Impact of acidity in ZrO_2-TiO_2-Al_2O_3 composite oxides on the catalytic activity and coking behaviors during n-decane cracking

摘要

Mn, Fe, Mo or W as a promotor was introduced into ZrO2-TiO2-Al2O3 (ZTA) composite oxides by impregnation method, in order to examine the influence of these promotors on catalytic activity and coking behaviors during n-decane cracking. The as-prepared catalysts were characterized by several different techniques: N-2 adsorption -desorption, X-ray diffraction (XRD), temperature programmed desorption of ammonia (NH3-TPD), in situ infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The characterization results revealed that the incorporation of these metal oxides enhanced the total amount of acid sites and gave rise to the formation of much stronger acid sites, especially Mo. Moreover, Mo-promoted ZTA catalyst was found to be the most efficient one for n-decane cracking (conversion 88.4%, heat sink 3.79 MJ/kg at 750 degrees C) due to an optimum balance between the number of strong acid sites (0.24 mmol NH3/g) and the total amount of acid sites (0.59 mmol NH3/g). Besides, the temperature programmed oxidation (TPO) results showed that Mo-modified ZTA catalyst exhibited more desirable anti-coke capacity in comparison to the others owing to its appropriate acid property.