Study On Hydrotalcite Precursor Application In Hydrogen Production By Methanol Steam Reforming

At present,the environmental problems caused by the continuous deterioration of global climate are becoming more and more serious.The development and utilization of clean energy,such as hydrogen,has gradually become one of the important directions in the field of energy research.Exploring hydrogen production methods with high hydrogen yield,mild reaction conditions and low CO selectivity has become the main content of many scientific researchers.Among many hydrogen production methods,methanol steam reforming technology stands out because of the above characteristics.In the early stage of our research group,hydrotalcite layered composite metal materials were used as precursors.After calcination,oxide carriers with larger specific surface area and better mechanical strength could be obtained.Then copper-based catalysts were prepared by impregnation method.The optimum copper loading,rare earth modified element cerium and its optimum loading were determined.On the basis of previous studies,the effects of hydrotalcite precursors with different elements on the Structure-Performance of the catalysts were investigated.A series of catalysts with high catalytic activity and low CO selectivity were prepared by changing the impregnation order of cerium and the calcination temperature of the catalysts.Specific research contents are as follows:（1）M-Al（M=Mg,Ni,Co,Zn）precursor hydrotalcite catalytic materials were synthesized on the support ofγ-Al₂O₃ by in situ synthesis method.A series of Ce/Cu/M-Al（M=Mg,Ni,Co,Zn）catalysts were prepared by sequential impregnation method.The effects of hydrotalcite precursors with different elements on the Structure-Performance of the catalysts were discussed.The catalysts were characterized by XRD,BET,H₂-TPR and N₂O titration.The results show that different hydrotalcite precursors have a great influence on the dispersion of copper,the specific surface area of copper and the reduction temperature of the catalyst.Among them,the catalyst prepared by Zn-Al hydrotalcite precursor shows the best catalytic performance.（2）The effect of the impregnation sequence of cerium on the catalytic performance of Cu/Zn-Al hydrotalcite-derived catalyst for methanol steam reforming to hydrogen was investigated.The results showed that the order of impregnation of cerium mainly affected the reduction properties of the catalysts,and then the catalytic performance.Comparing the three catalysts with different impregnation sequence,it was found that the three catalysts exhibited different properties.Among them,the catalysts impregnated with copper and then with Ce exhibited the highest specific surface area of copper,the highest dispersion of copper and the lowest reduction temperature,showing the best catalytic activity.（3）The catalysts were modified by changing the calcination temperature.The results showed that the calcination temperature mainly affected the specific surface area of copper,the surface oxygen vacancy content and the interaction between copper and cerium.When the calcination temperature is500 ℃,the specific surface area of catalyst copper is larger,the surface oxygen hole content is higher,and the interaction between copper and cerium is stronger,so the catalytic activity of methanol steam reforming is better.The methanol conversion was 100%and the CO content is 0.39%when the reaction temperature was 250 ℃,the ratio of water to methanol was 1.2 and gas hourly space velocity was 800 h^-11 in methanol steam reforming.When the calcination temperature rises to 700 ℃,the Cu species mainly exists in the form of stable CuAl₂O₄ spinel,which is not conducive to the reaction of methanol steam reforming,so the catalytic activity is poor.