微乳化法制备Ni/Al_2O_3催化剂及其在甲烷部分氧化反应中的高温稳定性和抗积炭性能

Highly Coking Resistant and Stable Ni/Al_2O_3 Catalysts Prepared Using Microemulsion for Partial Oxidation of Methane

用传统的浸渍法,溶胶 凝胶法和微乳化法三种不同的方法制备均含Ni/Al2O3(w(Ni)=10%)催化剂(分别简称为IMP,Sol gel,ME).利用比表面测定(BET)、原位X 射线粉末衍射(XRD)、透射电子显微镜(TEM)等手段研究这三种方法制备的催化剂的不同之处.在常压下,固定床反应器中评价了三种催化剂对甲烷部分氧化制合成气反应的催化性能,发现三种催化剂的反应活性相当,但抗积炭性能却有明显不同.其中ME催化剂抗积炭性能最好.在温度为923K,x(O2)/x(CH4)=0.53的条件下,ME催化剂反应20h没检测出积炭生成,而反应5h后,Sol gel催化剂有少量积炭生成,平均积炭率为0.002g·g-1·h-1,而IMP催化剂有大量积炭生成,平均积炭率为0.085g·g-1·h-1.ME催化剂具有较大的比表面,较小的Ni颗粒且Ni与Al2O3之间有强烈的相互作用,这是微乳化法制备的Ni/Al2O3催化剂具有良好的抗积炭性能的重要原因.

Three Ni/Al2O3 catalysts with the same nickel content (10%)were prepared by conventional impregnation (IMP), solgel and microemulsion (ME) methods, respectively. Their catalytic activity and coking resistivity for partial oxidation of methane (POM) to synthesis gas were studied in a continuousflow microreactor under atmospheric pressure. Although three catalysts had comparable activity, they showed a great difference in coking resistivity. ME catalyst had excellent coking resistivity with no obvious coke observed even after 20 h of reaction on stream, under thermodynamically severe conditions (x(O2)/x(CH4)=0.53, 923 K). After 5 h of reaction on stream, a little coke deposited on Solgel, with an average coking rate of 0.002 g(carbon)·g(cat.)-1·h-1, however, fast and heavy coke deposition occurred on IMP catalyst, with an average coking rate of 0.085 g(carbon)·g(cat.)-1·h-1. ME catalyst possesses very high BET surface area and small metallic Ni particles. The small size of metallic Ni particles and the Ni metalsupport strong interaction are two key factors to prevent coke formation.