Synthesis And Modification Of HNbWO₆ And Catalytic Activity For Friedel-Crafts Acylation

Layered materials HNbWO6 was attracting attention because of its unique structure, which had the strong surface acidity,the adjustable surface properties,the adjustable interlayer channel,the high surface area and properties of long usefullife and stability,environmental friendliness, so that the catalyst had great potential in the acylation reaction.This thesis research mainly was the preparation of a layered structure HNbWO6 and HNbWO6 was modulated through the Fe3+ exchange,stripping and pillared. The catalysts were characterized by means of powder X-ray diffraction (XRD),Scanning electron microscope (SEM),Transmission electron microscope(TEM),Fourier transform infra-red spectroscopy(FT-IR),Thermogravimetry-Differential thermal analyzer (TG-DTA) and NH3-temperature programmed desorption (NH3-TPD). The catalytic activity for Friedel-Crafts acylation with 1,3-dichlorobenzene and andacetyl chloride to synthesis 2,4-dichloroacetophenone was investigated by gas chromatography.The results indicate that theα-LiNbWO6 which was synthesized by solid phase was the typical layered structure,and as same as HNbWO6, Fe0.33NbWO6, HNbWO6/Fe2O3, HNbWO6/Fe2O3-SO42-, HNbWO6 nanosheets. There was a relative sliding of the adjacent slabs by (a+b)/2 after modification.The interlayer channel of Fe0.33NbWO6, HNbWO6 nanosheets did't obviously change for 0.2291nm,0.2168nm as same with HNbWO6 of 0.2269nm,which was the distance equilibrated between layers, but Fe2O3 can added the interlayer channel to 0.3138nm,0.3424nm, respectively. From the changes of skeleton peak by modification before and after through infrared research,it was found that the extension stretching vibration peaks of Nb=O and W-Od modified by H+,Fe3+,Fe2O3,Fe2O3-SO42- occurred shift to high-frequency region, relatively toα-LiNbWO6. The peaks of W-O-W of HNbWO6,Fe0.33NbWO6,HNbWO6/Fe2O3 and HNbWO6/Fe2O3-SO42- occurred shift to low-frequency area.The peaks of O-Nb-O of HNbWO6 and Fe0.33NbWO6 occurred shift to low-frequency area, because layer board electron density changed after ion-exchange by H+, Fe3+,but there was no change for HNbWO6/Fe2O3 and HNbWO6/Fe2O3-SO42-.In the acidity characteristic,the acid order was HNbWO6>HNbWO6/ Fe2O3-SO42->HNbWO6/Fe2O3>HNbWO6 nanosheets>Fe0.33NbWO6.the acid sites of HNbWO6 evenly distributed in the moderate strong acid 567K and strong acid 710K. The acid strength of HNbWO6 nanosheets were decreased obviously to 525K and 618K,but the acid content increased because the acid sites exposed out after exfoliating. The peaks of HNbWO6/Fe2O3, HNbWO6 /Fe2O3-SO42- was at 664K,689K respectively. There were a few more strong acid bits, located in 816K.819 K, which indicated that this result was caused by the coordination function of L acid and B acid.The results of catalytic activity of all catalyst for Friedel-Crafts acylation were that the catalyst HNbWO6 and Fe0.33 NbWO6 in the Friedel-Crafts acylation reaction for 2,4-dichloroacetophen-one with m-dichlorobenzene and acetyl chloride as raw material did't show catalysis because narrow interlayer channel prevented the reactant molecules to penetrate into the interlayer space to utilize the H+ and Fe3+ ions as a catalyst. HNbWO6 nanosheets exposed H+ between layers for m-dichlorobenzene and acetyl chloride reaction in surface,but the acid strength obviously reduced, so there was no catalytic function. HNbWO6/Fe2O3 and HNbWO6/Fe2O3-SO42- not only increased the interlayer channel,but also the catalytic activity. It was not ideal owing to the interlamellar spacing not enough to make m-dichlorobenzene overcome resistance to pass in and out smoothly, and led to low yield rate. The yield of HNbWO6Fe2O3-SO42- increased by extending time,but the reaction rate had basically unchanged.It testified that the repellant was the main reason for reaction speed.