Highly Active MnCoO<sub><i>x</i></sub> Catalyst toward CO Preferential Oxidation
Jun Yu, Yusen Yang, Meng Zhang, Boyu Song, Yang Han, Si Wang, Zhen Ren, Lei Wang, Pan Yin, Lirong Zheng, Xin Zhang, Min Wei
Abstract
Preferential oxidation of CO (CO-PROX) is an efficient method to eliminate residual CO in the feed stream to avoid Pt poisoning in proton-exchange-membrane fuel cells (PEMFCs), in which the development of high-performance, low-cost catalysts remains a big challenge. Herein, we report highly active spinel-like MnCoO x catalysts derived from layered double hydroxide (LDH) precursors, which are featured with abundant octahedron-distorted lattice oxygen. Impressively, the optimal catalyst MnCoO x -300 achieves the selective and complete removal of CO from a H 2 -rich stream at 80 °C, within a wide operation temperature window (80–200 °C, matching well with PEMFCs) at a rather high space velocity (80,000 h –1 ). This performance, to the best of our knowledge, outperforms previously reported non-noble metal catalysts and even exceeds the state-of-the-art CuO/CeO 2 system in the CO-PROX technology. A comprehensive investigation based on in situ Raman, in situ XAFS, in situ TPD-Mass, and in situ DRIFTS reveals that the Co oct 3+ –O 2– –Mn oct 4+ structure in MnCoO x -300 serves as the intrinsic active site that facilitates preferential oxidation: the lattice oxygen participates in the oxidation of CO to produce CO 2 and oxygen vacancy (O v ), followed by the replenishment of oxygen species from aerial oxygen (the rate-determining step) to regenerate Co oct 3+ –O 2– –Mn oct 4+ . Isotopic 18 O kinetic studies and in situ DRIFTS substantiate that the reaction temperature plays a crucial role in the competitive oxidation of CO vs H 2 at the same active site. This work provides a successful paradigm for the design and preparation of transition metal oxide catalysts toward the CO-PROX reaction, which shows potential applications in hydrogen purification for PEMFCs.