Chemical Reactivity, Catalysis, and Surface Processes
Catalysis in Molecular Context
Catalytic Cycles
Catalysts accelerate reactions by offering alternative pathways with lower barriers while being regenerated at the end of the cycle. Understanding catalytic turnover requires tracking intermediates, ligand exchange, redox events, and rate-limiting transformations.
Homogeneous and Heterogeneous Catalysis
Homogeneous catalysts act in the same phase as reactants and often provide fine electronic control, while heterogeneous catalysts operate at surfaces or interfaces and benefit from adsorption, cooperative sites, and transport effects.
Interface Insight
At surfaces, adsorption energy, coverage, and site heterogeneity can be as important as intrinsic chemical barriers.
Catalysis Types
Homogeneous
- Molecularly defined active sites
- Excellent mechanistic tunability
Heterogeneous
- Robust and scalable
- Complex surface-site distributions
What is a defining feature of a catalyst?
A catalyst provides an alternative pathway and is not consumed overall.
Correct answer: It lowers the activation barrier and is regenerated.
Why are adsorption effects important in heterogeneous catalysis?
Surface binding shapes coverage, orientation, activation, and desorption.
Correct answer: they determine how reactants bind and react at the surface
Reaction Networks and Selectivity
Modern catalytic analysis often treats reactions as networks rather than single-step transformations. Selectivity arises from branching ratios, intermediate lifetimes, transport limitations, and competing energetics across multiple pathways.
Catalyst Evaluation Checklist
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1
Identify active species and turnover protocol.
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2
Measure activity, selectivity, and stability under operating conditions.
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3
Probe intermediates with spectroscopy or kinetics.
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4
Compare proposed barriers and energetic span.
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5
Assess deactivation, poisoning, and regeneration pathways.