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开发高活性的顺酐加氢制丁二酸酐和γ-丁内酯催化剂具有重要的工业意义.顺酐加氢多采用Cu基和Ni基催化剂,但一般Cu基和Ni基催化剂存在反应温度高(170–260°C)和稳定性差等缺点,很有必要开发高活性的顺酐加氢催化剂.我们以拟薄水铝石作为Al_2O_3载体的前驱体,采用浸渍法制备了一系列镍铝尖晶石型衍生的不同Ni含量的Ni/Al_2O_3催化剂,并研究了它们在顺酐加氢反应中的催化性能.还原前Ni/Al_2O_3催化剂的X射线衍射结果表明,催化剂含有NiAl_2O_4物种.氮吸附结果显示,不同Ni含量的催化剂均具有介孔结构.氢-程序升温还原研究发现,Ni/Al_2O_3催化剂经750°C还原2 h后,其表面上NiAl_2O_4物种能被高效还原.X射线粉末衍射结果表明,750°C还原的Ni/Al_2O_3催化剂中金属Ni颗粒尺寸随着Ni负载量升高而增大.利用一氧化碳-程序升温脱附对750°C还原的Ni/Al_2O_3催化剂进行研究,发现750°C还原的催化剂上金属Ni物种含量从高到低依次为:Ni(7.5%)/Al_2O_3>Ni(5%)/Al_2O_3>Ni(2.5%)/Al_2O_3.采用CO化学吸附获得的Ni(2.5%)/Al_2O_3,Ni(5%)/Al_2O_3和Ni(7.5%)/Al_2O_3催化剂上金属Ni颗粒尺度分别为8.0,12.8和15.7 nm.活性研究结果表明,750°C还原的Ni(5%)/Al_2O_3催化剂具有最高的催化活性,这可能是由于Ni(5%)/Al_2O_3催化剂具有较多的Ni活性位点和较合适的Ni颗粒粒度所致.进一步研究发现,在650–750°C还原温度下,Ni(5%)/Al_2O_3催化剂的还原度随着还原温度的升高而升高,Ni分散度随着还原温度的升高而降低.活性结果研究表明,700°C还原的Ni(5%)/Al_2O_3催化剂具有较多的Ni活性位点和较合适的Ni颗粒粒度,具有最高的加氢催化活性,其在120°C,H_2压力为0.5 MPa和质量空速为2 h~(-1)的反应条件下,能获得近100%的顺酐转化率和90%的丁二酸酐选择性,同时该催化剂具有优良的稳定性.以上结果表明,尖晶石型衍生的Ni/Al_2O_3催化剂是一个十分有应用前景的顺酐加氢催化剂.
Development of highly active maleic anhydride hydrogenation of succinic anhydride and γ-butyrolactone catalyst has important industrial significance.Malladium-based and Ni-based catalysts are mostly used in the hydrogenation of maleic anhydride, but generally Cu-based and Ni-based catalysts have high reaction temperature (170-260 ° C) and poor stability, it is necessary to develop highly active maleic anhydride hydrogenation catalyst.We prepared pseudo-boehmite as a precursor of Al 2 O 3 support by impregnation method to prepare a series of nickel-aluminum tip Spinel-derived Ni / Al_2O_3 catalysts with different Ni contents and their catalytic performance in the hydrogenation of maleic anhydride were studied.The X-ray diffraction results of the Ni / Al_2O_3 catalyst before reduction showed that the catalyst contained NiAl_2O_4 species.The results of nitrogen adsorption It was found that the catalysts with different contents of Ni all have mesoporous structures.It has been found by the hydrogen-temperature programmed reduction study that NiAl_2O_4 species can be efficiently reduced on the surface of Ni / Al_2O_3 catalyst after reduction at 750 ° C for 2 h.The results of X-ray powder diffraction , The size of Ni metal particles increases with increasing Ni loading in Ni / Al_2O_3 catalyst reduced at 750 ° C. The reduction of Ni / Al_2O_3 catalyst at 750 ° C by carbon monoxide-temperature programmed desorption was studied and found that 750 ° C also (Ni) / Al_2O_3> Ni (2.5%) / Al_2O_3> Ni (2.5%) / Al_2O_3, respectively.The Ni (2.5%) / The Ni (5%) / Al_2O_3 and Ni (7.5%) / Al_2O_3 catalysts exhibited a typical Ni particle size of 8.0, 12.8 and 15.7 nm, respectively. The results of the activity studies show that the Ni (5%) / Al_2O_3 catalyst reduced at 750 ° C Which may be attributed to the fact that Ni (5%) / Al 2 O 3 catalyst has more sites of Ni active sites and more suitable size of Ni particles.Further study found that at 650-750 ° C reduction temperature, The reducibility of Ni (5%) / Al 2 O 3 catalyst increased with the increase of the reduction temperature and the Ni dispersion decreased with the increase of the reduction temperature.The results of the activity test showed that the reduction of Ni (5%) at 700 ° C, / Al 2 O 3 catalyst has more Ni active sites and more suitable Ni particle size and has the highest hydrogenation catalytic activity at 120 ° C, H 2 pressure of 0.5 MPa and mass space velocity of 2 h -1, Of the reaction conditions, can be nearly 100% conversion of maleic anhydride and 90% of succinic anhydride selectivity, while the catalyst has excellent stability of the above results show that the spinel-derived Ni / Al 2 O 3 catalyst is a very promising maleic anhydride hydrogenation catalyst.