Behavior of ceria-copper oxide sorbents under sulfation conditions

Abstract

Simultaneous removal of SO 2 and NO x using a regenerable solid sorbent will constitute an important improvement over the use of separate processes for the removal of these two pollutants from stack gases and possibly eliminate several shortcomings of the individual SO 2 and NO x removal operations. Alumina-supported cerium oxide sorbents perform well at relatively high temperatures (823–900 K) as regenerable desulfurization sorbents. Addition of copper oxide to ceria lowers the sulfation temperature of ceria down to 773 K and sulfated ceria-based sorbents can function as selective SCR catalysts even at elevated temperatures. Sorbents containing cerium oxide and copper oxide supported on alumina were prepared by impregnation. Their sulfation performance was investigated in a TGA setup, studying mainly the effects of temperature and sorbent composition. It was found that in the 723–823 K temperature range combined cerium oxide–copper oxide sorbents had specific sorbent capacities (mass of sulfur removed per unit mass of metal sorbent) and sulfation rates significantly larger than those of cerium oxide or copper oxide sorbents used alone. Best sulfation performance was shown by the sorbent containing 1 : 1 molar ratio of cerium and copper. Specific sulfur capacities decreased as the coverage of the support surface by the metal oxides approached mono-layer coverage. At 823 K, specific sulfur capacities more than 20% over the theoretical value were obtained by sorbents with Ce/Cu molar ratios over one. This was attributed to the bulk sulfation of the alumina support.