Direct observation of catalytic reaction of high temperatures by IR spectroscopy

点击翻译按钮获取中文摘要

Although IR method has been widely used for the modeling of mechanisms and active sites of catalytic reactions, the limited observation conditions have suppressed the clarification of authentic mechanisms of commercialized high temperature catalytic reactions (HTCR). This study subjects to establish the IR method for the observation of HTCR, and the system is used for the detailed consideration of mechanisms of HTCR, which have been changing.In 1999, adjustment of IR beam path together with construction of flow system and proper IR cell were established. This system was used from 2000 for the observation of 1) methanol oxidation over molybdenum catalysts supported on various oxides, and 2) isomerization of n-heptane over Pt loaded Hβ zeolites. For the reaction 1), methanol adsorbed forming methoxides on supports and was oxidized to formaldehyde by oxygen flow. No reaction of methoxides proceeded in the absence of molybdenum, indicating that molybdenum is the active site for oxygen activation, which is the rate determining step.The gasoline refining process, the reaction 2), suffers the cracking side reaction of hydrocarbon isomerization. Based on this background, comparison of highly active and selective catalyst with poorly effective catalyst was considered. From results of both catalytic performance and observation of surface species, Pt loading and hydrogen co-flow were found to be effective to suppress the formation of dehydrated compounds such as coke and polyolefins. Isotope experiments further reveal that hydrogen (H and D) exchange of surface species was rapid on the active catalyst, and that all the active species were in equilibrium in the steady state reaction. In summary, the system established in this study was regarded as a powerful tool for the observation of HTCR, and therefore is further applied for other reactions hereafter.