Characterizations of Bimetallic Pt-Fe Supported Catalysts and Selective Hydrogenation of Crotonaldehyde
Date Issued
2005
Date
2005
Author(s)
Cheng, Tai-Shin
DOI
zh-TW
Abstract
The selective hydrogenation of crotonaldehyde was studied in gas phase over bimetallic BN-supported catalysts which were prepared by co-incipient wetness impregnation. The compositions of these catalysts were platinum 1.1wt% and iron varied from 0.1 to 0.6 wt%. Monometallic catalysts Pt1.1wt%/BN and Fe0.8wt%/BN were prepared for comparison. Some commercial catalyst supports, graphite and γ-Al2O3, were chosen to compare with BN. The reaction results revealed that the higher iron content on three bimetallic supported catalysts, the higher selectivity to crotyl alcohol was, but the activity was depressed at the same time. On BN and graphite bimetallic Pt-Fe supported catalysts, there was an optimum yield of crotyl alcohol at 0.2wt% Fe (Fe/Pt=0.635).The improvement of selectivity to crotyl alcohol was not only attributed to the electropositive metal B (Fe) acting as an electron-donor that increased the electron density on metal A (Pt), thus depressing the C=C hydrogenation, but also the electropositive metal (oxidized metal species) on the surface acting as electrophilic or Lewis sites for the adsorption and activation of the C=O. In addition, the BN and graphite also donated their pi electron to Pt, thus the C=C hydrogenation was hardly to activate. The catalysts were characterized by BET surface area measurement by N2 adsorption , H2 and CO chemisorption, X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) , transmission electron microscope (TEM), scanning electron microscope/energy dispersive spectrometer (SEM/EDX), inductively coupled plasma-atomic emission spectrometer (ICP-AES) , and temperature programming reduction (TPR).Summarized XRD,XPS,TEM and TPR results, Pt-Fe alloy were formed on Pt-Fe/BN and the Fen+ above (or next to ) the alloy polarized the C=O to enhance the selectivity to crotyl alcohol appreciably. The reaction results on Pt-Fe/graphite were similar to that of Pt-Fe/BN. But graphite provided more pi electrons to Pt which raised the electron density to depress the C=C hydrogenation, resulting in the highest selectivity to crotyl alcohol－0.82 (Fe/Pt=1.91),but the yield of crotyl alcohol on Pt-Fe/graphite was lower than Pt-Fe/BN at the same iron content. Graphite is also a inert species, we found the reduction temperature of various metal compositions loaded on graphite were almost the same with loaded on BN ,and the structure of pure support graphite and BN（graphitic-like）were identical to each other revealed by XRD pattern. The selectivity to crotyl alcohol on γ-Al2O3 supported catalysts was not increased efficiently. However, the Fen+ presented at the surface which was detected by XPS. The slightly improvement of selectivity to crotyl alcohol was attributed to the yield of butyraldehyde decreasing appreciably and it might caused by the decrease of Pt dispersion. We suggested that there were not sufficient hydrogen atoms surrounding with Fen+ to enhance the rate of C=O hydrogenation and also related to Fen+ easily interacting with γ-Al2O3.
Subjects
巴豆醛
選持性氫化
Pt-Fe/BN catalyst
crotonaldehyde
selective hydrogenation
Type
thesis
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