Assessing the viability of K-Mo2C for reverse water–gas shift scale-up: molecular to laboratory to pilot scale

Abstract

Conversion of CO₂ to value-added chemicals and fuels is a potentially valuable route for renewable energy storage and a future CO₂-neutral economy. The first step is CO₂ conversion to CO via the reverse water–gas shift (RWGS) reaction. Effluent CO can then be hydrogenated to chemicals and fuels via Fischer–Tropsch (FT) synthesis over a tandem catalyst or within a second reactor. To implement this process on an industrial scale, low-cost, scalable and highly-selective catalysts are required, prompting investigations into materials that meet these design constraints. Potassium-promoted molybdenum carbide supported on gamma alumina (K-Mo₂C/γ-Al₂O₃) has recently been shown to be a highly active and selective RWGS catalyst in the laboratory, prompting us to investigate the viability of K-Mo₂C/γ-Al₂O₃ for scale-up. In this report, laboratory-scale (∼100 mg catalyst) reactor studies are extended to the pilot-scale (∼1 kg catalyst), and viability for scale-up is tested further with density functional theory (DFT) calculations, detailed characterization and reactor experiments under a range of temperatures (300–600 °C) and flow conditions. The pilot-scale experiments illustrate K-Mo₂C/γ-Al₂O₃ is a highly active and selective catalyst (44% CO₂ conversion, 98%+ CO selectivity at GHSV = 1.7 L kg⁻¹ s⁻¹ and T = 450 °C) that exhibits no signs of deactivation for over 10 days on stream. Together, experiments across the molecular, laboratory and pilot scales demonstrate that K-Mo₂C/γ-Al₂O₃ is an economically-viable RWGS catalyst with promising future applications in the US Naval Research Laboratory's seawater-to-fuel process, downstream methanol synthesis and FT.