Zeolite Mixes Up Pore Sizes To Good Effect

A complex zeolite with differently sized, interlocking pores shows promise for converting naphtha to diesel fuel while avoiding fouling by residual carbon that can sideline some catalysts (Nat. Chem., DOI: 10.1038/nchem.1253). Aluminosilicate zeolites with pores bounded by either 10 or 12 silicon or aluminum atoms are important petrochemical catalysts, raising interest in a material that combines the two pore sizes. A group led by Xiaodong Zou of Stockholm University and Avelino Corma of Polytechnic University of Valencia, in Spain, has synthesized just such a zeolite and solved its structure using electron crystallography of nanometer-sized crystals. Called ITQ-39, the material contains intersecting 10- and 12-ring channels that run perpendicular to each other. The diameters of the channels are about 6 Å and 7 Å, respectively. In tests of naphtha alkylation, ITQ-39 performed better than commercial zeolite catalysts.The researchers believe the 12-ring channels promote the formation and diffusion of alkylated products, whereas the 10-ring channels prevent coke deposits by precluding the formation of polyaromatic precursor molecules.