# Advances in Bio-Hydrogen Production: A Critical Review of Pyrolysis Gas Reforming
## Conclusions  
This review of the existing literature allows deriving that pyrolysis temperature is a key operating condition directly influencing hydrogen yield. Although a higher reaction temperature can enhance hydrogen yield, the associated increase in process energy demand must be carefully assessed when scaling up plants. Reforming temperature is another operating condition that strongly affects hydrogen yield. This literature review demonstrates that increasing reforming temperature enhances hydrogen yield. However, the positive effect of increasing temperature shows a maximum around 700 \({}^{\circ}\)C and 800 \({}^{\circ}\)C. Considering the main findings of the reviewed studies, while increasing pyrolysis and reforming temperatures leads to increased hydrogen production, energy consumption contextually increases. Also, catalyst sintering is another challenge \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Feedstock** & **Pyrolysis Temperature \({}^{\circ}\)C** & **Reforming** & **Catalyst** & **H2** & **H2 Yield (voll\%)** & **Ref.** \\ \cline{2-6}  & **(Ideating Rate \({}^{\circ}\)C/min)** & **Temperature \({}^{\circ}\)C** & **Catalyst** & **Concentration** & **(mmol/g)** & **Ref.** \\ \hline Rice husk & & & & 59.32 & 25.44 & \\ \cline{2-6} Sugar cage bagasse & 950 (20) & 950 & 10 wt \% Ni–dolomite & 57.4 & 25.41 & [63] \\ \cline{2-6} Wheat straw & & & & 58.3 & 24.47 & \\ \cline{2-6} Rice husk & & & & 57.63 & 18.22 & \\ \cline{2-6} Cocnut shell & & & & 58.21 & 22.11 & \\ \cline{2-6} Sugar cane & & & & 59.23 & 22.96 & \\ \cline{2-6} Palm kernel shell & & & & 57.36 & 25.35 & \\ \cline{2-6} Cotton stalk & & & & 57.95 & 20.74 & \\ \cline{2-6} Wheat straw & & & & 54.06 & 16.38 & \\ \cline{2-6} Lignin & & & & 64.02 & 25.25 & \\ \cline{2-6} Cellulose & & & & 56.43 & 19.72 & \\ \cline{2-6} Xylan & & & & 58.77 & 20.54 & \\ \hline Corncob & 900 (10) & 650 & \
\begin{tabular}{c} Ni–exchanged resin \\ char (Ni/RC) \\ \end{tabular} & 72.5 & 61.2 & [77] \\ \hline \multirow{6}{*}{Wood pellets} & & 700 & Tire char & 34.6 & 10.2 & \\ \cline{2-6}  & & 800 & Tire char & 38.2 & 15.1 & \\ \cline{2-6}  & 500 (40) & 900 & Tire char & 51.8 & 47.6 & [70] \\ \cline{2-6}  & & 700 & Acid-treated tire char & 14.3 & 3.11 & \\ \cline{2-6}  & & 800 & Acid-treated tire char & 28.3 & 10.2 & \\ \cline{2-6}  & & 900 & Acid-treated tire char & 47.1 & 36.7 & \\ \hline \multirow{6}{*}{Wood sawdust} & & \multirow{2}{*}{550 (40)} & \multirow{2}{*}{800} & Blank & 23.2 & 6 \\ \cline{2-6}  & & & Ni-Ca-Mg-Al (1:1:1:1) & 52.3 & 18.2 & \\ \cline{2-6}  & & & Ni-Mg-Al & 35.1 & 10.4 & \\ \cline{2-6}  & & & Sand & 17.5 & 2.4 & \\ \cline{2-6}  & & & & Fe-Zn/Al\({}_{2}\)O\({}_{3}\) (1:1) & 40.6 & 9.65 & \\ \cline{2-6} Wood sawdust & 500 (40) & 800 &
\begin{tabular}{c} Fe-Zn/Al\({}_{2}\)O\({}_{3}\) (1:2) \\ \end{tabular} & 35.1 & 7.25 & [65] \\ \cline{2-6}  & & & & Fe-Zn/Al\({}_{2}\)O\({}_{3}\) (1:3) & 35.6 & 6.79 & \\ \cline{2-6}  & & & Fe-Zn/Al\({}_{2}\)O\({}_{3}\) (1:4) & 35.1 & 6.59 & \\ \hline \multirow{6}{*}{Waste wood} & & \multirow{2}{*}{500 (2400)} & Sand & 18.2 & N.A & \\ \cline{2-6}  & & & NiO/Al\({}_{2}\)O\({}_{3}\) & 44.4 & N.A & \\ \cline{1-1} \cline{2-6}  & & & NiO/SiO\({}_{2}\) & 38.7 & N.A & \\ \cline{1-1} \cline{2-6}  & & & NiO/CeO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) & 43.1 & N.A & \\ \hline \hline \end{tabular} Note: N.A: not available.  
\end{table} 
Table 6: Hydrogen yield reported in different research studies of process of two-stage reforming of pyrolysis volatiles. when increasing reforming temperature. So, optimizing pyrolysis and reforming temperatures should be performed by considering energy consumption limitations and preventing catalyst sintering. It has to be stressed that reforming at higher temperatures requires more energy and more complex plants, so the optimum reforming temperature should be a balance between hydrogen yield and energy requirements. Also, the results show the positive effect of using steam as a reforming agent in enhancing hydrogen yield.