Which items are allowed on passenger flights but not on cargo ones?
I don't know of anything that is prohibited on a cargo flight but not on a passenger flight. There are some things that are the other way around. 

On a cargo flight you must declare any dangerous goods and usually pay a DG surcharge. Certain types of DG require seperation from other types. Some need to be segregated into a container that is accessible to the crew in an emergency or has a fire-suppression equipment.

Each country has its own laws as to what is acceptible and the proper documentation required. And each company will have their own set of rules. At my employer we use the slightly more stringent IATA guidelines. This ensures compliance with each country. 

The passenger airlines are also required to follow these rules. Passenger luggage is contained in class C cargo holds which are required (at least in the US) to have a fire suppression system as well as a smoke detection system. In an all-cargo aircraft much of the plane is a class E hold, which must have smoke detection, but not a fire suppression system. Therefore certain types of DG have to be segregated into a class B or C area. 

So, you can carry perfume in your luggage because the holds on a passenger plane are all class C, where there is fire suppression. But if you send a box of perfume in a cargo flight without declaring it, then it will most likely be loaded in a class E hold where it won't be compliant.