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

Iron supported on MY-zeolite and on alkali metal (Li, Na, K, Rb) ion exchan ged Y-zeolite prepared by impregnation technique have been characterized by XRD, AAS, BET surface area, CO2 chemisorption, temperature programmed redu ction (TPR) and temperature programmed decarburization (TPDC) techniques. T hese catalysts have been tested for catalytic activity for CO2 hydrogenatio n to hydrocarbons. The XRD patterns of Fe/HY catalysts indicate the formati on of Fe2O3 monolayer at 17 wt% Fe. It is found that alkali metals exchange d in zeolite-Y increase the basicity of the catalyst surface, which influen ce the activity and selectivity of the catalysts in CO2 hydrogenation. The TPR profile of Fe2O3 catalyst is observed to contain only two peaks, corres ponding to the reduction of Fe2O3 to Fe-0 through Fe3O4. However, the TPR p rofiles of Fe/MY catalysts contain three peaks, which indicate the formatio n of iron phase through FeO phase. The peak corresponding to the reduction of Fe3O4 to FeO is observed to increase in intensity and in area and to shi ft 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 struct ures, are also observed to increase in area and to shift to higher temperat ures. The CO2 conversion and the total hydrocarbon selectivity are found to vary over a narrow range, whereas the selectivities of C-2-C-4 olefins and C5+ hydrocarbons are very much influenced by the alkali metal present in t he catalyst. The activities of the catalysts are correlated with physico-ch emical characteristics of the catalysts. (C) 1999 Elsevier Science B.V. All rights reserved.