Attenuated total reflectance infrared (ATR-IR) spectroscopy was used to characterize the vibrational structure of H 2 O within the pores of zeolite samples with different densities of (SiOH) x . Zeolites (~30 mg) were first dispersed into CH 3 CN (~1 cm 3 ) via sonication and were subsequently drip coated onto a ZnSe cylindrical internal reflection element (IRE; International Crystal Labs). The catalyst-coated IRE was loaded into an ATR flow cell (Axiom, TNL-120), which was mounted onto a Fourier-transform infrared spectrometer (Bruker, Vertex 70). The cell was heated by a resistive heating cartridge placed within the wall of the cell, which was controlled by an electronic temperature controller (Watlow, EZ-Zone). Samples were first pretreated at 423 K (5 K min -1 ) for 2 h in flowing He (10 cm 3 min -1 ) to desorb CH 3 CN that was present from the catalyst deposition. Background spectra (2500 scans, 1 cm -1 resolution) were then taken at 303 K in He. H 2 O was subsequently introduced (1 cm -1 min -1 ) using a high-pressure piston pump (SSI, Series 1) and spectra (2500 scans, 1 cm -1 resolution) were acquired at a desired temperature (303 -343 K).