Department of Chemical and Petroleum Engineering, University of Kansas, Kansas 66049, USA.
Rev Sci Instrum. 2023 May 1;94(5). doi: 10.1063/5.0083201.
Numerous important catalytic reactions, such as Fischer-Tropsch synthesis (FTS), are performed under harsh conditions in terms of high temperature of a catalyst in a mixture of reactants at a high pressure. There has been a lack of an intrinsic correlation between a catalytic performance and its corresponding catalyst structure due to the unavailable information on the authentic structure of the catalyst during catalysis under a high-temperature high-pressure (HTHP) condition. Here, we report in situ/operando studies of Co catalysts during catalysis under HTHP conditions using x-ray absorption spectroscopy (XAS). A high-temperature high-pressure catalysis-XAS (HTHP Catalysis-XAS) system using a thin, small quartz or beryllium tube as the reactor was built for in situ/operando characterization of high-energy absorption edges of 4d transition metals or low-energy absorption edges of 3d/4d transition metals under high-temperature high-pressure conditions, respectively. This reactor can be used for HTHP catalysis performed at a temperature of up to 550 °C and a gas pressure of up to 60 bars for uncovering the chemical states and coordination environments of metal atoms of these catalysts during HTHP catalysis. The capability of collecting XAS data during HTHP catalysis was confirmed through tests at 400oC in the mixture of 20 bar mixture of reactants at beamline endstation. The operando studies of Ru catalyst particles under Fischer-Tropsch catalytic conditions with extended x-ray absorption fine structure spectroscopy revealed a restructuring of the Ru catalyst at 250 °C in the mixture of 6 bars CO and 12 bars H2 during FTS (30 ml/min), which was not observed at 300 °C in 1 bar H2 (20 ml/min). This observation suggests new chemistry for metal catalysts under HTHP condition inaccessible due to a lack of applicable characterizations. These tests confirmed the function of this HTHP Catalysis-XAS system for in situ/operando characterizations of catalysts during HTHP catalysis.
在高温、反应物高压的苛刻条件下，进行了许多重要的催化反应，如费托合成（Fischer-Tropsch synthesis，FTS）。由于在高温高压（high-temperature high-pressure，HTHP）条件下进行催化时，无法获得有关催化剂真实结构的信息，因此，催化性能与其相应的催化剂结构之间缺乏内在的相关性。在这里，我们使用 X 射线吸收光谱（X-ray absorption spectroscopy，XAS）报告了在 HTHP 条件下进行 Co 催化剂催化时的原位/操作研究。建立了一种高温高压催化-XAS（high-temperature high-pressure catalysis-XAS，HTHP Catalysis-XAS）系统，该系统使用薄的、小的石英或铍管作为反应器，分别用于在高温高压条件下对 4d 过渡金属的高能吸收边或 3d/4d 过渡金属的低能吸收边进行原位/操作表征。该反应器可用于在高达 550°C 的温度和高达 60 巴的气体压力下进行 HTHP 催化，以揭示这些催化剂在 HTHP 催化过程中金属原子的化学状态和配位环境。通过在反应物混合物中的 20 巴混合物中在 400°C 进行的测试，证实了在 HTHP 催化过程中收集 XAS 数据的能力。通过扩展的 X 射线吸收精细结构光谱对 Fischer-Tropsch 催化条件下 Ru 催化剂颗粒的操作研究表明，在 FTS（30 ml/min）中，在 6 巴 CO 和 12 巴 H2 的混合物中，在 250°C 时 Ru 催化剂发生了重构，而在 300°C 时在 1 巴 H2（20 ml/min）中未观察到这种情况。这一观察结果表明，由于缺乏适用的特性，在 HTHP 条件下金属催化剂存在新的化学性质。这些测试证实了该 HTHP Catalysis-XAS 系统在 HTHP 催化过程中对催化剂进行原位/操作表征的功能。
