| Dipentene is a by-product of camphor and terpineol manufacture from turpentine that can be used as an economical renewables.p-Cymene is an important fine chemical intermediate that widely used for syntheses of fragrances,flavourings,herbicides etc.The dehydrogenation of dipentene to p-cymene is an important pathways for using the readily available renewable feedstock.SBA-15 is a new kind of mesoprous silica material,which has large surface area and high hydrothermal stability.In this paper,using SB A-15 as carrier,a series of SO42-/ZrO2-MxOy/SBA-15 catalysts were prepared by simple impregnation followed by vacuum-treatment.Our work focuses on the supported SO42-/ZrO2-MxOy/SBA-15 catalysts and its selective dehydrogenation of dipentene to p-cymene.The paper is mainly includes three parts:1.The SO42-/ZrO2 solid acid catalysts were prepared by the way of deposition and infusion,then p-Cymene was prepared from dipentene through catalytic dehydrogenation over the catalysts.The effects of the catalysts' synthesis and reaction conditions on catalytic activity were investigated as well.The catalysts were characterized by Brunauer-Emmett-Teller(BET),X-Ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),Thermogravimetry analysis(TG),and Differential scanning calorimetry(DSC).The number of acid sites on the catalysts were measured by the potentiometric titration of n-butylamine.The results indicated that the SO42-/ZrO2 catalysts possessed a fairly high catalytic activity for the dehydrogenation reaction under the calcination temperature of 500?700?,tetragonal and monoclinic phase of ZrO2(in catalysts)were appeared and the SO42-could combined with ZrO2 through chelate and bridge connection mainly.However,at 800?,Most of the crystal structure of ZrO2 on the catalysts were monoclinic phase and only few were tetragoral phase,and the catalysts was deactivated.The acidity of catalysts could be regulated by changing H2SO4 concentration and the catalysts'calcination temperature.The decrease of H2SO4 concentration,the increase of calcination temperature and reaction temperature as well as,these three factors all contributed to the increase the conversion of dipentene and selectivity of p-cymene.The fresh prepared catalysts was more activity,and they could be reused for three times by simple treatment.Under the conditions(H2SO4 concentration of 0.1 mol·L-1,catalyst calcination temperature of 700?,reaction temperature of 170 ?,reaction time of 1 h and catalyst dosage of 2 wt.%),the dipentene conversion and the p-cymene selectivity could reach to 100%and 33.39%,respectively.2.Using SBA-15 as carrier,a series of SO42-/ZrO2/SBA-15 catalysts were prepared by simple impregnation followed by vacuum-treatment.The catalysts were characterized by BET,XRD,FT-IR,TG-DSC and Transmission electron microscope(TEM).The number of acid sites on the catalysts was measured by the potentiometric titration of n-butylamine.The effects of the catalysts' synthesis and reaction conditions on catalytic activity were investigated,and a possible reaction mechanism was proposed as well.The results indicated that the vacuum-impreged catalysts exhibited highly active in the conversion of dipentene.After loading of SO42-/ZrO2 on SBA-15 led to a decrease in its specific surface area.Meanwhile,total pore volumes,micropore surface areas and the micropore volumes of the modified catalysts were also much smaller than that of pristine SBA-15 while the average pores diameter showed higher.The most SO42-/ZrO2 species could be highly dispersed in the pores of host SBA-15 at low ZrO2 loadings,while at high ZrO2 loadings,the blocking of the SBA-15 mesoporous channels and the agglomeration of excessive SO42-/ZrO2 species on the external surface of the SBA-15 occurred.The decrease of ZrO2 loadings and S/Zr molar ratios,increase of calcination temperature,reaction temperature and reaction time all contributed to the increase the selectivity of p-cymene.Moreover,the selectivity of p-cymene well associated with acidity of these catalysts,and it could be improved by decreasing the strength of acid sites and the number of acid sites.Under the conditions(ZrO2 loadings of 4 wt.%,NH3·H2O/Zr=8,S/Zr=2,catalyst calcination temperature of 700?,reaction temperature of 170?,reaction time of 1 h and catalyst dosage of 2 wt.%),the dipentene conversion and the p-cymene selectivity could reach to 97.1%and 33.1%,respectively.And when the reaction time reached 6 h,the dipentene conversion and the p-cymene selectivity were increased to 100%and 40%respectively.The main products was p-cymene,and by-products were a-Terpinene,1-p-menthene,3-p-menthene and 2-p-menthene.Based on the selectivitys obtained for p-cymene and by-products,we proposed a mechanism relevant to the isomerization,polymerization and dehydrogenation/hydrogenation steps involved in the the reaction over SO42-/ZrO2/SBA-15 catalysts.3.Fe,Cu,Ni,Zn and Al were introduced into SO42-/ZrO2/SBA-15 as additives to improve the activity in catalytic dehydrogenation of dipentene.A sort of SO42-/ZrO2-MxOy/SBA-15(M=Fe,Cu,Ni,Zn,Al)catalysts were prepared by vacuum impregnation method,that characterized by BET.The number of acid sites on the catalysts was measured by the potentiometric titration of n-butylamine.The effects of the catalysts' acidity on catalytic activity were investigated.The characterization results indicated that loading of SO42-/ZrO2-MxOy on SBA-15 led to a decrease in specific surface area.Meanwhile,total pore volumes were also much smaller than that of pristine SBA-15 while the average pores diameter showed higher.The strength of acid sites of SO42-/ZrO2/SBA-15catalysts decreased significantly after modified by binary non-noble metals,and there were no very stronge acid sites on the surface of the catalysts.On the contrary,after modified by single non-noble metal,SO42-/ZrO2/SBA-15 catalysts' strength of acid sites increased slightly,and the catalysts still had very stronge acid sites.Activity test showed that the higher selectivity of p-cymene was over SZr-NiAl/SBA-15 and SZr-Zn/SBA-15 catalysts than others,and decrease of ZnO loadings and increase of calcination temperature all contributed to the increase the selectivity of p-cymene.Under the conditions(ZrO2 loadings of 4 wt.%,Zr/M=3:1,S/Zr=2,catalyst calcination temperature of 600?,reaction temperature of 130?,reaction time of 4 h and catalyst dosage of 2 wt.%),the p-cymene selectivity was maximized on SZr-Zn/SBA-15 than other SO42-/ZrO2-MxOy/SBA-15 catalysts,whereas the p-cymene selectivity were increased to 32.48%slightly higher than that of SZr/SBA-15(30.88%),and when the loadings of ZnO was decreased to 0.05%,the p-cymene selectivity was up to 36.17%.we also find that the SZr/SBA-15 catalysts modified by Ni and A1 Binary non noble metal is helpful to improve the selectivity of p-cymene,but needs to be further research. |
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