Basic reactivity of CaO: investigating active sites under operating conditions
Hugo Petitjean1, Céline Chizallet, Jean-Marc Krafft
1UPMC, University Paris 06, UMR 7197, Laboratoire de Réactivité de Surface, F-75005 Paris, France. hugo.petitjean@enscm.fr
Physical Chemistry Chemical Physics : PCCP
|October 15, 2010
Summary
The basic reactivity of calcium oxide (CaO) catalysts is determined by surface hydroxyl groups, not surface defects. Higher surface density of OH groups on CaO leads to increased basic reactivity, even after high-temperature pre-treatment.
Area of Science:
- Heterogeneous Catalysis
- Surface Chemistry
- Materials Science
Background:
- Calcium oxide (CaO) is a promising solid base catalyst.
- Surface properties of CaO significantly influence its catalytic activity.
- Reversible rehydration of CaO occurs during storage.
Purpose of the Study:
- To investigate the factors controlling the basic reactivity of CaO catalysts.
- To identify the active sites responsible for the catalytic conversion of 2-methylbut-3-yn-2-ol.
- To understand the role of surface hydroxyl groups and defects in CaO's basicity.
Main Methods:
- Preparation of CaO samples via thermal decomposition of various precursors.
- Pre-treatment of CaO at 1023 K under nitrogen flow.
- Characterization of surface properties including specific surface area and photoluminescence.
- Quantification of surface hydroxyl groups using proton nuclear magnetic resonance ((1)H NMR).
- Evaluation of basic reactivity through 2-methylbut-3-yn-2-ol conversion.
Main Results:
- CaO samples exhibited varying basic reactivity despite similar surface areas after pre-treatment.
- Basic reactivity did not correlate with surface defect concentration or deprotonation ability towards methanol.
- A positive correlation was found between the surface density of OH groups and basic reactivity.
- Surface hydroxylation remained the governing factor for basic reactivity even after high-temperature pre-treatment.
Conclusions:
- Surface hydroxyl groups, not surface defects, are the primary active sites governing the basic reactivity of pre-treated CaO.
- The density of surface OH groups dictates the catalytic performance of CaO in reactions like 2-methylbut-3-yn-2-ol conversion.
- The intrinsic reactivity of OH groups on CaO is higher than on Ca(OH)(2) and MgO.
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