# Influence of Aluminum Distribution in Cu-MOR Systems on Methane-to-Methanol Conversion: A Combined Experimental and Theoretical Study

## TL;DR

This study shows how the distribution of aluminum in copper-mordenite systems affects the conversion of methane to methanol, combining experiments and theory.

## Contribution

The paper establishes a synthesis-structure–activity relationship for mordenite in methane conversion, linking pore geometry and copper speciation.

## Key findings

- Aluminum distribution near 12-ring openings improves MTM activity compared to 8-ring openings.
- DFT simulations and spectroscopy reveal structural and electronic effects of different synthesis conditions on copper species.
- K+-based synthesis leads to more reactive Cu-MOR systems with acute Cu–O–Cu angles.

## Abstract

A series of copper-mordenite (MOR) samples of different
provenances
were investigated in the methane-to-methanol (MTM) reaction after
preparing their copper-exchanged analogues. Noticeable activity improvements
were observed when biasing the Al framework distribution of the confined
side-pocket toward 12-ring openings (T2 and T4 enrichment) over 8-ring
openings (T1 and T3), achieved by using K+ or Na+ in the synthesis gel, respectively. This was rationalized by performing
a geometry optimization algorithm using density functional theory
(DFT) simulations, which revealed distortions in the structure of
the pores among different idealized zeolite models. From this, effects
on the copper species were observed, as evidenced from both electron
paramagnetic resonance (EPR) spectroscopy and operando X-ray absorption spectroscopy (XAS), which suggested varying monomeric
[Cu]2+/[CuOH]+ concentrations with intrinsic
copper reducibility differences. Monte Carlo simulations on selected
MOR structures of the experimental series exposed dimeric structures
with more acute Cu–O–Cu angles, thereby suggesting a
more reactive system for Cu-MOR based on K+ in the synthesis
gel, in line with the experimental finding. The combined insights
from simulations, calculations, and experiments have enabled us to
establish a synthesis-structure–activity relationship for mordenite
in methane conversion, highlighting the reactive interplay between
pore geometry and copper speciation.