摘要
本文提出了用XRD 测定a_(440)/c_(331)、R/L、ΔL 等参数表征类NiAl_2O_4结构特征及变化的方法。测定结果表明,用XRD 可以得到活化温度较低、镍负载量在“阚值”以下的催化剂中形成类NiAl_2O_4的明显证据。根据XRD 和UV-vis 测定结果,提出了从表面类NiAl_2O_4到体相NiAl_2O_4是一连续渐变过程。在该过程中,六配位的Ni^(2+)始终占少数,四配位的Ni^(2+)占多数;基质晶格向δ-Al_2O_3结构的变化受到抑制,而向高对称性和高有序度NiAl_2O_4结构的变化逐渐加强。由XRD、UV-vis 与H_2-TGA测定结果之间出现的镍物种归属和不同配位的镍离子分布方面的显著矛盾,提出了在低温表面相互作用初期可能形成与载体表面羟基呈六配位的表面镍络合物的主要镍物种。
This paper suggests a method to characterized the structural feature and its change
of spinel-like NiAl_2O_4 by parameters of a_(440)/c_(311),R/L,AL etc.from XRD.Evidences of
forming spinel-like NiAl_2O_4 have been obtained by XRD method under the conditions of
lower activation temperature and below the “threshold valve” of Ni supported quanti-
ty.It is further demonstrated from XRD and UV-vis results that the transformation of.
surface spinel-like NiAl_2O_4 to bulk spinel-like is a continuous process.However,in the
course the hexa-coordinated Ni^(2+) is always in minor amount and the tetra-coordinated
Ni^(2+) is always the major;while the transformation of matrix crystal lattice to δ-Al_2O_3 is
depressed and the transformation of NiAl_2O_4 structure to higher symmetry and higher
order is strengthened.In view of the contradictions between the results of XRD,UV-vis
and H_2-TGA data about classification of Ni-species and distributions of the different-co-
ordinated Ni ions,it is proposed that the surface Ni-complex of hexa-coordinated with
hydroxyl groups of supports is formed probably as main Ni-specie in the early stage of
low temperature surface interactions.
出处
《石油学报（石油加工）》
EI
CAS
CSCD
北大核心
1993年第2期12-18,共7页
Acta Petrolei Sinica(Petroleum Processing Section)
