## 1 Introduction
The main reactions in the oxidation stage are as follows:  
\[\text{Complete combustion}:\text{C}+\text{O}_{2}\rightarrow\text{CO}_{2} \quad\Delta\text{H}=-394\text{ kJ mol}^{-1} \tag{2}\]  
\[\text{Partial combustion}:\text{C}+\frac{1}{2}\text{O}_{2}\rightarrow\text{CO} \quad\Delta\text{H}=-111\text{ kJ mol}^{-1} \tag{3}\]  
\[\text{CO oxidation}:\text{CO}+\frac{1}{2}\text{O}_{2}\rightarrow\text{CO}_{2} \quad\Delta\text{H}=-283\text{ kJ mol}^{-1} \tag{4}\]  
\[\text{H}_{2}\text{ oxidation}:\text{H}_{2}+\frac{1}{2}\text{O}_{2}\rightarrow \text{H}_{2}\text{O}\quad\Delta\text{H}=-242\text{ kJ mol}^{-1} \tag{5}\]  
At 700-90 \({}^{\circ}\)C, the oxidized products of the previous stage continue to undergo a reduction, producing small molecules of combustible gases such as CH\({}_{4}\), H\({}_{2}\), and CO, which is a heat-absorbing reaction. \[\text{Boudouard}:\text{C}+\text{CO}_{2}\rightarrow\text{2 CO}\quad\Delta\text{ H}=+172\text{ kJ mol}^{-1} \tag{6}\]  
\[\text{Water-gas}:\text{C}+\text{H}_{2}\text{O}\rightarrow\text{CO}_{2}+2\text {H}_{2}\quad\Delta\text{H}=+131.5\text{ kJ mol}^{-1} \tag{7}\]  
\[\text{Water-gas shift}:\text{CO}+\text{H}_{2}\text{O}\rightarrow\text{CO}_{2} +\text{H}_{2}\quad\Delta\text{H}=-41.2\text{ kJ mol}^{-1} \tag{8}\]  
\[\text{Methanation}:\text{C}+2\text{H}_{2}\rightarrow\text{CH}_{4}\quad\Delta \text{H}=-75\text{ kJ mol}^{-1} \tag{9}\]  
\[\text{Methanane Reforming}:\text{CH}_{4}+\text{CO}_{2}\rightarrow\text{2 CO}+2 \text{H}_{2}\quad\Delta\text{H}=+247\text{ kJ mol}^{-1} \tag{10}\]  
The oxidation and reduction phases are both referred to as biomass gasification. The liquid-phase tar generated from the biomass gasification also undergoes further reforming and cracking to produce some small molecule components. In addition, CO\({}_{2}\) could react with the tar produced, as shown in Equation (11), promoting its cracking to yield H\({}_{2}\) and CO. Moreover, the tar can be directly cracked to release H\({}_{2}\), as shown in (12). \[\text{Complete combustion}:\text{C}+\text{O}_{2}\rightarrow\text{CO}_{2} \quad\Delta\text{H}=-394\text{ kJ mol}^{-1} \tag{2}\]0\[\text{Complete combustion}:\text{C}+\text{O}_{2}\rightarrow\text{CO}_{2} \quad\Delta\text{H}=-394\text{ kJ mol}^{-1} \tag{2}\]1  
Syngas could replace some fossil fuels for power and heat generation. However, char and undesired tar are produced along with the syngas. Tar is a fluid combination of dense and viscous heavy aromatics. Tar could lead to a reduction in the calorific value of the syngas, slagging and corrosion of the heating surfaces, and catalyst deactivation [18; 19; 20; 21; 22; 23; 24]. In addition, numerous studies have provided evidence regarding the capacity of biochar to sequester carbon, soil fertility enhancement and stabilization, and wastewater and gas adsorption [25; 26; 27; 28; 29]. The properties of the products obtained via different heating methods vary considerably. Electric and microwave heating have been studied [30; 31; 32]. In contrast to electric heating methods, which rely on the conduction of heat from the surface to the core of a material through the temperature gradients, microwave heating operates by converting electromagnetic energy directly into heat at the molecular level [33]. The utilization of microwave heating demonstrates a rapid heating rate and the advantages of volumetric and uniform heat distribution. Many studies have reported that secondary cracking reactions are promoted in microwave pyrolysis [34; 35]. More syngas and less tar are produced for microwave gasification than other conventional gasification under the comparable conditions [34; 36; 37; 38]. Syngas from gasification could be applied in heat and power production and as feedstock for the synthesis of fuels. Tar could be highly toxic to the atmosphere and the environment. These characteristics contribute to reducing potentially harmful product formation and mitigating emission pollutants, thereby establishing the technique as environmentally sustainable [8; 9; 10; 11].