One-step upgrading of real flue gas streams into syngas over alumina-supported catalysts

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Flue gas is a major source of CO2 and the development of technologies for its utilization is of utmost interest both by environmental and industrial perspectives. Recently investigated CO2 valorization processes still face techno-economic challenges for implementation for costs associated with different steps, including CO2 purification steps. Thus, for the first time in literature, the feasibility of the direct one-step upgrading of real untreated flue gas into syngas is investigated here. For that end, classical alumina-supported catalysts (Ni, Co and Fe) were used for concept validation. The influences of temperature (500–900 °C), metal load (10–15 %), residence time (GHSV = 315–1260 h−1) and the effects of flue gas impurities (NOX and SO2) are reported here. Best CO2 and H2O conversion performances (XCO2 = 53.9 %, XH2O = 67.0 %) were obtained with the nickel catalyst with 15 wt% Ni at 900 °C and the highest residence time (GHSV = 315 h−1). The highest H2/CO ratio of the produced syngas was 0.70 and it was obtained with the same 15 wt% Ni catalyst at T = 700 °C, GHSV = 630 h−1. The NOx present in the FG was completely removed as part of the one-step upgrading strategy, while SO2 did not interact with the tested catalysts. Finally, a long-term operation strategy was proposed by supplementing the flue gas with H2 (H2/CO2 = 1.0), which yielded 24 h stable operation with around 40 % CO2 conversion and a syngas with H2/CO = 1.2–1.3. The results presented here, for the first time in the literature, demonstrate the feasibility of a novel one-step process for direct valorization of flue gas. The direct upgrading of flue gas would potentially decrease the costs associated with CO2 purification and valorization.