Answer:
"Which sentence?" you ask. I'm confused. You only provided one sentence, and that sentence does have a gerund functioning as an object of a preposition!
They thanked us exuberantly for meeting with them to discuss the deal.
Step-by-step explanation:
Did you intend to ask someone to identify the gerund that is functioning as the object of a preposition??? If so, then .....
prep. gerund
They thanked us exuberantly for meeting with them to discuss the deal.