A.A.C. Reule, J. Shen, N. Semagina
ChemPhysChem, 19, 1500-1506
Publication year: 2018

Mutual ion effects: In bimetallic CuZn/MOR, zinc prevents copper sintering, whereas copper promotes zinc ion exchange into 12‐ instead of 8‐membered rings:

Bimetallic ion exchange on a zeolite often impacts its catalytic properties compared to its monometallic counterparts. Here, we address the synergistic effect of simultaneous copper and zinc ion exchange on mordenite (MOR), as found earlier for dimethyl ether (DME) carbonylation. Samples with various Cu/Zn ratios were characterized by diffuse‐reflectance infrared Fourier‐transform spectroscopy (DRIFTS) in the 3600 and 720 cm−1regions, pore distribution analysis through Ar physisorption, X‐ray photoelectron spectroscopy (XPS), temperature‐programmed reduction (TPR), and transmission electron microscopy (TEM). When ion‐exchanged alone, copper preferentially occupies 12‐membered rings, whereas zinc occupies 8‐membered rings. In bimetallic combinations, the zinc addition was found to prevent the copper from sintering into nanoparticles and to increase its coordination strength to the zeolite. At a Cu/Zn ratio of 0.25 (for MOR with Si/Al=6.5), copper promotes zinc ion exchange into 12‐membered rings, more specifically, into T4 sites that are known for the formation of the coke precursor in DME carbonylation on a MOR. The sites became blocked during the bimetallic ion exchange, leading to suppressed catalyst deactivation. The study contributes to the understanding of mutual ion effects in bimetallic exchanged zeolites and highlights the major role of copper as a governing factor in determining the location of co‐exchanged zinc on a MOR. © 2018 Wiley-VCH.

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