The use of bioethanol (bEtOH) as an alternative (or additive) for automobile fuels has increased rapidly all over the world. This is one way of using renewable resources to suppress carbon dioxide emissions, while another challenge is the conversion of bEtOH to various olefins and their use for production of chemicals and polymers. [1][2][3][4][5][6][7] The latter would be very significant for the long-term fixation of carbon dioxide. Many efforts have therefore been devoted to the development of systems for converting bEtOH to ethene (C2 = ) and other lower olefins. In particular conversion to propene (C3 = ) is desirable due to the greater demand for C3= derivatives, such as propene oxide, acrylonitrile, and polypropene.[2]Catalytic conversions of EtOH on zeolites [3][4][5] and metal oxides [6, 7] have been widely studied. On zeolites, the activity and selectivity in the many studies reported so far are insufficient. The major weakness is catalyst deactivation. For example, the selectivity towards C3 = on proton-or metal-modified zeolites is usually ca. 20-30 % and decreases with reaction time, although sometimes higher C3 = selectivity values are observed upon catalyst degradation. [3][4][5] Oligomerization, polymerization, and fission reactions on strong acid sites in zeolite pores result in the formation of C3 = and butenes (C4 = ) due to shape selectivity. [3][4][5] However, the random reactions in the pores finally result in coke formation and short catalyst life times. EtOH can also react on metal oxide surfaces to give various chemicals. Acid sites are widely recognized to lead to dehydration of EtOH, giving C2 = , while basic sites lead to dehydrogenation to yield acetaldehyde (AA). [6, 7] As a result, many kinds of products, for example aldehydes, ketones, C2 [8] Therefore, Ni-M41 is a possible catalyst for the conversion of EtOH to C3 = since M41 is active for the dehydration of EtOH to yield C2 = .[8b] Indeed, this was confirmed by preliminary results from our group [9] and subsequently by Sugiyama et al.[10] The pore diameters of M41 are usually 1.5-5.0 nm, and, therefore the product distribution on the catalysts is not controlled by shape selectivity. The reaction mechanism/pathways are of interest, and the target of our present study.The influence of temperature on EtOH conversion over Ni-M41 is summarized in Figure 1. Many kinds of products were formed in addition to C2 = . Diethylether (DEE) was mainly obtained at around 523 K. DEE has been reported earlier as an intermediate compound in the dehydration, decomposing to yield EtOH and C2= at higher temperatures.[8b] The C2 = yield sharply increased at 573 K, and reached ca. 70 % at 623 K or above. The C4 = yield reached a maximum at 623 K, while maxima in C3 = yield occurred at 673 and 723 K. Notably, AA was formed at 573-723 K, although not in large amounts, which will be discussed later. The stability of Ni-M41 was examined at 673 K. As shown in Figure 2, the catalytic activity did not change during 20 h of continuous time on stream. In addi...
