Ca对PtSn/MgAl_2O_4结构及丙烷脱氢性能的影响

Effects of Ca on the Structure and Propane Dehydrogenation Performance of PtSn/MgAl2O4 Catalysts

比较研究了经Ｃａ改性的ＰｔＳｎ／ＭｇＡｌ２Ｏ４在氮气及水蒸汽稀释下的丙烷脱氢性能，并利用ＴＰＲ、Ｈ２－ＴＰＤ、ＸＰＳ及脉冲氢吸附对催化剂进行了表征．结果表明，ＰｔＳｎ／ＭｇＡｌ２Ｏ４中加入０．５％的Ｃａ，增加了催化剂的丙烷脱氢活性，抑制了积炭失活．过量Ｃａ的加入则促进了催化剂中Ｓｎ组分的还原，生成了零价锡并可能与Ｐｔ形成合金，从而导致催化剂失活．在水蒸汽中反应时，水蒸汽一方面可调变催化剂结构，增加其脱氢活性；另一方面还可抑制催化剂表面积炭，改善其稳定性．

おtSn/MgAl2O4 catalysts doped with Ca were tested in the dehydrogenation of propane diluted with N2 and H2O respectively. The addition of 0.5% Ca to PtSn/MgAl2O4 promoted dehydrogenation activity in N2 and improved the resistance to deactivation due to suppressing carbon deposition on the catalyst surface. However, the incorporation of excessive Ca deactivated the catalyst. TPR and XPS results indicated that excessive Ca promoted the reduction of Sn4+ to Sn0. The Sn0 probably could interacte with Pt to produce a PtSn alloy which inhibited the conversion of propane to propene. The introduction of steam instead of N2 to the dehydrogenation reaction resulted in a significant increase of activity for all the catalysts. XPS showed that the addition of steam modified the distribution and nature of the surface tin atoms. Hydrogen chemisorption experiment revealed that preating the catalyst in steam increased the high temperature adsorption sites of the catalysts. These results suggest that the activity increase of the catalysts for propane dehydrogenation in steam could be probably ascribed to the modification of catalysts by steam.