Mo/ZSM-5催化剂体系上NO的选择性催化还原反应

Selective Catalytic Reduction of NO over Mo/ZSM-5 Catalyst

首先用浸渍法在HZSM 5上负载了不同的金属元素 (Mo ,Sn和Ni) ,并比较了它们在含氧条件下对NO分解反应的影响 .结果表明 ,Mo/ZSM 5的催化活性最高 .进一步用离子扩散法、浸渍法、物理混合法及合成法制备了四种Mo/ZSM 5样品 ,并以NH3 为还原剂 ,考察了它们的NO的选择性催化还原反应性能 .结果表明 ,用离子扩散法制得的样品对NO还原反应的催化活性最高 ,在 36 0℃下 ,NO转化率可达 98% .同时 ,用XRD ,SEM ,ICP和EDS等技术对 4种样品的体相和表面结构进行了测试 .结果表明 ,用离子扩散法制得的样品 ,Mo元素在分子筛催化剂的内表面有很好的分散性 ,导致Mo/ZSM 5具有高的催化活性 .这可能是由于Mo元素迁移到分子筛的孔道内 ,在催化剂表面形成了有利于NO选择性催化还原反应的某种特殊活性结构 .

The objective of this work is to study the selective catalytic reduction (SCR) of NOx from diesel engine emissions over a new catalyst system and to find out the relationship between the activity of the catalyst and its surface structure. The catalysts doped with different metal elements (Mo, Sn and Ni) on HZSM-5 were prepared by using impregnation method. It was found that the Mo/ZSM-5 catalyst is the best one for NO decomposition reaction among Sn/ZSM-5, Mo/ZSM-5 and Ni/ZSM-5. Thus, four catalyst samples with Mo as active component were also prepared through different methods (ion-migration, impregnation, physically mixing and synthesizing). The results showed that, with NH3 as a reductant, and under the conditions of 0.06% NO-3.5 O-2-0.06%NH3-96.38%Ar and q(V)(feed)=300 ml/min, the catalyst prepared through ion-migration has the highest activity for SCR of NO and the NO conversion reaches to 95% at 360degreesC. The Mo/ZSM-5 samples were characterized by using XRD, SEM, ICP and EDS techniques respectively. The results indicated that the catalyst prepared through ion-migration has better dispersion of Mo on the inner surface of ZSM-5 than those prepared through other methods. This is probably responsible for its higher catalytic activity in SCR of NO. Then it was tentatively supposed that some special structure, which can favor the SCR of NO, may be in existence on the catalyst surface. On the other hand, the catalyst prepared through synthesis method showed good catalytic performance at low temperature, although its catalytic activity is lower than that of the sample prepared through ion-migration.