The Study On Oxidative Steam Reforming Of Methanol Over CeO₂-ZnO Catalysts

The oxidative steam reforming of methanol(OSRM) is considered as one of the most promising routes for the hydrogen production from methanol because of the low reaction temperature,the acceptable hydrogen yield and the possibility to eliminate CO due to the present of H₂O.In our study,Ce_1-xZn_xO_Y catalysts With different Ce/Zn ratio prepared by complexation-combustion,coprecipitation and wetness impregnation routes were used in OSRM process,XRD,XPS,H₂-TPR were used to characterize the structure and the properties for the catalysts.We found the addition of ZnO can improve the catalytic performance.When x＜0.1,the Ce_1-xZn_xO_Y by complexation-combustion showed the best activity which can be attributed to the formation of Ce_1-xZn_xO_Y solid solution.This piont was also proved by the XRD results and the catalytic activity of the fresh Ce_0.92Zn_0.08O_Y catalysts compared with the Ce_0.92Zn_0.08O_Y which was treated with aq.HNO₃.While x＞0.1, the catalytic performance for Ce_1-xZn_xO_Y catalysts was in the order as Ce_1-xZn_xO_Y-WI＞Ce_1-xZn_xO_Y-CP＞Ce_1-xZn_xO_Y-CC,however,all of them showed their own best catalytic performance at x=0.3.The result of XRD showed the Ce_1-xZn_xO_Y-WI(x＞0.1) catalysts exhibited the smallest CeO₂ and ZnO crystallite.It was proved by XPS that the ratio of OH group in the surface oxygen species of Ce_1-xZn_xO_Y-WI(x＞0.1) were more than that of those by other preparation methods. The amount of H₂ consumption for the low temperature reduction species in H₂-TPR was also corresponding to the ratio of OH group in the surface oxygen species,so Ce_1-xZn_xO_Y-WI consumed the most amount of hydrogen during H₂-TPR,which also made contribution for the catalytic performance when x＞0.1.Take the Ce_0.7Zn_0.3O_Y for comparison which showed the best catalytic performance in the catalysts by each rout.A 120 h TOS test was investigated,the results of which showed us the Ce_0.7Zn_0.3O_Y-WI was With the best stability,while Ce_0.7Zn_0.3O_Y-CP quickly deactivated.This could be contributed to the migration of ZnO to the surface of CeO₂ especially at higher temperature which was proved by XPS.By TPD and TPSR studies,we found that the addition of ZnO can improve the ability of the catalysts to adsorb methanol,the selectivity of CO can be reduced significantly.During the process,methanol and water were first chemisorbed on the surface of the catalysts,but both of them weren't in competition adsorption.A preliminary mechanism was proposed for OSRM process in our study.Methanol first decomposed to form formaldehyde,which was going to further decompose to CO and H₂,or reacted With H₂O.The CO produced was going to react by water-gas shift process or oxidized while the existence of water and oxygen.