in very different activities and morphologies. In situ DR UV−vis−NIR and CO-probe FT-IR spectroscopy revealed the formation of different types of Cr species for each catalyst material, suggesting that the linker (for the same metal and topological structure) plays a crucial role in the formation of Cr olefin polymerization sites. Activity in ethylene polymerization in toluene at 10 bar and 298 K was related to the observed spectra, corroborating the presence of different types of active sites, by their different activities for high-density polyethylene (HDPE) formation. SEM micrographs revealed that although MIL-100 and MIL-101 exhibit identical zeolitic MTN topology, only the latter is able to collapse upon addition of DEA and subsequent ethylene insertion and to fracture forming polymer beads, thus showing noticeable activity in HDPE formation. We ascribed this effect to the higher pore volume and, thus, fragility of MIL-101, which allowed for polymer formation within its larger cages. MOFs were compared to the nonporous chromium(III) benzoate [Cr 3 O(O 2 CPh) 6 (H 2 O) 2 ]-(NO 3 )•nH 2 O complex (1), in order to study the effect of the embodiment in the porous framework. The properties of the polymer obtained under identical reaction conditions were comparable to that of MIL-101(Cr) but very different morphologies were observed, indicating that the MIL-101(Cr) structure is necessary to impart a certain architecture at the microscale. This work clearly shows that MOFs can be used as catalytically active morphology regulators for ethylene polymerization. Moreover, even for an identical topology and metal in a MOF structure, the linker and the pore structure play crucial roles and have to be carefully considered in the design microporous coordination polymers for catalytic purposes.

The kinetics of 1-hexene polymerization using a family of three zirconium and hafnium amine bis-phenolate catalysts, M[t-Bu-ONXO]Bn2 (where M = Zr (a) or Hf (b), and X = THF (1), pyridine (2), or NMe2 (3)), have been investigated to uncover the mechanistic effect of varying the metal center M. A model-based approach using a diverse set of data including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction-specific rate constants involved in a given polymerization process. This study builds upon the mechanism of polymerization for 1a–3a, which has been previously reported by applying the same methodology to the hafnium containing analogues, 1b–3b. It has been observed that each elementary step-specific rate constant that involves the insertion of a monomer is reduced by an order of magnitude. As previously reported for catalysts 1a–3a, a quantitative structure–activity relationship was uncovered between the logarithm of the monomer-independent chain transfer rate constants and the Hf–X bond distance for catalysts 1b–3b. However, this dependence on the pendant ligand is 2.7 times weaker for the Hf-containing analogues versus those containing Zr. These findings underscore the importance of comprehensive kinetic modeling using a diverse set of multiresponse data, enabling the determination of robust kinetic constants and reaction mechanisms of catalytic olefin polymerization as part of the development of structure–activity relationships.