HCN Synthesis from Methane and Nitrogen Assisted by Magnetron Sputtering

As an important chemical, hydrogen cyanide (HCN) is conventionally prepared in industry through the conversion of methane (CH₄) and ammonia (NH₃) at a high temperature above 1000 °C, and in most cases, this process requires the use of the noble metal Pt as the catalyst. In this work, we designed and constructed a magnetron sputtering reaction device and utilized it to explore the direct synthesis of HCN at room temperature via the reaction of CH₄ and nitrogen (N₂), which was facilitated by the generated plasma. The experimental result shows that CH₄ and N₂ can produce HCN and NH₃ in this plasma reaction, and it is found that the reaction conditions such as reaction time, reaction current, ratio of initial reactants and type of metal target material have significant influences on the conversion rate of CH₄ and the yield of HCN. Through optimization experiments, the optimal reaction conditions of the developed reaction device have been obtained: Pt target is selected for the magnetron sputtering source, ratio of the reactant gases is set as CH₄:N₂ = 1:4 (total 450 Pa), reaction current is 90 mA and reaction time is 6 min. Under these conditions, conversion rate of CH₄ reaches 37.9%, and yield of HCN is 97.7 μmol. The developed method of synthesizing HCN assisted by the CH₄ and N₂ plasma generated through magnetron sputtering has the advantages of being green and direct, requiring no heating and no additional catalyst loading, and possessing high selectivity. This study not only provides a new method for HCN synthesis, but also demonstrates that the sputtering device has the potential to be employed for synthesizing other important compounds or investigating reaction mechanisms when it is combined with particular characterization instruments.