Is there any kind of reaction with two types of reactants (gases) and one product (also gas) such that the total volume after the reaction increases? I would like to think of the following equation:

$$\ce{aA(g) + bB(g) -&gt; cC(g)}$$

where $a + b &lt; c$ and $\ce{A},$ $\ce{B}$ and $\ce{C}$ are different gases.

Is there such chemical reaction?
Decomposition of ozone:

$\ce{O3 + O3 -&gt; 3 O2}$ 

Technically, not 3 different gases, but the introduction of isotopes may be judged as in compliant (and yes, contrived).