Acidic nanomaterials (TiO2, ZrO2, and Al2O3) are coke storage components that reduce the deactivation of the Pt–Sn/γ-Al2O3 catalyst in propane dehydrogenation

Abstract

Pt–Sn/γ-Al₂O₃ catalysts were physically mixed with various nanostructured metal oxides (TiO₂, ZrO₂, and Al₂O₃) and investigated as catalysts for propane dehydrogenation at 550 °C and atmospheric pressure. The additives did not affect the catalytic activity or selectivity for the main product (propylene), but they markedly enhanced the catalyst stability. The benefit arose because coke deposition on Pt–Sn/γ-Al₂O₃ decreased by approximately 3%, 19%, and 32% as a result of addition of Al₂O₃, ZrO₂, and TiO₂, respectively. The deposits of both aliphatic and aromatic coke on the Pt–Sn/γ-Al₂O₃ catalysts were reduced when the additives were present, as shown by temperature-programmed oxidation, infrared, and ultraviolet-visible data characterizing the used catalysts. Catalyst characterization data including surface areas, temperature-programmed reduction profiles, NH₃ (and O₂) temperature-programmed desorption profiles, X-ray photoelectron spectra, CO-chemisorption data, and in situ differential scanning calorimetry data show that the number of oxygen vacancy defect sites play a key role in the adsorption of coke precursors generated on Pt particles, leading to decreased coke deposition on Pt–Sn/γ-Al₂O₃ and, correspondingly, increased coke deposition on the acidic additives. Moreover, an in situ infrared investigation of propadiene adsorption led to the conclusion that aliphatic coke is transformed into aromatic coke and that this transformation is related to the deep dehydrogenation reaction.