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

The present study deals with the processing of coke oven gas mainly composed of H-2, CH4, N-2 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 O-2 by catalytic reaction with H-2. 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 O-2 at 200 degrees C and above with selective formation of H2S. However, below 200 degrees C the conversion of O-2 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 degrees 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 O-2 and the reaction to H2O is suppressed thus substantiating the decrease in performance at low temperatures. However, increasing the temperature to 200 degrees C and above leads to desorption of CO and sulfur compounds restoring the efficiency of the catalyst.