Study On Zr-based Composite Oxides For The Catalytic Conversion Of Ethanol To Light Olefins

Ethylene and propylene occupy an important position among chemical industry.Ethylene is mainly used in the production of polyethylene,ethylbenzene,ethylene oxide,two chloroethane,oligomer and so on.As the important basic chemical raw material in the petrochemical industry,the production trend of ethylene determines the development of the chemical industry.The demand for propylene downstream products,such as polypropylene,propylene oxide and acrylic acid,has been increasing.With the rapid development of bio-fermentation and bio-chemical technology,bioethanol production from biomass（especially lignocellulose）has made an important breakthrough,and is considered to be an important technology to increase ethylene and propylene production by combining organic chemistry and bio chemical industry.In order to promote the industrial application of ethanol to light olefins（ETO）technology,this paper mainly studies the preparation of zirconium based composite oxide catalysts.The catalytic performance of these Zr-based composite oxide catalysts for ethanol to light olefins was investigated.Molecular simulation methods were used to predict the catalytic reaction performance by calculating the defect formation energy of different metal doped zirconia catalysts.（1）The zirconia catalysts were synthesized by precipitation and calcination method.The zirconia catalysts were prepared by three different precipitation agents NH₃?H₂O,ethylenediamine and NaOH and two zirconium sources Zr（NO₃）₂?2H₂O and ZrOCl₂?8H₂O,then calcined at different temperatures 823、873、923 and 973 K.In the direct calcination method,the zirconia catalysts were also calcined directly in the same temperatures（823、873、923 and 973 K）.The catalysts were existed in the phase of monoclinic and had acidic and basic sites by BET、XRD、NH₃-TPD、CO₂-TPD characterizations.The catalytic performance for ethanol to light olefins was also investigated.With the increase of calcination temperature,the specific surface area and pore volume of the catalyst decreased,but the pore size increased.The excellent catalytic performance was obtained on zirconia catalyst.The optimum propylene yield reached 40.2%and the ethylene yield reached 33.0%,and the catalysts have favorable stability.（2）The catalytic performance of zirconia catalysts were improved by doping metals.The zirconium based composite metal oxides were synthesized by modification of the catalysts and applied into the ETO reaction.The BET characterization shows that the specific surface area of Bi（3）/ZrO₂ and Sr（5）/ZrO₂ catalysts increases from 49.7 m²/g to 70.4 and 71.8 m²/g,and the tetragonal zirconia is obtained by XRD spectrum analysis.The ethylene and propylene yields reached the highest 80.8%on Sr（1）/ZrO₂.Besides,the order of catalysts stability in ETO is Sr（1）/ZrO₂>Bi（1）ZrO₂>ZrO₂>H-ZSM-5（80）.（3）The effects of oxygen vacancies on the catalytic performance of these synthesized catalysts were investigated.Molecular simulation was carried out using DMol3 of materials studio through the first principles.The defect formation energy of zirconia and Sr or Bi modified zirconia were calculated.According to literatures and simulation results,the tetragonal zirconia（101）surface model was used to simulate the formation energy of oxygen defects of zirconia and its composite metal oxide.The simulation results showed that the oxygen deficiency formation energy of Sr doped zirconia was lower than that of pure zirconia and Bi doped zirconia,which was in accordance with the experimental results.The E_f of different oxygen defect on Sr/ZrO₂ was calculated:Osurf1<Osub1<Osurf2,which indicated that the oxygen vacancy in surf1 was the easiest to form.In addition,through the simulation of Sr/ZrO₂ charge density difference map and correlation analysis of the bond length,found the principle of oxygen defect becoming the active site:charges accumulated around the Zr atom increases.This indicates that after the loss of O,the unpaired electrons are transferred to Zr.This indicates that the role of O vacancy is to form an active site as an electron donor.