Upvote:3
No airline will board you on a direct flight to the US without a passport or green card. This is because check-in staff rely on the TIMATIC database to verify documentation, which says a passport, green card, emergency passport, transportation letter or (if flying from Canada) NEXUS card is required to enter the US by air.
(in addition, you cannot get a visa as a US citizen, and you state that your foreign passport would require one)
However, per TIMATIC, US citizens can fly to and enter Canada with only their naturalization certificate. From there you can cross into the US by land and, if need be, catch a domestic flight.
So either get that emergency passport, or book your return trip through Canada. In the latter case, if you face problems at check-in/boarding for the flight to Canada, insist that the staff check TIMATIC, putting USA as your nationality.