Fourier-transform infrared study of pyridine sorbed on zeolite HY

Abstract

Adsorption of pyridine on zeolites can show three modes of sorption: physisorption, sorption on the LF hydroxyls and sorption on the HF hydroxyls. In this study a separate IR spectrum was obtained for each of the three sorbed pyridine species and major differences were observed, especially in the ring-bending and stretching region (2000 to 1200 cm-'). A comparison of the spectra showed that pyridine sorbed on the LF hydroxyls is not physisorbed, but protonated to some degree. H/D exchange enabled the IR spectrum of the bonded Brlansted proton to be obtained for pyridine sorbed on the HF hydroxyl sites which proved to be a broad band from ca. 3600 to ca. 2600 cm-'. For pyridine sorbed on the LF hydroxyls, a broader more complex band was observed from ca. 3700 to ca. 2200 cm-'. Reversible sorption/desorption occurred for physisorbed pyridine and pyridine sorbed on the LF hydroxyls, but complete desorption of pyridine from the HF hydroxyls resulted in loss of acid sites.

Metal–Acid Synergy: Hydrodeoxygenation of Anisole over Pt/Al‐SBA‐15

“…The nature of the acid sites was further probed by using pyridine diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS; Figure ) . Unfunctionalized SBA‐15 did not exhibit any adsorption bands characteristic of chemisorbed pyridine in accordance with previous results .…”

Octyl Co‐grafted PrSO3H/SBA‐15: Tunable Hydrophobic Solid Acid Catalysts for Acetic Acid Esterification

“…The surface acid site loading of the Oc/PrSO 3 H‐SBA‐15 family was lower than the parent PrSO 3 H/SBA‐15 owing to a combination of the extra mass from octyl groups, and slight loss of thiol groups during the second grafting step. DRIFTS studies of pyridine adsorption confirm the presence of Brønsted acidic sites with bands at 1489, 1545, and 1637 cm −1 , indicative of pyridinium ion formation (Figure S4 in the Supporting Information).…”

Probing the acid sites of zeolites with pyridine: Quantitative AGIR measurements of the molar absorption coefficients

“…Py adsorption on zeolites is typically performed at 30-150°C followed by the removal of physisorbed Py species, which are held on the zeolite surface by weak hydrogen-bonding and vander-Waals interactions giving rise to the peaks at 1585-1595 and 1438-1445 cm -1 [1,45]. The effect of physisorbed Py on the intensity of the IR bands is exemplified by the spectra obtained for BEA-12 zeolite after Py desorption at 200°C ( Figure 6).…”