## 2 Experimental Section
### Experimental System and Procedure  
The gasification experiment for biomass is conducted in a fixed-bed reactor. Figure 1 shows a schematic diagram of the experimental system, which consists of four parts, including agent supply, biomass gasification, tar separation, and gas collection. CO\({}_{2}\) is supplied to the gasification system at a flow rate of 250 mL min\({}^{-1}\) through a pressure-reducing valve from a gas cylinder. The gasification system consists of the EG system and the MG system. The main part of the EG system is the electrically heated tube furnace (SZGL-1200, Jvjing, Shanghai, China). It consists of a quartz tube reactor with an inner diameter of 50 mm, a thermocouple, and a quartz hanging basket. The length of the heating part is 410 mm, and 1200 \({}^{\circ}\)C is the maximum heating temperature. The microwave \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{3}{c}{**Proximate Analysis**} & \multicolumn{6}{c}{**Ultimate Analysis**} \\ \cline{2-10}  & \(w\) **(FC)** & \(w\) **(V)** & \(w\) **(A)** & \(w\) **(M)** & \(w\) **(C)** & \(w\) **(H)** & \(w\) **(O)** & \(w\) **(N)** & \(w\) **(S)** \\ \hline Oak & 9.43 & 56.54 & 32.65 & 1.38 & 29.60 & 3.01 & 32.84 & 0.48 & 0.04 \\ Corn stalk & 17.49 & 64.19 & 8.80 & 9.52 & 40.34 & 4.63 & 35.36 & 1.17 & 0.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Proximate and ultimate analyses of biomass samples (wt.%, ad). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Compounds of**} & **Analysis Standard** & **Oak** & **Corn Stalk** \\ \hline \multirow{8}{*}{Ash analysis} & Fe\({}_{2}\)O\({}_{3}\) & & 3.87 & 3.67 \\  & Al\({}_{2}\)O\({}_{3}\) & & 6.17 & 7.69 \\  & CaO & & 20.58 & 18.43 \\  & MgO & & 0.01 & 4.07 \\  & SiO\({}_{2}\) & & 36.14 & 46.14 \\  & TiO\({}_{2}\) & GB/T 30725-2014 [50] & 0.37 & 0.50 \\  & SO\({}_{3}\) & & 1.45 & 1.65 \\  & K\({}_{2}\)O & & 0.05 & 5.09 \\  & Na\({}_{2}\)O & & 0.05 & 2.35 \\  & P\({}_{2}\)O\({}_{5}\) & & 0.95 & 1.49 \\  & MnO\({}_{2}\) & & 0.02 & 0.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ash composition analyses of oak and corn stalk (wt.%). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **Cellulose** & **Hemicellulose** & **Lignin** \\ \hline Corn stalk & 36.5\% & 34.9\% & 18.8\% \\ Oak & 44.9\% & 21.5\% & 29.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cellulose, hemicellulose, and lignin content of biomass samples. heating gasification system mainly comprises a microwave gasification stove (CY-PY1100C-S, Changyi, Hunan, China). Inside is a quartz furnace tube with a length of 750 mm and a wall thickness of 3 mm. The length of the microwave heating section is 150 mm. The gas collection system consists of gas-washing bottles and a gas collection bag. The gaseous products are removed from the reactor via gas flow. The condensable constituents are initially rapidly cooled and isolated within a cold-water bath, subsequently absorbed using gas-washing bottles containing chromatographically pure isopropanol and desiccated silicone. Before the experiment, the valve of the CO\({}_{2}\) cylinder is opened after checking the gas tightness of the device, and CO\({}_{2}\) of 150 mL min\({}^{-1}\) goes through the quartz tube for 30 min to remove air from tube. The gasification temperature is set to a predetermined temperature (600-1000 \({}^{\circ}\)C) on the temperature controller of the electric heating furnace or microwave heating furnace. When the predetermined temperature is reached, the CO\({}_{2}\) valve is opened with 250 mL min\({}^{-1}\). The gasification experiments are performed for 25 min. After the quartz tube is cooled to room temperature, the biochar samples are removed and weighed. An analytically pure ethanol solution is chosen to dilute the concentrated tar samples at a volume ratio of 1:100 to obtain the test samples. Anhydrous sodium sulfate is applied to remove any water that may be present in the tar sample.