Improvement of COS hydrolysis using γ-Al2O3 and Pt4/γ-Al2o3: first principles and experimental studies

Heterogeneous catalysis of carbonyl sulfide (COS) over gamma alumina (γ-Al2O3) and alumina supported platinum (Pt4/γ-Al2O3) has been theoretically studied via density functional theory (DFT). Roles of metal addition over catalyst support for improving the reaction has not been widely researched. Herein, roles of Pt4 upon γ-Al2O3 as a catalyst were emphasized. Thermodynamics and kinetics regarding the surface reaction were determined through energy span (ES) model. The effect of temperature towards elementary reaction was also included. The research found that COS physically adsorbs and chemically forms the bonds between S-Al and C-Osurface on the pristine γ-Al2O3. Pyramidal Pt4 existence over γ-Al2O3 leads to S-Pt, C-Pt, and O-Al formation. Pt4/γ-Al2O3 provides acidic sites and active species for the reaction. Electrons transfer towards Pt4/γ-Al2O3 (0.64 ⅼeⅼ) is larger than that on γ-Al2O3. COS hydrolysis involves 3 energy barriers including -OH attack at carbon (C), carbon-sulfur (C-S) breaking, and hydrogenation at S. Pt addition facilitates the C-S breaking which is the rate-controlling step for γ-Al2O3. Included the effect of thermal dependence (0 to 773 K), the results found that -OH attacking at C and H2S desorption become rate-controlling step within this temperature range. Pt addition enhances turnover frequency (TOF) up to the 7 order of magnitude (1.09 × 10E-15 and 2.25 × 10E2 s-1 for Pt4/γ-Al2O3; 1.15 × 10E-19 and 4.39 × 10E-5 s-1 for γ-Al2O3 at 373 and 773 K, respectively) and lowers the energy span (δG) throughout temperature range (2.06 and 1.66 eV for Pt4/γ-Al2O3; 2.36 and 2.69 eV for γ-Al2O3 at 373 and 773 K, respectively). Theoretical results corresponded to the experimental finding that Pt maintains longevity of the reaction. Concludingly, roles of Pt4 over γ-Al2O3 assist the C-S breaking and CO2 desorption with lowering δG (apparent activation energy) and improving TOF (rate of reaction).