不同晶体结构金属氧化物催化小分子分解的BEP关系

BEP Relation of Metal Oxides with Different Crystal Structures

研究了金红石型(MO_2)和NaCl型(MO)金属氧化物催化小分子CO、O_2、NO和N_2解离反应的Brnsted-Evans-Polanyi(BEP)关系,并比较了金属氧化物、过渡金属以及不同晶型金属氧化物之间的BEP关系差异。结果表明,金属氧化物和过渡金属整体相比,BEP关系斜率基本相同,而截距却表现出较大差异;金属氧化物具有比过渡金属平面更小的截距,甚至小于金属台阶面,其主要原因归咎于金属氧化物的"惰性"。金红石型MO_2(110)和NaCl型MO(100)氧化物具有相似的局部表面结构特征而展现出相似的BEP关系,此构效关系同样适用于金属碳化物、氮化物等。这些结果揭示催化材料的表面结构特征对BEP关系截距具有显著影响。此外,针对金属氧化物BEP关系,解离分子过渡态类型对BEP关系有一定影响,可使其呈现分段现象:后过渡态类型(late TS)比前过渡态类型(early TS)解离反应具有相对更大的斜率和更小的截距。

This work explored the Br nsted-Evans-Polanyi(BEP)relations for the dissociation reaction of small molecules such as CO,O 2,NO and N 2 on two metal oxides with different crystal structures,i.e.the rutile-and NaCl-typed ones,aiming to shed light on the differences on the BEP relation between the metal oxides and transition metal,as well as between the metal oxides with different crystal types.Firstly,they basically possessed the same slope of the BEP relation with that on the transition metal surface,but give a large difference for the intercept term;The intercept of the BEP relation on metal oxides was shown much smaller than that on the flat metals and even smaller than that on the stepped metals.The reason for reduction of the intercept of the BEP relations was mainly ascribed to the relative weak binding ability of metal oxides;The dissociation configuration at TS is more FS-like,and the energy barrier of reverse synthesis reaction is much lower.Secondly,the similar BEP relations were presented on the rutile-typed oxide(110)and NaCl oxide(100)surface,because of their similar local structure characteristics,implying the dependence of surface structure on the intercept of BEP relations,and an extended study on the metal carbide and nitrides confirmed this point.Furthermore,the BEP relation on metal oxides could be further divided into two groups based on the transition state(TS)configuration type,and the BEP relation with late typed TS exhibited a larger slope(close to 1)and a smaller intercept in comparison with that of early typed TS.