Shit is happening

[Lemonray]

Can't they give the robot some kind of knockout gas instead of a bomb...?

Not impossible but not practical. It would have to be potent enough to almost instantly put him under so he couldn't just kill himself. And even if gas this potent were readily available you would need a good delivery method. Certain masks would also render the gas useless and there's also the chance that the guy won't wake up at all after being knocked out.