Preparation Of Hexaaluminate Catalyst And Its Application In Catalytic Combustion Of The New Energy-Dimethyl Ether (DME)

The Dimethyl Ether(DME)Chemistry is a novel project for the researchers. The preparation of hexaaluminate catalysts and their application in catalytic combustion of new fuel-DME were studied in this thesis.A reverse microemulsion solution consisted of heptane,triton X-100,octanol and water was selected.The study on its phase transfer behavior showed that a relatively stable reverse microemulsion system was established at the Km(weigh ratio of octanol and emulsifier triton X-100)of 0.779.Hexaaluminate catalysts were prepared in the reverse microemulsion solution with different water contents,and characterized by XRD,BET and TEM.The results showed that the reverse microemulsion system with water of 15%(volume ratio)was suitable in the preparation of nanostructure hexaaluminate catalysts.The nanostructure of hexaaluminate catalyst BaMnAl₁₁O_19-δ showed a length of 10～30nm plate-like phase and surface area of 106m²/g when prepared in this system and calcined at 1200℃for 4 hours.Compared with sol-gel and coprecipitation methods,the reverse microemulsion method had obvious advantages in the preparation of hexaaluminate catalysts.In this thesis,when compared with common drying method,the supercritical drying method made the catalysts a bigger surface area in the preparation of hexaaluminate catalysts.The catalytic activity of BaMnAl₁₁O_19-δprepared by different methods was evaluated in the DME catalytic combustion.The catalyst prepared by reverse microemulsion method showed higher activity of T_10%at 160℃and almost 100 %conversion at 320℃.More than 100h of the DME catalytic combustion was carried out on the catalyst at 320℃.The result showed that the DME conversion remained almost unchanged for 100h,which meant that the catalyst had excellent stability.The catalyst BaMnAl₁₁O_19-δpreparated by the method of the recovery reverse microemulsion solution also showed high thermal stability and high activity in DME catalytic combustion.Thus,the reverse microemulsion method was an effective and economic way to prepare nanostructural hexaaluminate catalysts.The hexaaluminate catalysts modified by different mirror cations and active components were characterized by TG-DTA,XRD,BET and TEM.And they were used in DME catalytic combustion.It was found that Ba-hexaaluminate ofβ-Al₂O₃ structure had the best thermal stability and activity.The phase transition temperature of La-hexaaluminate of MP structure was lower than that of Ba-hexaaluminate.The impact of active components in hexaaluminate was determined by the radius of active component and the preparation method.In the hexaaluminates modified by Ni²⁺,Mn²⁺, Cu²⁺et al.,BaMnAl₁₁O_19-δshowed the best catalytic activity.BaMnAl₁₁O_19-δwas characterized by TPO,TPR and XPS and the results showed that the adsorbed oxygen in the catalyst might be a key in the ignition process of DME combustion,so the bigger surface area of the catalyst was,the more effective combustion could occur.The active component Mn could improve catalytic activity of hexaaluminate catalyst because of Mn³⁺/Mn²⁺redox reaction to make lattice oxygen of the catalyst produce effective action.The bond Al-O provided a stable structure for hexaaluminate,and the bond Ba-O provided better thermal stability when Ba was modified into hexaaluminate structure.The thermal decomposition kinetics of hexaaluminate precursor was studied by TG-DTA with various rising rates of temperature.Mechanism function of hexaaluminate precursor was determined by integral form G(α)=[-ln(1-α)]⁴ and differential form f(α)=(1/4)(1-α)[-ln(1-α)]^-3.The thermal decomposition reaction of the precursor was in random nucleation and subsequent growth mechanism.The result of activation energy calculated by Coats-Redfern method was 187.80kJ/mol,which had a good agreement with that calculated by Kissinger method.It showed the result was reliable.The combustion process was first analyzed by BP neural networks.Their corresponding relation was established.The XRD patterns of La,Sr,Ba-hexaaluminate were predicted.The forecasting of the catalytic effects during the DME catalytic combustion was partly intelligentized.The study on the DME Chemistry is very important,and we did some original researches on the DME combustion.