Hydrogenation of CO and CO2 to Higher Alcohols over a K–V-Promoted Fe–C Composite: Effect of Feed Composition

Abstract

The effects of feed composition on higher alcohol formation and catalyst phase composition were investigated during CO, CO2, and CO/CO2 hydrogenation over a K–V-promoted iron-carbon composite synthesized using a poly(vinyl alcohol) organic matrix. Electron microscopy revealed iron-containing nanoparticles predominantly 4-10 nm in size dispersed in the carbon matrix. Catalytic tests were conducted at 220-320 °C, 10.0 MPa, and a gas hourly space velocity of 2000 h-1. The temperature dependence of C2+ alcohol productivity varied with feed composition. For CO/H2 and CO/CO2/H2, the highest measured productivities occurred at 300 °C, reaching 114.6 and 125.5 g(C2+ alcohols)·kgcat-1·h-1, respectively. However, the ternary feed exhibited lower C2+ alcohol se-lectivity (16.6% versus 17.8%). For CO2/H2, C2+ alcohol productivity increased to 82.3 g(C2+ alco-hols)·kgcat-1·h-1 at 320 °C. X-ray diffraction indicated predominantly iron carbide after CO/H2 exposure, siderite and a spinel-structured iron oxide after CO2/H2 exposure, and coexisting oxide and carbide phases after CO/CO2/H2 exposure. These catalytic and phase differences are consistent with complementary roles of carbide and oxide sites in higher alcohol formation: carbide sites may promote carbon-chain growth, whereas oxide sites may facilitate C–O bond retention and hy-drogenation of oxygenated intermediates to alcohols.

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