Catalysis notes 2 - Reaction Mechanisms and Kinetics Recall...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
IIb-1 Reaction Mechanisms and Kinetics Adsorption Surface reaction Desorption Recall that there are 7 steps to a heterogeneous catalytic reaction, i.e., (1) external mass transfer from bulk to catalyst external surface; (2) diffusion into pores; (3) adsorption; (4) surface reaction; (5) desorption; (6) diffusion out of pores; and (7) mass transfer from external surface to bulk fluid phase. Three of these steps are considered part of the catalytic reaction mechanism . They are: So, the catalytic reaction mechanism includes the events involving the catalytic surface or species adsorbed on the catalyst surface A A B B C C D D
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Catalytic reaction mechanism The model most often used to describe catalytic reactions is the Langmuir-Hinshelwood (also called Hougen-Watson, or LHHW) model. The reaction mechanism is written as a series of elementary steps, e.g.: The rate expression for an elementary step follows mass action kinetics; e.g., for the step (irreversible adsorption of A), the elementary step rate is The catalytic reaction rate is assumed to be equal to the rate of the intrinsically slowest elementary step in the mechanism (the rate limiting step, rls; also called the rate determining step). A(g) + s ← → A s B(g) + s ← → B s A s + B s ← → C s + D s C s ← → C(g) + s D s ← → D(g) + s s A s g A A k → + ) ( v A A A C P k r = A.s represents chemisorbed A. Generally, one
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 11

Catalysis notes 2 - Reaction Mechanisms and Kinetics Recall...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online