There is no sin if cats pass in front of you while you are offering salah. Animals are not bound by Shariah. But if you think that they would make the ja-namaz (prayer mat) dirty, and they would disturb if they crawl around you, hence it is better for you to offer salah in such a place free from their interference.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband