Dimethyl ether (DME) is a potential clean fuel of the next generation, because of less toxicity, burning without Nox or particulates, and ease of handling. We have studied catalysts which will produce CO-free hydrogen with stream reforming of DME (SRDME) for the use of hydrogen in polymer electrolyte fuel membrane cells.
Catalysts prepared by the sol-gel method, such as γ-Al_2O_3, SiO_2, Cu/Al_2O_3, Ru/Al_2O_3, Cu/SiO_2, so on, Cu-Zn/Al_2O_3 prepared by the impregnation method, and CuO-ZnO as a commercial catalyst were used.
The Al_2O_3 catalysts prepared by the sol-gel method mainly produced H_2, and in the case only of Al_2O_3 methanol was formed. On the other hand, the Cu/SiO_2 which was excellent for methanol steam reforming and SiO_2 produced no H_2. These results suggest that γ-Al_2O_3, especially the Lewis acid sites, is excellent for hydrolyzing DME into methanol and the methanol produced is reformed to H_2 and CO_2 over active metal for methanol steam reforming, such as copper.
It is also found that the sol-gel method is excellent for preparing the suitable catalysts for SRDME, because γ-Al_2O_3, the Lewis acid sites, and active metal sites such as copper will be mixed and distributed well on the surfaces of the catalysts. Each addition of Zn, Fe, and Mn into Cu/Al_2O_3 that is one of the excellent catalysts for SRMDE improves the rate of H_2 production ; however, the CO production is not reduced. CO is formed with the opposite water gas shift reaction by generated H_2 and CO_2, therefore it was thought that the CO reduction in the ppm order or less orders is very difficult. However, for example, Cu-Zn(29-1wt%)/Al_2O_3 catalyst converts 95% of DME into H_2 and CO_2 containing 0.8% of CO at the reaction temperature, 275℃. The excellent catalysts for SRDME at low temperature (250-300℃) have been developed.
(We had 3 presentations in the conferences of Catalysis Society of Japan, and 7 presentations in the conferences of The Chemical Society of Japan for 2001-2003. We are grateful for support of this research.) Less