Javishk Shah, Jeremiah Ort and Maria L Carreon
Background: There is an increasing interest to consider carbon dioxide as a resource and a business opportunity rather than a waste with a disposal cost. Among the several specific motivations to produce platform chemicals such as carbamates from CO2 are the low or zero cost of this feedstock and the potential to be a more economic efficient route. However, this pathway requires the development of materials with tunable morphologies and textural properties that display enhanced catalytic performance, distinctive structural and adsorption properties than those of conventional materials. Gallium oxide can be rationally engineered into crystalline porous materials which combine highly desirable properties, such as controlled morphology, uniform micropores, and high surface areas with exceptional chemical and thermal stability.
Method: The synthesis was performed in a batch reactor with mesoporous gallium oxide as catalyst while n-octylamine and nproponal were the reactants. The reactor was pressured with CO2. The temperature of the reaction was at 200°C and the reaction time is 24 h.
Results: High surface area γ-mesostructured gallium oxide was tested as a catalyst for the synthesis of carbamates from CO2. The mesostructured catalysts displayed a high conversion of ≈ 69%, much higher than their non-mesostructured counterparts. After recycling the catalysts the γ-gallium oxide phase was preserved and displayed only a slight decrease in catalytic activity. The selectivity of carbamates was higher at small pore diameters which can be attributed to the enhanced diffusion of the linear chain carbamate compared to the branched urea derivatives.
Conclusion: The results from this work demonstrate the successful use of mesostructured gallium oxide for the synthesis of carbamates from CO2. The high conversion of the mesostructured γ-gallium oxide compared to the non-mesostructured catalysts can be attributed to the high surface area.
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