铂锡重整催化剂中锡的表面状态的研究

利用穆斯堡尔谱学对共浸法、共沉淀法制备的铂锡重整催化剂中锡的状态进行了研究。共浸法催化剂在还原之后,锡是以多种形态存在。随着锡总含量的增加(铂含量不变),正四价锡维持不变,而正二价锡和铂锡合金相应增加。共浸法是由正四价的锡(SnAl₂O₅,SnO₂)变为多种形态,再变为只含 SnO₂的正四价形态。共沉淀法则始终保持为正四价(SnAl₂O₅,SnO₂),只是颗粒大小不同。因此,认为离子态的锡对改善铂催化剂的催化性质起着一定的作用。

A STUDY OF THE SURFACE STATE OF SN IN Pt-Sn/η-Al2O3 REFORMING CATALYSTS

The state of Sn in reforming catalysts was studied by MÖssbauer spectroscopy. The catalysts were prepared by both co-impregnation and co-precipitation methods. Besides the effect of different Pt/Sn atomic ratio on the state of Sn,the state of Sn after calcination,reduction or reaction was also investigated.After reduction, Sn in the catalysts prepared by co-impregnation method exists in various forms: tetravalence(SnAl₂O₅,SnO₂),divalence(SnAl₂O₄,SnO)and Sn/Pt alloys(Pt₃Sn, Pt Sn₄).The amount of tetravalent tin remains constant while the amount of divalent tin increases with the increasing total amount of Sn(the amount of Pt is kept constant).As for the catalyst prepared by co-precipitation method,most of Sn exist in one state after reduction:tetravalence(SnAl₂O₅,SnO₂);and this tetravalent tin increases proportionally with total amount of Sn in the catalyst. For catalysts prepared by co-impregnation method,the change of the state of Sn after calcination,reduction or reaction is significant,i.e.,some of tetravalent tin(SnAl₂O₅,SnO₂)after calcination is changed to divalence and alloy form, but all of them changed to SnO₂ after reaction.Sn in the catalyst prepared by co-precipitation method remains tetravalence(SnAl₂O₅,SnO₂),but its size is changed.It is believed that ionic tin is beneficial to the performance of Pt/Al₂O₃ reforming catalyst.