Selective Oxidation Synthesis Of Terephthalaldehyde From P-Xylene On Mo-Fe Catalyst

Aromatic aldehydes have highly reactive aldehyde groups and,among all aromatic compounds,are particularly broad in the spectrum of applicability.Terephthalaldehyde (TPAL),in particular,which has two aldehyde groups in para-positions,is a promising material to be exploited in the production of pharmaceutical products,agrochemicals, dyestuffs,liquid crystal polymers,electrically conductive polymers,and heat resistant plastics,among other uses,and there is a demand for development of an uncostly technology which is practical significance and theoretical value for the production of TPAL.The supported and non-supported catalysts that Mo were main catalyst were prepared by impregnation and Sol-gel methods.Mo/Al₂O₃,Mo-Fe/Al₂O₃ and Mo-W/Al₂O₃ were prepared by impregnation method;Mo/SiO₂,Fe/SiO₂,Mo-Fe/SiO₂,Mo-Fe and Mo-Ce catalysts were prepared by Sol-gel method.The catalysts were tested using the gas-phase selective oxidation of p-xylene as the probe reaction.The effect of different loading of Fe, Mo and W supported on Al₂O₃ and Fe and Mo supported on SiO₂ were investigated;They were investigated that the effect of ratios of n(Mo)/nFe and n(Mo)/n(Ce)on properties of the catalysts.Mo-Fe/Al₂O₃,Mo-Fe/SiO₂ and Mo-Fe new catalysts were excellent activation for the synthesis of TPAL on selective oxidation ofp-xylene through procedure of catalyst screening. The catalysts were also charactered by IR,XRD,TG,TPR and XPS.The results showed that the catalysts supported on Al₂O₃ and SiO₂ were active and on selective oxidation of p-xylene. Mo-Fe/SiO₂ catalyst's conversion and selectivity reached 53.2%and 33.3%.Then Mo-Fe and Mo-Ce catalysts by sol-gel method were more excellent.At reaction condition of 550℃and 1000mL/min velocity of gas flow,the highest conversion of p-xylene and selectivity of TPAL reached 86%and 50%after 3 hours' reaction on Mo-Fe catalyst,which was calcined 10h in 500℃when the ratio of n(Mo)/n(Fe)was 3 and pH was 2～3.Mo-Fe catalyst had excellent activation and stability,and it can keep active for 15h continuous use.The main reasons of losing activation of the catalyst were reduced of its active component.It was indicated from TG,IR and XRD that Fe-O-Mo,Mo=O and Mo-O-Mo bond have formed in catalyst.The Mo=O double bond and Mo-O-Mo bond exited Einstein shift.It was showed that the combination of catalyst's crystal lattice oxygen and Mo atomic got weak, which was in favor of the reduction of catalyst.The MoO₃ and Fe₂(MoO₄)₃ crystal have formed in catalyst,which was more active in the gas-phase oxygen oxidations of p-xylene reaction.The results of TPR and XPS showed the Mo-Fe catalyst was reduced more easily and the crystal lattice oxygen had higher motion capability.The binding energys of Mo(3d_5/2) and Mo(3d_3/2)were 231.8eV and 234.9eV,which were also Mo peaks in(MoO₄)^2-.It indicated that Fe₂(MoO₄)₃ has exited linking to XRD analysis.