摘要
应用原位M(?)ssbauer谱考察了Al_2O_3、MgO、SiO_2及AC(活性炭)等载体负载的铂锡催化剂中锡组分的存在状态。结果发现:(1)PtSn/Al_2O_3还原后,锡组分仍为氧化态;(2)PtSn/MgO及PtSn/SiO_2还原后有部分零价锡生成并与金属铂形成了Sn^o/Pt^o合金;(3)PtSn/AC还原后所生成的零价锡则以游离态存在。这些结果为进一步了解催化剂中锡组分价态及存在方式对负载型铂锡催化剂反应性能的影响奠定了基础。
The supported PtSn catalyst is one of the most important catalysts for the catalytic conversion of hydrocarbons. It has been found recently that the states of tin play a crucial role in the catalytic proceses. But, the key problem is that the states of tin is very difficult to be determined by usual physical and/or chemical techniques due to the low loading of the tin component in the commercial catalysts.
Mossbauer spectroscopy is very sensitive to the changes in the valences of the elements, and is applicable to the tin element at normal conditions. The main disadvantage of Mossbauer spectroscopy is that it is only sensitive to one of the tin isotopes, i. e., tin-119. Therefore, it is necessary to use tin-119 enriched samples for the enhancement of sensitivity.
In this paper, four types of supports (activated carbon, SiO2, MgO and A12O3 ) supported PtSn catalysts were prepared and characterized by in-situ Mossbauer spectroscopy. Our results showed that a sub-
stantial amount of metallic tin was produced in the PtSn/AC (activated carbon)cataly s t after reduction at 480℃. The metallic tin formed is free from platinum. However, for the PtSn/SiO2 and PtSn/MgO catalysts, the alloys formed between Sn and Pt were detected in large quantities after reduction at 480 ℃. As for the A12O3 supported PtSn catalyst, there was no metallic tin formation after reduction at 480℃. It is obvious that the states of tin in supported PtSn catalysts after reduction depend upon the supports used.
出处
《分子催化》
EI
CAS
CSCD
1991年第3期209-216,共8页
Journal of Molecular Catalysis(China)
