There are many hotels in Bologna city center, and many of them are convenient to reach in few minutes by bus the CNR research center.
To plan your journey by bus from your hotel to CNR, or in general to travel around Bologna, you can use this travel planner.

Depending on the time of booking, hotels may offer cheaper rates.
Here you will find a detailed list of hotels, provided by the CNR congress center, you may choose and check prices independently.

I would suggest, since you will probably stay in Bologna only for the two days of the meeting, to choose one of the hotels in the central part of the city, inside the yellow circle ("i viali"), to enjoy the sightseeing at least going from the Hotel to the CNR and back!

In  this map you can find the location of the suggested hotels (marked in blue) and the bus 87 way through the center, with red pins indicating the stops.
You can reach the CNR in only 18 minutes leaving from the farthest hotels along the bus way.