Studies On Catalysts Of Methanol Steam Reforming For Hydrogen Production

The research background of this thesis was the development of methanol distributed hydrogen production system. An excellent performance of Cu-based catalyst for methanol steam reforming (MSR) was prepared. Finally, the application of the methanol steam reforming catalysts in the distributed hydrogen production system was realized. The new Cu-based catalyst of high activity, low CO selectivity and good stability in severe conditions was developed through the systematic research of the carriers, prepared methods and reaction mechanism, and the reasons of improved catalytic performance have been revealed.The Cu-based catalysts with different supports (CeO2, ZrO2and CeO2-ZrO2) for methanol steam reforming were prepared and the effect of different supports was investigated. The catalysts were characterized by means of X-ray diffraction, temperature-programmed reduction, oxygen storage capacity, N2O titration and X-ray photoelectron spectroscopy. The results showed that the Cu dispersion, reducibility of catalysts and oxygen storage capacity evidently influenced the catalytic activity and CO selectivity. It was noticed that the adding of ZrO2as support increased the dispersion of Cu species and improved the catalytic reducing capacity, and then improved the catalytic activity. The adding of CeO2as suppor increased the oxygen storage capacity, and then decreased the CO concentration in the reforming gas. The CeO2-ZrO2-containing catalyst showed the best performance with lower CO concentration, which was due to the high Cu dispersion and well oxygen storage capacity. Moreover, the dehydrogenation of methanol was promoted by the CeO2-ZrO2solid solution which was beneficial to the methanol steam reforming.The precipitation conditions were studied systematically on CuO/ZnO/CeO2/ZrO2catalyst. It was found that the precipitation process mainly affected on the size, dispersion and reduction ability of copper which significantly influenced the catalytic activity and selectivity. Considering the catalytic activity and CO selectivity, when the precursor concentration was0.1mol/L, the Na2CO3concentration was0.5mol/L, the preparation temperature was60℃, the stirring time was2h and the aging time was12h, the catalyst had the best performance. The catalytic performance for methanol steam reforming over CuO/ZnO/CeO2/ZrO2catalyst was investigated using a statistical set of experiments in order to optimize the methanol conversion with minimal carbon monoxide in the reforming gas. The operating temperature, steam to methanol (S/M) ratio, the methanol gas hourly space velocity (GHSV) was evaluated with a full factorial design experiment. The reaction temperature displayed a much greater influence on the response (the methanol conversion and CO concentration). The optimum theoretical conditions were found to lie within a reaction temperature of249-258℃and a S/M ratio of1.76-2.00.In the mini reformer, the performance of CuO/ZnO/CeO2/ZrO2catalyst was investigated. It was found that the reformer was started at room temperature and the starting time was less than60min. The catalyst had excellent reforming performance with no deactivation during150h stability test.The mechanistic research of methanol steam reforming on the CuO/ZnO/CeO2/ZrO2catalyst was investigated by FT-IR. The results showed that the methanol steam reforming was consist of methanol dehydrogenation, the methyl formate transformation and the reverse water gas shift (RWGS). The intermediates products was the methyl formate. Moreover, when the reaction temperature was below573K, the CO formation was mainly through the RWGS reaction. When the reaction temperature was above573K, the CO formation was through the methanol decomposition and RWGS reaction.