Ni2P/介孔分子筛催化剂的原位漫反射红外光谱研究

In Situ Diffuse Reflectance FTIR Spectroscopy Study of CO Adsorption on Ni_2P/Mesoporous Molecule Sieve Catalysts

以介孔分子筛MCM-41,MCM-48,SBA-15,SBA-16为载体,硝酸镍为镍源,磷酸氢二铵为磷源,通过浸渍法制备了含有磷化镍前体的介孔分子筛样品,然后在氢气气氛中进行程序升温还原,得到了磷化镍/介孔分子筛催化剂。采用原位漫反射红外光谱法,用CO作为探针分子,对样品的吸附特征进行了研究。结果表明,在介孔分子筛表面CO存在着较弱的物理吸附。在Ni2P/MCM-41催化剂样品表面有四种CO的吸附态:(1)在2055cm-1处形成的Ni(CO)4物种的吸附,(2)在2091cm-1处的配位不饱和Niδ+(0<δ<1)物种上的吸附,(3)在2127cm-1处的Ni+物种上的吸附,(4)在2198～2202cm-1范围内的P物种上的吸附。在Ni2P/MCM-48,Ni2P/SBA-15,Ni2P/SBA-16催化剂样品表面有二种CO的吸附态:在2051～2055cm-1处的Ni(CO)4吸附和在2093～2096cm-1处的配位不饱和Niδ+(0<δ<1)物种上的吸附。

The supported nickel phosphate precursors were prepared by incipient wetness impregnation using nickel nitrate as nickel source, diammonium hydrogen phosphate as phosphorus source, and MCM-41, MCM-48, SBA-15 and SBA-16 as supports, respectively. Then, the supported Ni2P catalysts were prepared by temperature-programmed reduction in flowing H2 from their nickel phosphate precursors. The in situ diffuse reflectance FTIR spectroscopy （DRIFTS）analysis with the probe molecule CO was carried out to characterize the surface properties. The results indicated that there were significant differences in the spectral features of the samples. The uco absorbances observed for adsorbed CO on mesoporous molecule sieve was attributed to weak physical adsorption. There are four different kinds of uco absorbances observed for adsorbed CO on Ni2P/MCM-41 catalyst with the following assignments. （1）the formation of Ni（CO）4 at 2 055 cm^-1. （2）CO terminally bonded to cus Ni^δ- （0〈δ〈1）sites at 2 091 cm^-1. （3）CO terminally bonded to Ni^＋ sites at 2 127 cm^-1. （4） CO terminally bonded to P and form P=C=O between 2 198 and 2 202 cm^-1. There are two different kinds of uco absorbances observed for adsorbed CO on Ni2P/MCM-48, Ni2P/ SBA-15 and Ni2P/SBA-16 catalysts. The absorbance observed at 2 051-2 055 cm^-1 for CO adsorption on Ni2P/MCM-48, Ni2P/ SBA-15 and Ni2P/SBA-16 catalysts is due to the formation of Ni（CO）4 species. The other uco absorbances observed at 2 093- 2 096 cm^-1 was attributed to CO terminally bonded to cus Ni^δ＋ （0〈δ〈1）sites.