Mg的添加对PtNa/Sn-ZSM-5催化丙烷脱氢反应性能的影响

通过X射线衍射(XRD)、N2吸附、透射电镜(TEM)、NH3程序升温脱附(NH3-TPD)、H2程序升温还原(H2-TPR)和O2程序升温氧化(O2-TPO)等多种表征手段及催化反应性能评价,研究了镁助剂的添加对PtNa/Sn-ZSM-5催化丙烷脱氢反应性能的影响.结果表明:适量Mg的添加(0.3%和0.5%,质量分数)能促进催化剂表面金属粒子的分散,减少反应过程中积碳的产生.Mg的引入能有效抑制催化剂中Sn组分的还原,使更多量的Sn组分以氧化态形式存在,有利于丙烷脱氢反应的进行.但是,过量Mg的加入导致催化剂表面金属颗粒易于发生团聚,高温下Sn组分易于被还原,不利于反应的进行.在本实验中,0.5%Mg加入后PtNa/Sn-ZSM-5催化剂显示出最佳的反应性能,反应7h后,丙烷转化率仍然高达38.7%,对应的丙烯选择性能够维持在95%以上.

Effects of Mg Addition on Catalytic Performance of PtNa/Sn-ZSM-5 in Propane Dehydrogenation

The effects of Mg addition on the catalytic performance of PtNa/Sn-ZSM-5 in propane dehydrogenation was investigated using catalytic reaction performance tests and physicochemical characterizations such as X-ray diffraction(XRD),nitrogen adsorption,transmission electron microscopy (TEM),NH 3 temperature-programmed desorption(NH3-TPD),H2 temperature-programmed reduction (H2-TPR),and O 2 temperature-programmed oxidation(O2-TPO).It was found that addition of appropriate amounts of Mg(0.3%and 0.5%,mass fraction)promoted the dispersion of metallic particles and decreased carbon deposition.In these cases,the presence of Mg in the PtMgNa/Sn-ZSM-5 catalyst could inhibit reduction of Sn species,thus more Sn could exist in oxidized states,which is advantageous to the reaction. However,when the content of Mg was excessive,the metallic particles were not well distributed and the particles agglomerated more easily.Moreover,the reduction of Sn species at high temperatures is relatively easy,which is disadvantageous to the reaction.In our experiments,the addition of 0.5%Mg to the PtNa/Sn-ZSM-5 catalyst gave the best catalytic performance.After reaction for 7h,higher than 95% selectivity toward propene was achieved with a corresponding propane conversion value of 38.7%.