scholarly journals Multiscale Models in Heterogeneous Catalysis: Incorporating Dynamics into Reaction Kinetics

2021 ◽  
Author(s):  
Toyin Omojola
Keyword(s):  
Heat Transfer ◽  
Charge Transport ◽  
Active Site ◽  
Heterogeneous Catalysts ◽  
Surface Composition ◽  
Catalyst Activity ◽  
Multiscale Model ◽  
Product Selectivity ◽  
Multiscale Models ◽  
Kinetic Investigations

Modern operando spectroscopy and microscopy, and kinetic investigations have provided qualitative evidence for active site dynamics, catalyst surface dynamics, and charge transport. On the macroscale, intraparticle and interparticle mass and heat transfer can be tuned to optimise selectivity over heterogeneous catalysts. On the microscale, adsorbate-induced restructuring, adsorbate mobility, surface composition, oxidation states, charge transport, bandgap, and the degree of coordination of the active site have been identified for controlling product selectivity. There exist, however, limited physics-based and data-driven multiscale models that can assimilate these qualitative descriptors in an integrated manner to extract quantitative catalyst activity, stability, and product selectivity descriptors. A multiscale model, which describes the evolution of gas species, adspecie accumulation due to reactivity, stability, lifetime, and mobility, charge transport involving electrons and holes, heat transfer for non-isothermal conditions due to reaction exothermicity, and the changing catalyst states is provided. Dynamical effects are included in these models to bridge the gap between laboratory-scale studies and industrial technical reactors.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

Coupled Electro-Thermal-Phase Change Modeling of a Chalcogenide Switch

2006 ◽  
Author(s):  
Navdeep Singh Dhillon ◽  
Jayathi Y. Murthy
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Charge Transport ◽  
Crystallization Kinetics ◽  
Change Models ◽  
Switching Model ◽  
Memory Switching ◽  
Continuity Equations ◽  
Thermal Phase ◽  
Fully Coupled

A coupled electro-thermal-phase change numerical model is developed to model the threshold and memory switching processes in a chalcogenide switch based on phase change memory (PCM) technology. Coupled electrical and thermal transport coupled to phase change and crystallization kinetics are solved. Charge transport has been implemented using simplified carrier continuity equations with a threshold switching model for electrical conductivity. Heat transfer is modeled using a Fourier model, accounting for latent heat through a fixed-grid enthalpy formulation. Phase change is modeled using the Johnson-Mehl equations for crystallization kinetics. Thermal conductivity and electrical resistivity changes due to phase change are modeled using a local percolation model. The charge transport and circuit equations are fully coupled with the heat transfer and phase change models to accurately simulate the switching process. SET and RESET pulses are simulated to demonstrate that the model is able to capture the underlying physics well.

Active surface centres in vanadium pentoxide/alkali metal sulphate heterogeneous catalysts for 2-propanol decomposition

1979 ◽  
Vol 57 (18) ◽  
pp. 2464-2469 ◽  
Author(s):  
David Victor Fikis ◽  
William John Murphy ◽  
Robert Anderson Ross
Keyword(s):  
Alkali Metal ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
Active Surface ◽  
Hydroxyl Groups ◽  
Kinetic Measurements ◽  
The Stability ◽  
The Individual

Infrared spectra of the surfaces of vanadium pentoxide and vanadium pentoxide containing 9.09 mol% caesium and potassium, as sulphates, have been determined after exposure to 2-propanol for various times. Interpretation of the spectra leads to the proposal that the principal source of catalyst activity may be associated with surface hydrogen and hydroxyl groups on V5+ and V4+ sites. The "stability" of the catalysts towards reduction by the alcohol was consistent with the activity series derived from kinetic measurements: V2O5 (pure) < V2O5 (Cs) < V2O5 (K). The degree of sample reduction has also been assessed qualitatively by measurements of the ratio of surface area before to that after reaction and the same catalyst sequence was established. The trend in surface area ratios was similar to that shown by the surface "Tammann" temperatures of vanadium pentoxide and alkali metal sulphates which has been taken to imply that the ease and (or) extent with which the sulphates enter into inter-solid reactions with the oxide in the preparation stage may exert influence on the subsequent reducibility of the individual members of the catalyst series.

Quantifying Oxygen Induced Surface Enrichment of a Dilute PdAu Alloy Catalyst

2021 ◽  
Author(s):  
Mustafa Karatok ◽  
Robert James Madix ◽  
Jessi van der Hoeven ◽  
Joanna Aizenberg ◽  
Christian Reece
Keyword(s):  
Selective Oxidation ◽  
Active Site ◽  
Surface Composition ◽  
Surface Enrichment ◽  
Site Density ◽  
Hydrogenation Reactions ◽  
Alloy Catalyst

Dilute PdAu alloys are promising catalysts for selective oxidation and hydrogenation reactions. However, the surface composition and active site density of the minority metal, Pd, is unknown. In this study,...

scholarly journals Carbon-Based Catalysts for Biodiesel Production—A Review

2020 ◽  
Vol 10 (3) ◽  
pp. 918 ◽  
Author(s):  
Jack Clohessy ◽  
Witold Kwapinski
Keyword(s):  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
High Surface ◽  
High Surface Area ◽  
Acid Catalyst ◽  
Biodiesel Production ◽  
Catalyst Characterization ◽  
Synthesis Methods ◽  
And Performance ◽  
Carbon Based

In recent years, a new class of superior heterogeneous acid catalyst for biodiesel production has emerged. These catalysts offer advantages over their predecessors such as high surface area, elevated acid site density, enhanced catalyst activity, good operation stability and relevant economic affordability in an environmentally friendly frame. This review was concerned with carbon-based solid acid (CBAS) catalysts derived from both carbohydrate and pyrolysis products. A series of CBASs with various origins such as D-glucose, sucrose, starch, cellulose and vegetable oil asphalt, converted to char and sulphonated, have been explored as potential heterogeneous catalysts. Catalyst preparation and synthesis methods were briefly summarized. Catalyst characterization and performance for biofuels related reactions were elucidated, identifying potential research applications. Three catalysts in particular were identified as having potential for industrial application and requiring further research.

scholarly journals Multiscale computing for science and engineering in the era of exascale performance

2019 ◽  
Vol 377 (2142) ◽  
pp. 20180144 ◽  
Author(s):  
Alfons G. Hoekstra ◽  
Bastien Chopard ◽  
David Coster ◽  
Simon Portegies Zwart ◽  
Peter V. Coveney
Keyword(s):  
Multiscale Model ◽  
Multiscale Simulation ◽  
Multiscale Models ◽  
Theme Issue ◽  
Science And Engineering ◽  
High Performing ◽  
The Face ◽  
Strong Scaling ◽  
Computing Environments ◽  
Modelling Simulation

In this position paper, we discuss two relevant topics: (i) generic multiscale computing on emerging exascale high-performing computing environments, and (ii) the scaling of such applications towards the exascale. We will introduce the different phases when developing a multiscale model and simulating it on available computing infrastructure, and argue that we could rely on it both on the conceptual modelling level and also when actually executing the multiscale simulation, and maybe should further develop generic frameworks and software tools to facilitate multiscale computing. Next, we focus on simulating multiscale models on high-end computing resources in the face of emerging exascale performance levels. We will argue that although applications could scale to exascale performance relying on weak scaling and maybe even on strong scaling, there are also clear arguments that such scaling may no longer apply for many applications on these emerging exascale machines and that we need to resort to what we would call multi-scaling . This article is part of the theme issue ‘Multiscale modelling, simulation and computing: from the desktop to the exascale’.

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