## 1 Introduction  
Energy shortage and air pollution are two severe problems worldwide in recent years. Non-renewable energy resources and fossil-based fuels currently fulfill over 80% of the energy demand [1]. The overconsumption of fossil fuels is accompanied by a great degree of CO\({}_{2}\) emission. Much evidence demonstrated that CO\({}_{2}\) emission contributes to the greenhouse effect, which could be one of the reasons for global climate change. Compared with conventional fossil fuels, the renewable energy resources could provide sustainable energy in the future due to their extensive reserves, low emissions, and renewability [1; 2; 3]. Biomass is a carbon-neutral energy source [4]. Biomass resources are abundant and have been extensively studied to offer sustainable and environmentally friendly energy and fuels for future applications [5; 6; 7]. Employing different heating methods and catalysts during the biomass gasification could effectively increase the syngas yield and reduce the generation of harmful tars. Microwave heating could improve the syngas yield, reduce the hazardous product formation, and minimize the emission pollutants [8; 9; 10; 11]. Additionally, microwave gasification produces biochar with a richer microporous structure, which could be employed for atmospheric carbon capture, storage, and climate change mitigation [12]. Physical, biochemical, and thermochemical conversions comprise most biomass conversions and utilization techniques [13]. Biomass thermochemical conversion technology is extensively employed. This technology has emerged as a prominent area of focus in biomass energy research [14]. The predominant thermochemical conversion methodologies commonly employed for biomass are combustion, pyrolysis, and gasification [15; 16]. Biomass gasification technology is widely regarded as a highly promising approach due to its versatility in accommodating diverse biomass feedstocks, as well as its superior efficiency and reduced environmental impact [14; 17]. Gasification is the process of converting hydrocarbons in biomass into high-grade syngas using gasification agents such as air, oxygen, and carbon dioxide. Biomass gasification with CO\({}_{2}\) has the advantage of reducing the atmospheric CO\({}_{2}\) emissions and converting CO\({}_{2}\) in the environment into CO. CO\({}_{2}\) gasification technology is important for the waste gasification and converting low-quality fuels into high-quality syngas. Biomass gasification with CO\({}_{2}\) consists of four stages, including drying, pyrolysis, oxidation, and reduction. At 105-300 \({}^{\circ}\)C, the water (extrinsic and intrinsic) in the biomass gradually releases out, yielding the dry material and water vapor. When the gasification temperature reaches 300 \({}^{\circ}\)C, the volatile matter in the biomass begins to release. At 400 \({}^{\circ}\)C, the biomass releases about 70% of the volatile matter. During the pyrolysis stage, the products are CO\({}_{2}\), CH\({}_{4}\), H\({}_{2}\), CO, tar, a few hydrocarbons, and semi-coke. The temperature range of pyrolysis is about 300 to 600 \({}^{\circ}\)C.  
\[\text{Gasification}:\text{Biomass}\rightarrow\text{H}_{2}+\text{CO}_{2}+ \text{Tar}+\text{C}_{\text{n}}\text{H}_{\text{m}}+\text{Char}\quad\Delta\text{ H}>0 \tag{1}\]  
The products of the biomass pyrolysis stage occur with the agent to produce H\({}_{2}\)O, CO\({}_{2}\), and CO. A large amount of heat is generated along with the oxidation reaction.