A synthesis route for preparing ITQ-13, a tridirectional medium-pore zeolite containing 9- and 10-member ring pores, has been found that allows the introduction of framework Al by direct synthesis. It has been shown that ITQ-13 can also be prepared in a fluoride-free media. The directly synthesized Al containing ITQ-13 sample presents acid sites as strong or even stronger than ZSM-5. The strong electric field gradient in ITQ-13 and the smaller pore dimensions are responsible for the strong acidity and shape selectivity that increases the production of propylene during the cracking of vacuum gasoil compared with ZSM-5.