Heterogeneous catalytic synthesis of ethanol from biomass-derived syngas

Abstract

The selective catalytic conversion of biomass-derived syngas into ethanol is thermodynamically feasible at temperatures below roughly 350 degrees C at 30 bar. However, if methane is allowed as a reaction product, the conversion to ethanol (or other oxygenates) is extremely limited. Experimental results show that high selectivities to ethanol are only achieved at very low conversions, typically less than 10%. The most promising catalysts for the synthesis of ethanol are based on Rh, though some other formulations (such as modified methanol synthesis catalysts) show promise.

The effect of Fe–Rh alloying on CO hydrogenation to C2+ oxygenates

“…Various promoters (Fe, CeO2, V, La, Mn, Ag, Ti, Ir) have been shown to increase ethanol selectivity, with Fe being particularly effective due to its combined methane suppression and the enhancement of ethanol production [2][3][4][5][6]. Studies have shown that Fe loading up to 10 wt% has increased ethanol production while suppressing methane formation for Fe-promoted Rh/Al2O3 [6].…”

“…The need to develop alternative sources of liquid fuels has led to renewed interest in developing catalysts for the efficient conversion of synthesis or ''syn'' gas (CO + H2), derived from biomass, coal, and natural gas, to simple alcohols and higher oxygenates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Currently, the only industrially applied process involves syngas conversion to methanol over a Cu-based catalyst (CuZnO/Al2O3) at temperatures above 500 K [1].…”

“…Among the transition metals, Rh surfaces are known to promote C-C coupling, which should allow the direct conversion of syngas to ethanol and C2+ oxygenates, yet Rh-based catalysts primarily produce methane when used without promoters [2,3]. Various promoters (Fe, CeO2, V, La, Mn, Ag, Ti, Ir) have been shown to increase ethanol selectivity, with Fe being particularly effective due to its combined methane suppression and the enhancement of ethanol production [2][3][4][5][6].…”

“…While Cu-based catalysts are effective for methanol synthesis, they have poor performance for the production of ethanol and other C2+ oxygenates, which is desirable for its higher energy density, ease of handling, and nontoxicity. The search for new catalysts for higher oxygenate synthesis has taken a number of different approaches including the chemical modification of Cu-based methanol catalysts (metal promoters and doping), modified Fischer-Tropsch catalysts (Co, Ru, and Fe), and promoted MoS2-based catalysts [2,3].…”

How well can renewable resources mimic commodity monomers and polymers?

“…42,43 Alternatively, ethanol can be obtained from biomass using a gasification strategy followed by hydrogenation of CO (eq 1) or CO 2 (eq 2). 44 These exothermic hydrogenation reactions require temperatures below 350 C at 30 bar and utilize Rh or modified Fischer-Tropsch catalysts. Depending on the reaction conditions and catalyst, methanol formation and methanation (eqs 3 and 4) lower the yield of ethanol.…”