Synergistic Catalytic Oxidation of Acidic Gas H ₂ S and Impurities (NH ₃ ) over a Cu-Substituted Hexaaluminate Catalyst: A Pretreatment Strategy for the Claus Process

The thermal reaction furnace, the cornerstone of the Claus process for converting H2S to sulfur, faces severe challenges when containing NH3 and hydrocarbons. A Cu-substituted hexaaluminate catalyst (LaCu2.5) is presented for the synergistic catalytic oxidation of acidic gas H2S and impurities (NH3), achieving almost complete conversion of H2S and NH3 simultaneously at ∼580 °C—with SO2 and N2 yield approaching 100%—and maintaining stability for 100 h. Furthermore, the presence of C3H8 exhibited a negligible negative impact in this process and the subsequent Claus reaction. Mechanistic studies by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis revealed that lattice-incorporated, electron-deficient Cu2+ species generated favorable active sites, which promoted the activation of H2S and NH3. Surface sulfate species formed during the reaction exerted a limited but measurable influence proved by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), primarily inhibiting NH3 activation to NHx intermediates and suppressing C3H8 oxidation. Density functional theory (DFT) calculations showed the activation barriers followed the order H2S < NH3 < C3H8, aligned with the observed catalytic activity. This catalytic strategy offers an energy-efficient alternative to the conventional thermal process (>1200 °C), with significant potential for industrial application.