Study On Hydrogen Production From Methanol Steam Reforming By Rare Earth Modified Ni - Base And Cu - Based Catalyst

In recent years, because of the growing demand for energy of global, development of a new energy supply system is imminent. It is well known that 3/4 of the earth is made up of hydrogen, which is mainly in the form of hydrocarbons and water, besides its stock is extremely rich. The only product of hydrogen combustion is water which harmless to the environment, therefore, as a energy carrier is the most suitable for new clean energy. Methanol has the advantages of high energy density, easy access and preservation, as a source of hydrogen is a good choice.This paper focuses on the investigate of Ni/Al2O3 and a series of modified Ni/Al2O3 with the different rare earth catalysts, in addition the effects of reaction temperature, metal load, water-methanol ratio, carrier and other experimental conditions on the catalytic performance are studied. Although the addition of rare earth to a certain extent reduces the reaction temperature of nickel based catalyst which promoted its performance. But the reaction temperature of nickel based catalyst is still relatively high, for this reason the Cu/Al2O3 has also been studied.Also illustrated the reason of the merit and defect of the catalysts by XRD, H2-TPR characterization. A few research conclusions were summarized as follows:(1) When the Ni loading is 10%. the Ni/Al2O3 catalyst show the best performance, increasing the ratio of water-methanol can improve the performance of the catalyst as well. Less reducible species has be responsible for bad performance of low Ni loading, and high nickel loading can increase of the reduction temperature which generate more difficult reduction NiAl2O4 phase to degradation catalyst performance. Rare earth have a opposition effect on the catalyst performance which is good or bad, but it can decrease the selectivity of carbon monoxide. Especially, La. Pr and Sin not only enhance the conversion of methanol and hydrogen selectivity greatly, but also reduce the selectivity of carbon monoxide and reaction temperature.(2)In the study of Ni-La/Al2O3 catalyst, it was found that the catalyst show best performance when the nickel loading was 10% and the ratio of water-methanol was 6:1. XRD characterization results showed that the addition of La had promote the dispersion of nickel on the carrier, and TPR results showed that the addition of La could promote the low temperature reduction of nickel oxide, moreover the selectivity of CO is greatly decrease. The effect of different supports on the Ni-La catalyst had be investigate, the order of catalytic activity:10Ni-10La/Al2O3>10Ni-10La/SiO2> 10Ni-10La/MgO. XRD results show that the MgO as the support had the worst dispersion, and TPR suggests that it requires high reduction temperature. And with Al2O3 and SiO2 as supports, both are beneficial to the dispersion of active component, besides reduction temperature had little difference, however with Al2O3 as support show the lowest CO selectivity, therefore Al2O3 is the best support.(3) In the study of Ni-Pr/Al2O3 catalyst, it was found that the catalyst show best performance when the nickel loading was 10% and the ratio of water-methanol was 6:1 as well as Ni-La/Al2O3. The XRD also showed that the addition of Pr can also promote the dispersion of nickel on the support. TPR showed that Pr not only promoted the low temperature reduction of nickel oxide but also enhance the interaction between the active component and the support. The performance of 10Ni-10Ce/Al2O3 and 10Ni-10Pr/Al2O3 were investigated, and the MeOH conversion of 10Ni-10Ce/Al2O3 is unsatisfactory at low temperature. XRD results show that the additionof Ce and Pr can promote the dispersion of Ni on the support, but Ce itself on the support dispersion is not good, while Pr is not only promote the dispersion of Ni on support but also himself as well, hence the addition of Pr enhance the performance of catalyst. At the same time, the reduction temperature of 10Ni-10Ce/Al2O3 was higher than 10Ni-10Pr/Al2O3, and the interaction between the support is not as strong as 10Ni-10Pr/Al2O3.(4) In the investigate of Ni-Sm. came to the conclusion as Ni-La and Ni-Pr: when the nickel loading was 10% show the best performance. XRD results show that Sm can more promote the dispersion of Ni on the support, it is not detectable diffraction peaks of NiO when Ni loading were 5% and 7.5%. TPR showed that the reduction peak was main in low temperature. It declare that Sm further promote the nickel reduction at low temperature. In addition. Ni/Al2O3 modification with Sm showed the highest hydrogen selectivity in the three of La. Pr and Sm. In the stable test at 350℃ of 10Ni-10Sm/Al2O3 without deactivation after 450 hours of reaction. TEM and Raman characterization showed that there was no carbon deposition on it.(5) In the research process of Cu/Al2O3 catalyst, we found that when the loading of copper is 7.5% show the best performance. Compared with the nickel based catalyst, it lower the reaction temperature greatly as well as carbon monoxide selectivity.(for methanol conversion is close to 100% at 280℃, selectivity of hydrogen is close to 100% in the 240℃, and not detectable carbon monoxide). Similar to Ni/Al2O3, high loading would lead to the reduction peak move to high temperature, making the reducing property bed, and the low loading also had bed performance due to not enough active site.7.5Cu/Al2O3 modified with Sm show a undesirability performance, especially with 12.5%Sm. TPR showed that the addition of Sm which resulted in reduction peak shifts to higher temperature and even makes the low temperature reduction peaks of Cu/Al2O3 disappearing. Therefore, showed a undesirability performance in the methanol steam reforming.