Catalytic conversion of carbon dioxide into hydrocarbons over iron supported on alkali ion-exchanged Y-zeolite catalysts

Abstract

Iron supported on HY-zeolite and on alkali metal (Li, Na, K, Rb) ion exchanged Y-zeolite prepared by impregnation technique have been characterized by XRD, AAS, BET surface area, CO 2 chemisorption, temperature programmed reduction (TPR) and temperature programmed decarburization (TPDC) techniques. These catalysts have been tested for catalytic activity for CO 2 hydrogenation to hydrocarbons. The XRD patterns of Fe/HY catalysts indicate the formation of Fe 2O 3 monolayer at 17 wt% Fe. It is found that alkali metals exchanged in zeolite-Y increase the basicity of the catalyst surface, which influence the activity and selectivity of the catalysts in CO 2 hydrogenation. The TPR profile of Fe 2O 3 catalyst is observed to contain only two peaks, corresponding to the reduction of Fe 2O 3 to Fe 0 through Fe 3O 4. However, the TPR profiles of Fe/MY catalysts contain three peaks, which indicate the formation of iron phase through FeO phase. The peak corresponding to the reduction of Fe 3O 4 to FeO is observed to increase in intensity and in area and to shift to higher temperatures in the order: H<Li<Na<K<Rb. The peaks in the TPDC profiles of the catalysts, which represent the reduction of carbide structures, are also observed to increase in area and to shift to higher temperatures. The CO 2 conversion and the total hydrocarbon selectivity are found to vary over a narrow range, whereas the selectivities of C 2–C 4 olefins and C 5+ hydrocarbons are very much influenced by the alkali metal present in the catalyst. The activities of the catalysts are correlated with physico-chemical characteristics of the catalysts.