Laser-Induced Activation of N2 and Catalyst-Free Synthesis of HCN

Abstract

Hydrogen cyanide (HCN) is typically synthesized using ammonia and methane as sources of nitrogen and carbon, respectively, over expensive platinum catalysts at high temperatures. However, continuous high-temperature processing deactivates the catalyst, resulting in limited durability of the process. Besides, there are serious hazards and limitations in the further separation and utilization of HCN. From the perspective of sustainable synthesis and safe utilization, low-cost catalyst or catalyst-free synthesis, mild reaction conditions, and elimination of exposure to toxic reagents are becoming increasingly important. Direct synthesis of HCN from nitrogen (N2) at room temperature without any catalysts and its safe fixation into functional inorganic cyanides are desirable. Here, we report the catalyst-free synthesis of HCN by laser-induced activation of N2 and methanol (CH3OH) at room temperature and then the in situ synthesis of inorganic cyanides (silver and copper cyanides) without purification and separation by reacting the synthetic solution with noble metals. We also establish the possible reaction paths by density functional theory calculations and molecular dynamics simulations to elucidate the thermodynamics and kinetics of the reactions involved in the laser chemistry process, i.e., laser bubbling in liquid (LBL). The high temperature inside the laser-generated bubble overcomes the energy barrier and drives the successful coupling of carbon and nitrogen sources endergonically in the following process. Bubbles experience a rapid quench during the LBL process, resulting in the kinetic control product HCN with high efficiency. The method is viable for the catalyst-free direct synthesis of HCN from N2 and CH3OH at normal conditions for safe fixation into inorganic cyanides.