The Effect of Promoter over La0.9M0.1Ni0.5Fe0.5O3 (M = Pr, Ce, Sr, Ca) Catalyst in Steam CO2 Reforming - Eun-hyeok Yang; Jinhee Lee; Kim Daehwan; Hyun Jin Kim; na-young Kim; Kim, Sang Woo; Ahn, Byoung Sung; Moon, Dong Ju