I agree with what Sherrine told you. I have had cats for many years and have spent a lot of time integrating cats with cats, cats with dogs, etc...believe me, cats with cats is much easier than cats with dogs LOL!!
You might want to try just putting them on opposite sides of a closed door, so they can sniff one another. Your older one will probably want to make a point that he's been there longer, is the , well now, I cannot think of the word...talk about a bad fibro flare day for me...well, he is going to want to let the little guy know he's on top. They need time to adjust, to understand each other. Try to be patient, show the older one LOTS of extra attention and love. The crate is a good idea, but a closed door will do just as well, maybe even better, so they don't stare at each other and can sniff without causing too much stress...Remember to reward good behaviour in both!!
We recently adopted a rescue Golden Retriever, from a Golden rescue group. We have a Golden who is 5 and we wanted him to have a sibling, someone to play with. I walk him daily, he is such a good motivator for me to walk, but that simply isn't enough and as all of you understand, there are times that I simply do not have the energy for him and it always makes me feel so bad, him wanting to romp and play and I can barely get off the couch. So we adopted an adult dog, thinking he would have someone to play with all the time. Well...Benji is 6 years old and we couldn't ask for a better, sweeter, more well mannered dog, BUT...he does NOT want to play with Cheyenne, my 5 year old...not sure why. They eat together, sleep together and play NEXT to each other, but won't play together, so now I have TWO I have to entertain...oh boy! We've had him now, actually today, 4 months. I've gotten all kinds of advice, but one woman who's raised dogs for over 30 years told me it can take up to 1.5 years for them to really become comfortable and secure enough to play...oh well...LOL. All we know about Benji, the rescue, is he comes from a home where he lived with an alcoholic man, who really neglected him. His thigh muscles were severely underdeveloped because of lack of exercise, just lying around the house. We don't know if he was abused, but obviously neglected. He freaks out when we try to leave the house, so we think he must have been left alone a lot. Yes, he has "issues" but what a loving boy! Anyway, I sure rambled...sorry... really meant to try to help you and I ended up going on about Benji...be well,