2: Adsorption of Molecules on Surfaces
- Page ID
- 25349
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 2.1: Introduction to Molecular Adsorption
- This page emphasizes the critical role of adsorption in surface-mediated chemical processes, especially in surface-catalyzed reactions, comprising five main steps: diffusion of reactants, adsorption, surface reaction, desorption, and diffusion of products. It underscores the importance of adsorption and desorption while defining key terms like substrate, adsorbate, adsorption, coverage, and exposure.
- 2.2: How do Molecules Bond to Surfaces?
- This page explains two types of adsorption: physisorption, which relies on weak Van der Waals forces, and chemisorption, which involves stronger chemical bonds and electron reorganization. It highlights their differences in characteristics like specificity, temperature, enthalpy, and kinetics. Additionally, it emphasizes the importance of spectroscopic techniques such as IR and UPS in verifying chemisorption by detecting bond formation between the adsorbate and substrate.
- 2.3: Kinetics of Adsorption
- This page discusses the kinetics of molecular adsorption on surfaces, highlighting how the adsorption rate, \(R_{ads}\), correlates with gas partial pressure and molecular flux. It emphasizes the role of sticking probability, which depends on surface coverage and activation energy, often showing first-order behavior.
- 2.4: PE Curves and Energetics of Adsorption
- This page covers adsorption energetics and kinetics, using a potential energy diagram to illustrate the adsorption process. It distinguishes between physisorption, characterized by weak van der Waals forces, and chemisorption, which involves stronger chemical bonds. The energy variations with adsorbate distance and the effects of surface coverage, activation energies, and barriers on adsorption and desorption processes are examined.
- 2.5: Adsorbate Geometries and Structures
- This page explores the adsorption of molecules on metal surfaces, detailing local geometry and adsorbate structures. It highlights chemisorption behaviors of hydrogen, halogens, oxygen, nitrogen, and carbon monoxide. Hydrogen and halogens tend to dissociate upon adsorption, while oxygen forms strong bonds. The page also examines bonding characteristics of carbon monoxide and ammonia, addressing limitations of simple models and the role of coordination sites.
- 2.6: The Desorption Process
- This page examines the behavior of adsorbed species on surfaces across different temperatures, emphasizing that higher temperatures can lead to decomposition, reaction with substrates, or desorption. It highlights the desorption process, typically involving the same species as the adsorbate, and discusses desorption kinetics, including the influence of surface concentration and activation energy on the desorption rate.