Thermal decomposition of sodium amide, NaNH2, and sodium amide hydroxide composites, NaNH2–NaOH

Abstract

Sodium amide, NaNH₂, has recently been shown to be a useful catalyst to decompose NH₃ into H₂ and N₂, however, sodium hydroxide is omnipresent and commercially available NaNH₂ usually contains impurities of NaOH (<2%). The thermal decomposition of NaNH₂ and NaNH₂–NaOH composites is systematically investigated and discussed. NaNH₂ is partially dissolved in NaOH at T > 100 °C, forming a non-stoichiometric solid solution of Na(OH)_1−x(NH₂)_x (0 < x < ∼0.30), which crystallizes in an orthorhombic unit cell with the space group P2₁2₁2₁ determined by synchrotron powder X-ray diffraction. The composite xNaNH₂–(1 − x)NaOH (∼0.70 < x < 0.72) shows a lowered melting point, ∼160 °C, compared to 200 and 318 °C for neat NaNH₂ and NaOH, respectively. We report that 0.36 mol of NH₃ per mol of NaNH₂ is released below 400 °C during heating in an argon atmosphere, initiated at its melting point, T = 200 °C, possibly due to the formation of the mixed sodium amide imide solid solution. Furthermore, NaOH reacts with NaNH₂ at elevated temperatures and provides the release of additional NH₃.