Effect of acid leaching and catalytic properties of zeolite [Al,B]-MWW utilized as ethene methylation catalyst

Hydrothermally synthesized H-[Al,B]-MWW zeolite was dealuminated with oxalic, nitric and citric acids. The obtained samples were characterized with XRD, ICP-AES, FT-IR, NH3-TPD, pyridine-adsorption IR, 27Al MAS NMR techniques and nitrogen sorption experiment. Citric acid mainly removed the acid sites located on the external surface pockets with small amounts of extraframework Al species retained in the interlayer void space, while nitric acid leached both the internal (sinusoidal channels and supercages) and the external surface (side pockets) acid sites although significant amounts of extraframework Al species were generated in the sinusoidal channels. As for the oxalic acid, it primarily eliminated the acid sites in the supercages and side pockets without generation of considerable amounts of extraframework Al species in the internal channels, consequently greatly increasing the catalytic stability of the sample in methylation of ethene by methanol. The sample dealuminated with oxalic acid for 24 h showed a catalytic life of 300 h as a result of a reduction in coking rate.