雙金屬觸媒Pt-Sn/BN在巴豆醛選擇性氫化之研究

Abstract

In the present study we focused on the selective hydrogenation of crotonaldehyde over bimetallic BN-supported catalysts which were prepared by co-incipient wetness impregnation. The compositions of the catalysts were platinum 1.1 wt% and tin from 0.25 to 0.75 wt%. Besides we also prepared monometallic catalysts 1.1wt%Pt/BN and 1.0wt%Sn/BN. We chose some commercial catalyst supports γ-Al2O3 and activated carbon to compare with BN. The reaction results revealed that the more tin in Pt-Sn/BN, the higher the selectivity to crotyl alcohol. The Pt-Sn(0.75)/BN has the selectivity to crotyl alcohol 0.63 under the conversion 60%. The improvement of the selectivity to crotyl alcohol was contributed to Snn+ as Lewis acid sites that adsorb and activate C=O bond. The catalysts were characterized by N2 adsorption BET method, hydrogen and carbon monoxide selective chemisorption, temperature programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM) technique. By the XPS analysis, we found mostly the tin remained Sn2+ after reduction in flowing hydrogen at 300oC and PtxSn alloys were formed in Pt-Sn/BN. However we could not find any PtxSn alloys in Pt-Sn/γ-Al2O3 by XRD as the PtxSn particles might be possibly too small to be detected by XRD. BN is more inert than γ-Al2O3 and interacts weakly with metal precursors, and therefore the metal aggregation is more severe. The selectivity to crotyl alcohol in Pt-Sn/γ-Al2O3 was also increased as the tin content increased at the same reaction temperature. However the yield of the butyraldehyde was decreased appreciably and it may be caused by the decrease of the Pt dispersion and the possibly small bimetallic clusters PtxSn. The yield of the crotyl alcohol was not improved apparently due to the different surroundings of the Sn2+. The reaction results of the Pt-Sn/AC were similar to those of Pt-Sn/γ-Al2O3.