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

Pt-Sn/γ-Al2O3 catalysts were physically mixed with each of various nanostructured metal oxides (TiO2, ZrO2, and Al2O3) and investigated as catalysts for propane dehydrogenation at 550 oC 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 the 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 of coke deposition on the Pt-Sn/γ-Al2O3 and, correspondingly, increased coke 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.