What is the difference between airport express travel pass,on loan octopus and sold octopus?

Well, the travel pass is a kind of Octopus Card with either one or two Airport Express single journey(s) plus 3 consecutive days of unlimited travel on MTR (except Airport Express, East Rail Line First Class, Lo Wu and Lok Ma Chau stations). When you top up the card, it will function like a normal octopus card, which can be used on bus, subway and ferry.

The sold octopus card has no deposit, after you buy the card, you need to reload it. And you cannot refund the fee for the card itself but only for the balance value.

Well, On loan octopus has a refundable HK$50 deposit. When you do not want to use the card, you can get back both the balance value and the deposit fee for the card.