Bulavchenko Olga A, Vinokurov Zakhar S, Saraev Andrey A, Tsapina Anna M, Trigub Alexander L, Gerasimov Evgeny Yu, Gladky Alexey Yu, Fedorov Alexander V, Yakovlev Vadim A, Kaichev Vasily V
Boreskov Institute of Catalysis , Ak. Lavrentiev Avenue, 5 , Novosibirsk 630090 , Russia.
Novosibirsk State University , Pirogov Street, 2 , Novosibirsk 630090 , Russia.
Inorg Chem. 2019 Apr 15;58(8):4842-4850. doi: 10.1021/acs.inorgchem.8b03403. Epub 2019 Apr 4.
The reduction of Fe-based nanocomposite catalysts doped with Al and Cu has been studied using in situ X-ray diffraction (XRD), in situ X-ray absorption near-edge structure (XANES), and temperature-programmed reduction (TPR) techniques. The catalysts have been synthesized by melting of iron, aluminum, and copper salts. According to XRD, the catalysts consist mainly of FeO and AlO phases. Alumina is in an amorphous state, whereas iron oxide forms nanoparticles with the protohematite structure. The Al cations are partially dissolved in the FeO lattice. Due to strong alumina-iron oxide interaction, the specific surface area of the catalysts increases significantly. TPR and XANES data indicate that copper forms highly dispersed surface CuO nanoparticles and partially dissolves in iron oxide. It has been shown that the reduction of iron(III) oxide by CO proceeds via two routes: a direct two-stage reduction of iron(III) oxide to metal (FeO → FeO → Fe) or an indirect three-stage reduction with the formation of FeO intermediate phases (FeO → FeO → FeO → Fe). The introduction of Al into FeO leads to a decrease in the rate for all reduction steps. In addition, the introduction of Al stabilizes small FeO particles and prevents further sintering of the iron oxide. The mechanism of stabilization is associated with the formation of FeAl O solid solution. The addition of copper to the Fe-Al catalyst leads to the formation of highly dispersed CuO particles on the catalyst surface and a mixed oxide with a spinel-type crystalline structure similar to that of CuFeO. The low-temperature reduction of Cu to Cu accelerates the FeO → FeO and FeO → Fe transformations but does not affect the FeO → FeO/Fe stages. These changes in the reduction properties significantly affect the catalytic performance of the Fe-based nanocomposite catalysts in the low-temperature oxidation of CO.
采用原位X射线衍射（XRD）、原位X射线吸收近边结构（XANES）和程序升温还原（TPR）技术研究了掺杂Al和Cu的铁基纳米复合催化剂的还原过程。催化剂通过铁、铝和铜盐的熔融合成。根据XRD分析，催化剂主要由FeO和AlO相组成。氧化铝处于非晶态，而氧化铁形成具有原赤铁矿结构的纳米颗粒。Al阳离子部分溶解在FeO晶格中。由于氧化铝与氧化铁之间的强相互作用，催化剂的比表面积显著增加。TPR和XANES数据表明，铜形成高度分散的表面CuO纳米颗粒并部分溶解在氧化铁中。结果表明，CO还原氧化铁通过两条途径进行：氧化铁直接两步还原为金属（FeO→FeO→Fe）或间接三步还原并形成FeO中间相（FeO→FeO→FeO→Fe）。向FeO中引入Al导致所有还原步骤的速率降低。此外，引入Al可稳定小的FeO颗粒并防止氧化铁进一步烧结。稳定化机制与FeAlO固溶体的形成有关。向Fe-Al催化剂中添加铜导致在催化剂表面形成高度分散的CuO颗粒以及具有类似于CuFeO的尖晶石型晶体结构的混合氧化物。Cu低温还原为Cu加速了FeO→FeO和FeO→Fe的转变，但不影响FeO→FeO/Fe阶段。还原性能的这些变化显著影响了铁基纳米复合催化剂在CO低温氧化中的催化性能。
