Synthesis of Niobium Carbonitride by Thermal Decomposition of Guanidine Oxaloniobate and Its Application to the Hydrodesulfurization of Dibenzothiophene
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A production method that uses lower temperatures than the temperatures of commonly utilized methods (950–1,100 °C) is proposed for the synthesis of niobium carbonitride and niobium carbide. This methodology consists of three stages: (i) the synthesis of guanidine oxaloniobate via a solid-state reaction at 150 °C between monohydrated ammonium oxotris(oxalate)niobate (niobium ammoniacal complex) and guanidine carbonate; (ii) the thermal decomposition of the guanidine oxaloniobate at 400 °C under an inert atmosphere; and (iii) the subsequent decomposition under an inert atmosphere at temperatures varied between 450 and 900 °C. The structure of the guanidine oxaloniobate was also calculated by density functional theory. The characterization results suggest that at a decomposition temperature of 700 °C, niobium carbonitride (NbC x N1−x , x < 1) was formed, which was transformed into NbC at higher temperatures (≥850 °C). From the X-ray refinement results, which were performed using the Rietveld method, the formation of NbC was proposed to occur in stages: oxaloniobate → oxynitride → carbonitride → carbide. The materials synthesized at 600, 650 and 700 °C exhibited steady state activities for more than 24 h in the hydrodesulfurization of dibenzothiophene, which predominantly occurred via the direct desulfurization route.
KeywordsNiobium carbide Niobium carbonitride Hydrodesulfurization Guanidine oxaloniobate
The authors thank CBMM for kindly supplying the monohydrated ammonium oxotris(oxalate)niobate. C.A.C. would like to thank the CNPq for the awarded scholarship.
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