Preparation of Spherical Mordenite Zeolite Assemblies with Excellent Catalytic Performance for Dimethyl Ether...

Millimeter-sized spherical mordenite (MOR) zeolite with good mechanical strength was successfully prepared via vapor-assisted transformation of Na- and Al-doped SiO₂ spheres. It is demonstrated that the precursor prepared by vacuum impregnation is essential for the achievement of well-retained morphology; the presence of organic amine (such as TEAOH, TMAOH, and HMI) in the vapor can help promote the crystallization, avoid the core-shell morphology, and improve the zeolite Si/Al ratio, although the MOR crystal morphology in the spherical products varies with the choice of organic amines. The resultant MOR-TEAOH spheres, which were synthesized under the assistance of TEAOH, possess large amount of Brønsted acid sites in the 8-MR side pockets (0.76 mmol/g), which is about 3 times higher than in the 12-MR main channels. The preferential siting of H⁺ sites in the 8-MR helps MOR-TEAOH show excellent catalytic performance in the DME carbonylation reaction. A 90% of DME steady conversion is observed on MOR-TEAOH, which is obviously higher than that on commercial sample (23%). This work offers millimeter-scale spherical MOR with good mechanical strength and excellent catalytic performance, which is very promising for the industrial applications.