(344k) Conversion of Methane to Methanol in Cu-Exchanged SSZ-13

Selective conversion of methane to higher valued methanol has remained a challenge, which has gained significant attention recently due to the increased availability of natural gas. The major challenge for this reaction is to only activate the first C-H bond without converting methane to the thermodynamically stable, overoxidized products CO and CO₂. One promising method to accomplish high selectivity to methanol is in the stepwise conversion of methane to methanol over Cu exchanged zeolites [1,2]. Despite significant efforts, the nature of the active sites during this process is still under debate.

We have developed a thermodynamic model for Cu-SSZ-13 used to evaluate the stability of many unique Cu active sites and terminations including Cu monomers, as well as Cu-oxo and –hydroxy dimers and trimers bound to a series of local Al configurations. Using phase diagrams, we then studied the thermodynamically favored sites under different reaction conditions, and we found that the most stable Cu active site depends on the activation process used. Based on these predictions, we designed experiments to stabilize the desired active sites and evaluated the impact of the active site structure on the performance in the stepwise conversion of methane to methanol. We expect that the insights obtained here can be used to further improve and optimize the stepwise conversion of methane to methanol.

References

[1] Ravi, M.; Sushkevich, V. L.; Knorpp, A. J.; Newton, M. A.; Palagin, D.; Pinar, A. B.; Ranocchiari, M.; Bokhoven, J. A. V. Nature Catalysis 2019, 2 (6), 485–494.

[2] Ipek, B.; Wulfers, M. J.; Kim, H.; Göltl, F.; ACS Catalysis 2017, 7 (7), 4291–4303.