Adsorption/desorption diffusion

To specify these transition probabilities we make the further assumption that the residence time of a particle in a given adsorption site is much longer than the time of an individual transition to or from that state, either in exchange with the gas phase in adsorption and desorption or for hopping across the surface in diffusion. In such situtations there will be only one individual transition at any instant of time and the transition probabilities can be summed, one at a time, over all possible processes (adsorption, desorption, diffusion) and over all adsorption sites on the surface. To implement this we first write... 

Development of Advanced Reservoir Characterisation and Simulation Tools for Improved Coalbed Methane Recovery. Led by Imperial College of Science Technology and Medicine, the main objective of this project is to develop technology and tools to more accurately assess the potential for improved methane recovery and COj sequestration by investigating the basic scientific phenomena of COj coal injection and retention. The researchers primary objective is to achieve a more comprehensive understanding of the fundamental mechanisms of water and CO2-CH4 adsorption/desorption, diffusion/counter diffusion, and 2-phase flow under simulated reservoir conditions (stress, pore pressure, and temperature). The results of these studies will then be applied to design of a CO2-ICBM recovery and COj sequestration simulator for the European industry. 

In order to get a more realistic description of surface reactions energetic interactions must be taken into account. We introduced in Section 9.2.1 a general model which is able to handle systems which include mono- and bimolecular steps like adsorption, desorption, diffusion and reaction [38]. Here we apply this model to an extended version of the ZGB-model which incorporates particle diffusion and desorption [41]. 

Analysis of structure formation processes by using Monte Carlo methods. Monte Carlo methods will he used extensively for the calculation of processes during which new phases are formed. In particular, these are adsorption-desorption, diffusion, and reactions on the surfaces of solids. The results of this modelling will be used to decode structures formed on catalyst surfaces. 

Photochemistry on solid surfaces has unveiled the important role of sufaces as reactant media. Solid surfaces work as acids or bases sensitizers or quenchers reaction space for size-specific reactions seed crystals for epitaxial growth etc. Thus, the molecule-surface interaction enhances or reduces photoabsorption, reaction rates, and selectivities. Since there are a lot of parameters for surface reactions, such as adsorption, desorption, diffusion, nucleation etc., it has been difficult to control the photochemistry on solid surfaces. Recently, as it becomes possible to characterize the surface conditions with techniques of ESCA, SIMS, and STM and also to use new light sources, new research field appears as Surface Photochemisty ". 

The two standard approaches in any treatment of kinetics [28] are to explain the system in terms of me thermodynamic driving forces (namely, VjJ.) or in terms of the fnndamental rate eqnations. The rate equations can be fnrther subdivided into an atomistic, or microscopic, approach that accounts for individual molecules as they go through the various processes (adsorption, desorption, diffusion, capture, and release) or a phenomenological, or macroscopic, explanation that looks for correlations and the so-called scaling laws over large distances (much larger than the lattice spacing). 

In this section the dynamics of film growth will be discussed in terms of the steps mentioned earlier adsorption, desorption, diffusion, attachment, and nucleation. The dynamics of the first monolayer can be explained by calculating the density of islands... 

The SHG and SFG techniques are also suitable for studying dynamical processes occurring on slower time scales. Indeed, many valuable studies of adsorption, desorption, diffusion and other surface processes have been performed on time scales of milliseconds to seconds. 

Infrared "Macro"- and "Mkro"-Spectroscopic Investigations of Adsorption, Desorption, Diffusion, and Co- and Counter-Diffusion in Zeolites... 

The complexity of the catalytic reaction is a common thread through most of the chapters that follow. We describe the issues associated with the different time and length scales that underpin the chemical events that constitute a catalytic system. For example, a typical time scale for the overall catalytic reaction is a second with characteristic length scales that are on the order of 0.1 micron. The time scales for the fundamental adsorption, desorption, diffusion and surface reaction steps that comprise the overall catalytic cycle, however, are often 10 sec or shorter. The time scales associated with the movement of atoms, such as that which must occur for surface reconstruction events, may be on the order of a nanosecond. The vibrational frequencies for adsorbed surface intermediates occur at time scales on the order of a few picoseconds. The different processes that occur at these time scales obey different physical laws and, hence, require different methods in order to calculate their influence on reactivity. In this book we will show how the... 

We conjecture that the actual adsorption mechanism results in a source term rather than a storage that provides a coefficient to the term dc/dt. This perspective, however, is relevant only if the theory is developed through a formulation that couples the microscale phenomena with the macroscale behavior. This is because in the classical theory, it is simple to evaluate an experimental result macroscopically due to adsorption as Kd. Here we will develop an alternative adsorption/desorption/diffusion theory, which is based on MD (molecular dynamics) and HA (homogenization analysis). 

The first stages of deposition from a vapour, are generally divided into three steps adsorption-desorption, diffusion-migration, and nucleation and growth, schematized on Fig. 5.1. 

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