Kanungo Subhashree S, Mishra Abhaya Kumar, Mhamane Nitin B, Marelli Udaya Kiran, Kumar Dharmesh, Gopinath Chinnakonda S
Catalysis and Inorganic Chemistry Division, CSIR─National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201 002, India.
Inorg Chem. 2022 Dec 5;61(48):19577-19587. doi: 10.1021/acs.inorgchem.2c03493. Epub 2022 Nov 16.
In this work, we demonstrate a simple sol-gel technique to prepare metal-ion(s)-doped ceria-zirconia solid solution for efficient catalytic methane activation. The cation-depicting formula units are CeZr (CZ), CeZrM (CZM), and CeZrMM (CZMM) (M and M = V, Mn, Fe, Co, and Cu), employed for undoped, mono-metal-ion-doped, and bi-metal-ion-doped solid solutions, respectively. Methane activation with Mn, Fe, Cu mono-metal-ion-doped CZ favors the C1 product, while CZCo assists C-C coupling with the formation of acetaldehyde. On the other hand, the Co- and Fe-doped bi-metal-ion combination catalyst (CZCoFe) shows significant ethanol but predominant formic acid formation. This is further promoted by the Co + V bi-metal-ion combination (CZCoV) catalyst, and it shows ethanol as the major product along with methyl hydrogen peroxide, methanol, and formic acid as minor products. An impressive ethanol yield of 93 μmol/g h with 76% selectivity obtained with the CZCoV catalyst is at par with that obtained with noble-metal-based catalysts under comparable reaction conditions. When Co and V content was increased two and four times from 0.005 to 0.01 and 0.02, ethanol yield increased at the expense of formic acid. The 213 μmol/g h ethanol yield (86% selectivity) observed with CeZrCoV is probably the highest observed. The partial oxidation of CH in Co-based bi-metal combinations (Co + V or Co + Fe) suggests the synergistic effect of doped metal ions owing to the heterogeneous near-neighbor environment. The present results are attributed to the surface heterogeneity between the host and the dopants, which selectively promotes methane activation as well as C-C coupling. This indicates a large scope to tune the activity of partial oxidation of methane and product selectivity with different metal-ion(s) combinations.
在这项工作中，我们展示了一种简单的溶胶-凝胶技术，用于制备金属离子掺杂的二氧化铈-氧化锆固溶体，以实现高效的催化甲烷活化。阳离子描述的化学式单元分别为CeZr（CZ）、CeZrM（CZM）和CeZrMM（CZMM）（M和M = V、Mn、Fe、Co和Cu），分别用于未掺杂、单金属离子掺杂和双金属离子掺杂的固溶体。用Mn、Fe、Cu单金属离子掺杂的CZ进行甲烷活化有利于生成C1产物，而CZCo则有助于C-C偶联并形成乙醛。另一方面，Co和Fe掺杂的双金属离子组合催化剂（CZCoFe）显示出显著的乙醇生成，但主要生成甲酸。Co + V双金属离子组合（CZCoV）催化剂进一步促进了这一过程，它以乙醇为主要产物，同时以甲基过氧化氢、甲醇和甲酸为次要产物。在可比的反应条件下，CZCoV催化剂获得了令人印象深刻的93 μmol/g h的乙醇产率和76%的选择性，与基于贵金属的催化剂相当。当Co和V的含量从0.005分别增加两倍和四倍至0.01和0.02时，乙醇产率增加，而甲酸产率降低。用CeZrCoV观察到的213 μmol/g h的乙醇产率（86%的选择性）可能是所观察到的最高值。在基于Co的双金属组合（Co + V或Co + Fe）中CH的部分氧化表明，由于异质近邻环境，掺杂金属离子具有协同效应。目前的结果归因于主体和掺杂剂之间的表面非均质性，它选择性地促进了甲烷活化以及C-C偶联。这表明通过不同的金属离子组合来调节甲烷部分氧化的活性和产物选择性具有很大的空间。
