On my computer, the MQ137 is shaded and does not come up as an active link. It may not be available yet.
The MQ7 is active. It seems to have a very slow response time and is probably more suitable for static measurements, for example at a fixed location in a mine.
If you check the methane monitor, a typical analog circuit is given. The driver and output functions might give you some ideas of how to do much of the same with a PIC. Although, when you consider the current needs of the sensor, you might be better off (i.e., simpler)just building a similar analog circuit and using the PIC only to monitor output.
John