A facile direct route to N-(un)substituted lactams by cycloamination of oxocarboxylic acids without external hydrogen

Lactams are privileged in bioactive natural products and pharmaceutical agents and widely featured in functional materials. This study presents a novel versatile approach to the direct synthesis of lactams from oxocarboxylic acids without catalyst or external hydrogen. The method involves the in situ release of formic acid from formamides induced by water to facilitate efficient cycloamination. Water also suppresses the formation of byproducts. This unconventional pathway is elucidated by a combination of model experiments and density functional theory calculations, whereby cyclic imines (5‐methyl‐3,4‐dihydro‐2‐pyrrolone and its tautomeric structures) are found to be favorable intermediates toward lactam formation, in contrast to the conventional approach encompassing cascade reductive amination and cyclization. This sustainable and simple protocol is broadly applicable for the efficient production of various N‐unsubstituted and N‐substituted lactams

A DFT study of CO oxidation at the Pd-CeO\u3csub\u3e2\u3c/sub\u3e(110) interface

\u3cp\u3eCeria-supported Pd is one of the main components in modern three-way catalysts in automotive applications to facilite CO oxidation. The exact form in which Pd displays its high activity remains not well understood. We present a DFT+U study of CO oxidation for single Pd atoms located on or in the ceria surface as well as a Pd\u3csub\u3en\u3c/sub\u3e nanorod model on the CeO\u3csub\u3e2\u3c/sub\u3e(110) surface. The oxidation of Pd to the 2+ state by ceria weakens the Pd-CO bond for the single Pd models and, in this way, facilitates CO\u3csub\u3e2\u3c/sub\u3e formation. After CO oxidation by O of the ceria surface, Pd relocates to a position below the surface for the Pd-doped model; in this state, CO adsorption is not possible anymore. With Pd on the surface, O\u3csub\u3e2\u3c/sub\u3e will adsorb and dissociate leading to PdO, which can be easily reduced to Pd. The reactivity of the Pd nanorod is low because of the strong bonds of the metallic Pd phase with CO and the O atom derived from O\u3csub\u3e2\u3c/sub\u3e dissociation. These findings show that highly dispersed Pd is the most likely candidate for CO oxidation in the Pd-CeO\u3csub\u3e2\u3c/sub\u3e system.\u3c/p\u3

Lattice oxygen activation in transition metal doped ceria

\u3cp\u3eDensity functional theory calculations were carried out to investigate the influence of doping transition metal (TM) ions into the ceria surface on the activation of surface lattice oxygen atoms. For this purpose, the structure and stability of the most stable (111) surface termination of CeO \u3csub\u3e2\u3c/sub\u3e modified by TM ions was determined. Except for Zr and Pt dopants that preserve octahedral oxygen coordination, the TM dopants prefer a square-planar coordination when substituting the surface Ce ions. The surface construction from octahedral to square-planar is facile for all TM dopants, except for Pt (1.14 eV) and Zr (square-planar coordination unstable). Typically, the ionic radius of tetravalent TM cations is much smaller than that of Ce \u3csup\u3e4+\u3c/sup\u3e, resulting a significant tensile-strained lattice and explaining the lowered oxygen vacancy formation energy. Except for Zr, the square-planar structure is the preferred one when one oxygen vacancy is created. Thermodynamic analysis shows that TM-doped CeO \u3csub\u3e2\u3c/sub\u3e surfaces contain oxygen defects under typical conditions of environmental catalysis. A case of practical importance is the facile lattice oxygen activation in Zr-doped CeO \u3csub\u3e2\u3c/sub\u3e(111), which benefits CO oxidation. The findings emphasize the origin of lattice oxygen activation and the preferred location of TM dopants in TM-ceria solid solution catalysts. \u3c/p\u3

Aerobic oxidation of HMF-cyclic acetal enables selective FDCA formation with CeO2-supported au catalyst

The utilization of 5‐(hydroxymethyl)furfural (HMF) for the large‐scale production of essential chemicals has been largely limited by the formation of solid humin as a by‐product, which prevents continuous operation of step‐wise batch‐type processes and continuous flow‐type processes. The reaction of HMF with 1,3‐propanediol produces an HMF‐acetal derivative that exhibits excellent thermal stability. Aerobic oxidation of the HMF‐acetal with a CeO2‐supported Au catalyst and Na2CO3 in water gives a 90‐95% yield toward furan 2,5‐dicarboxylic acid, an increasingly important commodity chemical for the biorenewables industry, from concentrated HMF‐acetal solutions (10‐20 wt%) without humin formation. The stability of the six‐membered acetal ring suppresses thermal decomposition and self‐polymerization of HMF in concentrated solutions. Kinetic studies supported by density functional theory calculations identify two crucial steps in the reaction mechanism, i.e., the partial hydrolysis of the acetal into 5‐formyl‐2‐furan carboxylic acid involving OH‐ and Lewis acid sites on CeO2, and subsequent oxidative dehydrogenation of the in situ generated hemiacetal involving Au nanoparticles. The present results represent a significant advance over the current state of the art, overcoming an inherent limitation of the oxidation of HMF to an important monomer for biopolymer production

A facile direct route to N-(un)substituted lactams by cycloamination of oxocarboxylic acids without external hydrogen

Lactams are privileged in bioactive natural products and pharmaceutical agents and widely featured in functional materials. This study presents a novel versatile approach to the direct synthesis of lactams from oxocarboxylic acids without catalyst or external hydrogen. The method involves the in situ release of formic acid from formamides induced by water to facilitate efficient cycloamination. Water also suppresses the formation of byproducts. This unconventional pathway is elucidated by a combination of model experiments and density functional theory calculations, whereby cyclic imines (5‐methyl‐3,4‐dihydro‐2‐pyrrolone and its tautomeric structures) are found to be favorable intermediates toward lactam formation, in contrast to the conventional approach encompassing cascade reductive amination and cyclization. This sustainable and simple protocol is broadly applicable for the efficient production of various N‐unsubstituted and N‐substituted lactams

Theoretical study of ripening mechanisms of Pd clusters on Ceria

We carried out density functional theory calculations to investigate the ripening of Pd clusters on CeO2(111). Starting from stable Pdn clusters (n=1-21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have a high mobility than Pd¬n clusters on the CeO2(111) surface, Ostwald-ripening is predicted to be the dominant sintering mechanism. Particle coalescence is only possible when very small clusters with less than 5 Pd at-oms are involved. These ripening mechanisms are facilitated by adsorbed CO through lowering barriers for the cluster diffusion, detachment of a Pd atom from clusters, and transformation of initial planar clusters

A facile direct route to N-(un)substituted lactams by cycloamination of oxocarboxylic acids without external hydrogen

Lactams are privileged in bioactive natural products and pharmaceutical agents and widely featured in functional materials. This study presents a novel versatile approach to the direct synthesis of lactams from oxocarboxylic acids without catalyst or external hydrogen. The method involves the in situ release of formic acid from formamides induced by water to facilitate efficient cycloamination. Water also suppresses the formation of byproducts. This unconventional pathway is elucidated by a combination of model experiments and density functional theory calculations, whereby cyclic imines (5‐methyl‐3,4‐dihydro‐2‐pyrrolone and its tautomeric structures) are found to be favorable intermediates toward lactam formation, in contrast to the conventional approach encompassing cascade reductive amination and cyclization. This sustainable and simple protocol is broadly applicable for the efficient production of various N‐unsubstituted and N‐substituted lactams

A linear scaling relation for CO oxidation on CeO\u3csub\u3e2\u3c/sub\u3e-supported Pd

\u3cp\u3eResolving the structure and composition of supported nanoparticles under reaction conditions remains a challenge in heterogeneous catalysis. Advanced configurational sampling methods at the density functional theory level are used to identify stable structures of a Pd\u3csub\u3e8\u3c/sub\u3e cluster on ceria (CeO\u3csub\u3e2\u3c/sub\u3e) in the absence and presence of O\u3csub\u3e2\u3c/sub\u3e. A Monte Carlo method in the Gibbs ensemble predicts Pd-oxide particles to be stable on CeO\u3csub\u3e2\u3c/sub\u3e during CO oxidation. Computed potential energy diagrams for CO oxidation reaction cycles are used as input for microkinetics simulations. Pd-oxide exhibits a much higher CO oxidation activity than metallic Pd on CeO\u3csub\u3e2\u3c/sub\u3e. This work presents for the first time a scaling relation for a CeO\u3csub\u3e2\u3c/sub\u3e-supported metal nanoparticle catalyst in CO oxidation: a higher oxidation degree of the Pd cluster weakens CO binding and facilitates the rate-determining CO oxidation step with a ceria O atom. Our approach provides a new strategy to model supported nanoparticle catalysts.\u3c/p\u3