Understanding C-H activation in light alkanes over Cu-MOR zeolites by coupling advanced spectroscopy and...

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Direct methane to methanol (MTM) conversion is a crucial industrial process.
• Cu-oxo sites in zeolites are key catalysts for MTM, but their reduction behavior is not fully understood.
• Understanding metal-oxo site oxidation and C-H activation is essential for catalyst design.

Purpose of the Study:

• To elucidate the evolution of copper (Cu) species during the reduction phase of MTM.
• To correlate Cu speciation changes with methane consumption and CO2 production.
• To investigate the atomic structure of active Cu sites using advanced spectroscopic techniques.

Main Methods:

• Temperature-programmed reduction experiments using methane (CH4), ethane (C2H6), and carbon monoxide (CO) as reductants.
• X-ray absorption spectroscopy (XAS), UV-vis, and FT-IR spectroscopy to monitor Cu speciation.
• Multivariate curve resolution alternating least-square (MCR-ALS) and wavelet transform (WT) analysis for spectral deconvolution and atomic structure determination.

Main Results:

• Identified up to six distinct Cu(II) and Cu(I) species during reduction using MCR-ALS analysis of XANES spectra.
• Established a direct correlation between Cu(II) to Cu(I) reduction, CH4 consumption, and CO2 production.
• Observed a reducibility-activity relationship for Cu-MOR zeolites and resolved atomic speciation up to 4 Å using WT analysis of EXAFS.

Conclusions:

• All identified Cu(II) components are multimeric Cu(II)-oxo sites with varying Cu-Cu distances.
• The study provides detailed insights into the dynamic changes of copper active sites during catalytic reduction.
• Findings advance the understanding of C-H activation mechanisms and inform the design of improved MTM catalysts.