Direct observation of catalytic reaction of high temperatures by IR spectroscopy

虽然IR方法已被广泛用于催化反应机理和活性中心的模拟，但有限的观测条件抑制了商业化高温催化反应（HTCR）真实机理的澄清。本研究的目的是建立HTCR的红外观测方法，并利用该系统详细考虑HTCR不断变化的机理。1999年，调整了红外光路，并建立了流动系统和合适的红外池。该系统从2000年开始用于观察1）在负载于各种氧化物上的钼催化剂上的甲醇氧化，以及2）在负载Pt的Hβ沸石上的正庚烷异构化。对于反应1），甲醇吸附在载体上形成甲醇盐，并被氧气流氧化成甲醛。在没有钼的情况下，甲醇盐不发生反应，表明钼是氧活化的活性中心，这是速率控制步骤。汽油精制过程，反应2），遭受烃异构化的裂化副反应。在此背景下，考虑了高活性和选择性催化剂与低效催化剂的比较。从催化性能和表面物种的观察的结果，Pt负载和氢共流被发现是有效的，以抑制脱水化合物，如焦炭和聚烯烃的形成。同位素实验进一步表明，氢（H和D）交换的表面物种是快速的活性催化剂上，所有的活性物种在稳态反应中处于平衡状态。综上所述，本研究所建立的系统被认为是观察HTCR的有力工具，因此可以进一步应用于以后的其他反应。

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.