Structure–activity relationships of Fe-Co/K-Al2O3 catalysts calcined at different temperatures for CO2 hydrogenation to light olefins

A Critical Look at Direct Catalytic Hydrogenation of Carbon Dioxide to Olefins

“…Adding a small amount of Co (2.6 wt %) to aF e( 12.4 wt %) catalyst showedh igher CO 2 conversion than an unpromotedF ec atalyst. [69] O/P ratios were up to 7.3 if calcined at 800 8C, at the expense of CO 2 conversion. In another study,h ighly alkalized CoÀFe/K/Al 2 O 3 catalyst (8.7 wt% of K) decreased the amounto fw eakly adsorbed H 2 and enhanced CO 2 adsorption, resulting in ad ecrease in the hydrogenation of produced olefins.…”

“…[68] Another study showed higher O/P ratios if highercalcination temperatures were used during synthesis of the catalyst. [69] O/P ratios were up to 7.3 if calcined at 800 8C, at the expense of CO 2 conversion. At higher calcination temperatures, iron oxide particles are bigger and harder to reduce than that at lower calcination temperatures, which diminishes CO 2 conversion values.…”

“…[67] The addition of potassium remains essential to produce olefins. [57,69] This catalystg ave a5 .2 O/ Pratio.…”

“…In the redox pathway,C O 2 adsorbs and dissociates on the reduced active sites, which leads to the oxidation of actives ites. [69] Several mechanismsf or the FTS processw ere proposed. This intermediate de- [83] The c-Fe 5 C 2 iron carbide, usually formed under reactionc onditions, is considered to be the active phase for the FTS reac-tion, because hydrocarbon speciesa re only detected after its formation.…”

“…Although methane production is still considered to be an issue if using cobalt, the latest advances showt hat these catalysts can restrict the formation of CH 4 to 15 %o r less. [57,69]…”