Determination of the Acid Strength of Binary Oxide Catalysts Using Temperature-Programmed Desorption of Pyridine

Abstract

Abstract The temperature-programmed desorption of pyridine (Py-TPD) was performed for measuring the acid strength and acid amount of binary oxide catalysts. First, the optimum measurement conditions were determined by comparing the TPD spectra with the infrared spectra of adsorbed pyridine measured under the same conditions in order to minimize the shift in the desorption temperature and contribution of physically absorbed and/or weakly held pyridine. The following conditions were found to be optimum: purging at 423 K for 2 h, W/F (W, sample weight; F, flow rate of the carrier) of 100 mg/150 cm 3 min −1, and a heating rate of 5 K min−1. This method was applied then to a series of binary mixed oxide catalysts. The amount of desorbed pyridine was 15—24% of the full coverage of pyridine on the catalyst surface with few exceptions. The highest acid strength, determined from the Py-TPD spectra, was well-correlated to that determined from a color change of Hammett indicators. The potential of the Py-TPD for determining the acid strength and the acid amount on binary oxide catalysts is discussed.