Nanostructured bimetallic copper-gallium catalysts for the production of methanol from carbon dioxide
Vidal Urquiza, Wella Hardy
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The hydrogenation of carbon dioxide (CO2) to methanol is an alternative to mitigate the problems caused by global warming. Industrially, methanol is produced by hydrogenation of CO2/CO over heterogeneous catalyst Cu/ZnO/Al2O3. However, this technology has two limitations: low productivity in the absence of CO and susceptibility to poisons generated from CO2-free syngas. In this sense, we sought to synthesize catalysts that can work under mild reaction conditions of temperature and pressure that are capable of converting CO2 in a selective way to methanol. Thus, it was proposed to use Cu and Ga metals for this study. The hypothesis is that the addition of Ga to Cu in the preparation of bimetallic catalysts, will help promote the formation of methanol while minimizing CO formation, by changing the adsorption energy of reactant and intermediate molecules, hence favoring carbon dioxide hydrogenation to methanol. Catalysts were synthesized by the incipient wetness impregnation (IWI) method. To investigate the formation of bimetallic structures, particle size, and chemical composition, our bimetallic catalysts were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and inductive coupling plasma - atomic emission spectrometer (ICP-OPS). The study of catalytic performance was carried out in a packed bed reactor, at a pressure of 30 Bar, in a temperature range of 210 ºC-250 ºC, with a molar ratio of H2/CO2: 3/1 and flow rate of 60 ml/min to 100 ml/min. The results show that the conversions of CO2 at the temperature of 250 ºC does not present a difference between the monometallic catalyst (Cu/SiO2) and the bimetallic catalyst (Cu-Ga/SiO2), reaching a maximum CO2 conversion of 4%. On the other hand, the selectivity towards methanol is positively affected with the Cu-Ga/SiO2 catalyst, reaching a selectivity of 50.34% while for the Cu/SiO2 catalyst was 9.27%. Another important improvement that Ga provides is the decrease in the apparent activation energy for methanol synthesis of 44 kJ/mol for Cu/SiO2 at to 28 kJ/mol for Cu-Ga/SiO2; thus, obtaining a higher rate of methanol formation.