Synthesis, Characterization And Catalytic Performance Of Octahedra-based Aluminoborate

In this thesis, chromium doped aluminoborate Cr-PKU-5is synthesized usingborate melting method, the surface morphology, specific surface area, acidity strengthand hydrothermal stability of Cr-PKU-5are investigated using TEM, XRD, ESD, XPS,BET and TPD-NH3. Meanwhile, the catalytic ability of Cr-PKU-5in alcohol (methanol,ethanol and isopropyl alcohol) dehydration reactions is also investigated. The mainresults are as follow.1. The results of TEM show that the as-preparedCr-PKU-5samples is composedof nano-scaled brick-like particles with distinct facets, and the average diameter ofCr-PKU-5is in the range of30~60nm. XRD and EDS studies prove that Cr has beendoped into the PKU-5skeleton. TPD-NH3measurement indicates that by replacingAl3+with Cr3+, the acidity strength of PKU-5will be slightly affected and thus the acidamounts and acid site distribution will be slightly changed. The result of hydrothermalstability test implies that Cr-PKU-5can remain stable at600℃under hydrothermalenvironments, proving that the hydrothermal stability of Cr-PKU-5is relatively good.2. Methanol reaction system1) Cr-PKU-5have been used as catalysts in the catalytic decomposition ofmethanol. The main product of this reaction is dimethyl ether and the by-products areH2, CO and CH4. Thus, this decomposition reaction is mainly the methanoldehydration reaction and as Cr-PKU-5has a lot of strong acid center, methanol willdeeply dehydrate and those by-products are formed.2) The influences of reaction temperature, methanol WHSV and carrier gas flowrate on the catalytic activity of Cr-PKU-5are investigated. The results show that in thetemperature range of300~400℃, the conversion rate of methanol increases as thetemperature increased while the selectivity of DME decreases as the temperatureincreased. The selectivity reaches the highest value at400℃. In the WHSV range of0.79h-1~7.92h-1, the selectivity of DME increases and the conversion rate decreases asWHSV increased and after WHSV reached1.58h-1the selectivity tend to be constant.The flow rate of carrier gas only slightly influences the catalytic activity.3) The stability of Cr-PKU-5’s catalytic activity is also investigated and theresult shows that it will keep active for more than24h.4) The influence of Cr doping amount toward the catalytic activity is studied. The results collected at400℃are as follow. Conversion rate:12%Cr-PKU-5<8%Cr-PKU-5<10%Cr-PKU-5<14%Cr-PKU-5. DME selectivity:12%Cr-PKU-5>8%Cr-PKU-5>10%Cr-PKU-5>14%Cr-PKU-5. Yield:14%Cr-PKU-5>10%Cr-PKU-5>8%Cr-PKU-5>12%Cr-PKU-5.5) The influence of catalyst structure is investigated that the catalytic activity ofCr-PKU-1, Cr-PKU-5and Cr-Al4B2O9are compared and Cr-PKU-5possesses thehighest catalytic activity, which is owing to its unique structure.6) The comparison of the catalytic property between aluminoborate and γ-Al2O3is made. The results show that the DME selectivity ofγ-Al2O3is higher andaluminoborate has a stronger ability of hydrogen producing.7) The comparison of the catalytic property between Al4B2O9and Cr-Al4B2O9isalso carried out. The results show that activity of Al4B2O9is higher than it ofCr-Al4B2O9, while14%Cr-Al4B2O9can produce higher amount of hydrogen.3. Isopropyl alcohol reaction system1) The catalytic activities of PKU-1and PKU-5towards the dehydration ofisopropyl alcohol are tested and the results show that only dehydration reaction willoccur. When Cr-PKU-1and Cr-PKU-5are used, a dehydrogenation reaction will alsooccur along with the dehydration reaction.2) In order to investigate the effect of the Cr doping amount, PKU-1(Al-PKU-1,4%Cr-PKU-1,8%Cr-PKU-1and20%Cr-PKU-1) and PKU-5(8%Cr-PKU-5,10%Cr-PKU-5and12%Cr-PKU-5) with different Cr doping amount are used as catalyst inthe isopropyl alcohol dehydration reaction. The results show that as the Cr dopingamount increased, the catalytic activity of PKU-1in dehydrogenation and dehydrationreaction increase, while the Cr doping amount affect the catalytic activity of PKU-5slightly.4. Ethanol reaction system1) The catalytic property of Cr-PKU-5in ethanol reaction system is explored andpreliminary result is obtained that Cr-PKU-5has a catalytic effect on ethanol.