摘要
应用O_2-TPD,脉冲实验,原位Weiss磁测量以及TAP(temporal analysis of products)技术对NiO上的乙烷氧化脱氢制乙烯催化作用机理进行了研究.结果表明,NiO中的非化学计量氧表现出与气相氧交换的可逆性,其中在较低温度下脱附的α氧(很可能是O_2^-,O_2^(2-))仅存在于催化剂表面,与气相氧交换迅速,而较高温下脱附的β氧(很可能是O^-)不仅存在于催化剂表面,还存在于催化剂体相.β氧较α氧表现出更高的乙烯选择性.在反应条件下,Ni均应处于高氧化态(Ni^((2+δ)+),0≤δ≤1),一旦催化剂中有微量Ni^0生成,乙烷便发生裂解反应,乙烯选择性立即降为零.乙烷在NiO上的氧化脱氢(ODHE)的可能反应机理为:首先乙烷与NiO中的非化学计量氧O_(n(s))作用脱除一个α-H生成乙基自由基,然后进一步脱除一个β-H生成乙烯,乙烯生成的整个过程是在催化剂表面上进行的;副产物CO_2是由表面乙烯进一步氧化(很可能是与O_2^-,O_2^(2-)作用)生成的.失去O_(n(s))的NiO在反应体系(一定的氧分压)中,重新生成含非化学计量氧的NiO.
The mechanism of catalytic action on oxidative dehydrogenation of ethane over NiO has been investigated by means of O2 - TPD, pulse measure, in situ Weiss magnetic methods and TAP (temporal analysis of products) experiments. It is found that the oxidized Ni is maintained in the course of ODHE reaction. The exchange between gas phase oxygen and nonstoichiometric oxygen (a,β oxygen species) is reversible, and the β oxygen species (possibly O- ) , which exists both on the surface and in the bulk of the catalyst, shows higher selectivity towards ethylene than the a one (possibly O2- ,O22- ) which just exists on the surface of the catalyst. The mechanism is proposed that the ethylene, which is not only the product but also the intermedium of forming CO2, forms from the reaction of the O- with ethane on the catalysts' surface, and the CO2 forms by the reaction of ethylene and/or C2H5 with O2- ,O22- and O2(s). The catalyst is reoxidized with the help of the reaction between oxygen vacancy, lattice oxygen and oxygen adsorpted.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
1999年第9期986-991,共6页
Acta Chimica Sinica
关键词
催化剂
氧化镍
乙烷
氧化脱氢
乙烯
NiO, nonstoichiometric oxygen, oxidative dehydrogenation of ethane, mechanism
