Research On Hydrogen Production From Steam Reforming Of Ethylene Glycol At Low Temperature

The technology of hydrogen production by catalytic reforming of biomass derivatives?such as ethylene glycol, glycerol, sorbitol, etc? is one of the hot topics in the study of new energy. At present, the complex path and unclear mechanism of reforming reaction and the traditional supported metal catalysts which are very active for coke formation or sintering become the main problems of restricting its industrialization. In this paper, we studied steam reforming activity of ethylene glycol over Ni catalysts at low temperature. Ni catalyst was modified by two aspects, respectively. Firstly, modified the support with others oxide species, prepared the Ni catalysts supported on composite support, then the interaction between active component and support and the effect of different supports were investigated. Secondly, Fe, Cu, Co, Au and Pt as the second metal were introduced into Ni catalyst formed bimetallic catalysts, and then the synergies between the active components were investigated. The physical and chemical properties of catalysts were characterized by H₂-TPR, XRD, N₂ physisorption and XPS, and these results were associated with the catalytic performance.In this paper, the main results summarize as follows:1. The experiment reaction conditions and catalysts preparation conditions were optimized, the reaction activity of supported Ni catalysts in hydrogen production by ethylene glycol steam reforming was studied. The results indicate that the best activity was achieved over Ni/CeO₂ catalyst due to unique cubic fluorite structure of CeO₂, which not only stabilizes the active component and then improves the dispersion of Ni active phase and also contributes to the CO water gas shift reaction. Higher reaction temperature is beneficial to the rupture of C-C bonds, the optimal reaction temperature is 400 °C.Calcination temperature of catalyst has remarkable effects on the structure and size of active component particles, considering the activity and stability of catalysts, the most appropriate calcination temperature is 500 °C. The lower load of active component shows lower activity due to the less surface active site. But excessive high load will lead to aggregation of active components, the optimal load is 15%.2. The Ni catalysts supported on composite support were prepared by modifying the support of catalysts. The results show that the interaction between active phase and support was influenced by different preparation method. Take Ni/CeO₂-ZrO₂ for example,an ethylene glycol conversion of 84.9% with a H₂ yield of 58.2% was achieved over the most active catalyst prepared by deposition-precipitation method. Ni/CeO₂-Al₂O₃ catalyst prepared by deposition-precipitation method shows the best catalytic activity due to the larger specific surface area,which promoted the dispersion of active phase. The ethylene glycol conversion was 94.0% and the H₂ yield was 67.0% at 300 °C. But extending the reaction time, the catalyst was easily inactivated with poor stability. By adding a small amount of lanthanum series oxide?La₂O₃, Pr₂O₃? improved the catalytic activity and inhibited methane formation, the H₂ selectivity was enhanced.3. Ni-M/CeO₂ bimetallic catalysts were prepared by adding transition metal as additives which used to improve the performance of catalysts. The results show that,Ni-Fe or Ni-Cu bimetallic catalysts were not applicable for hydrogen production from ethylene glycol steam reforming. It's worth noting that a considerable amount of CO was generated on these two kinds of bimetallic catalyst.The Co catalysts showed relatively good activity of ethylene glycol steam reforming, but the activity was less than monometallic Ni catalyst. Moreover, the catalyst prepared by CP method exhibited the highest ethylene glycol conversion?93.1%? and H₂ yield?72.6%?. NiO particles and CeO₂ particles are dispersed uniformly, the smaller particle can provide more active sites.4. The introduction of precious metals Au or Pt is to improve the catalyst performance.The Ni-Au bimetallic catalysts prepared by IMP method were not applicable for hydrogen production from ethylene glycol steam reforming. Preparation method of Ni-Au bimetallic catalysts were optimized, and the catalytic activity of Au³⁺Ni₇/CeO₂ catalyst perepared by DP method was relatively good. The ethylene glycol conversion was80.1% and the H₂ yield was 57.4%. Adding Pt, the reducibility of NiO was related with the impregnation sequence, the Pt₁-Ni₉/SiO₂ catalyst given the highest ethylene glycol conversion?88.5%? and H₂ yield?60.9%? at 300 °C. Moreover, the activity of bimetallic catalysts increased gradually with the increase of Pt/Ni radio. The TPR results proved that the Pt doping efficiently enhanced the NiO reducibility. The XPS results proved the presence of electron transfer, the addition of Pt plays a role for stabilizes the Ni⁰.Pt₃-Ni₇/SiO₂ and Pt₃-Ni₇/CeO₂ catalyst exhibited good stability, no obvious deactivation was observed during 100 h continuous on-line testing.