Study On Selective Hydrogenation Performance Of Aromatic Nitro Compounds Over Nano-Pt Catalysts

Aromatic azo compounds and aromatic oxidized azo compounds are useful chemical organic raw materials and reaction intermediates.They have similar chemical structures and properties.From aromatic nitro compounds,under the mild conditions,high-efficiency catalytic hydrogenation to aromatic azo compounds and aromatic oxidized azo compounds is a challenging subject.In this thesis,SiO₂ was modified with different nitrogen-containing functional groups to modulate the geometric and electronic properties of the active component Pt,achieving efficient hydrogenation of aromatic nitro compounds to form aromatic azo compounds and aromatic oxidized azo compounds.The specific conclusions are as follows:1.SiO₂ modified by Schiff-base was prepared by condensation of amine aldehyde,and Pt/SiO₂-Schiff was prepared by liquid phase reduction method,which has good catalytic activity and selectivity in hydrogenation of p-nitrochlorobenzene to 4,4'-dichloro azobenzene At 50?and 0.5 MPa H₂,ethanol as solvent,and KOH as alkali,the highest yield achieved is ca.91.1%for 4,4?-Dichloroazobenzene with the average TOF up to 2601 h^-1 over the Pt_0.5/SiO₂-Schiff catalyst.XRD,STEM,FT-IR,XPS results showed that Pt nanoparticles?NPs?with an average size of 2.3 nm were highly dispersed on the surface of SiO₂-Schiff.The strong metal-support interaction derived from the coordination of nitrogen sites on Schiff-base to Pt NPs enables of stabilizing the Pt NPs and achieving the catalytic recyclability.2.SiO₂ modified by-NH₂ group were prepared by sol-gel method,and the Pt/SiO₂-NH₂catalyst was prepared by liquid phase reduction method,which can efficiently synthesize aromatic oxyazo compounds without alkaline additives.At 50?,1 MPa H₂,ethanol as solvent,the conversion of p-nitrochlorobenzene was 94.3%over Pt_0.5/SiO₂-NH₂ catalysts for 30 min,The highest yield achieved is ca.90.8%for 4,4'-dichloroazoxybenzene with the average TOF up to 2452 h^-1,which is higher than the literature reported values.XRD,STEM,FT-IR,XPS resulsts showed that Pt nanoparticles were highly dispersed on the SiO₂-NH₂,and there was a strong interaction between them.At the same time,-NH₂ group provided the alkaline environment required for the reaction.