Hydrolysis of carbonyl sulfide over rare earth oxysulfides

A novel type of rare earth oxysulfide catalysts was investigated for the hydrolysis of carbonyl sulfide. The catalytic activity could be well related to the easiness of the sulfidization from the rare earth oxides to the corresponding oxysulfides. The activity of the sulfidized rare earth oxides was in the following order: La≈Pr≈Nd≈Sm>Eu>Ce>Gd≈Ho>Dy>Er. An almost complete conversion of carbonyl sulfide (COS) was obtained over the most active catalysts at 200 °C and no substantial decrease in conversion efficiency was observed by changing the space velocity from 5,000 to 20,000 h−1. The rare earth oxysulfide catalysts showed very superior to the traditional Al2O3- and TiO2-based catalysts in anti-poisoning of oxygen. The presence of 1.5% of oxygen in feed did not affect the activity while the conversion of COS was over 90% at O2 concentration of 2.0% and temperatures above 150 °C. On the other hand, the presence of SO2 caused a decrease in the COS conversion, but the poisoning effect could be suppressed by increasing reaction temperature and the catalytic activity was recovered once SO2 was shut off. In addition, the competitive adsorption between COS and H2O on the surface of rare earth oxysulfides was also discussed.