How can we help our newly neutered adult dog "calm down" faster?

My fianc� and I just adopted a male adult Pomeranian (about 6 years old) from a rescue shelter. He was neutered yesterday and is still things. I know that it takes some time, maybe up to six months, for adult dogs to fully calm down after being neutered, but he is aggressively pestering my female cat (3 years old) ever since he got to our house. She has tried to "smack" him a few times, which makes him cry, but he continues to want to jump her every time he sees her. we have them separated by a pet gate, which has helped, but he still gets very anxious/excited when he sees her. Does anyone have any suggestions as to what we can do to help this situation? Is there anything we can do to help him calm down faster so she wont be so intimidated by him? Thanks!