Production of methanol with catalytic reactors in fuel cells
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Date
2025-10-10
Authors
Μάνθος, Δημήτριος
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Abstract
The catalytic hydrogenation of carbon dioxide (CO2) to methanol (CH3OH) is a key reaction to mitigate greenhouse gas emissions and provide a flexible renewable fuel and chemical feedstock. This research is focused on overcoming the constraints of conventional industry catalysts by developing and optimizing new copper-based catalysts supported on zirconia (ZrO2) and ceria (CeO2), which will be discussed in detail later in this paper, as it relates to catalysts in hydrogenation reactions of CO2. A detailed thermodynamic analysis was performed as the first step to establish the theoretical limitations of the process. The thermodynamic analysis confirmed that the direct hydrogenation reaction was exothermic, demonstrating that low temperature and high-pressure favoured the main hydrogenation reaction. The thermodynamic analysis also showed that limitations existed for the direct hydrogenation reaction, as the competing endothermic reverse water-gas shift (RWGS) reaction provided undesirable carbon monoxide (CO). The experimental aspects of this work were primarily focused on preparing a series of CuZrOx and CuZrCeOx catalysts using the hydrothermal method and methodically altering the hydrothermal temperature (120–180 oC), the calcination temperature (300–500 oC), and the Zr:Ce ratio used for the support material. The synthesized materials were fully characterized. The samples were analysed by N2 adsorption (BET), XRD, XRF, SEM, and H₂-TPR to compare the physicochemical properties of the catalyst and the catalytic performance. Catalytic testing at atmospheric pressure (1 bar) and temperatures between 200-280 °C was conducted in order to characterize the effectiveness of the catalysts. The binary catalyst CuZrOx-150-400 (that was synthesized at 150 oC hydrothermally and calcined at 400 oC) showed the most promising activity during the testing, with the highest methanol selectivity, as it maintained catalytic activity at higher temperatures. The unique morphology (well-defined nanoflower nanostructure), stable mesoporosity (better-defined pore shape), and improved redox properties contributed to the performance of the catalyst. Optimization of the feed gas ratio also discovered that a stoichiometric CO₂:H₂ ratio of 1:3 achieved the highest methanol selectivity. Notably, the incorporation of ceria showed improved structural stability and improved redox properties but had non-negligible consequences as it completely suppressed methanol formation. All the reactivity shifted to CO production via the RWGS. This exemplifies a fundamental trade-off between stability and yield on methanol production selection when CeO2 is employed as a support in these synthesis conditions. Overall, the identified catalyst, CuZrOx-150-400, proved to be the most effective synthesis for low-pressure CO₂-to-methanol conversion. The results thus suggest the strong influence of synthesis parameters on the structure and functioning of catalysts with respect to changes in their synthesis parameters and provide insight for the rational design of high-performance catalysts for sustainable methanol synthesis. Future work should assess the catalytic performance at industrially relevant high-pressure conditions and evaluate different promoters to improve both stability and methanol yield.
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Keywords
CO2 hydrogenation, Catalytic reaction, Methanol production