Study On The Reaction Behaviors Of NH₂OH Intermediate Over Titanosilicates/H₂O₂ System

Titanosilicates/H₂O₂ ammoximation system is the development direction of the green production of oxime chemicals.Ammonia and hydrogen peroxide are adsorbed on the active site of Ti to form hydroxylamine（NH₂OH）intermediate,and hydroxylamine reacts with substrate ketone to form target product ketoxime.The current research mainly focuses on how to improve the utilization rate of nitrogen atoms in the reaction process and reduce the generation of greenhouse gas N₂O in the reaction process.The paper aims at high N atomic economy and green reaction process.First of all,we explored the active center of NH₂OH decomposition and the origin of N₂O generation,further summarized the hydroxylamine reaction pathway network.Secondly,for the inevitable ineffective decomposition of hydroxylamine,the key factors to reduce N₂O production are explored.The main work is divided into the following parts:1.The reaction behavior of hydroxylamine was systematically investigated over titanosilicates/H₂O₂system.The reaction behaviors of NH₂OH included main valuable nucleophilic addition reaction（pathway a）,oxidative decomposition（pathway b）and pathway c.Pathway a will compete with pathway b,and highly active ketones can inhibit the ineffective oxidative decomposition of NH₂OH.However,oxidative decomposition（pathway b）is inevitable.In order to reduce the greenhouse N₂O,our findings demonstrate that the reaction behaviors of free H₂O₂ affect product differences in NH₂OH decomposition.Pathway b was further divided into two parts:NH₂OH was oxidized by free H₂O₂ releasing N₂ and N₂O（PathwayⅠ）which is a noncatalytic reaction,and it was oxidized by Ti-OOH species to form N₂ only（PathwayⅡ）.Improving Lewis strength of titanosilicates（such as TS-1^s and F-Ti-MWW）and adjusting the hydrogen-bonding interactions for the stability of Ti-OOH species（such as KH₂PO₄ and CH₃OH）can enhance the catalytic oxidation to reduce harmful N₂O.In a word,the synergistic effect of the formation,stability and transfer of the Ti-OOH active intermediate is the key factor affecting the economy and greening of the N atom in the system.2.Combined with characterization and hydroxylamine decomposition experiments,the increase of N₂O in industrial deactivated titanosilicate molecular sieve was analyzed.Results show that amorphous Si O₂-Ti O₂ mixed binary oxides were formed due to alkaline soluble silicon,and the non-framework titanium can produce free radicals and react with hydrogen peroxide,accelerate the invalid decomposition of hydroxylamine,produce large amounts of greenhouse gas N₂O.Adding an amount of radical trap to the reaction mixture can inhibit this free radical reaction.Thus,inhibiting the invalid decomposition of hydroxylamine,and reduce the production of N₂O.