Ni-W/Al2O3表面NiWO4化合物的生成及其对加氢反应活性的影响

采用ＰＡＳＣＡ,ＥＳＣＡ,ＴＡ和微型反应色谱等技术研究了Ｎｉ－Ｗ／Ａｌ２Ｏ３催化体系。本工作是文献［４］工作的继续。由于固体表面在原子水平上的不均匀性,钨分散在氧化铝的“活性表面”上,并形成“微晶岛”。当钨以一个单分子层分散时,Ｗ／Ａｌ２Ｏ３表面仍然存在未被钨占据的“惰性表面”。在这种情况下,当镍分散到Ｗ／Ａｌ２Ｏ３中时,镍将优先占据这些“惰性表面”,并同其相邻的钨原子结合生成ＮｉＷＯ４化合物。Ｎ

FORMATION OF NiWO_4 AND ITS EFFECT ON HYDROGENATION ACTIVITY OF Ni-W/Al_2O_3 CATALYSTS

PASCA (positron annihilation spectroscopy for chemical analysis), ESCA, TA and micro-reactor have been used to study the Ni-W/Al2O3 catalysts with various Ni/W atomic ratios (R) .An interaction model for interpreting the states of Ni and W on alumina surface is presented, which is similar to the "island model" proposed by Clausen and Hall.The alumina surface can be divided into two parts: active area, where exists a number of surface sites, and inactive area.When loaded as a PASCA monolayer, the W reacts with surface sites on the active area to form metal-support interaction complexes.When Ni is introduced onto the W/A12O3 system, it will load on the inactive area, interacting with its neighboring W and forming NiWO4 which has been considered as the precursor of the active phase, Ni-W-S, on the surface.Some of the W atoms may locate on the center of the islands, which are unable to be reached by the Ni atoms.This is why the optimal R value may be less than 1.0.The optimal R value may be increased up to 1.0 by slightly reducing the W loading.