Study On High Surface Area CeO₂ Material Supported Pt Catalysts To Produce Hydrogen From Ethanol Steam Reforming

Producing hydrogen from bio-ethanol steam reforming is a green and renewable developing route. A thermodynamics analysis of the different producing hydrogen techonolgy of ethanol is carried out in this thesis using the method of Gibbs free energy minimization. Besides, the activity and stability of high surface area CeO₂ material supported Pt catalyst is investigated in ethanol steam reforming.Thermodynamics of hydrogen and carbon from the different producing hydrogen techonolgy of ethanol (steam-reforming, partial-oxidation, auto-thermal reforming, dry reforming and dry steam reforming) is investigated using the method of Gibbs free energy minimization. Compared with other related ethanol reaction peocesses, ethanol steam reforming can achieve the maximum moles of hydrogen (5.39mol/mol) with the optimum controlled range (reaction temperature>800K, S/E>5). Equilibrium molar numbers of each species for ethanol steam reforming are calculated over the ranges of temperature 400¹200K, pressure 1⁵atm and water-ethanol ratio 0¹0, respectively. High temperature and high water-ethanol molar ratio favor the hydrogen yield of unit mole ethanol, while high temperature and low water-ethanol ratio are conducive to raising the hydrogen molar fraction on a wet basis. The effect of water-ethanol ratio upon hydrogen concentration on a dry basis is negligible (T>800K). Concentration of hydrogen over a dry basis can be largely influenced by temperature, the higher the temperature, the larger the concentration. It is also displayed by the calculation that low pressure favor hydrogen production, while high pressure is conducive to inhibiting carbon monoxide formation. Considering factors related to increasing hydrogen productivity and efficiency as well as preventing carbon and carbon monoxide formation, it is suggested that the thermodynamic favorable condition should be 850K or more for temperature, atmosphere pressure and 8:1 for water-ethanol ratio.XRD, XPS characterization of the high surface area CeO₂ (HSA) indicated that CeO₂ (HSA) had the similar structure as traditionl prepared CeO₂ material. NH3-TPD characterization showed that surface acid sites of CeO₂ (HSA) reduced gradually with the increase of calcination temperature. When the calcination temperature was 1073K, CeO₂ (HSA) surface acid decreased obviously. HR-TEM revealed that CeO₂ (HSA) prepared by CTAB got smaller and uniformer particle size than that prepared by traditional method.Comparaed with Pt/CeO₂ catalyst prepared by traditional method, high surface area cerium-based Pt catalyst obtained better catalytic activity and stability. Under 973K and GHSV 5000h-1, moles of hydrogen production were 2.98mol/mol(S/E=3) , 4.26mol/mol(S/E=4) over 2Pt/45CeO₂/Al₂O₃ catalyst, respectively. XRD and XPS characterization indicated that 45wt% loading CeO₂ material had the similar characteristics of the crystal structure as pure CeO₂. H2-TPR results revealed that high surface area cerium-based carrier increased oxidation-reduction capacity with increasing CeO₂ loading. When CeO₂ loading was greater than 35wt%, there had been two distinct reduction peaks similar as that of pure CeO₂ by H2-TPR.KNO3 modified 2Pt/Al₂O₃ catalyst exhibited the best catalystic activity in the different potassium source. 2Pt/1K/45CeO₂/Al₂O₃ acquired 4.29 mol/mol and no ethylene was dectected under the reaction temperature 973K, S/E 4 and GHSV 5000h-1. NH3-TPD showed that the surface acid sites of 2Pt/45CeO₂/Al₂O₃ catalyst decreased significantly by adding 1wt% K. IR analysis of pyridine absorbed showed that there only existed Lewis acid sites in the high surface area cerium-based carrier. Besides, the Lewis acid sites was almost not detected in the 2Pt/1K/45CeO₂/Al₂O₃ catalyst with inceasing K loading. TG results showed that carbon deposition was inhibited in the ethanol steam reforming process with the increase of potassium content.