不同载体负载Pd催化剂上氢气选择催化还原氮氧化物

将酸碱性不同的载体负载Pd催化剂用于氢气选择催化还原氮氧化物(H₂-SCR)研究。在0.091%NO、0.009%NO₂、0.5%H₂、10%O₂以N₂为平衡气和气体质量流速(W/F)0.06 g·s·cm^-3条件下,碱性载体MgO负载Pd催化剂表现出较好的催化活性,而酸性载体HZSM-5负载Pd催化剂上几乎没有氮氧化物转化。采用BET、CO₂-TPD、Py-FTIR、NOx-TPD和反应红外(IR)对载体及其负载Pd催化剂进行比表面积、表面酸碱性、吸附NOx能力以及NOx吸附生成表面物种进行表征。结果表明,载体酸性越弱,碱性越强,其吸附NOx能力较强,催化剂载体表面吸附生成的含氮物种较多,在Pd表面吸附活化生成的H溢流至载体并将含氮物种还原,这是负载Pd催化剂在H₂-SCR反应中活性较高的原因。

Selective catalytic reduction of NOx by hydrogen over Pd catalyst with different supports

Supports with different acid-base properties were used as carriers in Pd based catalyst in study of selective catalytic reduction of nitrogen oxide by hydrogen in presence of excess oxygen (H₂-SCR).Under the condition of 0.091%NO,0.009%NO₂,0.5%H₂,10%O₂,N₂ as balance gas and gas mass flow rate(W/F)=0.06g·s·cm^-3,Pd/MgO exhibited higher activity in H₂-SCR,while Pd/HZSM-5 showed almost no conversion of NO_x.BET,carbon dioxide -temperature programed reduction (CO₂-TPD),pyridine-infrared spectroscopy (Py-FTIR),nitrogen oxide-temperature programed reduction (NOx-TPD) and FT-IR were employed to characterize the specific surface area,surface acidity and basicity,adsorption capacity of NO_x and the surface species of NO_x over catalyst.The results indicated that the weaker the acidity of the carrier and the stronger the alkalinity of the support,the higher adsorption capacity of NO_x.In H₂-SCR,more nitrogen species were formed on the support surface,and H₂ was adsorbed and activated into H on Pd surface,then H was overflowed to the support and the nitrogen species were reduced,which should be the origin of the higher activity of stronger alkalinity support based Pd catalyst.