1,045 research outputs found
Carbon Dioxide Cycloaddition to Epoxides Promoted by Nicotinamidium Halide Catalysts: A DFT Investigation
Get PDFThe utilization of CO2 as building block for the production of cyclic carbonate is a promising route to simultaneously mitigate the global warming issue and obtain valuable commercial chemicals. In this work, the activity of nicotinamidium halide catalysts towards the CO2 conversion into cyclic carbonate has been explored by means of density functional theory (DFT) calculations. DFT calculations support the ability, suggested experimentally, of the pyridium & alpha;-C-H proton of the catalysts to activate the epoxide ring via a hydrogen bond. Interestingly, DFT calculations underline the involvement of the n-octyl substituent of the pyridyl ring in the epoxide activation, while the hydrogen atom of the amide group N-H is rather involved in the stabilization of the iodide trough electrostatic interactions. Moreover, the replacement of the pyridium & alpha;-C-H proton with the bulkier methyl group leads to a different reaction mechanism. The calculated energy barriers well reproduce the experimental trends of the studied catalysts, and the computed activation barrier of 29.0 kcal/mol, relative to the ring opening step of the most active catalyst, is in line with the experimental working temperature of 80 & DEG;C. Those results shed light on the CO2 fixation reaction contributing to the development of more efficient catalytic systems
Density functional theory methods applied to homogeneous and heterogeneous catalysis: a short review and a practical user guide
Get PDFThe application of density functional theory (DFT) methods in catalysis has been growing fast in the last few decades thanks to both the availability of more powerful high computing resources and the development of new efficient approximations and approaches. DFT calculations allow for the understanding of crucial catalytic aspects that are difficult or even impossible to access by experiments, thus contributing to faster development of more efficient and selective catalysts. Depending on the catalytic system and properties under investigation, different approaches should be used. Moreover, the reliability of the obtained results deeply depends on the approximations involved in both the selected method and model. This review addresses chemists, physicists and materials scientists whose interest deals with the application of DFT-based computational tools in both homogeneous catalysis and heterogeneous catalysis. First, a brief introduction to DFT is presented. Then, the main approaches based on atomic centered basis sets and plane waves are discussed, underlining the main differences, advantages and limitations. Eventually, guidance towards the selection of the catalytic model is given, with a final focus on the evaluation of the energy barriers, which represents a crucial step in all catalytic processes. Overall, the review represents a rational and practical guide for both beginners and more experienced users involved in the wide field of catalysis
ABC di corpi: alcuni alfabeti figurati del XVI secolo del Gabinetto Disegni e Stampe della Pinacoteca Nazionale di Bologna
No full textFra le diverse tipologie di motivi ornamentali, gli alfabeti figurati costituiscono un vero e proprio genere a se stante, che attinge al repertorio iconografico del proprio tempo e lo riflette in composizioni dotate di grande fascino e originalità. Per la quantità, la qualità e l’eterogeneità degli esemplari custoditi, il Gabinetto Disegni e Stampe della Pinacoteca Nazionale di Bologna costituisce un caso più unico che raro in Italia, vantando alfabeti figurati che abbracciano ampi confini geografici e cronologici, spaziando dal tardo gotico al XIX secolo. Dopo una breve introduzione sulle vicende collezionistiche di un nucleo grafico così insolito e particolare, l’articolo si concentra su alcuni esemplari di alfabeti figurati del Cinquecento di area transalpina. Partendo dall’alfabeto dei bambini di Hans Weiditz (1521), costruito rispettando le più rigorose regole geometriche, codificate nei coevi trattati rinascimentali, ma anche riflesso del rinato gusto per i fregi all’antica con putti, si passa agli alfabeti di Peter Flötner (1534) e di Jost Amman (1567), dove le lettere sono integralmente costituite da corpi umani, forzati in complicate posture, talvolta persino licenziose. Questi esemplari rappresentano degli interessanti esperimenti calligrafici, dove l’uomo diviene concretamente l’unità di misura dei caratteri dell’alfabeto
Funambolici equilibri. Gli alfabeti antropomorfi della Pinacoteca Nazionale di Bologna
No full textL'oggetto di questo studio sono due rari alfabeti antropomorfi a stampa di provenienza fiamminga e tedesca, realizzati tra XV e XVI secolo, conservati nella Pinacoteca Nazionale di Bologna. Gli esemplari sono messi a confronto con i loro modelli conservati presso altre istituzioni europee, dal punto di vista iconografico, stilistico e tecnico. Si indagano anche le vicende collezionistiche che spiegano una presenza così insolita sul territorio bolognese
Fra ironia e gioco. Alfabeti figurati della Pinacoteca Nazionale di Bologna
No full textAttraverso alcuni esemplari di alfabeti figurati conservati presso il Gabinetto Disegni e Stampe della Pinacoteca Nazionale di Bologna, l'articolo traccia una breve storia di questo genere, dal Tardogotico al pieno Rinascimento. Le stampe della collezione bolognese, talvolta assai rare, testimoniano le evoluzioni dei repertori iconografici e ornamentali di una tipologia artistica, sempre caratterizzata da un estro bizzarro e da un'inesauribile fantasia
DFT Study of GaN Clusters Decorated with Rh and Pt Nanoparticles for the Photochemical Reduction of CO2
No full textObtaining chemicals and fuels from the reduction of carbon dioxide (CO2) represents a promising strategy to mitigate the growing greenhouse gas emissions. Because of the high thermodynamic stability of CO2, the real challenge is the development of efficient and selective catalysts. In this regard, photocatalysis is receiving much attention because it exclusively relies on energy input from sunlight. Gallium nitride (GaN) semiconductors can effectively promote the CO2reduction. Moreover, the addition on the semiconductor surfaces of transition metal nanoparticles, such as Rh and Pt, can further improve the efficiency and selectivity toward CH4rather than CO, along with improving the optical absorptions in the visible spectral region by decreasing the wide band gap of the pristine GaN. Water is commonly used as an atomic hydrogen donor for CO2reduction. In this regard, GaN was previously reported as an excellent photocatalyst for water oxidation. Here, we present a density functional theory investigation based on a cluster model approach to shed light on the effective role of the metal nanoparticles on the CO2reduction in the presence of water. Our calculations have underlined a more favored dissociative adsorption of H2O with respect to CO2. Moreover, while the dissociative H2O adsorption on the GaN surface occurs without the involvement of the Rh metal, the role of the metal center in activating the CO2molecule is found to be crucial. Highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and calculated absorption spectra have shown that the presence of the adsorbed nanoparticles not only intensifies the absorption next to the UV region but also extends it to all visible regions. Particularly, while the presence of Rh exhibits a stronger light absorption property in the visible region, enhanced in the blue-green region, Pt nanoparticles have a clear red-shift effect
Insights into the mechanistic CO2 conversion to methanol on single Ru atom anchored on MoS2 monolayer
No full textSingle atom catalysts (SACs) have received great attention due to their promising catalytic activity and sustainability. In this regard, the catalytic activity toward CO2 conversion reaction can be efficiently improved by the addition of single transition metal anchored on the 2D MoS2 monolayer. In this work, we explore the potential utilization of Ru@MoS2 as a promising SAC for the CO2 reduction reaction (CO2RR) by using first-principles simulations. The stability of the so-formed SAC was evaluated in terms of binding energy, and the reaction paths leading to the production of CO and methanol was investigated. Our results show the great potential of Ru@MoS2 as SAC for the CO2 conversion to methanol as the main product, and contribute to shed light on the complex reaction mechanism aiming at the development of more efficient catalytic systems
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