LiH_2PO_4改性对铂钨铝催化剂的影响

Effects of LiH_2PO_4 modification on platinum supported tungsten-aluminum composite oxide catalysts

采用浸渍-焙烧法制备不同用量LiH_2PO_4改性的铂钨铝催化剂(Pt-W/Al),通过X线衍射(XRD)、H_2程序升温还原(H_2-TPR)、CO脉冲吸附、H_2程序升温脱附(H_2-TPD)和NH_3程序升温脱附(NH_3-TPD)方法对催化剂进行表征。采用固定床反应器考察催化剂催化甘油氢解制1,3-丙二醇的性能。结果表明:一定量LiH_2PO_4的引入对Pt-W/Al的晶相结构影响不大,但会在催化剂表面形成少量无定形磷酸铝;一定量LiH_2PO_4的引入,有利于增大Pt-W/Al表面Pt的分散度,提高催化剂的H_2吸附性能,且在不影响催化剂总酸量的情况下,使强酸量减少,弱酸量增多;LiH_2PO_4的引入提高了Pt-W/Al催化甘油氢解的转化率和生成1,3-丙二醇的选择性,在引入LiH_2PO_4的用量为3%时,甘油转化率达到79.8%,1,3-丙二醇的选择性达到50.6%,而过量LiH_2PO_4的引入对其催化性能的进一步提升不明显。

A series of catalysts for platinum supported tungsten-aluminum composite oxide (Pt-W/Al) modified with LiH2PO4 were prepared via impregnation-calcinations.The physical-chemical properties of catalysts were characterized by X-ray diffraction (XRD),H2 temperature programmed reduction (H2-TPR),CO pulse adsorption,H2 temperature programmed desorption (H2-TPD) and NH3 temperature programmed desorption (NH3-TPD).The performance for glycerol hydrogenolysis to 1,3-propanediol over the prepared catalysts was investigated in a fixed-bed continuous-flow reactor.The modified catalysts with an appropriate amount of LiH2PO4 had little effect in the crystal structure.However,a certain amount of amorphous aluminum phosphate would form on the surface.LiH2PO4 could improve the dispersion of platinum in the catalysts and increase the hydrogen adsorption capacity of the catalysts.LiH2PO4 had little effect on the total acid of catalysts,but it could decrease the strong acid content and increase the weak acid one.An appropriate amount of LiH2PO4 could improve the conversion of glycerol and the selectivity of 1,3-propanediol.Pt-W/Al catalysts with 3% content of LiH2PO4 would improve conversion of glycerol to 79.8% and the yield of 1,3-propanediol to 50.6%.However,the introduction of excessive LiH2PO4 could not to further enhance the catalytic performance obviously.