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...

Ethanol, 1-propanol, 2-propanol, and 1-butanol were quantitatively dehydrated to the corresponding olefins on mesoporous silica MCM-41 catalyst. The reaction rates were high and no deactivation was observed for 50 h. Two reaction routes were suggested: the intermolecular dehydration of alcohol and subsequent decomposition of ether and the direct dehydration of alcohol.Utilization of bioethanol (bEtOH) as alternative to or as an additive of automobile fuel has rapidly expanded all over the world. This is of course a way to use renewable resources and suppress carbon dioxide emission, while another challenge is the conversion of bEtOH to various olefins and their use for production of chemicals and polymers.1 The latter would be very significant to fix carbon dioxide for the long-term period. Many efforts have, therefore, been devoted to development of selective conversion systems of bEtOH to ethene (C2 = ). It is widely known that the dehydration of alcohols is well catalyzed on various types of acids including modified aluminas, 2 supported heteropolyacids, 3 zeolites, 48 mesoporous materials, 9 and others, 10 but the activity and selectivity reported so far have been insufficient. For example, the reaction rates and the selectivity of C2 = on proton-or metal-modified zeolites should be improved, the selectivity is often restricted to ca. 96% due to strong acidic sites which cause oligomerization, polymerization, and fission of the produced lower olefins. 5,6 The various reactions in the zeolite pores finally result in coke formation and short lifetime. 57Niobium silicate 8 or silicotungstic acid supported on mesoporous silica 3 have been reported to show good selectivity for C2 = formation, but the reaction rates are not high due to the low surface areas. In addition, the low stability of loaded active components under high partial pressure of water would be a disadvantage for practical use.The novel acidic properties of mesoporous silica material, MCM-41 (M41), have been reported from the present 11,12 and other groups. 13 The acidity is not strong but unique to promote various selective catalyses. Our efforts have, therefore, been devoted to revealing the catalytic activity of M41 for the dehydration of EtOH, 1-and 2-propanol (PrOH), and 1-butanol (BuOH) to C2 = , propene (C3 = ), and butenes (C4 = ). We found the fast, quantitative, and stable catalyst can solve the above problems. The catalytic dehydration of alcohols is well known to be an easy heterogeneous catalytic reaction, but quantitative progress without deactivation is still necessary.M41 was prepared in the reported manner by using C 12 H 25 N(CH 3 ) 3 Br as the template and colloidal silica as the silica source.14 After calcination of M41 at 873 K for 6 h in air, the BET surface area and the BJH pore diameter determined by a N 2 adsorption measurement were 1010 m 2 g ¹1 and 2.12 nm, respectively. The hexagonal structure of resulting M41 was confirmed by appearance of 2ª = 2.580, 4.476, and 5.124 degree peaks in X-ray diffraction patterns (Cu K¡, ...