Here is a list of articles so far about methane capture and biogas. This is lab based experiments in small quantities (~50ml) but it could be scaled up. So in a foggy smog future where we all live in domes, these methane processors could slowly grab the energy back from the atmosphere.
[1] https://www.newscientist.com/article/dn18977-innovation-meth...
[2] http://pubs.rsc.org/en/Content/ArticleLanding/2008/CC/b80440...
[3]http://www.rsc.org/suppdata/cc/b8/b804405h/b804405h.pdf