Tuning Copper Active Site Composition in Cu-MOR through Co-Cation Modification for Methane Activation

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Direct methane to methanol conversion offers environmental and economic advantages.
• Copper mordenite zeolites are effective catalysts for this reaction, particularly at low temperatures.
• Previous studies identified [CuOCu]2+ and [CuOH]+ sites in mordenite, but the active site for low-copper methane activation remained unknown.

Purpose of the Study:

• To investigate copper speciation in Na+ mordenite with varying copper loadings.
• To identify the active site responsible for methane activation at low copper concentrations.
• To develop a novel method for active site identification in heterogeneous catalysts.

Main Methods:

• Utilized varying copper loadings in Na+ mordenite.
• Employed spectroscopic analysis to study copper speciation.
• Manipulated co-cation composition to differentiate overlapping spectroscopic signals.

Main Results:

• Discovered a new active site, labeled 'MOR3', at low copper loadings.
• Observed significant spectroscopic signal overlap between MOR3 and the [CuOH]+ site.
• Successfully differentiated MOR3 by altering the co-cation, identifying it as a [CuOCu]2+ site.

Conclusions:

• The active site for methane activation in copper mordenite at low loadings is a [CuOCu]2+ species (MOR3).
• Changing co-cation composition is an effective strategy to resolve overlapping signals and identify active sites in heterogeneous catalysts.
• This approach has broad implications for the study and optimization of copper zeolites in methane conversion and NOx catalysis, as well as heterogeneous catalysis in general.