The Effect of Copper Addition on the Activity and Stability of Iron-Based CO2 Hydrogenation Catalysts

Abstract

Iron-based CO2 catalysts have shown promise as a viable route to the production of olefins from CO2 and H2 gas. However, these catalysts can suffer from low conversion and high methane selectivity, as well as being particularly vulnerable to water produced during the reaction. In an effort to improve both the activity and durability of iron-based catalysts on an alumina support, copper (10–30%) has been added to the catalyst matrix. In this paper, the effects of copper addition on the catalyst activity and morphology are examined. The addition of 10% copper significantly increases the CO2 conversion, and decreases methane and carbon monoxide selectivity, without significantly altering the crystallinity and structure of the catalyst itself. The FeCu/K catalysts form an inverse spinel crystal phase that is independent of copper content and a metallic phase that increases in abundance with copper loading (>10% Cu). At higher loadings, copper separates from the iron oxide phase and produces metallic copper as shown by SEM-EDS. An addition of copper appears to increase the rate of the Fischer–Tropsch reaction step, as shown by modeling of the chemical kinetics and the inter- and intra-particle transport of mass and energy.

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

“…[55] It is also used as an active site in the RWGS reaction, which inhibits methane production, in contrast with Co, Ni, and Ru. [56] The obtained O/P ratio was 4.9, which was similart othat of the sample without Cu (4.3). The correct Cu/Fe ratio is needed to obtain ap ositive effect from adding Cu.…”

“…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). [56] The obtained O/P ratio was 4.9, which was similart othat of the sample without Cu (4.3). 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.…”

“…[45] At higher temperatures, RWGS is favored and CO selectivity increases. [51,56] Af urtheri ncreaseo ft he temperature to 340 8Cdecreased the O/P ratio. [45] However,e xperimental data does not show the same tendency.I ron-based catalysts (used in the MFTS route) or SAPO-34-based materials (methanol-mediated route) show higher CO 2 conversion upon increasing the temperature over the temperature range of 250-400 8C.…”

“…showed that reaction temperatures of around 400 8Cw ere suitablef or synthesizingl ight olefins. [50,51,56,87,93,95] Optimal temperatures differ between studies, but ah igherO /P ratio was obtained upon increasingt he temperature from 200 to 300 8C. [87] Moreover,C O 2 conversion decreases at temperatures ranging from 100 to 450 8C.…”

“…[87] Moreover,C O 2 conversion decreases at temperatures ranging from 100 to 450 8C. [56] Thermodynamic studies at 400 8Ca nd a3 :1 H 2 /CO 2 ratio showedt hat CO 2 conversion increaseds harply if the pressure increased between0and2MPa. [50,51,56,87,93,95] Optimal temperatures differ between studies, but ah igherO /P ratio was obtained upon increasingt he temperature from 200 to 300 8C.…”