The 15 N{ 1 H} cross polarization magic angle spinning (CPMAS) NMR spectrum of SZO300 contacted with 15 N-pyridine after evacuation at room temperature for 30 min contains a signal at 200 ppm assigned to pyridinium sites and a second signal at 271 ppm for pyridine adducts of SO3 (see the Supporting Information). At higher pyridine surface coverage a third signal at 277 ppm appears, which is assigned to either weak Brønsted or weak Lewis sites (Figure ). 17