PdCl_2/SiO_2和Pd-B/SiO_2非晶态合金催化剂的Raman光谱表征

Characterization of PdCl 2/SiO 2and Pd B/SiO 2 Amorphous Alloy Catalyst by Raman Technique

采用共焦显微Ｒａｍａｎ光谱和Ｘ－射线衍射方法表征了负载型ＰｄＣｌ２／ＳｉＯ２和Ｐｄ－Ｂ／ＳｉＯ２非晶态合金催化剂的结构。结果表明ＰｄＣｌ２分散在ＳｉＯ２载体上后，与载体表面的相互作用使其在室温时即发生β→α构型转变。Ｐｄ－Ｂ／ＳｉＯ２非晶态合金的Ｒａｍａｎ光谱在３００－５００ｃｍ－１区域内呈现一大的弥散峰。与无负载Ｐｄ－Ｂ非晶态合金比较初步认定该弥散峰与Ｐｄ－Ｂ键振动有关，温度升高Ｐｄ－Ｂ／ＳｉＯ２催化活性下降，其主要原因为Ｐｄ－Ｂ／ＳｉＯ２非晶态合金在高温下逐渐晶化为Ｐｄ金属所致。ＰｄＣｌ２与ＳｉＯ２载体表面的相互作用使其具有较高的分散性，由此还原制备的Ｐｄ－Ｂ／ＳｉＯ２非晶态合金较之无负载Ｐｄ－Ｂ非晶态合金更加微细化。

Confocal micro Raman spectroscopy and XRD have been used to characterize the silica supported PdCl 2powder (PdCl 2/SiO 2) and Pd B amorphous alloy catalyst (Pd B/SiO 2) formed by reducing PdCl 2on silica with KBH 4 The results show that PdCl 2undergoes a change in configuration from hexametric Pd 6Cl 12 with octahedral clusters of Pd atoms (β form) to infinite chains of coplanar PdCl 4/2 (α form) at room temperature The assignment of Raman peaks of Pd B/SiO 2amorphous alloy is quite difficult A broad band appeared in the 300-500 cm -1 region may be due to Pd B bond vibration by comparision with that of supporter free Pd B amophous alloy. Pd B supported on SiO 2converted gradually to metallic Pd when heated in N 2from 673 K up to 873K This may be the reason for its decreasing catalytic ability with increas ing temperature The interaction between PdCl 2and silica supporter makes a higher degree of dispersion of PdCl 2, resulting in a larger active surface for Pd B/SiO 2than the supporter free Pd B amorphous alloy