Modification Of TS-1 And Its Performance In Aldehydes/Ketones Ammoxidation

The conventional aldehyde/ketone ammoxidation reaction suffers from low reaction efficiency,many by-products and the use of strong acids and toxic substances,while the titanium-silica molecular sieve TS-1 with MFI topology has been more studied in ammoxidation.Among them,TS-1/H₂O₂ catalytic oxidation system has the advantages of green and high efficiency,high atomic utilization and mild reaction conditions,and the reaction product is water,which does not pollute the environment and can overcome the drawbacks of traditional processes and meet the requirements of green chemistry.In recent years,TS-1 molecular sieve has been widely used in catalytic oxidation reactions,and its catalytic ammoxidation of large molecule cyclohexanone has been industrialized,however,the catalytic selectivity of catalytic ammoxidation of small molecule acetone is poor.In order to improve the activity and selectivity of TS-1 catalyzed aldehyde/ketone ammoxidation reaction,the conformational relationship between the structure and catalytic activity of TS-1 catalyst is investigated in depth in this paper as follows:（1）Based on the application of titanosilicate/H₂O₂ catalytic oxidation system in acetone ammoximation,the catalytic activities of TS-1、Ti-MOR and Ti-MWW molecular sieves were investigated for the synthesis of acetone oxime by acetone ammoximation and the synthesis of 2-nitropropane by acetone ammoxidation reactions.And the experiments showed that Ti-MOR and Ti-MWW were excellent catalysts for the synthesis of acetone oxime by acetone ammoximation,while TS-1 was the ammoxidation for the synthesis of2-nitropropane reaction.The TS-1 and Ti-MWW molecular sieves were characterized by XRD,N₂ adsorption,SEM,UV-Vis and Py-IR,and the morphology,structure and surface acidity of both molecular sieves were investigated.It was found that TS-1 with microporous structure and strong oxidation property were the key factors for the excellent performance in the acetone ammoxidation reaction.Finally,the reaction mechanism of acetone ammoxidation was discussed in combination with the catalyst characterization and catalytic reaction process analysis,which provided a theoretical basis for improving the yield of 2-nitropropane synthesis by acetone ammoxidation.（2）Modified TS-1 catalysts for the synthesis of 2-nitropropane by ammoxidation-oxidation reaction of acetone were prepared by post-treatment of TS-1molecular sieves with different concentrations of tetrapropylammonium hydroxide（TPAOH）/triisopropanolamine（TIPA）,and the effects of different alkali treatments on the structure and properties of the catalysts were systematically investigated.The catalysts were characterized by X-ray diffractometer,scanning electron microscope,transmission electron microscope and nitrogen adsorption techniques.The results showed that the alkali treatment increased the number of pores and pore capacity in the molecular sieve without affecting the skeletal structure and titanium content of the molecular sieve.It was shown that the increased catalytic activity of the molecular sieve after alkali treatment was attributed to the increase of pores in the molecular sieve and the decrease of diffusion limitation.In addition,the 2-NP selectivity of TS-1 in the acetone ammonia oxidation reaction was obtained up to 96.8%by optimization of the process conditions.The results indicate that the modified TS-1 molecular sieve is a promising catalyst for the ammoxidation-oxidation reaction of acetone.（3）A series of metal-doped modified Ni/TS-1 catalysts were prepared using the ultrasonic impregnation method,and a green process was developed for the one-step synthesis of benzonitrile from benzaldehyde and ammonia.Compared with the unmodified TS-1,Ni/TS-1 showed better catalytic performance in the benzaldehyde ammonia oxidation reaction,in which,Ni/TS-1（3 wt.%Ni loading）showed the best catalytic performance and the benzaldehyde conversion could reach 92.2%,while TS-1 was only62.2%.By characterizing the TS-1 and Ni/TS-1 catalysts before and after modification,it was found that the high catalytic activity was attributed to the synergistic effect between the metal Ni and TS-1.The Ni species existed on the surface of TS-1 in the form of Ni O,which effectively neutralized the acid center of TS-1 and inhibited the ineffective decomposition of H₂O₂,and also enhanced the electrophilicity of the Ti active center.In addition,compared with the traditional two-step oxime oxidation-dehydration process,this process achieves a one-step reaction,which effectively shortens the synthesis route,avoids the separation of intermediates and reduces the reaction energy consumption.