The Decomposition Of KNO₃on The Surface Of MgO/ZrO₂and The Stablity And Alkaline Activity Of The Surface Tetragonal Phase

In this paper, ZrO₂was served as the supporter and Mg²⁺was the ion that couldstabilize the ZrO₂tetragonal phase, which were impregnated in the KNO₃solution withdifferent KNO₃content, and a certain amount of La₂O₃were also added to the solution asthe promoter. After that, the solid base catalysts of K₂O-x/MgO-ZrO₂andK₂O-x/MgO-ZrO₂-La₂O₃were prepared. The catalytic performances of the catalysts wereevaluated by XRD, Raman spectrum, CO₂-TPD, acid base titration method and BET method.In the results, there is only tetragonal phase for the catalysts with distilled waterwashing, which were calcined at600and700oC. With La（NO₃）3co-precipitation, the ZrO₂tetragonal phase content increased in the catalysts. The BET surface area of the catalystcould be obviously increased by alcohol washing, which more easily interacted with KNO₃to form the K₂O-ZrO₂solid solution. After calcined at700oC, there were a small number ofmonoclinic phases in the catalyst, and the surface crystalling phase of ZrO₂could be greatlyinfluenced by the loading amount of KNO₃. The appropriate amount of KNO₃loaded couldeffectively stabilize the surface ZrO₂tetragonal phases, while the excess amount loaded isadverse for the stabilization of the surface ZrO₂tetragonal phase, and could generate thesurface monoclinic phases.With increasing the loading amount, the super basic sites on the surface could be moreeasily formed. However, for excessive amount loaded, the basic sites of the catalyst can becovered by the potash dispersed on the catalyst, which drastically decreased the specificsurface area and the surface alkaline. With La（NO₃）3co-precipitation, the total alkali contentof the catalyst increased, and the co-precipitation process was beneficial for thedecomposition of KNO₃to form the super basic sites. The overmuch solid solution could beeasily generated by the catalyst washed by alcohol and KNO₃, which increased the strongbasic sites on the ZrO₂supporter and the total alkali content of the catalyst. During thesynthesis process of DEHC from the transesterification of DMC and EHOH, theproductivity increased as the loading amount K/Zr increased, which was between0.1and0.5. At700oC, a lot of potash was decomposed, which enchanced the alkalinity of thecatalyst, and the catalytic activity was higher. The increase of the loading amount couldeffectively promote the esterification of DMC and EHOH. For the above reaction, the optimum operation condition was determined as followed: with atmospheric condition,reaction time of3.5h was selected, the ratio of DMC to EHOH was about0.7:1, and theratio of catalyst to the feedstock was1.25%.In order to determine the synthetic product, FT-IR,1H-NMR, MS and gaschromatography were used. From above method, DEHC proved to be the synthetic product.According to the analyses of MS and gas chromatography, DECH appeared at1.5h, andintermediate product was completely vanished at3.5h, which indicated that theesterification was complete.