# Advances in Bio-Hydrogen Production: A Critical Review of Pyrolysis Gas Reforming
## 3 Hydrogen Production by Catalytic Reforming of Pyrolysis Volatiles
### Slow Pyrolysis
#### 3.1.2 Reforming Temperature  
Different research studies show that reforming temperature is among the most relevant factors impacting hydrogen yield. [PERSON] et al. [71] investigated the two-stage pyrolysis and catalytic reforming of oak wood. The temperature range of the catalytic reforming was from 700 \({}^{\circ}\)C to 800 \({}^{\circ}\)C, and three different catalysts were used in this experimental study. The results proposed by the authors showed that using the nickel catalyst, the hydrogen production volume increased from 34.1% to 41.7% when the reforming temperature increased from 700 \({}^{\circ}\)C to 750 \({}^{\circ}\)C. Also, it could be seen that the hydrogen production volume was decreased by 0.6% by additionally increasing the reforming temperature from 750 \({}^{\circ}\)C to 800 \({}^{\circ}\)C. Moreover, the results indicated that the hydrogen production volume using a cobalt catalyst at 700 \({}^{\circ}\)C, 750 \({}^{\circ}\)C, and 800 \({}^{\circ}\)C was 22.7%, 31.1%, and 32.1%, respectively. Based on the results, the hydrogen concentration with the Ni and Co-Ni catalysts was maximized at 750 \({}^{\circ}\)C [71]. [PERSON] et al. [62] analyzed syngas production using biowaste as a feedstock and a three-stage process including pyrolysis, catalytic steam reforming, and catalytic hydrogenation. Waste wood sawdust was used as a feedstock in this study and the selected catalyst for the first two steps of the process was a 10 wt% Ni catalyst loaded on an Al\({}_{2}\)O\({}_{3}\) support. It must be mentioned that the weight of the biomass sample and catalyst for the steam reforming step was 1 g. The temperature range for catalytic reforming in this study was 600-900 \({}^{\circ}\)C. The results showed that increasing the reforming temperature from 600 \({}^{\circ}\)C to 900 \({}^{\circ}\)C led to an increase in the hydrogen yield from 26.8 to 28.94 mmol/g of biomass. Also, the hydrogen volume percentage was decreased from 72% to 60.4% by increasing the reforming temperature in this range. Also, the results of the experiments revealed that the H\({}_{2}\)/CO ratio was decreased by 108.8% by increasing the reforming temperature from 600 \({}^{\circ}\)C to 900 \({}^{\circ}\)C [62]. The effect of reforming temperature on syngas and hydrogen gas yield was also evaluated by [PERSON] et al. [66]; they performed an experiment by using a two-stage fixed-bed reactor to study the influence of different factors on syngas yield. Using a 10 wt% Ni/char catalyst to reform poplar wood pyrolysis gas, they showed that increasing the temperature from 600 \({}^{\circ}\)C to 700 \({}^{\circ}\)C increased the hydrogen yield from 23.186 mmol/g to 26.767 mmol/g. [PERSON] et al. [72] also used the pyrolysis and catalytic reforming process to produce hydrogen-rich gas from corncob feedstock and natural limonite ore as a catalyst. In their experiments, the reforming temperature increased from 400 \({}^{\circ}\)C to 750 \({}^{\circ}\)C, and results showed that the hydrogen yield increased by 191.7 percent over this range. Moreover, the maximum  
Figure 5: Effect of pyrolysis temperature on hydrogen yield and its trendline [61; 67; 68; 69; 70]. hydrogen yield was observed between 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, when the hydrogen yield increased by 73 percent to 31.4 mmol/g. The obtained results also showed that the hydrogen yield was not significantly affected by increasing the reforming temperature above 700 \({}^{\circ}\)C, as they reported that this value increased only 1.15 percent to reach 52.8 mmol/g. The presented results also demonstrated that the hydrogen volume concentration was 59.2 vol% at 400 \({}^{\circ}\)C, and increasing the reforming temperature to 750 \({}^{\circ}\)C resulted in increasing the hydrogen volume up to 71 vol% [72]. Figure 6 shows the effect of reforming temperature on hydrogen yield in different research studies.