| 摘要: | 甲烷乾式重整反應由於活化能高需要在高溫下進行，因此觸媒會有嚴重的結焦。取得突破的方法之一是改進觸媒。Ni/MgO-Al2O3觸媒、Ni/MgO-Al2O3-AlPO4觸媒和核殼型觸媒具有活性高、選擇性好、穩定性好等優點，因此是目前有效的方法。第一種觸媒是Ni/MgO-Al2O3，將Ni負載在MgO-Al2O3上以改善其金屬分散性，從而提高其活性和抗燒結性。為了改善Ni/MgO-Al2O3觸媒，選擇用Al2O3-AlPO4來替換MgO-Al2O3擔體中的Al2O3。對不同鋁磷比和不同鍛燒溫度的Al2O3-AlPO4進行XRD及氮吸附分析並且和Al2O3比較，能發現Al2O3-AlPO4 (Al/P=5/1； 700°C鍛燒)的擔體其BET表面積大幅增加。因此如果將其製作成Ni/MgO-Al2O3-AlPO4觸媒，便能有效提升原本觸媒的反應表面積，進而在擁有一定穩定度下再次提高甲烷轉化率。Al2O3-AlPO4 (Al/P=5/1；700°C鍛燒)的擔體特性最好，可以進一步提高Ni/MgO-Al2O3-AlPO4 觸媒的性能。因此使用了不同鋁磷比但鍛燒溫度都為700°C的MgO-Al2O3-AlPO4擔體和Ni/MgO-Al2O3-AlPO4觸媒。研究發現，MgO-Al2O3-AlPO4 (Al/P=5/1)的擔體具有良好的特性，且擁有較高的 BET表面積以及BJH吸附累積孔體積。另一種觸媒為核殼形觸媒，其內部的活性金屬鎳被氧化鋁所包覆。此觸媒的製作過程中會有離子交換的反應，在此作用下鎳與擔體之間的作用力為三度空間，不同於常規觸媒的二度空間，從而增強活性金屬與擔體之間的相互作用力，進而提高觸媒的穩定性。而隨著鋁鎳比的增加，離子交換程度逐漸變強，因此呈現緻密的外殼，使的脫附平均孔徑降低，進而讓BET表面積增加且比一般的負載型觸媒來的大。;Methane dry reforming reaction needs to be carried out at a high temperature due to high activation energy, so that the catalyst would have serious coking. One of the ways to make a breakthrough is to improve the catalyst. The use of Ni/MgO-Al2O3 catalyst, Ni/MgO-Al2O3-AlPO4 catalyst and core-shell catalyst were the effective methods because of their high activity, high selectivity and excellent stability. The first catalyst was Ni/MgO-Al2O3, which Ni was supported on MgO-Al2O3 to improve its metal dispersion, thereby improving its activity and sintering resistance. To improve the Ni/MgO-Al2O3 catalyst, Al2O3-AlPO4 was chosen to replace the Al2O3 in the MgO-Al2O3 support. XRD and N2 sorption analysis were used to characterize the Al2O3-AlPO4 with different aluminum-phosphorus ratios and different calcination temperatures, to compare with Al2O3. It was found that the BET surface area of the Al2O3-AlPO4 (Al/P=5/1, calcined at 700°C) support increases greatly. Therefore, it was used in Ni/MgO-Al2O3-AlPO4 catalyst to effectively increase the surface area of the catalyst, and then increase the methane conversion and stability. The characteristics of Al2O3-AlPO4 (Al/P=5/1, calcined at 700°C) was the best, one can further increase the performance of the Ni/MgO-Al2O3-AlPO4 catalyst. Therefore, MgO-Al2O3-AlPO4 supports and Ni/MgO-Al2O3-AlPO4 catalysts with different aluminum-phosphorus ratios with the same 700°C calcination temperature were used. It was found that the support of MgO-Al2O3-AlPO4 (Al/P=5/1) had good characteristics, it has high BET surface area and BJH adsorption cumulative volume of pores. The other catalyst was with core-shell structure, which the active metal nickel was surrounded by the Al2O3 support. To product this catalyst, there was an ion exchange reaction. Under such reaction, the force between the active metal nickel and the support was 3-D space, which was different from the 2-D space of the conventional catalysts, so that the interaction force between the metal and the support was enhanced. It was beneficial to improve the stability of the catalyst. With the increase of aluminum-nickel ratio, the degree of ion exchange gradually became stronger, so it presented a dense shell, which reduced the desorption average pore diameter, then it would increase the BET surface area and was greater than that of conventional catalysts. |
