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Structural studies of high dispersion H3PW12O40/SiO2 solid acid catalysts
Andrew D Newman1, D Robert Brown, Prem Siril
1Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Physical Chemistry Chemical Physics : PCCP
|June 16, 2006
Summary
This study synthesized H(3)PW(12)O(40)/SiO(2) catalysts, revealing that interfacial species enhance reactivity for non-polar hydrocarbons. Higher loadings favor polar chemistry by utilizing a pseudo-liquid phase.
Area of Science:
- Heterogeneous catalysis
- Materials science
- Surface chemistry
Background:
- Silica-supported heteropoly acids like H(3)PW(12)O(40) are crucial catalysts.
- Understanding the structure-activity relationship at the interface is key for catalyst design.
Purpose of the Study:
- To synthesize and characterize highly dispersed H(3)PW(12)O(40)/SiO(2) catalysts.
- To investigate the influence of catalyst loading on interfacial species and acid properties.
- To correlate catalyst performance with hydrocarbon polarity.
Main Methods:
- Synthesis of H(3)PW(12)O(40)/SiO(2) catalysts with varying loadings (3.6-62.5 wt%).
- Characterization using X-ray Photoelectron Spectroscopy (XPS) and Extended X-ray Absorption Fine Structure (EXAFS).
- Ammonia adsorption calorimetry to determine acid strength and properties.
Main Results:
- XPS identified a distinct interfacial H(3)PW(12)O(40) species due to W atom perturbation at the SiO(2) interface.
- EXAFS confirmed the Keggin unit integrity across all loadings.
- Acid strength was largely invariant with loading, but lower loadings showed weaker acidity.
- Interfacial species correlated with higher reactivity for non-polar hydrocarbons.
Conclusions:
- Catalyst performance is dictated by the interplay between interfacial species and bulk H(3)PW(12)O(40) properties.
- High dispersion and accessible interfacial tungstate favor non-polar hydrocarbon reactions.
- Higher loadings, enabling a pseudo-liquid phase, are beneficial for polar chemistry.
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