The adsorption characteristics of the catalyst surface was studied using FT-IR (DRIFT) to determine the promotion and the causes as W is added through Mn/Ce/Ti and Mn/Ce/W/Ti catalysts. Addition of W to Mn/Ce/Ti catalyst promotes activity below 200 degrees C. In the FT-IR performed DRIFT test, the Mn/Ce/W/Ti catalyst showed an excellent reaction activity at the SCR reaction when NH3 was introduced; also, compared with the Mn/Ce/Ti catalyst, the absorption-acid site of the NH3 increased with a NH4+ that adsorbed to the Bronsted-acid site. Afterward, when NO + O-2 was introduced to cause a reaction with the adsorbed NH3, the NH3 adsorbed species quickly decreased at the Mn/Ce/W/Ti catalyst. Next, when the NO (+) O-2 was initially adsorbed, monodentate nitrate, bidentate nitrate, and bridged nitrate adsorbed species were created on the surfaces of the Mn/Ce/W/Ti and Mn/Ce/Ti catalysts. When NH3 was introduced for the reaction, part of the bridged nitrate reacted, but the NO adsorbed species on the catalyst surface were generally less reactive. Therefore, the NO adsorbed on the catalyst surface exhibit a very low reaction activity as compared with the adsorbed NH3. The Mn/Ce/W/Ti catalyst with the W had the inhibited. overall nitrate adsorbed species than the Mn/Ce/Ti catalyst. Therefore, the Mn/Ce/W/Ti catalysts increased the low-temperature SCR reaction activity by the increase of the ammonia adsorbent species having excellent reactivity and the decrease of the adsorption of the less reactive nitrogen oxide, compared with the Mn/Ce/Ti catalyst.