Switching low-temperature CO2 hydrogenation product selectivity over metal–organic framework derived Co-based catalyst

Abstract

Reductive recycling of CO₂ is a promising strategy towards climate and energy issues, while the control of the product selectivity in CO₂ hydrogenation has posed an enormous challenge. By utilizing alkali metal promoters, purposeful modification of active sites is expected to realize tuning selectivity in CO₂ hydrogenation, while the chemical state and specific role of alkali metal promoters are not fully understood yet. Here, we reported a metal–organic framework (MOF)-transformed carbon encapsulated KMgO/Co nanoparticles catalyst (KMgO/Co@C) with MgO/Co interfaces by solid-state impregnation method, and studied mechanistically about the effect of potassium promoter on overturning the CO₂ hydrogenation product selectivity at low temperatures (<350 °C). Experiments coupled with in situ infrared analysis and theoretical calculations revealed that redox pathway occurred on both the potassium-promoted KMgO/Co@C catalyst and the unpromoted MgO/Co@C catalyst, and the addition of potassium promoter to MgO/Co@C catalyst was beneficial for CO production due to the high energy barrier for deep hydrogenation, thus the product selectivity of CO₂ hydrogenation switched from 97.13 % CH₄ selectivity for MgO/Co@C to 94.11 % CO selectivity for KMgO/Co@C. Most astonishingly, the KMgO/Co@C catalyst exhibited CO₂ conversion of 32.46 % at 350 °C, close to the thermodynamic equilibrium conversion (33.93 %), and the exceptionally high STY_CO of 81.82 mmol·g_cat.⁻¹·h⁻¹ outperformed most of the RWGS catalysts, even surpassed many of the noble metal-based catalysts. This work provides new insights into the role of potassium promoter and emphasizes the crucial role of CO hydrogenation activity in regulating CO₂ hydrogenation selectivity over Co-based catalysts, which may inspire the strategic design of advanced low-temperature reverse water–gas shift catalysts.