UPDATE 2-Motiva cat cracker shut at Norco refinery-filing

* Gasoline-making unit shut at refinery

* Shutdown prompts penny boost in gasoline diffs (Updates market reaction paragraph 2; adds detail paragraph 3)

Sept 27 (Reuters) - Motiva Enterprises [MOTIV.UL] on Tuesday reported a controlled shutdown of a gasoline-making fluid catalytic cracking unit at its 234,700 barrel-per-day refinery Norco, Louisiana, according to a filing with U.S. National Response Center.

Gulf Coast M3 gasoline differentials climbed 2.75 cents per gallon to 0.75 cent under the November RBOB contract on the New York Mercantile Exchange by midday EDT Tuesday (1600 GMT). Traders said the boost was due to news of the shutdown as well as the fuel's latest five-day lifting cycle scheduling to move on the Colonial Pipeline.

Space on the Colonial, which transports refined products to the U.S. Northeast from the Gulf Coast, is limited because of allocations.

A spokeswoman for Royal Dutch Shell, (RDSa.L) which operates the refinery as part of a 50/50 venture with Saudi Aramco, declined comment on the plant's operations.

The filing said there were emissions from the overhead of a distillation column due to a leak on the reactor stripper overhead line while performing the shutdown. (Reporting by NR Sethuraman in Bangalore and Kristen Hays in Houston; Editing by Bob Burgdorfer and Andrea Evans)