We used a flexible organic structure-directing agent (OSDA) and high-throughput (HT) synthesis techniques to explore a large composition region. A zeolite with the largest pores reported to date (ITQ-33) was found under very unusual synthesis conditions, together with other known structures. A second HT experimental design allowed, finally synthesizing pure ITQ-33. We studied the thermal and hydrothermal stability and acid properties of the zeolite. We investigated the role of pore diameter on zeolite acid strength by comparing the 18-ring pore (ITQ-33) with a 12-MR pore (ITQ-17) zeolite with the same framework composition. Finally, we compared the catalytic properties of ITQ-33 for reactant molecules of different sizes with those of 12-MR (Beta) and 14-MR (UTD-1) zeolites. (c) 2007 Published by Elsevier Inc.