碱金属改性对Pd-Au/Al2O3催化剂上异戊二烯选择加氢性能的影响

采用等体积浸渍法制备出了不同K2O、Li2O含量的Pd-Au/Al2O3催化剂，采用低温氮吸附法、FT-IR、H2-TPR等方法进行了表征研究。吡啶吸附红外光谱表征结果表明，催化剂表面只有L酸，无B酸，K2O改性比Li2O改性催化剂的表面酸性弱。H2-TPR表征结果表明，催化剂表面形成了Pd-Au二元合金，加入碱金属改性后，催化剂的还原峰向高温方向移动。以异戊二烯的模型化合物为原料评价了自制的改性Pd-Au/Al2O3催化剂的选择加氢性能，结果表明：催化剂经过Li2O改性后，异戊二烯的转化率和单烯烃选择性提高，而用K2O改性时，异戊二烯的转化率降低，单烯烃选择性提高； 采用K2O-2催化剂，在反应温度为70 ℃时异戊二烯的转化率为90.0%，单烯烃的选择性为86.0%。

EFFECT OF ALKALI METAL MODIFICATION ON SELECTIVE HYDROGENATION OF ISOPRENE ON Pd-Au/AL2O3 CATALYSTS

A series of Pd-Au/Al2O3 catalysts modified by different amount of alkali metal K or Li were prepared by incipient wetness impregnation and characterized by low temperature nitrogen adsorption, FT-IR and H2-TPR techniques. The isoprene was used to evaluate the selective hydrogenation performance of the modified catalysts. The FT-IR results show that only Lewis acid sites exist on the catalysts, no Bronsted acid is found. The acid strength of K-modified catalyst is weaker than Li-modified catalyst. The H2-TPR results indicate that Pd-Au binary alloy is formed, the reduction peaks of catalysts shift to higher temperature after modified by alkali metals. The reaction results of isoprene selective hydrogenation on the modified Pd-Au/Al2O3 catalysts show that the isoprene conversion and isopentenes selectivity increase when addition of K2O. The LiO modification reduces the conversion of isoprene but isopentenes selectivity increases. At 70 ℃, isoprene conversion reaches 90.0%, isopentenes selectivity is 86.0% on the catalyst Pd-Au/Al2O3 with 1.2% K2O.