Fe–Cu Bimetallic Catalysts for Selective CO₂ Hydrogenation to Olefin-Rich C₂⁺ Hydrocarbons

Abstract

This paper reports on Fe–Cu bimetallic catalysts supported on γ-alumina for selective CO2 hydrogenation to olefin-rich C2 + hydrocarbons. A strong synergetic promoting effect on C2 + hydrocarbon synthesis was observed over Fe–Cu bimetallic catalysts when the Cu/(Cu + Fe) atomic ratio was 0.17. Compared to monometallic Fe catalyst, the Fe–Cu bimetallic catalyst significantly enhances C2–C7 hydrocarbon formation and suppresses the formation of undesired CH4. The addition of K into Fe–Cu bimetallic catalysts inhibits the methanation and further enhances the formation of C2 + hydrocarbons in the meantime. The synthesis of olefin-rich C2–C4 hydrocarbons from CO2/H2 was achieved by using K-promoted Fe–Cu/Al2O3 catalysts with higher K/Fe atomic ratios (e.g., K/Fe ≥ 0.5), where the selectivity of C2–C4 olefin contents was even higher than K-promoted Fe–Co catalysts under the same reaction conditions.

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

“…[33] Thus,a dding coppere nhances CO 2 conversion while keeping the product distribution constant. [57] This bimetallic catalysts upported on Al 2 O 3 reachedt he highest CO 2 conversion among all tested ratios. The addition of 10 % Cu to aF e ÀK/Al 2 O 3 catalysti ncreased CO 2 conversion to 41 %, relative to the unpromoted catalyst (24 %ofCO 2 conversion).…”

“…Higher Cu loadings showedl ower CO 2 conversion.W ang et al found that the optimal Cu/(Cu + Fe) atomic ratio was0 .17, whichc orresponded to 17 %t otal metal loading. [57] This bimetallic catalysts upported on Al 2 O 3 reachedt he highest CO 2 conversion among all tested ratios. Its XRD pattern showed an ew peak at 458,w hich was ascribed to FeÀCu alloy species.…”

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

“…Although they showed promising results, the addition of apromoter was neededt operformthe reaction selectively. [52] Mçssbauer analysis of 57 Fe showedt hat the sample FeK1.5/HSG after the reaction contained more c-Fe 5 C 2 (74 %) and could stabilizea ne xtra carbide phase, e'-Fe 2.2 C( 8.5 %), comparedw ith that of the unpromoted Fe/HSG catalyst (50.4 % c-Fe 5 C 2 ). Addingp otassium as ab asic promoter is an established practice.…”

“…[54] Recently, Wu et al showed that iron catalystss upported on a3 Dg raphene called honeycomb-structured graphene (HSG) and promoted with potassium converted more CO 2 and gave higher selectivity towards C 2 -C 4 = than that of the unpromoted catalyst. [52] Mçssbauer analysis of 57 Fe showedt hat the sample FeK1.5/HSG after the reaction contained more c-Fe 5 C 2 (74 %)…”