The removal mechanisms of HF and HCl gases using Mg-Al adsorbent prepared by sol-gel synthesis method

In this study, a series of Mg-Al mixed oxide adsorbents have been introduced to simultaneously remove hydrogen chloride (HCl) and hydrofluoric acid (HF) in low-temperature environment (100 °C). These adsorbents prepared by the sol-gel method, the effects of Mg loading amount and calcination temperature for adsorbents on their performance were investigated. The optimal adsorbent (modified by 20 wt% Mg and calcined at 500 °C, referred to as Mg20Al80OX-500) exhibited the highest adsorption capacity among all the adsorbents tested. The role of MgO loaded on Mg-Al mixed oxide adsorbent was investigated using various analytical methods, including Brunauer-Emmet-Teller (BET), X-ray diffractometer (XRD), scanning electron microscopy (SEM-EDS), thermogravimetric analysis (TG-DTG), temperature programmed desorption of CO2 (CO2-TPD), X-ray photoelectron spectroscopy (XPS), in-situ infrared (in-situ IR) and transmission electron microscopy (TEM). These results indicated that MgO and lattice oxygen (Oα) played a crucial role in promoting the adsorption activity of the adsorbents. Mg were highly dispersed, and moderate levels of Mg content and calcination temperature could enhance the performance of adsorbents according to XRD, SEM-EDS and TG-DTG results. BET analysis showed that the modification of Mg did not change the pore type of the γ-Al2O3 largely. CO2-TPD results revealed that the calcination temperature significantly affected the number and strength of the basic sites on the surface of the adsorbent. In addition, XPS, in-situ IR and TEM analysis demonstrated that the consumption of MgO and Oα as well as the accumulation of reaction products on the surface and within the pores of the adsorbent, and they were the main reasons the deactivation. And MgF2 (MgCl2) and H2O were the main products after the inactivation of adsorbent.