Effect of Cu Insertion into SnO₂ Framework on Surface Properties and Carbonyl Sulfide Adsorption Performances

The objective of this study is to introduce Cu into SnO₂ sorbent for improving its COS adsorption capacity. Cu-doped SnO₂ adsorbents were synthesized using a conventional sol-gel method with citric acid. X-ray diffraction studies revealed that up to 0.4 mol of Cu ions were well-inserted within the SnO₂ framework. Scanning electron microscopy images confirmed that the addition of Cu ions reduced the particle size of the SnO₂ sorbents. Additionally, it led to an increase in the Brunauer-Emmett-Teller surface area of the sorbents. The COS adsorption tests were carried out in the temperature range of 300-400 °C with a gas hourly space velocity of 8,500 h^-1. It was found that Cu_0.6SnO₂ displayed higher COS adsorption capacity than the sorbents of other compositions, and the breakthrough time and COS adsorption capacity on it at 400 °;C were 170 min and 4.87 mg/g, respectively. X-ray photoelectron spectroscopy results indicated that the Cu²⁺ ions in the CuxSnO₂ adsorbent converted into CuS by binding to the S^2- ions in COS gas, while the remaining CO segments combined with the Sn atoms in SnO₂ and then are adsorbed as SnCO. Overall, this study showed that the hard-soft acid-base rule is better followed in the Cu_0.6SnO₂ adsorbent than in the SnO₂ adsorbent and that the adsorption is more stable.