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Preparation, Characterization Of Pt-Sn Catalyst And Its Application In Selective Hydrogenation Of Acetic Acid To Ethanol

Posted on:2014-11-27Degree:MasterType:Thesis
Country:ChinaCandidate:Y T HuFull Text:PDF
GTID:2251330425486667Subject:Pharmaceutical Engineering
Abstract/Summary:PDF Full Text Request
Supported Cu and Pt-Sn catalysts were prepared with incipient-wetness impregnation (co-impregnation) method by using Cu(NO3)2·3H2O, Pt(NO3)2and SnC2O4as the precursors. The catalysts were then used for selective hydrogenation of acetic acid to ethanol. The catalytic performance of Raney Cu, Cu and Pt-Sn catalysts were compared. Effects of Pt content, Sn/Pt molar ratio, support, modifier, calcination and reduction temperature were investigated. Several characterization methods were taken to study the relationship between the catalyst characteristics and its performance. Besides, the technological conditions of acetic acid hydrogenation including reaction temperature, pressure and H2flow rate were investigated. At last, active site of Pt-Sn catalyst and reaction mechanism were proposed. The research content and experimental results are as follows:Raney Cu and Cu/CaSiO3-SiO2catalysts were not suitable for selective hydrogenation of acetic acid to ethanol, whereas Pt-Sn/CaSiO3-SiO2catalyst showed high performance for that. At the same condition, acetic acid conversion and ethanol selectivity were around66%and80%for Pt-Sn/CaSiO3-SiO2catalyst. While for Raney Cu and Cu/CaSiO3-SiO2catalysts, acetic acid conversion were only around13%and2.5%, respectively.For Pt-Sn/CaSiO3-SiO2catalyst, Pt content had a great effect on acetic acid conversion, whereas ethanol selectivity remained almost the same and ethyl acetate selectivity was low. At250℃and2.2MPa, acetic acid conversion, ethanol and ethyl acetate selectivity were22.53%,87.62%and10.07%with1.5%Pt, whereas with the increase of Pt content to3%, acetic acid conversion and ethanol selectivity approached to90.23%and94.50%. With the increase of Sn content, catalytic activity, acid conversion and ethanol selectivity increased firstly and then decreased. The appropriate Sn/Pt molar ratio was unity. Catalytic activity, acid conversion and ethanol selectivity were0.27mmol*s-1*gPt-1,83.69%and86.87%at the optimum reaction condition. Both acetic acid conversion and ethanol selectivity for Pt-Sn/CaSiO3-SiO2were higher than those for Pt-Sn/SiO2. With a high level of90%, ethanol selectivity remained almost the same for Pt-Sn/CaSiO3-SiO2, Pt-Sn/γ-Al2O3and Pt-Sn/TiO2catalysts, while the first one showed the highest catalytic activity of0.29mmol*s-1*gPt-1. For Pt-Sn/CaSiO3-SiO2, the optimum calcination and reduction temperature were500℃and350℃respectively, where the highest acetic acid conversion (around90%) was obtained and ethanol selectivity was higher than86%at the optimum reaction condition.TG analysis showed that Pt-Sn/CaSiO3-SiO2catalyst had almost no weight loss after500℃, which could be the appropriate calcination temperature. XRD result showed that all Pt and Sn were reduced to zero valence state and mainly formed PtSn alloy with niggilite structure. The CaSiO3modifier contributed to the well dispersed PtSn alloy particles. H2-TPR result showed that there were interactions between Pt and Sn and between PtSn alloy and support, which could be beneficial to the stability and life of the catalyst.TEM analysis indicated that the three sample catalysts consisted of nano-sized particles and that the mean particle size increased from2.08nm to2.60nm with the increase of calcination temperature from400to600℃, which were smaller than the sizes obtained from XRD.The investigation of the technological conditions for acetic acid hydrogenation over Pt-Sn catalyst showed that acetic acid conversion and ethanol selectivity increased, whereas ethyl acetate selectivity decreased with the increase of reaction temperature, and that acetic acid conversion increased quickly, whereas the increase of ethanol selectivity was unconspicuous with the increase of reaction pressure, and that acetic acid conversion increased firstly and then decreased, whereas ethanol selectivity remained almost unchanged with the increase of H2flow rate. The optimum reaction temperature, pressure and H2flow rate were325℃,2.2MPa and260mL*min-1, respectively.The active site of Pt-Sn catalyst for acetic acid hydrogenation was nano-sized and well-dispersed PtSn alloy particles. Possible reaction mechanism could be proposed as follows:Pt in PtSn alloy activates H2to produce active hydrogen, while Sn absorbs and activates acetic acid to produce acetate intermediate. The C=O group in acetaldehyde produced by the reaction of active hydrogen and acetate intermediate is then adsorbed by Sn. Finally, it is attacked by the active hydrogen to produce ethanol.
Keywords/Search Tags:Raney Cu catalyst, Cu catalyst, Pt-Sn catalyst, catalytic activity, acetic acidconversion, ethanol selectivity
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