Pt，Pd助剂对Ni基催化剂中Ni的分散度及抗积碳性能的影响

研究了添加少量贵金属(Pt,Pd)的Ni/Al2O3催化剂对甲烷水蒸汽重整反应抗积碳能力和催化性能的影响.催化活性实验表明,添加少量Pt的样品显著提高了Ni/Al2O3催化剂的活性,稳定性,抗积碳和抗氧化能力,而添加Pd的样品对Ni/Al2O3催化剂的催化性能提高并不明显.利用氢气程序升温还原(H2-TPR),X射线晶体衍射(XRD),热重-差热分析(TG-DTA)等手段对反应前后的催化剂进行了表征,研究发现在Ni-Pt/Al2O3催化剂中Ni与Pt之间存在较强的相互作用力,在主要由Ni覆盖的表面形成了Ni-Pt双金属簇,提高了Ni的分散度,在催化剂的表面易于形成较小的Ni颗粒,抑制了Ni的烧结,改善了Ni基催化剂的抗积碳能力;贵金属Pt通过H2的溢流效应促进了Ni的还原,抑制了催化剂的氧化.而在Ni-Pd/Al2O3中,Ni和Pd存在着一定的偏析效应,不能有效的形成Ni-Pd双金属簇,在还原过程中分别被还原.

The Effect of Pt, Pd Promoters on the Dispersion of Ni and the Ability to Coke Resistance of Ni-based Catalyst

This paper studies the effect of noble metal addition (Pt, Pd) to supported Ni/Al2O3 towards the ability to coke resistance and catalytic activity for the reaction of steam reforming of methane. The results have shown that in the case of Ni/Al2O3 catalyst, the addition of Pt strongly enhances the catalytic activity, stability, the abilities to coke resistance and oxidization. The sample with addition of Pd does not improve the catalytic performance obviously. On the basis of H2-TPR, XRD and TG-DTA characterization measurements, it has been proposed that there exist strong metal-metal interaction between Ni and Pt due to the formation of Ni-Pt clusters with the surface mainly covered by Ni. This leads to an increase in the metallic dispersion, favoring the formation of small Ni particles on the surface of Ni-based catalysts, which in-turn inhibit the sintering of Ni and improve the ability to coke resistance. The presence of Pt promotes the reduction of the Ni precursor by a spillover effect of H2, retarding the oxidization of Ni. However, in Ni-Pd/Al2O3 catalyst, Ni and Pd tends to be separately reduced with a segregation effect of Pd and Ni on the surface, Ni-Pd clusters do dot formed in the sample.