A Microwave-Assisted Boudouard Reaction: A Highly Effective Reduction of the Greenhouse Gas CO2 to Useful CO Feedstock with Semi-Coke.

Huan Dai,Hong Zhao,Siyuan Chen,Biao Jiang

doi:10.3390/molecules26061507

Abstract

The conversion of CO2 into more synthetically flexible CO is an effective and potential method for CO2 remediation, utilization and carbon emission reduction. In this paper, the reaction of carbon-carbon dioxide (the Boudouard reaction) was performed in a microwave fixed bed reactor using semi-coke (SC) as both the microwave absorber and reactant and was systematically compared with that heated in a conventional thermal field. The effects of the heating source, SC particle size, CO2 flow rate and additives on CO2 conversion and CO output were investigated. By microwave heating (MWH), CO2 conversion reached more than 99% while by conventional heating (CH), the maximum conversion of CO2 was approximately 29% at 900 °C. Meanwhile, for the reaction with 5 wt% barium carbonate added as a promoter, the reaction temperature was significantly reduced to 750 °C with an almost quantitative conversion of CO2. Further kinetic calculations showed that the apparent activation energy of the reaction under microwave heating was 46.3 kJ/mol, which was only one-third of that observed under conventional heating. The microwave-assisted Boudouard reaction with catalytic barium carbonate is a promising method for carbon dioxide utilization.

Highlights

In the face of climate change due to global warming, converting carbon dioxide into synthetic, flexible and useful molecules rather than capturing CO2 for storage is the most attractive approach to climate change mitigation solutions (Scheme 1) [1]
Carbonaceous materials are known as excellent microwave receptors [9] and the high temperatures required for the Boudouard reaction could be provided by microwave irradiation [10]
The results showed that microwave radiation was more effective than conventional heating and the reaction temperature was reduced by approximately 200 ◦C in a short time

Summary

Introduction

In the face of climate change due to global warming, converting carbon dioxide into synthetic, flexible and useful molecules rather than capturing CO2 for storage is the most attractive approach to climate change mitigation solutions (Scheme 1) [1]. Efficient reducing agents and precious metal catalysts are required to facilitate its conversion into useful chemicals [2]. High-temperature microwaves have a special advantage in inducing chemical reactions derived from heterogeneous catalysts with unique opportunities to control the energy input [7]. The ideal microwave catalyst has a dual role both as a catalyst for chemical reactions and as an efficient converter of the thermal energy required for the event and reaction activation from microwave energy [8]. Carbonaceous materials are known as excellent microwave receptors [9] and the high temperatures required for the Boudouard reaction could be provided by microwave irradiation [10]. The reactivity of biochar was found to be dependent on the pore structure of the char and its morphology, the catalytic activity of the associated Molecules 2021, 26, x FOR PEER REVaIEsWh, the availability of carbon active sites as well as catalytic active sites on the cha2r,otfh1e1 thermal history of the char during pyrolysis and the type of carbon source

Methods

Results

Conclusion