CO&lt;sub&gt;2&lt;/sub&gt; Methanation of Biogas Over 20 wt% Ni-Mg-Al Catalyst: On the Effect of N&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt;, and O&lt;sub&gt;2&lt;/sub&gt; on CO&lt;sub&gt;2&lt;/sub&gt; Conversion Rate