铁助剂对Pd／Al_2O_3催化剂抗硫性能的影响

Effect of Iron Promoter on the Resistance to Sulfur-Poisoning of Pd/Al_2O_3 Catalyst

借助ＣＯ探针分子原位红外（ｉｎ－ｓｉｔｕＩＲ）、ＴＥＭ（ＥＤＳ）、ＸＰＳ和ＸＲＤ对一系列Ｐｄ－Ｆｅ／Ａｌ_２Ｏ_３、Ｐｄ－Ｐｔ／Ａｌ_２Ｏ_３和Ｐｄ（或Ｐｔ）／Ａｌ_２Ｏ_３模型催化剂进行了表征，结果表明，硫在中毒Ｐｄ（或Ｐｔ）／Ａｌ_２Ｏ_３时，毒物Ｈ_２Ｓ优先吸附于催化剂的多位活性中心上，主要以电子效应影响催化剂的活性．铁的引入，提高了活性组分Ｐｄ的分散度，多位活性中心的减少不利于Ｈ_２Ｓ在催化剂上的吸附；Ｐｄ－Ｆｅ协同作用的结果，增强了催化剂对吸附Ｓ^（２－）氧化成毒性较小的Ｓ^（６＋）或可逸出系统的ＳＯ_２的能力，从而明显地提高了催化剂的抗硫中毒能力．

A series of modelled palladium- iron supported on alumina catalysts were prepared by impregnating method. By use of H2oxidation as a model reaction and H2S as a poison, the catalytic activity and the resistance to sulfur-poisoning of Pd-Fe/Al2O3catalyst for eliminating hydrogen from CO2feed gas for urea synthesis were evaluated in a fixed bed microreactor gas chromatograph system and were compared with DH-2 (Pd-Pt/Al2O3) and CN-101 (Pt/Al2O3) catalysts both of which have already been applied in industry. The results showed that the catalytic activity of the former was equivalent to that of the latter two and the former's resistance to sulfur-poisoning was much higher than that of the latter two. The medelled catalysts were characterized by in situ-IR (with CO as a probe molecule) ,TEM with EDS, XPS and XRD. It manifested that sulfur species initially poisoned the polyatomic active sites and then single ones of the catalysts. This involved not only blocking effect, but mainly an electronic effect, because of the weakening of d-π antibonding between the Pd sites and adsorbed CO. The addition of iron into the catalyst increased the dispersion of active component palladium hence decreased the number of polyatomic active sites. It indicates that the addition of iron was not in favor of H2S adsorption on the catalyst. The iron promoted the oxidation of adsorbed H2Sinto S6+ , which poisoned the catalyst only weakly, or SO2 , which may be released from the system and thus renders the catalyst more sulfur-resistant.