Quantifying Kinetically Relevant Species on Zr-SiO₂ Materials for MPV Reduction

Area of Science:

• Heterogeneous catalysis
• Materials science
• Surface chemistry

Background:

• Supported metal catalysts like Zr-SiO2 present challenges in distinguishing active site properties from environmental influences.
• Accurate characterization of active sites is crucial for understanding and optimizing catalytic performance.

Purpose of the Study:

• To quantitatively describe kinetically relevant zirconium (Zr) species on Zr-SiO2 catalysts using in-situ titration.
• To elucidate the role of different Zr species in the Meerwein-Ponndorf-Verley (MPV) reduction of cyclohexanone.

Main Methods:

• In-situ titration of Lewis acid sites with phosphonic acid to quantify Zr species.
• Meerwein-Ponndorf-Verley (MPV) reduction of cyclohexanone using Zr-SiO2 catalysts.
• Comparison of phosphonic acid titration with UV-vis spectroscopy for Zr dispersion analysis.

Main Results:

• Catalytic activity for MPV reduction correlates with both titratable (well-dispersed Zr) and non-titratable (supported ZrOx) Zr species.
• The fraction of well-dispersed Zr depends on surface grafting density, not the Zr precursor.
• Phosphonic acid titration provides a more relevant and quantitative measure of Zr dispersion than UV-vis.

Conclusions:

• Phosphonic acid titration is an effective method for quantitatively characterizing Zr dispersion and active sites on Zr-SiO2 catalysts.
• This technique can monitor changes in the catalyst material during regeneration, offering insights into catalyst stability and reusability.