Elucidating the nature and role of Cu species in enhanced catalytic carbonylation of dimethyl ether over Cu/H-MOR

Abstract

To investigate the role of Cu species in dimethyl ether (DME) carbonylation over Cu/H-MOR catalysts, ion-exchange with copper ammonia solution (Cu/H-M(x)) and solid state ion-exchange with CuCl (SSIE Cu/H-M(x)) methods were applied to prepare a series of samples with different Cu loadings. Compared to H-MOR, the reduced Cu/H-M(x) samples dramatically facilitated the conversion of DME, in which Cu⁺ and Cu⁰ species as well as Brønsted acid sites coexisted. Physical adsorption, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were carried out to prove the negligible influence of the preparation processes on the textural and morphological properties of MOR. Fourier transform infrared (FTIR) spectroscopy, adsorption of pyridine, CO temperature programmed desorption (CO-TPD), and X-ray photoelectron spectroscopy (XPS) were employed to qualitatively and quantitatively explore the variation of both Brønsted acid sites and Cu species in 8-membered ring (8-MR) and 12-membered ring (12-MR) channels. With an increase of the Cu dopant, the amount of Cu⁰ increased gradually while Cu⁺ had no obvious regularity. The relationship between Cu⁰ and catalyst activity was established for Cu/H-M(x) catalysts. In addition, the formation of methyl acetate (MA) over SSIE Cu/H-M(x) catalysts decreased sharply with increasing Cu⁺ loading, which further excluded the promoting effect of Cu⁺ species present in MOR.