Surface Carbon Formation and its Impact on Methane Dry Reforming Kinetics on Rhodium-Based Catalysts by Operando Raman Spectroscopy.

A mechanism for carbon deposition and its impact on the reaction kinetics of Methane Dry Reforming (MDR) using Rhodium-based catalysts is presented. By integrating Raman spectroscopy with kinetic analysis in an operando-annular chemical reactor under strict chemical conditions, we discovered that carbon deposition on a Rh/α-AlO catalyst follows a nucleation-growth mechanism. The dynamics of carbon aggregates at the surface is found to be ruled by the CO/CH ratio and the inlet CH concentration.

Increasing Computational Efficiency of CFD Simulations of Reactive Flows at Catalyst Surfaces through Dynamic Load Balancing.

We propose a numerical strategy based on dynamic load balancing (DLB) aimed at enhancing the computational efficiency of multiscale CFD simulation of reactive flows at catalyst surfaces. Our approach employs DLB combined with a hybrid parallelization technique, integrating both MPI and OpenMP protocols. This results in an optimized distribution of the computational load associated with the chemistry solution across processors, thereby minimizing computational overheads.

Quantitative Kinetic Insights from Operando-UV/Vis Spectroscopy: An Application to NH-SCR of NOx on Cu-CHA Catalysts.

We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show-case the Cu/Cu redox dynamics during the reduction half cycle of the NH-Selective Catalytic Reduction (SCR) on Cu-CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas-phase evolution during the reaction.

UV-vis spectroscopy for real-time monitoring of nanoparticle size in reaction conditions: a case study on WGS over Au nanoparticles.

We propose the use of surface plasmon resonance (SPR) as a distinctive marker for real-time monitoring in reaction conditions of gold nanoparticles supported on α-AlO. The study leverages the SPR shape-and-size dependency to monitor metal nanoparticles in reaction conditions, evidencing an influence of both dimensions and agglomerations on the SPR peak position. measurements, coupling UV-vis spectroscopy and catalytic testing, allows to follow the dynamics during nanoparticle formation (Au to Au reduction) and during the reverse water gas shift reaction (CO + H → CO + HO).

Biophysical parameters control signal transfer in spiking network.

Introduction: Information transmission and representation in both natural and artificial networks is dependent on connectivity between units. Biological neurons, in addition, modulate synaptic dynamics and post-synaptic membrane properties, but how these relate to information transmission in a population of neurons is still poorly understood. A recent study investigated local learning rules and showed how a spiking neural network can learn to represent continuous signals.

Shadows and Lights: Perspectives of Training and Education in Neurosurgery for Undergraduate Students.

Introduction: Neurosurgical education should start during medical school to involve more students, favoring the recruitment of the most prepared and motivated ones and spreading this subject to the future medical generations. Despite multiple investigations, a dedicated educational plan does not exist. This study aims to assess the undergraduates' interests, needs, and perceptions of this subject.

Mechanistic and multiscale aspects of thermo-catalytic CO conversion to C products.

The increasing environmental concerns due to anthropogenic CO emissions have called for an alternate sustainable source to fulfill rising chemical and energy demands and reduce environmental problems. The thermo-catalytic activation and conversion of abundantly available CO, a thermodynamically stable and kinetically inert molecule, can significantly pave the way to sustainably produce chemicals and fuels and mitigate the additional CO load. This can be done through comprehensive knowledge and understanding of catalyst behavior, reaction kinetics, and reactor design.

Local Ordering of Molten Salts at NiO Crystal Interfaces Promotes High-Index Faceting.

Given the strong influence of surface structure on the reactivity of heterogeneous catalysts, understanding the mechanisms that control crystal morphology is an important component of designing catalytic materials with targeted shape and functionality. Herein, we employ density functional theory to examine the impact of growth media on NiO crystal faceting in line with experimental findings, showing that molten-salt synthesis in alkali chlorides (KCl, LiCl, and NaCl) imposes shape selectivity on NiO particles. We find that the production of NiO octahedra is attributed to the dissociative adsorption of H O, whereas the formation of trapezohedral particles is associated with the control of the growth kinetics exerted by ordered salt structures on high-index facets.

A Fundamental Investigation of Gas/Solid Heat and Mass Transfer in Structured Catalysts Based on Periodic Open Cellular Structures (POCS).

In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed.

Coupling Euler-Euler and Microkinetic Modeling for the Simulation of Fluidized Bed Reactors: an Application to the Oxidative Coupling of Methane.

We propose a numerical methodology to combine detailed microkinetic modeling and Eulerian-Eulerian methods for the simulation of industrial fluidized bed reactors. An operator splitting-based approach has been applied to solve the detailed kinetics coupled with the solution of multiphase gas-solid flows. Lab and industrial reactor configurations are simulated to assess the capability and the accuracy of the method by using the oxidative coupling of methane as a showcase.

The Influence of a Changing Local Environment during Photoinduced CO Dissociation.

Though largely influencing the efficiency of a reaction, the molecular-scale details of the local environment of the reactants are experimentally inaccessible hindering an in-depth understanding of a catalyst's reactivity, a prerequisite to maximizing its efficiency. We introduce a method to follow individual molecules and their largely changing environment during a photochemical reaction. The method is illustrated for a rate-limiting step in a photolytic reaction, the dissociation of CO on two catalytically relevant surfaces, Ag(100) and Cu(111).

Development and Assessment of a Criterion for the Application of Brønsted-Evans-Polanyi Relations for Dissociation Catalytic Reactions at Surfaces.

We propose and assess a criterion for the application of Brønsted-Evans-Polanyi (BEP) relations for dissociation reactions at surfaces. A theory-to-theory comparison with density functional theory calculations is presented on different reactions, metal catalysts, and surface terminations. In particular, the activation energies of CH, CO, and -COOH dissociation reactions on (100), (110), (111), and (211) surfaces of Ni, Cu, Rh, Pd, Ag, and Pt are considered.

A topological model for predicting adsorption energies of polycyclic aromatic hydrocarbons on late-transition metal surfaces.

We introduce and validate by first-principles calculations an analogy between metal coordination chemistry and the adsorption of polycyclic aromatic hydrocarbons (PAHs) at metal surfaces for the derivation of a model for predicting the PAH adsorption energies. We correlate the binding of PAH on the metal surface with the coordination between metal atom and the ligands in the metal complex, where the formation enthalpy of metal complexes is mainly determined by the strength of a single metal-ligand (M-L) bond and by the number of the M-L bonds. This analogy allows estimation of the adsorption energies only on the basis of the structure of the PAHs and of their adsorption configurations.

Coupling CFD-DEM and microkinetic modeling of surface chemistry for the simulation of catalytic fluidized systems.

In this work, we propose numerical methodologies to combine detailed microkinetic modeling and Eulerian-Lagrangian methods for the multiscale simulation of fluidized bed reactors. In particular, we couple the hydrodynamics description by computational fluid dynamics and the discrete element method (CFD-DEM) with the detailed surface chemistry by means of microkinetic modeling. The governing equations for the gas phase are solved through a segregated approach.

Prediction of morphological changes of catalyst materials under reaction conditions by combined thermodynamics and microkinetic modelling.

In this article, we couple microkinetic modelling, thermodynamics and Wulff-Kaishew construction to describe the structural variation of catalyst materials as a function of the chemical potential in the reactor. We focus specifically on experiments of catalytic partial oxidation (CPO) of methane on Rh/α-AlO. We employ a detailed structureless microkinetic model to calculate the profiles of the gaseous species molar fractions along the reactor coordinate and to select the most abundant reaction intermediates (MARIs) populating the catalyst surfaces in different zones of the reactor.

First-principles theoretical assessment of catalysis by confinement: NO-O reactions within voids of molecular dimensions in siliceous crystalline frameworks.

Density functional theory methods that include dispersive forces are used to show how voids of molecular dimensions enhance reaction rates by the mere confinement of transition states analogous to those involved in homogeneous routes and without requiring specific binding sites or structural defects within confining voids. These van der Waals interactions account for the observed large rate enhancements for NO oxidation in the presence of purely siliceous crystalline frameworks. The minimum free energy paths for NO oxidation within chabazite (CHA) and silicalite (SIL) frameworks involve intermediates similar in stoichiometry, geometry, and kinetic relevance to those involved in the homogeneous route.

Escaping the trap of complication and complexity in multiscale microkinetic modelling of heterogeneous catalytic processes.

In this feature article, the development of methods to enable a hierarchical multiscale approach to the microkinetic analysis of heterogeneous catalytic processes is reviewed. This methodology is an effective route to escape the trap of complication and complexity in multiscale microkinetic modelling. On the one hand, the complication of the problem is related to the fact that the observed catalyst functionality is inherently a multiscale property of the reacting system and its analysis requires bridging the phenomena at different time and length scales.

First-Principles Simulation of Raman Spectra of Adsorbates on Metal Surfaces.

A general method is proposed to simulate the Raman spectra of adsorbates on metal surfaces. This method is based on an electrostatic-corrected cluster model with additional charges to compensate the loss of coordination of metal atoms, and an external field added to simulate the surface dipole and to reproduce the charge distribution obtained from periodic calculations. As a result, it is possible to couple the phonon calculation with the Raman tensors computed by this corrected cluster model to simulate the Raman spectra of the adsorbates on metal surfaces.