Investigation on the simultaneous removal of COS, CS2 and O2 from coke oven gas by hydrogenation on a Pd/Al2O3 catalyst

Abstract

The present study deals with the processing of coke oven gas mainly composed of H₂, CH₄, N₂ and CO to provide a feedstock for the synthesis of base chemicals. In this respect, the particular focus of this work is the simultaneous reduction of critical trace components like COS, CS₂ and O₂ by catalytic reaction with H₂. The investigations were performed in synthetic coke oven exhaust using a Pd/Al₂O₃ catalyst. The results of the hydrogenation tests showed complete conversion of COS, CS₂ and O₂ at 200 °C and above with selective formation of H₂S. However, below 200 °C the conversion of O₂ was markedly reduced and CH₃SH appeared as a by-product. Mechanistic studies were performed by in situ diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry. These investigations demonstrated dissociative adsorption of COS on the catalyst at 150 °C resulting in the formation of bridged CO adsorbates and probably elemental sulfur. It is assumed that these species predominate the active Pd surface under reaction conditions. Consequently, the adsorption of O₂ and the reaction to H₂O is suppressed thus substantiating the decrease in performance at low temperatures. However, increasing the temperature to 200 °C and above leads to desorption of CO and sulfur compounds restoring the efficiency of the catalyst.