Gases produced by pyrolysis of cellulose
During pyrolysis, organic compounds are thermally decomposed in the absence of oxygen. The pyrolysis products are classified into categories based on their physical state of existence: char (solid), bio-oil (liquid) and non-condensable gases (gas). The relative proportions of these three product fractions significantly vary depending upon the process conditions, as is shown in the table below.

$$ \small
\begin{array}{lcc}
\hline
\text{Pyrolosis Technology} &amp; \text{Residence Time} &amp; \text{Heating Rate} &amp; \text{Temperature} &amp; \text{Char} &amp; \text{Bio-Oil} &amp; \text{Gases} \\
\hline
\text{Conventional} &amp; \text{5-30}\ \mathrm{min} &amp; \text{&lt;50} ^\circ \mathrm{C\ min^{-1}} &amp; \text{400-600} ^\circ \mathrm{C} &amp; \text{&lt;35%} &amp; \text{&lt;30%} &amp; \text{&lt;40%}\\
\text{Fast Pyrolysis} &amp; \text{&lt;5}\ \mathrm{s} &amp; \text{~1000} ^\circ \mathrm{C\ s^{-1}} &amp; \text{400-600} ^\circ \mathrm{C} &amp; \text{&lt;25%} &amp; \text{&lt;75%} &amp; \text{&lt;20%}\\
\text{Flash Pyrolosis} &amp; \text{&lt;0.1}\ \mathrm{s} &amp; \text{~1000} ^\circ \mathrm{C\ s^{-1}} &amp; \text{650-900} ^\circ \mathrm{C} &amp; \text{&lt;20%} &amp; \text{&lt;20%} &amp; \text{&lt;70%}^{[1]}\\
\hline
\end{array}
$$

The exact compositions of the products of cellulose pyrolysis at different temperatures can be seen below.

$$ \small
\begin{array}{lcc}
\hline
\text{Products} &amp; \text{Peak Temp,}\ 500 ^\circ \mathrm{C} &amp; \text{Holding Temp,}\ 400 ^\circ \mathrm{C} &amp; \text{Peak Temp,}\ 750 ^\circ \mathrm{C} &amp; \text{Peak Temp,}\ 1000 ^\circ \mathrm{C}\\
\hline
\ce{CO} &amp; \text{0.99%} &amp; \text{0.25%} &amp; \text{15.82%} &amp; \text{22.57%}\\
\ce{CO2} &amp; \text{0.3%} &amp; \text{1.45%} &amp; \text{2.38%} &amp; \text{3.36%}\\
\ce{H2O} &amp; \text{3.55%} &amp; \text{6.49%} &amp; \text{8.72%} &amp; \text{9.22%}\\
\ce{CH4} &amp; \text{0%} &amp; \text{0%} &amp; \text{1.11%} &amp; \text{2.62%}\\
\ce{C2H4} &amp; \text{0%} &amp; \text{0%} &amp; \text{1.05%} &amp; \text{2.18%}\\
\ce{C2H6} &amp; \text{0%} &amp; \text{0%} &amp; \text{0.17%} &amp; \text{0.28%}\\
\ce{C3H6} &amp; \text{0%} &amp; \text{0%} &amp; \text{0.70%} &amp; \text{0.80%}\\
\ce{H2} &amp; \text{0%} &amp; \text{0%} &amp; \text{0.36%} &amp; \text{1.18%}\\
\ce{CH3OH} &amp; \text{0.25%} &amp; \text{0.21%} &amp; \text{1.03%} &amp; \text{0.98%}\\
\ce{CH3CHO} &amp; \text{0.01%} &amp; \text{0.05%} &amp; \text{1.58%} &amp; \text{1.7%}\\
\text{tar} &amp; \text{16.37%} &amp; \text{83.35%} &amp; \text{59.92%} &amp; \text{49.12%}\\
\text{char} &amp; \text{83.63%} &amp; \text{6.17%} &amp; \text{3.32%} &amp; \text{3.91%}\\
\text{other} &amp; \text{0.19%} &amp; \text{0.16%} &amp; \text{2.14%} &amp; \text{1.78%}\\
\text{total} &amp; \text{105.25%} &amp; \text{98.36%} &amp; \text{98.8%} &amp; \text{99.86%}\\
\hline
\end{array}
$$

The holding time for each of these reactions was $30\ \mathrm{s}^{[2]}$. As shown in the table, $\ce{CO}$, $\ce{H2O}$, and $\ce{CO2}$ are the major gaseous products, with $\ce{H2}$ and hydrocarbons being produced in considerably smaller proportion.




$^{[1]}$ Patwardhan, Pushkaraj Ramchandra, "Understanding the product distribution from biomass fast pyrolysis" (2010). Graduate Theses
and Dissertations. Paper 11767.
$^{[2]}$ Hajaligol, M. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Product Compositions and Kinetics for Rapid Pyrolysis of Cellulose. Industrial &amp; Engineering Chemistry Process Design and Development Ind. Eng. Chem. Proc. Des. Dev. 1982, 21, 457–465.