Synergistic Effect of Alkali Na and K Promoter on Fe-Co-Cu-Al Catalysts for CO2 Hydrogenation to Light Hydrocarbons

Yuhao Zheng,Qiong Wu,Chenghua Xu,Xia Zhang,Jie Liu

doi:10.3390/catal11060735

Yuhao Zheng, Qiong Wu + Show 3 more

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https://doi.org/10.3390/catal11060735

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Abstract

Alkali metal K- and/or Na-promoted FeCoCuAl catalysts were synthesized by precipitation and impregnation, and their physicochemical and catalytic performance for CO2 hydrogenation to light hydrocarbons was also investigated in the present work. The results indicate that Na and/or K introduction leads to the formation of active phase metallic Fe and Fe-Co crystals in the order Na < K < K-Na. The simultaneous introduction of Na and K causes a synergistic effect on increasing the basicity and electron-rich property, promoting the formation of active sites Fe@Cu and Fe-Co@Cu with Cu0 as a crystal core. These effects are advantageous to H2 dissociative adsorption and CO2 activation, giving a high CO2 conversion with hydrogenation. Moreover, electron-rich Fe@Cu (110) and Fe-Co@Cu (200) provide active centers for further H2 dissociative adsorption and O-C-Fe intermediate formation after adsorption of CO produced by RWGS. It is beneficial for carbon chain growth in C2+ hydrocarbons, including olefins and alkanes. FeCoCuAl simultaneously modified by K-Na exhibits the highest CO2 conversion and C2+ selectivity of 52.87 mol% and 89.70 mol%, respectively.

Highlights

With the development of industrialization and urbanization, a large amount of CO2 with a greenhouse effect has been discharged due to excessive use of fossil fuels, such as petroleum, coal and natural gas
The obtained FeCoCuAl catalyst, using sodium alkali as a precipitant, was found by ICP-OES to contain low residual Na with a Na/Fe molar ratio of 0.16%, and using potassium alkali as a precipitant gives a residual amount of K of the K/Fe molar ratio of 0.18%
It is clear that Na modification can further increase the BET specific surface area, pore volume and average pore diameter of FeCoCuAl catalysts

Summary

Introduction

With the development of industrialization and urbanization, a large amount of CO2 with a greenhouse effect has been discharged due to excessive use of fossil fuels, such as petroleum, coal and natural gas. The negative effects associated with increasing atmospheric concentrations of CO2, climate change and ocean acidification, are considered as the most challenging issues of the 21st century [1,2]. Many efforts must be put forth to decrease CO2 direct emissions, permanently sequester CO2 and convert CO2 to valuable products [3]. CO2 catalytic conversion has been a rapidly growing field because CO2 is an abundant, non-toxic and low-cost C1 feedstock that can be converted to many valuable chemicals and energy storage substances, such as methane [4], methanol [5,6,7], low-carbon alkanes [8] and olefins [9,10]. Ethylene and propylene are the top two petrochemicals produced worldwide with a high demand for the production of plastics, polymers, solvents and cosmetics

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