Tribocatalytic Nitrogen Fixation Assisted by Active Nitrogen Atoms on the Surface of Si3N4 at Room Temperature

Ammonia synthesis by nitrogen and water reaction is essentially a process of nitrogen and hydrogen ion coupling, with electrons forming an N–H bond. In this paper, friction can continuously provide electrons and hydrogen ions in the catalytic reaction of Si3N4 to realize the nitrogen fixation process, so as to achieve high efficiency of friction catalytic nitrogen fixation at room temperature. For the direct nitrogen fixation of air and water to produce ammonia, the ammonia yield can reach 1273.4 μmol/g at 5 h, while the ammonia yield can reach 1865.2 μmol/g at 5 h under pure nitrogen and water nitrogen fixation. The rapid contact and separation between a PTFE rod, Si3N4 particles, and a glass reactor causes continuous positive and negative charge formation on the surface of Si3N4. The positive charges react with the sacrificial agent methanol and water to generate hydrogen ions, which not only consumes the positive charges, inhibits the recombination of positive and negative charges, and improves the utilization rate of electrons but also provides a large number of hydrogen ion sources for the reaction. Based on the results of density functional theory (DFT) calculations, which indicate that silicon atoms on the surface of silicon nitride have no catalytic activity, while nitrogen atoms can effectively activate nitrogen molecules and catalyze the nitrogen fixation reaction, we designed a tribocatalysis process to continuously break the catalyst particles to expose more surface nitrogen atoms as active sites in situ to promote the nitrogen fixation reaction. In addition, the friction force can provide energy for the reaction in the instantaneous process, which is conducive to the activation of nitrogen molecules to promote the reaction, and together with the continuous charge provided by the friction process, it finally enables Si3N4 to catalyze nitrogen fixation efficiently at room temperature.